~ 128 Ei il~ 28IIE~ U ~ IIIII~10 10 Ii shy~W ~W 22

lidIIi ~ W ~W

IIiIIir W r W M M11 11

II I 11111125 1111114 1111116 11111125 1111114 1111116

MICROCOPY RESOLUTioN TEST CHARTMICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS-J963-AtltATIONAL BUREAU or 51 ANDARDSmiddotJ963-lt

~~~~==~~==TECHwcAL BUL~TtNNQ 170 ~ JANUARY 1930

UNITED STATFS DEPARTMENT OF AGRlCULJUREWASffiNGTON D C

A PIPETTE METHOD OF MECHANICAL ANALYSIS OF SOILS BASED iON IMshyPROVED DISPERSION PROCEDURE

By L B OLMSTEAD Physpoundcist LYLE T ALEXANDER J1mior Physicist an H EMIDDLETQN Associate PhySicist Dilliiion (Jf Boil Chemistry and PhY81C8 Botlbivestigatpoundons Bureau of Chemistry and Soils 1

CONTENTS

Introduction ___ ____________________ ---____ Pllg~ IOutline oC metflOd__________ bull_______________ bull Pa~Dispersioll__bullbullbull _______ 3 General statement_______ _______ bullbull___ _Hydrogen peroxide trel1tment__________ 143 Preparation and dispersion oC sample____ 16Acid treatment___ bull__ bull__ bullbull___________ 5 Separation into size classes______________ 151Vashingbullbull __ _________________ _ IDispersing agents_______ bull_____bull___ bullbullbull 9 Calculation lIC results____________________ 18Apparatus___ __ bull______bull________________ III

~~e~[g~~~~~s_~ U ~W~~ro-citeiCSeparntioa into size classes_ bullbull_ __bullbullbullbull___ _ il12Size clusses employed__ bullbullbull_bullbull____ 2Method oC 5lparationbullbullbull_bullbullbullbullbull____ bullbull ___ 13Sedimentation velocity and particle size_ 3

INTRODUCTION

In all methods of mechanical soil analysis some separations arebased on the well-Imown fact that the smaller particles in watersuspensions fail more slowly than larger ones_ In elutriation methodsthe smaller particles ar-e borne upward by a ~ising water colunmwhile larger parti~les fall In the early work of the Bmeau of S9i~the Osborne (20)~ beaker method was used to make silt and clarseparations Whitney (5) apparently was the first to use the centnshyfuge to increase the settling velocities of soil particles The centrishyfuge method was then worked out independently by Hopkins (12)and Snyder (27) In 1904 the Bureau of Soils published its centrishyfuge method (5) which with modifications (9) has been used untilrecently The centrifuge method was much more rapid than the beakermethod and gave better dispersion than elutriation methods Inthis method the silt and clay were separated from the sands by dec1lshytations from a shalring bottle and the silt was separated from the

I The authors desire to express their appreciation to those who have assisted in thls work Thanks nredue especially to G D DoUmnn oC the University oC Oalifornla for sofl samples Cor uualysls to W H FryCor microscopical examination oC soli separates toHubert Lakin Mrs Dorotha M Darnell and WllllrunSwvens oC the soli physics luborntory for assistance in the analytical work and to C J Crawley and J N)Jail of soils investigations instrument shop for lid in the design and for the constructionoC ap~tus1 Reference is made hy italic numbers In parentheses to Liternture cited p 2182395deg-29-1

GIFT

JAN S 0 1930

2 T]lCHNICALBULLETIN 170 U S DEPT OF AGRICULTURE

clay by centrifuging With trained men checking their silt and clay separations with a microscope micrometer the analyses generally were reproducible Dispersion was obtained by shaking a 5-gm 1 soil sample with 150 c c of distilled water containing 1 c c of con~ c6Dtrated ammnia As many as 40 centrifugings were necessary ill sOme cases to give a complete separation In such cases rubbing the wet sample ith a lubber policeman hastened the operation Later (6) rubber balls with lead centers were put into the shaking bottles to assist in cleaning colloid coatings from sand grains and in br(~aling colloidnl aggregates I About 1919 when attempts were made to determine guantiLatively the amount of colloid in soils it was ioundthat dispersion was not always so complete as had previously been believed Davis and Middleton (8) then studied a number of methods of dispersing soils preparatory to their sepa~ation ~y the centrif~lge lnethod They concluded that some chenucal aSSIstance was necessary for complete dispersion and recommended treatment with 01 N HOI for one hour followed by wl1fYgtmg in the centrifuge to remeJve excess acid and exchanged ions fhe sample was then shaken seven hours in 005 N NaOH

The introduction of the pipette method developed independently by Robinsonin Wales (23) Krauss in Germany (16) and Jennings fhomas and Gardner in the United States (13) necessitated a more stable and more complete dispersion than was reguired in the centri- fuge method A study of dispersion was undertaken by the first commission (soil physics) of the International Society of Soil Science j

that resulted in the adoption at the First International Soil Science Oongress held in Washington in 1927 of two methods for mechanical soil analysis (19) One method called thepmotical method secured i dispersion by shaking wi$ ammonia boiling and rubbin~ The other method designed to secure complete dispersion prescnbed (1) treatment with hydrogen peroxide to remove organic matter (2) treatment with 02 N HOI followed by washing to remove alkaline earth carbonates and adsorbed bases and (3) treatment with ammonia 1 or sodium carbonate to secure dispersion The latter method willmiddotbe referred to hereafter as the international method No attempt was made to fL~the 8ize classes but an arbitrary relilihlonship between sedimentation velocity and particle size was established

These two methods one intended toO give partial and the other complete dispersion represent two diverse purposes of mechanical analysis In so-called practical methods such as the first the endeavor is madpound to avoid removing the coating from soil particles or breaking apart slightly cemented sand ~ains or aggregates of finer material wbich would not be resolved ill tillage operations (1 under severe weather conditions in the field Hilgard (11 p 88) objects to the use of acids to disintegrate compound particles particularlyin cal- ~ careous sands In prnctical methods it is difficult to detennine just when a proper degree of dispersion has been reached For example I Bouyoucos (4) in an effort to secure an analysis of th~ ultimate natural soil structure does not give the sample as rigorous treatment as the international practical method proposes

A mechanical analysis bllsed on complete disporsion does not give i so true a picture of field Rtructure anel Itssociated physical properties as does the practical method but it does give information more vaIshy

2 T]lCHNICALBULLETIN 170 U S DEPT OF AGRICULTURE

clay by centrifuging With trained men checking their silt and clay separations with a microscope micrometer the analyses generally were reproducible Dispersion was obtained by shaking a 5-gm 1 soil sample with 150 c c of distilled water containing 1 c c of con~ c6Dtrated ammnia As many as 40 centrifugings were necessary ill sOme cases to give a complete separation In such cases rubbing the wet sample ith a lubber policeman hastened the operation Later (6) rubber balls with lead centers were put into the shaking bottles to assist in cleaning colloid coatings from sand grains and in br(~aling colloidnl aggregates I About 1919 when attempts were made to determine guantiLatively the amount of colloid in soils it was ioundthat dispersion was not always so complete as had previously been believed Davis and Middleton (8) then studied a number of methods of dispersing soils preparatory to their sepa~ation ~y the centrif~lge lnethod They concluded that some chenucal aSSIstance was necessary for complete dispersion and recommended treatment with 01 N HOI for one hour followed by wl1fYgtmg in the centrifuge to remeJve excess acid and exchanged ions fhe sample was then shaken seven hours in 005 N NaOH

The introduction of the pipette method developed independently by Robinsonin Wales (23) Krauss in Germany (16) and Jennings fhomas and Gardner in the United States (13) necessitated a more stable and more complete dispersion than was reguired in the centri- fuge method A study of dispersion was undertaken by the first commission (soil physics) of the International Society of Soil Science j

that resulted in the adoption at the First International Soil Science Oongress held in Washington in 1927 of two methods for mechanical soil analysis (19) One method called thepmotical method secured i dispersion by shaking wi$ ammonia boiling and rubbin~ The other method designed to secure complete dispersion prescnbed (1) treatment with hydrogen peroxide to remove organic matter (2) treatment with 02 N HOI followed by washing to remove alkaline earth carbonates and adsorbed bases and (3) treatment with ammonia 1 or sodium carbonate to secure dispersion The latter method willmiddotbe referred to hereafter as the international method No attempt was made to fL~the 8ize classes but an arbitrary relilihlonship between sedimentation velocity and particle size was established

These two methods one intended toO give partial and the other complete dispersion represent two diverse purposes of mechanical analysis In so-called practical methods such as the first the endeavor is madpound to avoid removing the coating from soil particles or breaking apart slightly cemented sand ~ains or aggregates of finer material wbich would not be resolved ill tillage operations (1 under severe weather conditions in the field Hilgard (11 p 88) objects to the use of acids to disintegrate compound particles particularlyin cal- ~ careous sands In prnctical methods it is difficult to detennine just when a proper degree of dispersion has been reached For example I Bouyoucos (4) in an effort to secure an analysis of th~ ultimate natural soil structure does not give the sample as rigorous treatment as the international practical method proposes

A mechanical analysis bllsed on complete disporsion does not give i so true a picture of field Rtructure anel Itssociated physical properties as does the practical method but it does give information more vaIshy

A PIPETTE METHOD OF ANALYSIS OF BOILS 3 uable for most pmposes It gives the amount of coarser materialstripped of adhering material the Itmount of colloid and usually theapproximate amolmt of organic matter Since the colloid is the seatof most soil chemical reiwtions and governs or strongly influences

i~

most of the physical properties the quantitative determination of thepoundnest soil fraction is the most important single determination in amechanical analysis In the case of concretions of irreversiblecolloidalmatedal having adsorptive properties less than that of disshypersed colloid but lllore than that of solid mineral grains there issomE question as to how far dispersion should be ctUTiedThis bulletin reports an investigation of methods of obtaining disshypersion of soil material with special reference tothe effect of acidtreatment and the use of allmline dispersing agents A method forthe ]~ellloval of organic matter from manganese soils is included11 procedure for mechanical soil analysis based on the most satisshyfactory of severnl methods of soil dispersion investigated is hereoutlined This is the method now used in the Bureau of Ohemistryand Soils This method is designed to secure complete dispersionof soil material below 2 nun in diameter after organic matter andwater-soluble Illtwinl have been removed Sieves are used to makeall separations except those at 5 II- and 2 11- where the pipette is used

DISPERSION

Good dispersion is the key to accurate mechanical analysis Bycomplete dispersion is meant the removal of colloid coatings on sandand silt grains and the separation of aggregates into single grains orgroups smaller than 2 II- equivalent diameter The problem of disshypersion is (1) to obtain and (2) to maintain suspensions free fromaggregation The chemical and mechanical r~ids to dispersion conshysidered are treatment with (1) hydrogen perliixide (2) hydrochloricacid (3) water ilid (4) dispersing agents 3 electrodialysis andshaking HYDROGEN PEROXIDE TREATMENT

In the analysis of soils high in organic matter G W Robinson (22)iotmd that dispersion was aided by the removal of organic matterwith hydrogen peroxide He ascribes this effect to the removal ofmaterial which cements soil particles into aggregates strongly enoughto resist ordinary dispersion methods Although it is not necesshysary to remove olganic matter in order to secure dispersion of themineral portion of the soil (14) its presence interferes with th3separation of the material into size classes For this reaaon all samshyples for routine analysis in this laboratory are treated with 6 per centH20~1 in accordance with the intelllational methodWhen manganese dioxide is present in sufficient quantity it is not possible to remove the organic matter by the usual treatment Sincemanganese dioxide is the only form of manganese which catalyticallydecomposes hydrogen peroxide so rapidly that the organic matter isvery slowly attacked the obvious lemedy is to convert it into someother man~anese compound W O Robinson (25) found that if asmall fractlon of 1 per cent of manganese dioxide was present it couldbe destlmiddotoyed by evaporating the sample with a very s~lall excess of

AmmQDiUlU hydroxide sodiuUl hydroxide sodium carbonate and BodillDl oxalate

4 TECHNICAL BULLETIN 170 USDEPT OF AGRlCUITURE

oxalic acid In this investigation if manganese dioxide was known to be present or its presence was indicated by the violence of the reaction acetic acid was added followed by hydrogen peroxide the purpose being to convert the manganese dimdde into the manganous form which does not interfere with the decomposition of organic matter by hydrogen peroxide

The effectof acetic acid treatment was determined on duplicate samples of Wabash silt loam iTOm Nebraska The samples contained about 3 per cent organic matter and 011 per cent manganese calcushylated as manganous oxide (MnO) The rate of decomposition of hydrogen peroxide indicated that the manganese is not in the form of manganese dioxide To 10-gm samples of this soil were added various amOtmts of finely precipitated manganese dioxide and acetic acid The amount of carbon dioxide evolved upon the addition of 20 c c or more of 6 per cent hydrogen peroxide is shown in Table 1 The amount of carbon dioxide evolved decreased rapidly with the addition of ma ganese dioxide The -presence of 01 per cent (10 mg) of manganese dioxide did not ~ter~ere with the decomposition oi organic matter whel 10 mg of acetil~ aCld was used Blanks rtm by treating acetic acid with hydrogen 1gtero-ide in the presence of manganese dioxide showed practically no evolution of 002 due to o-idation of the acid

TABLE I-Effect of manganese dioxide and acetic acid on the liberation of carbon dioxide jrJm soil treated with hydrogen peroxide

Carbon Soil dioxide

evolved

Wabnshsiltloatn (lOg11l) Do

Ig o

10 o o

c c 20 20

illIg lOSS 553

Do 50 o 20 175 Do Do

100 o

o 10

20 20

40 1122

Dobullbullbullbull bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull Do

10 50

10 20

20 20

1127 105

Do 50 20 40 741 Do 50 20 60 1742

TABLE 2-0rganic multer removed by the Robinson method from manganese soil treated with acetic acid

middotMangllnese d Hydrogen OrganicSoil 11Iatterdioxide COt-IC IlCI peroxide

lidded added (6 ~dcft) removed

Mg Mg CC Per cellt Wllb(~h silt 108111 (10 gm) ____ bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 o 40 081

Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 100 40 138 Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 o 60 1111 Do 100 100 60 173 Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 1003 o 80 148 Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 100 SO 185 Do o o (l 310 Do 10 110 ltl 2bull 95 Do 100 1100 (Il l85 Do 200 200 (I 203

IA slight eltcess over the CCHliv81ent Ilmount of ucJtic Ilcid was used IAn excess of hyd~ogcJl peroxide

4 TECHNICAL BULLETIN 170 USDEPT OF AGRlCUITURE

oxalic acid In this investigation if manganese dioxide was known to be present or its presence was indicated by the violence of the reaction acetic acid was added followed by hydrogen peroxide the purpose being to convert the manganese dimdde into the manganous form which does not interfere with the decomposition of organic matter by hydrogen peroxide

The effectof acetic acid treatment was determined on duplicate samples of Wabash silt loam iTOm Nebraska The samples contained about 3 per cent organic matter and 011 per cent manganese calcushylated as manganous oxide (MnO) The rate of decomposition of hydrogen peroxide indicated that the manganese is not in the form of manganese dioxide To 10-gm samples of this soil were added various amOtmts of finely precipitated manganese dioxide and acetic acid The amount of carbon dioxide evolved upon the addition of 20 c c or more of 6 per cent hydrogen peroxide is shown in Table 1 The amount of carbon dioxide evolved decreased rapidly with the addition of ma ganese dioxide The -presence of 01 per cent (10 mg) of manganese dioxide did not ~ter~ere with the decomposition oi organic matter whel 10 mg of acetil~ aCld was used Blanks rtm by treating acetic acid with hydrogen 1gtero-ide in the presence of manganese dioxide showed practically no evolution of 002 due to o-idation of the acid

TABLE I-Effect of manganese dioxide and acetic acid on the liberation of carbon dioxide jrJm soil treated with hydrogen peroxide

Carbon Soil dioxide

evolved

Wabnshsiltloatn (lOg11l) Do

Ig o

10 o o

c c 20 20

illIg lOSS 553

Do 50 o 20 175 Do Do

100 o

o 10

20 20

40 1122

Dobullbullbullbull bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull Do

10 50

10 20

20 20

1127 105

Do 50 20 40 741 Do 50 20 60 1742

TABLE 2-0rganic multer removed by the Robinson method from manganese soil treated with acetic acid

middotMangllnese d Hydrogen OrganicSoil 11Iatterdioxide COt-IC IlCI peroxide

lidded added (6 ~dcft) removed

Mg Mg CC Per cellt Wllb(~h silt 108111 (10 gm) ____ bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 o 40 081

Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 100 40 138 Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 o 60 1111 Do 100 100 60 173 Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 1003 o 80 148 Dobullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 100 100 SO 185 Do o o (l 310 Do 10 110 ltl 2bull 95 Do 100 1100 (Il l85 Do 200 200 (I 203

IA slight eltcess over the CCHliv81ent Ilmount of ucJtic Ilcid was used IAn excess of hyd~ogcJl peroxide

~ PJPETlEMljllHODOF ANALYSIS bF SOILS 5

ben soil if treated with hydrogen peroxide the organic matter ilither is destroyed with the evolution of carbon dioxide or is brought into solution Table 1 shows only the amount of organic carbon oxidized to 002bull Table 2 gives the total organic matter removed by both mellns when the same soil containing amounts of manganese dio~ide is treated with different amounts of hydrogen peroxide The quantity of acetic acid added was It slight excess over the molecuhtr eq1rivalent of the manganese dioxide present The addition of acetic acid is qmte effective when the soil contains 1 per i cent of manganese dioxide 40 c c of hydrogen peroxide removing 4 nearly as much organic matter when acid was present as was removed by 80 c c of peroxide without acid In the case of the last four samples hydlOgen peroxid(~ was added until decomposition of the Ol~anic matter was complete The sample was then washed and dned and the nmount of organic matter determined by loss in weight according to the method of W O Robinson (25) who removed 303 per cent of org~Lnic mattE from this soil The results show that organic matter can be completely removed in the presence of manshyganese dioxide up to 2 per cent It is possible that soils containing both manganese dioxide and lime carbonates would not respond so readily to acetic acid and hydrogen peroxide treatment The amount of peroxide required increases with the amOlmt of mnnganese dioxide present The removal of organic matter from the sample containing 2 per cent manganese dioxide reqmred the use of excessive quantities of hrdrogen peroxide The removal of organic matteI is not essential to th6 method described in this bulletin and may well be omitted in the case of soils lrigh in manganese dioxide and low in organic matter

In some cases hydrogen peroxidp decomposes the organic matter slowly and incompletely In one case lecently noted hydrogen peroxide attacked the organic matter only slightly After thp -pddishytioli of 1 or 2 mg of manganese dioxide theolganic matter was quickly attacked and apparently completely decomposed

ACID TREATMENT

In the pipette method of mechanical analysis it is necessary to prepare soil suspensions in such mannel that they may be kept in a sedinlentation chamber for several days without coagulation into flocs larger than 2p equivalent diameter For this purpose treatshyment of the soil sample with hydrochloric acid has been found helpful because it dissolves alkaline earth carbona-iies and lemoves exchange bases II which later might cause flocculation of the suspension There are however some objections to the use of acid treatment

In the international method the soil after decomposition of organic matter is treated with enough hydrochlolic abid to decomfose the carbonates and still leave 250 c c of solution of 02 N HO Such rigorous treatment dissolves sesqmoxides of iron and aluminum and some silica plthou~h it may not dissolve all the carbonates An exarnple of this is gIven by Bodman (3) When It sample of Monteshyzuma clay adobe subsoil from Oaijfornia was boiled with 01 N HOI the amotmt of acid consumed was equivalent to 908 per cent calcium carbonate but if treated with 02 N HOI at loom temperature in accordance with the international method acid eqmvalent to onlyshy127 per cent of calcium carbonate- was consumed and part of this

consumption must be ascribed to the solution oJO81percentilt)f sesquiopdes and silica The amount of carbonates in this soil deshy

ternrined by the official method (1 p 22-24) was 828 per cent The mechanical analysis oj this material is given later in Table 5

Even though carbonates might be removed completely -and easilYt such removal is Wldesirable in sOme soils such as glacialsos contain ing large amounts of limestoneor dolomite because it vould be likely to change soil teA-tural classifications Other soils -may have relatively permanent grains or crystals of precipitated carbonate whose presence should be expressed in the results of mechawcal analyshysis An example of this is the Goliad fine sandy loam subsoil from exas Ten-grRID samples of this material Ier~treated With vary mg amounts of a~ld followmg the reguli1r peroXide treatment The washed residues were shaken with 5 c cof normal sodium carbonate and analyzed by the pipette method described later The results are shown in Table 3 An examination of the materialbyWilliam H Fry soil petrographer of this division showedtliatthe carbonate material amounting to about 38 percent was present largely in the form of small calcite crystals

TABLE a-Effect of acid treatment on the resul8 of mechanicalanalY8t8 1 of Goliail fine 8andymiddotloam (350 48 inches)

Treatment

No acidbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 2 c c N HOslIObullbull bullbullbullbullbullbull bullbullbullbullbullbullbullbullbull___bullbull10 Cc N HOl____bull __ bullbull __ _bullbullbullbullbullbullbullbull__ _ Oarbonates remQved+lO c c N HOl_bullbullbull_ No acid dispersed with sodium oxalate__

Sands 20 to 005 mm

Silt 005 to 0005 mm

Olay lt0005 mm

Colloid lt0002 mm

Hydrogenperoxideand solumiddot tion1oss

Per cent Pti cent Per cent Per cent Per cent 360 38 6 242 18 3 02 366 379 241 181 14shy366 314

3~ 7 96

23 3 199 194180

53 amp90

370 343 284 210 2

I JtesuIts in all mccbatlical8llll1ysis tables are on oven-dry basis (105deg 0) and silt is reported by diller- ence

For some special purposes such as dam construction or other engineering uses an analysis based on vigorous acid treatment might be preferred for a soil such as the Goliad although an analysis withshyout acid treatment togeth3l with a determination of total carbonates would be preferable Analyses by both methods are required to furnish a complete description of the soil

These analyses (Table 3) are presented primarily to showt1tat acid treatment may alter the amount of material in the different size classes enough to change markedly the~xtural classific8tion Incidentally they indicate that acid treatment is not essential to good dispersion a matter which will now be examined more fully

Since ltappears that treatment with 02 N HOI is notalwayseffecshytive in removing the carbonates from soil and in some cases preshysents a distorted picture of the soil it seemed desirable to ascertain whether complete dispersion can be obtained without its use

Table 4 gives the results of mechanical analysis of a number of soils with and without acid treatment All samples (10 gm) were first treated with hydrogen peroxide Those given acid treatment were allowed to stand overnight in HOI solution of middotsufficient strength to leave 150 c c of 02 N HOl after the carbonate content is removed

i

)j Thediference indry wei~htof the srunple befre and after pretrea~

moot lS reported as solution loss This comprISes the 10ssoi orgaruc matter sesquioxides (R20s)silica1ime carbopa~esorother dissolved material All sample) were peptized by shaking wIth 150 c c of wlte1 conta~~ 10 c cof 05 N N a2C20 4bullbull These~amples emhr8cea wIde range of soil types and are representatI~e of soil samples receIved for analysis

TABLE 4-EJlect of miid prereatmenton Tl4echanicdlanalysisof soils

Samshy Sand Snt ICol Sclu ple SIU tfll6 and source Depth Treat- CaCO 20 to OoHoqlay JOid- tlcn- Ih03 No ment 005 0105 lt51 lt2 I loss loss

mm nun 1---------1middot--------------------

Per Per Per Per Per Per Incht3 Perct1lt cent ctnt cent cent cent cerltcld____425250 Buston fine SIludy loam po to 70__ 0 562 139 297 25 6 01 02

(MissWslppl) bull _____dD___-________________ ___de____A25250 No ncld_ 0 56~ 141 293 270 1 001 to 2____ Acld____3(tOl Isabcllalolltn (Michigan) _ 0 580 305 68 42 45 5 ____dc_____________________ ___dc____3(t041 Ncacid_ 0 570 290 87 38 43 JAcld____2437200 Cowlle clay loam (Scuth 5 to 15___ 0 177 262 551 45 5 12 6

Carclina) _____dc_____________________ ___dc____2437200 Ncacid_ 0 175 252 563 488 10 05Acld____376337 PlUten very fine sandy 24 to 44_ 56 521 270 114 04 86 13 IcaIn (Nebraska) _____dc___________________ __ dc____376337 No acld_ 56 55 1 245 290 161 4 bull 01Otel2__ cld___------ Hcustcn black c1ay 1117 41 250 563 507 14 7 17

___(Texas)_____________________dc __ dc_____ No acid_ 1117 59 285 638 538 10 1 __ dc____ cld____- -_ llndcbdc (SudanmiddotQoziroy__ 50 180 624 22___ ____________________ bull 63 697 60 ___dc____ Ncncid_ 59 84 147 75 9 646 1bull 0 94Rendzina (Cejc) __________ ___dc_____ Acid____ 51 264 302 116 25--_ - _____de--___________________ ___dc____ 257

No ncid_ 51 318 290 36 6330 34 a 288 Pcdsol (Zdnr) _____________ ___de____ Acld____ ----- _____dc__________________ 0 25 7 354 371 390 16 13 ___dc____ ~cncid_ 0 256 364 378 302 2 05

I Dcterminaticn by Rcblnsen and Holmes (poundff) Igt

The last three sets of analyses are from samples stibmittedfor analysis to some 20 laboratories by a committee of the iirst commisshysion of the Intemational Society of Soil Science The unpubliShed results collected by this committee and furnished us by R OE Davis give the amolllit of organic matter in the badob lendzinaand podsol as 1 per ~lent 46 per cen()and 04 per ~ent re~pecthely The average (unpublished) result collected by thIS COmmlttee from the leporting laboratories for the percentage 2pclay (colloid) when hydrogen peroxide and hydrochloric-iacid treatment was used was 605 for the badob 267 for the renclzina and 286 for thepodsol Joseph and Snow (14-) using their method which consists of sholcing with sodium carbonate puddling and decanting by the beaker method without the use of peroxide or acid obtained 633 per cent 29 per cent and 27 per cent for the aIhountof 2p clay in the badob rendzina and podsol respectively WO Robinson (25) reports 36 per cent organic matter in the Houstonblackclay determined by the hydrogen peroxide method and 42 per cent determined by comshybustion It is appareht from the results in Table 4 that the organic matter was not all removed by peroxide treatment from either the Houston black clay or the rendzina

Recently Bodman (3) published analyses of five well-selected Calishyfornia soils using two methods At request of the writers Doctor Bodman furnished this laboratory with samples of these soils The results of the analyses together with those of Bodman are shown in

bull

8 TECHNICAL BULLETIN 170 U S DEPT ltOF AGRICULTUEE

Table 5 The Montezuma clay adobe soil has a high content of organic matter and its subsoil has a high content of lime The Fresno sandy lo~m has a yengh content of sodi~ carbonate the ~ken clay loam subsoil has a high percentage of Iron and the last IS the difficultly dispersible hardpan horizon of the San Joaquin sandy loam

TABLE5-ilfechanical analyses of soils by c01Jparative methods

Sand Silt 005 ClaySoli typo Depth Method I 2 to 005 to 0005 lt0005 Colloid

mm mm mm ------------

Inchu Per cent Per cent Per Ct1lt Per centMontezuma ell) adooo ___ _bullbull__ bullbullbullbull__ 0 to 12__ _ A 250 32 5 360 281Uu____ ~_ __ bull_____ bull_____ bull_______ bull ______do_____ _

13 240 303 3lI 150 C 238 328 402 auDo____ ________________________________do_____

Do___ __ bullbull ___bull__________________ 32 to 40___ ~

A 308 341 323 262 B 2i5 430 267 144B~==~== =Jr~ Q 273 346 379 317Fresno 5nuly IOIUl_________ bull __ ________ 0 to12____ A- 61S 203 75 37

Do____ _____bull_______________ bull__________do______ Do___ _ _____________________bull________do__ bull ___ B 642 264 78 37

Q 62 3 288 82 55Aiken clay loam ________________________ 12 to 14___ _ A- 65 348 583 457 Do____ ________________________________do_____ _ Do_____________ bullbull _________bull_ ____ ____do_____ _

13 70 352 573 434 c 82 313 581 486San Joa(uiil sandy loam ________________ 25 to 30__ A 707 180 107 49Do__ bull_________________---_-- ___ _____do- ___ _ B 584 255 155 64

DO __t ___ ___ _______ __ _ ~ __ _ __do_ ~ C 661 157 179 118

1 Method A hydrogen poroxidemiddothydrochloric acid pretreatment shaken with ammonia Method Brubbed with ammonla shakon with ammonia separates treated with hydrogen peroxide Metbod Q hydrogen-porodde pretreatment shaken with sodium oml~te

2 Methods A and B colloid pipetted ut 11 Method Q colloid pipetted at 2 1

The results given under methods A and B are those published by Bodman and lmder method 0 those obtained in this laboratory Method A is the international method designed to give complete dispersion In methods B and 0 hydrochloric-acid treatment is omitted hydrogen peroxide being used as the last step in the analysis of the former and the first step in that of the latter In method B the sample wet with a dilute ammoniacal solution is rubbed with It rubber pestle for 10 minutes before being shaken In methods A and B 5-gm samples dispersed with ammonia and in method 0 10-gm samples dispersed with SOdilUll oxalate are used

That the larger amount of colloid obtained by method 0 is not entirely due to the separation being made at 2 p instead of 1 JI is shown by the fact that the amount of clay is also greater by this method

The resultsin Tables 4 and 5 typical of hundreds of analyses of soils developed from a wide range of materials and under a wide range middotof climatic conditions are presented to show that in no case is there any indication that acid treatment is necessary to dispersion Joseph and Snow (14) reach the same conclusion in the case oithe heavy alkaline soils of Sudan In their bealer (or centrifuge) method in which ~e repeated pud~g and dec~tation of suspensions produces a washing effect flocculatJon merely mcreasesthe number of decant ashytions required for complete separation into size classes In the pipette method however it is necessary ior the material to remain in the seclinlentationcylinder wijihout coagulation for at least t~o or middotthree days Duplicate pipettiDgs of th~ same suspensio~ taken a week apart show no evidence of flocculation even though acid pretreatment was omitted Since acid treatment appears to serve no essential

1

~ ~

consumption must be ascribed to the solution oJO81percentilt)f sesquiopdes and silica The amount of carbonates in this soil deshy

ternrined by the official method (1 p 22-24) was 828 per cent The mechanical analysis oj this material is given later in Table 5

Even though carbonates might be removed completely -and easilYt such removal is Wldesirable in sOme soils such as glacialsos contain ing large amounts of limestoneor dolomite because it vould be likely to change soil teA-tural classifications Other soils -may have relatively permanent grains or crystals of precipitated carbonate whose presence should be expressed in the results of mechawcal analyshysis An example of this is the Goliad fine sandy loam subsoil from exas Ten-grRID samples of this material Ier~treated With vary mg amounts of a~ld followmg the reguli1r peroXide treatment The washed residues were shaken with 5 c cof normal sodium carbonate and analyzed by the pipette method described later The results are shown in Table 3 An examination of the materialbyWilliam H Fry soil petrographer of this division showedtliatthe carbonate material amounting to about 38 percent was present largely in the form of small calcite crystals

TABLE a-Effect of acid treatment on the resul8 of mechanicalanalY8t8 1 of Goliail fine 8andymiddotloam (350 48 inches)

Treatment

No acidbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 2 c c N HOslIObullbull bullbullbullbullbullbull bullbullbullbullbullbullbullbullbull___bullbull10 Cc N HOl____bull __ bullbull __ _bullbullbullbullbullbullbullbull__ _ Oarbonates remQved+lO c c N HOl_bullbullbull_ No acid dispersed with sodium oxalate__

Sands 20 to 005 mm

Silt 005 to 0005 mm

Olay lt0005 mm

Colloid lt0002 mm

Hydrogenperoxideand solumiddot tion1oss

Per cent Pti cent Per cent Per cent Per cent 360 38 6 242 18 3 02 366 379 241 181 14shy366 314

3~ 7 96

23 3 199 194180

53 amp90

370 343 284 210 2

I JtesuIts in all mccbatlical8llll1ysis tables are on oven-dry basis (105deg 0) and silt is reported by diller- ence

For some special purposes such as dam construction or other engineering uses an analysis based on vigorous acid treatment might be preferred for a soil such as the Goliad although an analysis withshyout acid treatment togeth3l with a determination of total carbonates would be preferable Analyses by both methods are required to furnish a complete description of the soil

These analyses (Table 3) are presented primarily to showt1tat acid treatment may alter the amount of material in the different size classes enough to change markedly the~xtural classific8tion Incidentally they indicate that acid treatment is not essential to good dispersion a matter which will now be examined more fully

Since ltappears that treatment with 02 N HOI is notalwayseffecshytive in removing the carbonates from soil and in some cases preshysents a distorted picture of the soil it seemed desirable to ascertain whether complete dispersion can be obtained without its use

Table 4 gives the results of mechanical analysis of a number of soils with and without acid treatment All samples (10 gm) were first treated with hydrogen peroxide Those given acid treatment were allowed to stand overnight in HOI solution of middotsufficient strength to leave 150 c c of 02 N HOl after the carbonate content is removed

i

)j Thediference indry wei~htof the srunple befre and after pretrea~

moot lS reported as solution loss This comprISes the 10ssoi orgaruc matter sesquioxides (R20s)silica1ime carbopa~esorother dissolved material All sample) were peptized by shaking wIth 150 c c of wlte1 conta~~ 10 c cof 05 N N a2C20 4bullbull These~amples emhr8cea wIde range of soil types and are representatI~e of soil samples receIved for analysis

TABLE 4-EJlect of miid prereatmenton Tl4echanicdlanalysisof soils

Samshy Sand Snt ICol Sclu ple SIU tfll6 and source Depth Treat- CaCO 20 to OoHoqlay JOid- tlcn- Ih03 No ment 005 0105 lt51 lt2 I loss loss

mm nun 1---------1middot--------------------

Per Per Per Per Per Per Incht3 Perct1lt cent ctnt cent cent cent cerltcld____425250 Buston fine SIludy loam po to 70__ 0 562 139 297 25 6 01 02

(MissWslppl) bull _____dD___-________________ ___de____A25250 No ncld_ 0 56~ 141 293 270 1 001 to 2____ Acld____3(tOl Isabcllalolltn (Michigan) _ 0 580 305 68 42 45 5 ____dc_____________________ ___dc____3(t041 Ncacid_ 0 570 290 87 38 43 JAcld____2437200 Cowlle clay loam (Scuth 5 to 15___ 0 177 262 551 45 5 12 6

Carclina) _____dc_____________________ ___dc____2437200 Ncacid_ 0 175 252 563 488 10 05Acld____376337 PlUten very fine sandy 24 to 44_ 56 521 270 114 04 86 13 IcaIn (Nebraska) _____dc___________________ __ dc____376337 No acld_ 56 55 1 245 290 161 4 bull 01Otel2__ cld___------ Hcustcn black c1ay 1117 41 250 563 507 14 7 17

___(Texas)_____________________dc __ dc_____ No acid_ 1117 59 285 638 538 10 1 __ dc____ cld____- -_ llndcbdc (SudanmiddotQoziroy__ 50 180 624 22___ ____________________ bull 63 697 60 ___dc____ Ncncid_ 59 84 147 75 9 646 1bull 0 94Rendzina (Cejc) __________ ___dc_____ Acid____ 51 264 302 116 25--_ - _____de--___________________ ___dc____ 257

No ncid_ 51 318 290 36 6330 34 a 288 Pcdsol (Zdnr) _____________ ___de____ Acld____ ----- _____dc__________________ 0 25 7 354 371 390 16 13 ___dc____ ~cncid_ 0 256 364 378 302 2 05

I Dcterminaticn by Rcblnsen and Holmes (poundff) Igt

The last three sets of analyses are from samples stibmittedfor analysis to some 20 laboratories by a committee of the iirst commisshysion of the Intemational Society of Soil Science The unpubliShed results collected by this committee and furnished us by R OE Davis give the amolllit of organic matter in the badob lendzinaand podsol as 1 per ~lent 46 per cen()and 04 per ~ent re~pecthely The average (unpublished) result collected by thIS COmmlttee from the leporting laboratories for the percentage 2pclay (colloid) when hydrogen peroxide and hydrochloric-iacid treatment was used was 605 for the badob 267 for the renclzina and 286 for thepodsol Joseph and Snow (14-) using their method which consists of sholcing with sodium carbonate puddling and decanting by the beaker method without the use of peroxide or acid obtained 633 per cent 29 per cent and 27 per cent for the aIhountof 2p clay in the badob rendzina and podsol respectively WO Robinson (25) reports 36 per cent organic matter in the Houstonblackclay determined by the hydrogen peroxide method and 42 per cent determined by comshybustion It is appareht from the results in Table 4 that the organic matter was not all removed by peroxide treatment from either the Houston black clay or the rendzina

Recently Bodman (3) published analyses of five well-selected Calishyfornia soils using two methods At request of the writers Doctor Bodman furnished this laboratory with samples of these soils The results of the analyses together with those of Bodman are shown in

bull

8 TECHNICAL BULLETIN 170 U S DEPT ltOF AGRICULTUEE

Table 5 The Montezuma clay adobe soil has a high content of organic matter and its subsoil has a high content of lime The Fresno sandy lo~m has a yengh content of sodi~ carbonate the ~ken clay loam subsoil has a high percentage of Iron and the last IS the difficultly dispersible hardpan horizon of the San Joaquin sandy loam

TABLE5-ilfechanical analyses of soils by c01Jparative methods

Sand Silt 005 ClaySoli typo Depth Method I 2 to 005 to 0005 lt0005 Colloid

mm mm mm ------------

Inchu Per cent Per cent Per Ct1lt Per centMontezuma ell) adooo ___ _bullbull__ bullbullbullbull__ 0 to 12__ _ A 250 32 5 360 281Uu____ ~_ __ bull_____ bull_____ bull_______ bull ______do_____ _

13 240 303 3lI 150 C 238 328 402 auDo____ ________________________________do_____

Do___ __ bullbull ___bull__________________ 32 to 40___ ~

A 308 341 323 262 B 2i5 430 267 144B~==~== =Jr~ Q 273 346 379 317Fresno 5nuly IOIUl_________ bull __ ________ 0 to12____ A- 61S 203 75 37

Do____ _____bull_______________ bull__________do______ Do___ _ _____________________bull________do__ bull ___ B 642 264 78 37

Q 62 3 288 82 55Aiken clay loam ________________________ 12 to 14___ _ A- 65 348 583 457 Do____ ________________________________do_____ _ Do_____________ bullbull _________bull_ ____ ____do_____ _

13 70 352 573 434 c 82 313 581 486San Joa(uiil sandy loam ________________ 25 to 30__ A 707 180 107 49Do__ bull_________________---_-- ___ _____do- ___ _ B 584 255 155 64

DO __t ___ ___ _______ __ _ ~ __ _ __do_ ~ C 661 157 179 118

1 Method A hydrogen poroxidemiddothydrochloric acid pretreatment shaken with ammonia Method Brubbed with ammonla shakon with ammonia separates treated with hydrogen peroxide Metbod Q hydrogen-porodde pretreatment shaken with sodium oml~te

2 Methods A and B colloid pipetted ut 11 Method Q colloid pipetted at 2 1

The results given under methods A and B are those published by Bodman and lmder method 0 those obtained in this laboratory Method A is the international method designed to give complete dispersion In methods B and 0 hydrochloric-acid treatment is omitted hydrogen peroxide being used as the last step in the analysis of the former and the first step in that of the latter In method B the sample wet with a dilute ammoniacal solution is rubbed with It rubber pestle for 10 minutes before being shaken In methods A and B 5-gm samples dispersed with ammonia and in method 0 10-gm samples dispersed with SOdilUll oxalate are used

That the larger amount of colloid obtained by method 0 is not entirely due to the separation being made at 2 p instead of 1 JI is shown by the fact that the amount of clay is also greater by this method

The resultsin Tables 4 and 5 typical of hundreds of analyses of soils developed from a wide range of materials and under a wide range middotof climatic conditions are presented to show that in no case is there any indication that acid treatment is necessary to dispersion Joseph and Snow (14) reach the same conclusion in the case oithe heavy alkaline soils of Sudan In their bealer (or centrifuge) method in which ~e repeated pud~g and dec~tation of suspensions produces a washing effect flocculatJon merely mcreasesthe number of decant ashytions required for complete separation into size classes In the pipette method however it is necessary ior the material to remain in the seclinlentationcylinder wijihout coagulation for at least t~o or middotthree days Duplicate pipettiDgs of th~ same suspensio~ taken a week apart show no evidence of flocculation even though acid pretreatment was omitted Since acid treatment appears to serve no essential

1

~ ~

)j Thediference indry wei~htof the srunple befre and after pretrea~

moot lS reported as solution loss This comprISes the 10ssoi orgaruc matter sesquioxides (R20s)silica1ime carbopa~esorother dissolved material All sample) were peptized by shaking wIth 150 c c of wlte1 conta~~ 10 c cof 05 N N a2C20 4bullbull These~amples emhr8cea wIde range of soil types and are representatI~e of soil samples receIved for analysis

TABLE 4-EJlect of miid prereatmenton Tl4echanicdlanalysisof soils

Samshy Sand Snt ICol Sclu ple SIU tfll6 and source Depth Treat- CaCO 20 to OoHoqlay JOid- tlcn- Ih03 No ment 005 0105 lt51 lt2 I loss loss

mm nun 1---------1middot--------------------

Per Per Per Per Per Per Incht3 Perct1lt cent ctnt cent cent cent cerltcld____425250 Buston fine SIludy loam po to 70__ 0 562 139 297 25 6 01 02

(MissWslppl) bull _____dD___-________________ ___de____A25250 No ncld_ 0 56~ 141 293 270 1 001 to 2____ Acld____3(tOl Isabcllalolltn (Michigan) _ 0 580 305 68 42 45 5 ____dc_____________________ ___dc____3(t041 Ncacid_ 0 570 290 87 38 43 JAcld____2437200 Cowlle clay loam (Scuth 5 to 15___ 0 177 262 551 45 5 12 6

Carclina) _____dc_____________________ ___dc____2437200 Ncacid_ 0 175 252 563 488 10 05Acld____376337 PlUten very fine sandy 24 to 44_ 56 521 270 114 04 86 13 IcaIn (Nebraska) _____dc___________________ __ dc____376337 No acld_ 56 55 1 245 290 161 4 bull 01Otel2__ cld___------ Hcustcn black c1ay 1117 41 250 563 507 14 7 17

___(Texas)_____________________dc __ dc_____ No acid_ 1117 59 285 638 538 10 1 __ dc____ cld____- -_ llndcbdc (SudanmiddotQoziroy__ 50 180 624 22___ ____________________ bull 63 697 60 ___dc____ Ncncid_ 59 84 147 75 9 646 1bull 0 94Rendzina (Cejc) __________ ___dc_____ Acid____ 51 264 302 116 25--_ - _____de--___________________ ___dc____ 257

No ncid_ 51 318 290 36 6330 34 a 288 Pcdsol (Zdnr) _____________ ___de____ Acld____ ----- _____dc__________________ 0 25 7 354 371 390 16 13 ___dc____ ~cncid_ 0 256 364 378 302 2 05

I Dcterminaticn by Rcblnsen and Holmes (poundff) Igt

The last three sets of analyses are from samples stibmittedfor analysis to some 20 laboratories by a committee of the iirst commisshysion of the Intemational Society of Soil Science The unpubliShed results collected by this committee and furnished us by R OE Davis give the amolllit of organic matter in the badob lendzinaand podsol as 1 per ~lent 46 per cen()and 04 per ~ent re~pecthely The average (unpublished) result collected by thIS COmmlttee from the leporting laboratories for the percentage 2pclay (colloid) when hydrogen peroxide and hydrochloric-iacid treatment was used was 605 for the badob 267 for the renclzina and 286 for thepodsol Joseph and Snow (14-) using their method which consists of sholcing with sodium carbonate puddling and decanting by the beaker method without the use of peroxide or acid obtained 633 per cent 29 per cent and 27 per cent for the aIhountof 2p clay in the badob rendzina and podsol respectively WO Robinson (25) reports 36 per cent organic matter in the Houstonblackclay determined by the hydrogen peroxide method and 42 per cent determined by comshybustion It is appareht from the results in Table 4 that the organic matter was not all removed by peroxide treatment from either the Houston black clay or the rendzina

Recently Bodman (3) published analyses of five well-selected Calishyfornia soils using two methods At request of the writers Doctor Bodman furnished this laboratory with samples of these soils The results of the analyses together with those of Bodman are shown in

bull

8 TECHNICAL BULLETIN 170 U S DEPT ltOF AGRICULTUEE

Table 5 The Montezuma clay adobe soil has a high content of organic matter and its subsoil has a high content of lime The Fresno sandy lo~m has a yengh content of sodi~ carbonate the ~ken clay loam subsoil has a high percentage of Iron and the last IS the difficultly dispersible hardpan horizon of the San Joaquin sandy loam

TABLE5-ilfechanical analyses of soils by c01Jparative methods

Sand Silt 005 ClaySoli typo Depth Method I 2 to 005 to 0005 lt0005 Colloid

mm mm mm ------------

Inchu Per cent Per cent Per Ct1lt Per centMontezuma ell) adooo ___ _bullbull__ bullbullbullbull__ 0 to 12__ _ A 250 32 5 360 281Uu____ ~_ __ bull_____ bull_____ bull_______ bull ______do_____ _

13 240 303 3lI 150 C 238 328 402 auDo____ ________________________________do_____

Do___ __ bullbull ___bull__________________ 32 to 40___ ~

A 308 341 323 262 B 2i5 430 267 144B~==~== =Jr~ Q 273 346 379 317Fresno 5nuly IOIUl_________ bull __ ________ 0 to12____ A- 61S 203 75 37

Do____ _____bull_______________ bull__________do______ Do___ _ _____________________bull________do__ bull ___ B 642 264 78 37

Q 62 3 288 82 55Aiken clay loam ________________________ 12 to 14___ _ A- 65 348 583 457 Do____ ________________________________do_____ _ Do_____________ bullbull _________bull_ ____ ____do_____ _

13 70 352 573 434 c 82 313 581 486San Joa(uiil sandy loam ________________ 25 to 30__ A 707 180 107 49Do__ bull_________________---_-- ___ _____do- ___ _ B 584 255 155 64

DO __t ___ ___ _______ __ _ ~ __ _ __do_ ~ C 661 157 179 118

1 Method A hydrogen poroxidemiddothydrochloric acid pretreatment shaken with ammonia Method Brubbed with ammonla shakon with ammonia separates treated with hydrogen peroxide Metbod Q hydrogen-porodde pretreatment shaken with sodium oml~te

2 Methods A and B colloid pipetted ut 11 Method Q colloid pipetted at 2 1

The results given under methods A and B are those published by Bodman and lmder method 0 those obtained in this laboratory Method A is the international method designed to give complete dispersion In methods B and 0 hydrochloric-acid treatment is omitted hydrogen peroxide being used as the last step in the analysis of the former and the first step in that of the latter In method B the sample wet with a dilute ammoniacal solution is rubbed with It rubber pestle for 10 minutes before being shaken In methods A and B 5-gm samples dispersed with ammonia and in method 0 10-gm samples dispersed with SOdilUll oxalate are used

That the larger amount of colloid obtained by method 0 is not entirely due to the separation being made at 2 p instead of 1 JI is shown by the fact that the amount of clay is also greater by this method

The resultsin Tables 4 and 5 typical of hundreds of analyses of soils developed from a wide range of materials and under a wide range middotof climatic conditions are presented to show that in no case is there any indication that acid treatment is necessary to dispersion Joseph and Snow (14) reach the same conclusion in the case oithe heavy alkaline soils of Sudan In their bealer (or centrifuge) method in which ~e repeated pud~g and dec~tation of suspensions produces a washing effect flocculatJon merely mcreasesthe number of decant ashytions required for complete separation into size classes In the pipette method however it is necessary ior the material to remain in the seclinlentationcylinder wijihout coagulation for at least t~o or middotthree days Duplicate pipettiDgs of th~ same suspensio~ taken a week apart show no evidence of flocculation even though acid pretreatment was omitted Since acid treatment appears to serve no essential

1

~ ~

8 TECHNICAL BULLETIN 170 U S DEPT ltOF AGRICULTUEE

Table 5 The Montezuma clay adobe soil has a high content of organic matter and its subsoil has a high content of lime The Fresno sandy lo~m has a yengh content of sodi~ carbonate the ~ken clay loam subsoil has a high percentage of Iron and the last IS the difficultly dispersible hardpan horizon of the San Joaquin sandy loam

TABLE5-ilfechanical analyses of soils by c01Jparative methods

Sand Silt 005 ClaySoli typo Depth Method I 2 to 005 to 0005 lt0005 Colloid

mm mm mm ------------

Inchu Per cent Per cent Per Ct1lt Per centMontezuma ell) adooo ___ _bullbull__ bullbullbullbull__ 0 to 12__ _ A 250 32 5 360 281Uu____ ~_ __ bull_____ bull_____ bull_______ bull ______do_____ _

13 240 303 3lI 150 C 238 328 402 auDo____ ________________________________do_____

Do___ __ bullbull ___bull__________________ 32 to 40___ ~

A 308 341 323 262 B 2i5 430 267 144B~==~== =Jr~ Q 273 346 379 317Fresno 5nuly IOIUl_________ bull __ ________ 0 to12____ A- 61S 203 75 37

Do____ _____bull_______________ bull__________do______ Do___ _ _____________________bull________do__ bull ___ B 642 264 78 37

Q 62 3 288 82 55Aiken clay loam ________________________ 12 to 14___ _ A- 65 348 583 457 Do____ ________________________________do_____ _ Do_____________ bullbull _________bull_ ____ ____do_____ _

13 70 352 573 434 c 82 313 581 486San Joa(uiil sandy loam ________________ 25 to 30__ A 707 180 107 49Do__ bull_________________---_-- ___ _____do- ___ _ B 584 255 155 64

DO __t ___ ___ _______ __ _ ~ __ _ __do_ ~ C 661 157 179 118

1 Method A hydrogen poroxidemiddothydrochloric acid pretreatment shaken with ammonia Method Brubbed with ammonla shakon with ammonia separates treated with hydrogen peroxide Metbod Q hydrogen-porodde pretreatment shaken with sodium oml~te

2 Methods A and B colloid pipetted ut 11 Method Q colloid pipetted at 2 1

The results given under methods A and B are those published by Bodman and lmder method 0 those obtained in this laboratory Method A is the international method designed to give complete dispersion In methods B and 0 hydrochloric-acid treatment is omitted hydrogen peroxide being used as the last step in the analysis of the former and the first step in that of the latter In method B the sample wet with a dilute ammoniacal solution is rubbed with It rubber pestle for 10 minutes before being shaken In methods A and B 5-gm samples dispersed with ammonia and in method 0 10-gm samples dispersed with SOdilUll oxalate are used

That the larger amount of colloid obtained by method 0 is not entirely due to the separation being made at 2 p instead of 1 JI is shown by the fact that the amount of clay is also greater by this method

The resultsin Tables 4 and 5 typical of hundreds of analyses of soils developed from a wide range of materials and under a wide range middotof climatic conditions are presented to show that in no case is there any indication that acid treatment is necessary to dispersion Joseph and Snow (14) reach the same conclusion in the case oithe heavy alkaline soils of Sudan In their bealer (or centrifuge) method in which ~e repeated pud~g and dec~tation of suspensions produces a washing effect flocculatJon merely mcreasesthe number of decant ashytions required for complete separation into size classes In the pipette method however it is necessary ior the material to remain in the seclinlentationcylinder wijihout coagulation for at least t~o or middotthree days Duplicate pipettiDgs of th~ same suspensio~ taken a week apart show no evidence of flocculation even though acid pretreatment was omitted Since acid treatment appears to serve no essential

1

~ ~

A PUliTTEMElHODOF ANALYSISOFSOILS

ltl purpose and may be objectionable it is omitted in the method iii r01ltineanalysis

WASWNG

bull After the soil sample has been pretreated it is washed to remove soluble organic matter dissolved lime leplaced ions (especially bivalent and trivalent cations) hydrogen peroxide and excess acid if hydroehIoric 01 acetic acid is used Experiments by Wiegner (29) indicate that the lemoval of electrolytes by thorough washing is necessary in order to obtain a high degree of dispersion by any subseshyquent treatment Soils from humid regions are low in soluble salts and usually do not require much washing to prevent flocculationin the disperElion cylinder For soils subject to low rainfall however thorough washing is essentinl to good dispersion

As washing proceeds the soil] flocculated by acid treatmeiLt gladushyally cleflocculates again slmving the filtering rate Occasionally howshyever a soil such as the Cecil of Georgia does not deflocculate 011 washing For this reason it was chosen for the followin~ test Eight duplicate IO-gill samples were given hydrogen peroxide and hydroshychloric-acid treatment The samples were then washed 12 4 56 7 9 and 15 times respectively by the method described later and the tllll0unt of clay was determined by the pipette method There was no correlation between the munber of washings and the percentage of day the lesults agreeing within the limits of experimental error The Cecil It soil developed in It humid clinate is low in soluble salts and does not require much washing The loutine treatment is 6 Yashings of about 125 c c each removing the solution completely each time The entire operation leltQuires about one day When acid treatment is omitted only a fraction of 1 pe cent of soluble matter is removed by fishing and no chemical analysis of it is made

I

DISPERSING AGENlS

The dispersing agents most used in mechanical analysis are ammonia sodium hyrooxide and sodium carbonate In the centrishyfuge method in w1Jich the soil after dispersion is lepeatedly washed and the pmcentl1geof clay determined by difference any of the disshypersing agents may be used When ammonia is used in the pipette method the amotmt of ammonia held by the dried colloid is somewhat uncertain The pipetted solutions are alkaline and consequently absorb carbon dioxide from the air giving an uncertain increase of weight of the aliquot If soditim oxalate is used as a dispersing agent this difficulty disappears

Ammonium and sodium hydroxides give good dispersion when calcitun and magnesium carbonates have been removed from the soil This removallequires a thorough acid pretreatment and washing of the sample If calcium carbonate remains in the soil after pretreatshyment sodium carbonate is a better dispersing agent than either sodium or ammonium hyrooxidebecause the carbonate decreases the solushybility of the calcium carbonate while the hydroxides may produce large amounts of the flocculating calcium ions Sodium oxalate is even better as a dispersing agent than sodium carbonate Unlike the hydroxides sodium oxalate frees no allaline earth hyrooxides asa result of chemical equilibriums established Also the solubility of the oxalates of calcium and magnesium is llluch Iower than that of the

82395-29----2

l1ECmlICAlTj) SULLEllW 170U bullS JgtEJgtl QFAGRICULTURE

corresponding carbonates The middotoxalatedoesnot ieact with carhon middotdioxide 1rom the air

Surface layers of three soil types were treated with hydrogen peroxide but no acid andshaken with ilie four dispers41g agents

equimdlecular concentratioIis(rOC c ~) being usedrhisisasmall~r amount oJ ammonia than is generally used butmiddotismiddotan adeguatequan tity of theotherdeflocculents Table 6 gives themiddotquautities of 5 p and 2 iJclay obtained by the pipette method Dhe total lime computed ss GaOOa was leSS than 2 jler cent for the Garrington and Wabash soils and 139 per cent for the HOllston The ieSults indicate that ammonivm andsodiumhYdroxides arenotsuitabledeflocculei1tsfor soils which have not had acid pretieatmentand that middotof the other two sodium oxalate gives consistently higher results The Mtivityofthe oxalate ion may cause this increased dispersion OxalC acid is middotoften llsed to clean minerals for petrographicexaminationTests are soon to be made upon the efficiency of lithiumoxaiateasadeflocculent

T~LE 6-Yield of clay obtained with variou8 dispersing agentsmiddot1

Percentage of cl1Y obtained from treatment withshy

bull Soil type and source ~onia I Sodhlll hy- Sodium cnr- Sodium oxnshy droude bpnnte late

51 21 51 I 21 51 21 51 ~I Per cent Per cent~IIper ctnt Per cent Per cent P~r cent Per cent

Wabasb slit loam (Nehraska)_______ 307 241 332 2851 331 283 345 206 Houston black clay (Texas) ____bull ____ 384 264 44 5 306 613 53 5 638 538 CnrrIngtonloam (IoWa) __ _____1 78 64 249 218 2341 199 I 247 229

lvernge of duplicnte d~terminntioD~

After it was determined that sodium oxa1ategave thebest dispershysion oi soils containing calcium carbonateJ tests were made on soils containing gypsum which is much more soluble in water Table 7 gives the results middotof comparative analyses of sOme special samples of gypsum soils unclassified as to soil type Nos 28U2and 28743 are from South Dakota Nos 28655 and 28668 from Montana No 29735 from Hungaryand No 5218 from KRIlsas Analyses care made iby the international method dispersing with sodium carbonate and by our methodJ described later in which acid treatrofillt is omitted and sodium oxalate is used~s the dispersing agent~ With theexception of sample N 05218J which contams only 1 Jler cent oigypsum the routine washing was insufficient toremdve middotall thegypsum from the soils not given acid treatment The loutineamountof sodium oxalate (10 cc N 2) was sufficient to remove from solution the calcium ions formed during the three days in which the suspension stood in the sedimentation chamber There was Doindication of flocculation The amount of clay and colloid obtained was in each case greater by method 2 thRJl by method 1 It is likely that in soils containing larger quantities of a soluble calcium salt such as gypsum mOre thor~ugh lYashing acid treatmen~ orelectr~dialysis may be required iordisperslOn unless largerquantitlesoisodiumoxalate are used

------ ------

A PIPETTE METaODOF WALYSIS0F SOILS H

TABLE 7-Mechanical analysis of soils containing gypsun~

Sand 2 SUt005Sample Clay 1Colloid SolutionGypsuml Method to 005 to 0005No~ lt51 lt21 lossmm mm

~--------Rer cellI Percent Per cent Per cent Per cellt jgtercenl

28742 2 52 1 379 14 5 429 401 47 28742 202 2 373 168 438 408 20 28743 228 1 551 106 263 24 9 82 28743 228 2 562 109 31 7 263 13 28655 161 1 148 211 512 389 129 28655 161 ~ 155 235 600 443 12 28668 529 1 316 310 310 271 05 28668 529 2 317 307 328 286 48 29735 282 2 33 461 482 384 24

5218 104 2 30 340 609 52 7 16I I Computed lIS CnSObull2H0 from analysis of total S03 Hydrogen peroxide and hydrochloric acid treatment dispe~d with sodium carbonate 3Hydrogen peroxide troutment only dispersed with soditim Olltalat~

Occasionally a sample flocqulates in the sedimentation chambers This may occur with any of the dispersing agents and with or without a mild acid treatment The difficulty may -be due to the presence of some soluble soil material or of an excess or deficiency of dispersing aOent It is impossible to determine accurately from inspection wblch is the cause No investigation of the electrokinetic potentials of these suspensions has oeen made but a simple remedy has been found which USually restores dispersion A Pasteur-Chamberland suction filter is placed in the suspension and the liquid volume is reduced fro~ 1000c c t some smaller definite volume ~ay -200or 250 c c DIstilled water IS then added to make up the ongmal volshyume The suspension is thoroughly stirredand allowed to stand If flocculation again takes place measured amounts of defioccultmt ~are added until the suspension is stable This procedure leaves some uncertainty as to the weight middotof dispersing agent to be deducted from the pipetted aliquots It is assumed that the filtrate lemovedhas the same concentration as the material left in the cylinder

ELECTRODIALYSIS

Another means of effecting dispersion is electrodialysis For samshyples dispersed in this way the Mattson cell (17) was used By this method carbonates and exchange bases as wellasthe chlorides sulphates and phosphates can be removed sothatJ in addition to giving an excellent pretreatment for dispersion electrodialysis enshyables one to detennine the amount of exchange -bases in the soil The advantage of electrodialysis over hydrochloric acid treatment is that it does not introduce intothe soil a foreign ion which must be washed out later No washing is required after electrodialysis The method requires considerableextra equipment extra time additional transfers of the sample with attendant possibilities of loss and where determination of exchangeable bases ~s not desired yields no results that can not more easily be obtained by acid treatment

SHAKING

After the hydrogen peroxide treatment the sample is wash~d dried at 1050 C and weighed It is this weight which is later maae the basis for the determination of the percentage of material in each size class when the results are used for textural classification The

diied sample ls transfetred tci a250c c nmsing hottle thedisperso ing agent is added1 arrd the materialis shaken ovetnightThe shaker has a hOI~ontal moyement of 10 cm and a lateof 120 comshypIete osciJlations _p~r -n$lute Josepnand Snow1~)find middot~h(UlS shaking to he suffiCIent In theexpernnents of DaYls and MIddleton (8) -the materil1 was shaken 1 hours Since thesamplesused in the laboratory were fitstfuiedat 1050 0 it is possible that10ngershaking is reqJtied Although 16110urs is long~ shaking than necessarv ~tis corrvellient to letthe shakerrlJll 0VelDlghtThe amomtopoundgnnding of soil grams is negligible

SEPARATION INTO SIZE CLASSES

SIZE -CLASSES EMPLOYED

Early in the )York of thefonner Bureau of Soils th~ls0ils~ple (or mechaniCal analysis WaS sElparated into the ifollowing seven size classes

Diameterbullzrun iConventlonalname 20 to 10__ _ __ -----~_------)------------~ Fine gra~ellOto 05 ___ __________________________------ CQarse sand05 to 025______ ____________________________ MediUm sand 025 to 010____ _____ __-- _______ - __________ Fine sand 010 to 005 _______________ _______ __________ Yeryfinesand 005 toOOQ5__ __ - ______ -----~____ __ ~______ Silt ltO005 _________ - _________ __ -~----__-__ Clay

~alyses hased o~ the percent~e ibyeight Jgt these size dasse~~re used bYthe lbureau for the textUTitl clasSificl)tion ofsoils Cr) Dhe bureaus records contain sQme50000analyses ~b~ed onthese siz~ classes and fox this reasOn no change has beenmade in fJreseelasses except tOleport alsothe amountof material below2 p effective diameter This ~s called the icolloidpoundractionThf)5 fLclayand iihe2 p colloid both contain allparticleslbelow- diameters pi 5 II and ~ p respectively Usually less tthan 10 percent Qf the day is between 5pand 2p in effectivedjame~r Most of the material below2 p hasmiddotadiameter of only afewtenths of a ipicron or less so Jihis fraction may be regardedas essentiallyc01l6idal incharRcter ~ Xnaddition to theeig ht~ize cIasses this laboratory ~epons thello~s by pretreatment of orgaruc matter and soluble mateoal middotwllen a~ld treatment is omitted the solution loss xepresElnts roughly the amount of organic matter (Seeirable4) Neither it4esolution loss por the amount of 2p colloid is ufjed inteKturaiclas~ification Theyl~re Jeported fOl informationoniymiddot middoti

The number ofsand poundractions may he greater thannecesjary but these separations arequickly andeasily mad~ iJhedecimtilsystemlt of grading with separations madeah 20 02002 and Ol002 rmnj wouldnot furnish an adequate numhero~sizeclllcsses lor theextenshysive systemof texturaJ Cla~sification of soils uSed lhthe VnitedStates Although the coarseclay is siltyin character landiihe larger silt might be classed as very fine sand it now seems middotdesirable itO maintain the preseJlt size classification The simplest changes middotwo11ld be to omit the 5 p separation place the material between 5 bullJL and2p in the silt class and also omit the l inmsand separation throwing the mateshyrial between 2 mIil and 05 mmintp one class

(I A PIPEriE) METRO]) OF ANALTSIS OF SOILS

1lETIlQDOFSEPARAllON

After the sample has middotheen shaken withdispersingl)gent it is wet sievedthrQugh a Tyler 300-meshphQflphor brQ~etwilled wire-clbth screen which passes material finer than 50 JJ equiyalentdiametEil AU the clay and t~e diner PQ)tiQn Qfthe silt is vltshedthrQlghthe sien into a 1-liter sedimcmtation ohamber The siltremaining with the sands is dry sifted thrQughanQther300-mesh sieve added to the nest Qf sand sieves

TnefledimentatiQnchamber cQntainsQnly fine material with lQW settling velQ~itieswhere the accuracv )f pipettes8IDrgt1ig is greatest

L The suspenSlOn ill the sedimentatiQn chamher 18 stIrred andan aliquQtis quickly taken wltha 25 c cLQwyautQmaticpipette Aftermiddot the suspensiQn has stoQd 77 minutes (at 20deg c) tindagain -after stampnding 8 hQUlSaliquQts are taken at a depth middotQf 10 cm the material in the chamber being stirredthQrQughlyeach time at the beginning Qf the sedimentation periQd bull

SEDIMENTAIlON VELOCIY ANDPARIlCL) SJZJ~

All decantatiQn 01 pipette methQds Qfdeterlnining~e classes depend Qn the relatiQn Qf settling llelQcity to p8Jtkle size---andthis

relatiQnship is nQt accurately knmvnThe relaQnsbip mQst uSeg is Stokess formula (28) fQr the fallQa SQlid sphere in a viscousflUid

2 (d-iJ)V=-9 9 r

7J

vhere V i~ the settling velQcityQf I- sphere 0pound radJus r and Aen~~tyd ill a medium Qf denSlty d and VlSCQSlty 1 under a grawtationalacCeleratiQn Qr centrifugal fQreeg

The internatiQnal methQdarbitrarily nxed 8 hQmsas the time fQr a particle 2 JJ in diameter to poundall 10 em in waterat2000 ThlsJ is the value determiriedexperhnentallyby Atterherg (2) $lthoughne dQesnQt state the teniperature If StQkesslawhblds asitisassumed

in determining settling velocities in other sizes thenfuingthe reshymiddotlatiQn between settling velQcity and particle size isequivalent to fixing the density Qf tIie SQil particles Assuming d = 1 takin~the values Qf the vl8cQsitYQf water given in the internationalcntical tablesand the abQve values fQr V and TStQkess formula ~ves261 for the density of the soil particle2 JJ in diameterTh~tthis sett-ling velocity may nQtbe very aceutate is indicated by the iactthat densities Qf larger particles cQmputed from Atterbergssettling velocities and StQkess fQ~mqla range IIom 164 to 203

Joseph and SnQw (14-) use a settling velQcityof IOcm in 75 hours which cQrresPQnds to an average particle densitYQf 271~ Most specific-gravity ~easurements Qf clay give values abQve 27 RcihinshySQn and Hobnes (26) have shQwn -that the average chemicalcQmshyPQsitiQn Qf SQil CQllQid is quite ~different frQmthecbmpositiQn Qf the sand fractiQn The higher specific gravitY-Qf the collQid may be due then either to difference incQmpQsitlQn 01 to the change in density Qf water in the micrQPoresandin the surface films Qf high curyature and large tQtal area surrQunding the partieles FQr purposes of mechanical analysis it is impQrtant to knQW nQtQnly the average density of the soil particle Qf diameter 2 JJ blltalso middotthe chaJacter Qf the particle whethei it is asQlidmineral grain Qr an aggregateQr

14 lECHNlCALBULLETIN 170 USDEPT middotOF AGRICUL1URE

whether it is agel or hass gel coating The particles are too small to permit the application of the usual petrographic methods

- There is also someuncettainty as to the validity ofStokesslaw Ifor such a large range of particle shapes and sizesMillikan (18) found it necessary to add a correction to Stokess formula for spheres falling in a gas when the mean free path of the gas molecules exceededa small fraction of the diameter of the sphere In applying Stok~ss Jaw to the settling of slud~es C So Robinson (21) usedthe viscosity and density of the suspenSlOn instead of the solution and a coefficierit other than 29 for the particle shape factor It is proposed to study the relationship of settling velocity and particle siz2in the near future In the meantime it seems bestro conform to the relationshipused in the international method

The average density of soil particles at any given size is chiefly a matter of academic interest if size fractions are expressed in terms of set~ling vpoundlocities as recommended by G W Robinson (24) rather than in terms of equivalent diameters But in a method in which five separations are madu by sieving and only two by settlin~ velocishyties and the results apounde for the use of field investigators It seems preferable to hold to the concept of particle size

Joseph and Snow (14) have shown that for five soils considerable variation in temperature time or depth of pipetting producesa negligible error in the determination of 2p clay but that a hi~her relative accuracy is required for larger particles It has been notIced in this laboratory that the higher the sedimentationvelocity the mote difficult it is to secure good checks from pipette sampling One reason is that after the suspension has beenstirrp~ several minutesare required for the turbulent motion to die down and permit settling to proceed undisturbed

Formerly when all material smaller than 100p was sieved into the i

sedim~ntation chamber a pip~tte determinLtion was made at 50 p The pIpette was then fitted WIth a metal tIP closed at the bottom and provided with si( small equally spaced holes drilled horizontally through the wall of the tip near its lower end This tip assisted greatly in securing good duplicates but it was found preferable to make this separation with a finer sieve The tip Was then used in the determinations of clay and colloid in an effort tOsecure a cross section of the liquid at the deSired depth Observations on particles of lampblack indicated that a pear-shaped volume with the tip near the bottom of the pear was removed by this means The results thus obtained were no more consistent than those obtained with the pl~ straight glass tip so that the removable tip was aban~one~ According to Kohn (15) who has worked out the hydrodynamlc principles involved a pipette with any kind of tip atraight or bent shol1ld remove a sphere of liquid whose center is the opening of the pipette tip It is necessary that the rate of filling the pipette be high in comparison with the settling veloQity of the largest particles

OUTLINE OF METHOD

GENERAL STATEMENT

In view of the foregoing facts the writers desire to present a detailed method of procedure for carrying out the mechanical analysis of soils This procedure is the one now in use in the Bureau of Chemistry and

15 A PlPETTE METHODOF ANALY~IS OFSQLS

Soils It differs from the in~mational method in certain particulars viz the omission of hydrochloric acid treatmeIltthe method of filtershymg and washing the drying and weighing of the sample af~r preshytreatmeIltthe use of sodium oxala~ as disperSing agent the use ofa finer sieve for wet sieving and the fact that there is only a single transfer of the sample before separation into size classes This proshycedure is more rapid and it is believed more accurate than the international method

PREPARATION AND DISPERSION OJSAMPLE

The sample of soil for analysis is mied with alarge spatula and is then quartered The quarter reserved for analysis is rolled with a wooden rolling-pin to break up clods and then is passed through 0 sieve with 2-mm round holes Oare is taken in all mixing and quartering to see that the fine material on the paper is properly distributed Samples are run in sets of eight

Two samples ofeach soil are weighed out at the same time a 10-~m sample for analysis and a 5-gm sample for moisture determinatIOn

The latter is dried at 1050 C for 16 hours cooledin a desiccator and weighed The 10-gm sample is putiuto 0250 cc PyJex electrolytic beaker ~

To the 10-gm sample is added 40 c c of 6 per cent hydrogell pershyo~de and the bealer is covered with a watch glass The bealc~ris frequently shaken in order to bring all the organic matter in contact with the peroxide When the reaction has quieted down m)re peroxide may be added where experience indicates that it is needed and the beaker is placed on a slow steam bath overnight Thenif all organic matter does not appear to have been removed more hydrogen peroxide of full strength (about 30 per cent) is added If manganese dioxide is known to be present or its presence is indicated by decomshyposition of the hYITogen peroxide without removal of organic matter then a small quantity of acetic acid is added About 50 mg of glacial acetic acid is usually sufficient for a soil containing 0 5 per cent Mn02 Repeated additions of small amounts of hydrogen peroxide appear to give best results After decomposition of the organic matter the excess peroxide is boiled off

If acid treatment is desired the sample is cooled andthen treated with 10 c c of N HCI made too volume of 100 c c and allowed to stand overnight If it is desired to remove all the carbonates enough acid is added so that the concentration of acid in the beaker after the carbonates are dissolved will be 01 N This reallyinvolves a prior ~etermination of carbonates In this laboratory method B of the Association of Official Agricultural Chemists (1) IS used for carbonate determination

The sample with or without acid treatment is now ready for washshying This is done by removing as completely as possible the solution from the sample in the beaker with a short Pasteur-Chamberland suction filter The lower 12cm of the filter is sawed off Jittedwith a removable stopper and used for this purpose The liquid is then removed from the hollow filter core and replaced with distilled water By means of a rubber bulb back pressure is applied to the filter in order to remove adhering soil material The sample is well stirred with 125 c c of distilled water and the solution again removed by

15 A PlPETTE METHODOF ANALY~IS OFSQLS

Soils It differs from the in~mational method in certain particulars viz the omission of hydrochloric acid treatmeIltthe method of filtershymg and washing the drying and weighing of the sample af~r preshytreatmeIltthe use of sodium oxala~ as disperSing agent the use ofa finer sieve for wet sieving and the fact that there is only a single transfer of the sample before separation into size classes This proshycedure is more rapid and it is believed more accurate than the international method

PREPARATION AND DISPERSION OJSAMPLE

The sample of soil for analysis is mied with alarge spatula and is then quartered The quarter reserved for analysis is rolled with a wooden rolling-pin to break up clods and then is passed through 0 sieve with 2-mm round holes Oare is taken in all mixing and quartering to see that the fine material on the paper is properly distributed Samples are run in sets of eight

Two samples ofeach soil are weighed out at the same time a 10-~m sample for analysis and a 5-gm sample for moisture determinatIOn

The latter is dried at 1050 C for 16 hours cooledin a desiccator and weighed The 10-gm sample is putiuto 0250 cc PyJex electrolytic beaker ~

To the 10-gm sample is added 40 c c of 6 per cent hydrogell pershyo~de and the bealer is covered with a watch glass The bealc~ris frequently shaken in order to bring all the organic matter in contact with the peroxide When the reaction has quieted down m)re peroxide may be added where experience indicates that it is needed and the beaker is placed on a slow steam bath overnight Thenif all organic matter does not appear to have been removed more hydrogen peroxide of full strength (about 30 per cent) is added If manganese dioxide is known to be present or its presence is indicated by decomshyposition of the hYITogen peroxide without removal of organic matter then a small quantity of acetic acid is added About 50 mg of glacial acetic acid is usually sufficient for a soil containing 0 5 per cent Mn02 Repeated additions of small amounts of hydrogen peroxide appear to give best results After decomposition of the organic matter the excess peroxide is boiled off

If acid treatment is desired the sample is cooled andthen treated with 10 c c of N HCI made too volume of 100 c c and allowed to stand overnight If it is desired to remove all the carbonates enough acid is added so that the concentration of acid in the beaker after the carbonates are dissolved will be 01 N This reallyinvolves a prior ~etermination of carbonates In this laboratory method B of the Association of Official Agricultural Chemists (1) IS used for carbonate determination

The sample with or without acid treatment is now ready for washshying This is done by removing as completely as possible the solution from the sample in the beaker with a short Pasteur-Chamberland suction filter The lower 12cm of the filter is sawed off Jittedwith a removable stopper and used for this purpose The liquid is then removed from the hollow filter core and replaced with distilled water By means of a rubber bulb back pressure is applied to the filter in order to remove adhering soil material The sample is well stirred with 125 c c of distilled water and the solution again removed by

filtration Si sueh washings lJe usUally sufficient If it is desired

to determine the quantity of dissolved lo~des of iron and aluminum

the washings from each sample are saved sepruately made slightly

alkaline with ammonia and boiled The precipitate is washed on a

filter paper dried ignited and w(ighed

ter cleaning and temovingthe suction filter the soil sample is

i~vaporated to dryness on It steam hath and then dried in an elecbic

oven at 1Qi5deg C for 16 hours (overnight) Upon cooiogin a desiccator

the sample still in the beaker is quicldyweighed on a Ohainomotic

balance If this weighing is done rapidly the sample will not take up

more than 1 mg of moisture The sample-~s then soaked for 0 few

minutes with about 25 c c of water stirred with a rubber policemanThe beaker is againand tmnsferred to a 250 e c nmSing hottle

dtied and weighed the difference in wei~ht being the portion of the

sample left after Qrgallic matter and solution loss Tills is the portion

of the sample upon which the percentage of size classes is based when

the results are used for textural classification To the shaking bottle

is added 10 c c of 05 ijsodium oxalate and the volume is made up

to 150 c c It is stlaken overnight on the reciprocating shaker

described in Bureau of Soils Bulletin 84 (9)

SEPAltATlON INTO SIZE CLASSES

11 sieye fitted with Tyler )~OO-mesh wire screen cloth is clamped

above a I-liter graduated gliiss sedimentation cylinder on foot and

the clay and liner silt are decanted from the nursing bottle through

the sieve into the sedimentation cylinder After a few pourings theThe entireclay is completely removed from the shaking bottle

contents are then trans~erred to the sieve by means of a stream of The cylinder is filled to the I-liter mark with distilleddistilled water

water and set aside for sedimentation ECQnOlnical use of water is

necessary in decantation and washing on the sieve becauae the total

volume of the siltond clay suspension isfunited to 1 liter The sands and remaining siltmay then be washed into a platinum

dish and dried but the preferred procedure is to set the wet sieve in a

shallow alumimun dish place in an oven to dry and then transier

the dry sand and silt into the platinum dish While the sands are

drying aTlother sieve is used on the next sample Afte drying for

two homs at 105deg Cuh~ sands are cooled in a desiccator weighed

separated by a nest of graded sieves into size classes and the weight

of each class determined The summation method of weighing the

silt and sands is used The first sand is weighed the second sand is

added the total weight determined and so on If the sum of the

weights of the fractions is equal to the total weight itis assumed thnt

no error in weighing or recording weights has been made The material in the sedimentation cylinder is stirred with a motorshy

driven propeller shown in Figure 1 and immediately the pipette isThe pipettefilled before the coarser silt htis had time to settle out

is emptied into a low-form glass-covered weighing dish and the The time at ~hichthis stirringwashings from the pipette added

was made is noted The time required for a particle 5 IJ in diameter

to settle 10 em is computed from Stokess formula using a density of

261 and the viscosity of pure water for various temperatures (77

minutes at 20deg 0) A curve is plotted with temperatures as ordinates

17 A PIPETTE METHOD OF ANALYSIS OF SOILS

and time as abscissae At the time shown on the graph for the tempemture as read from a thermometer hanging in air near the cylinder the suspension is again pipetted for clay This time the pIpette clamped vertically to a SUppOlt (fi~ 1) and with stopcock closed is carefully lowered by a rnek and pInion until the tip is just 10 cm below the liquid surface as shown by a pointer moving over a poundied scale In case pipetting can not be done at the correct time the additional depth required for any delny can easily be computecJ time

FIGCIlI J-It Jell motor lind propeller used to stir suspensions at right pipette and stand

and depth being directly proportional This time the pipette is filled with an eyen suction in about 40 seconds and the entire contents run into a weighing dish The pipette is washed two or three times and tho washings added to the dish

Pipetting of the colloid is similar to that of clay except in this case settling time is fixed at six and a half hours and a graph (fig 2) comshyputed from Stokess law giving the relation of depth to temperature is used

18 ffECHNICAL RwwETlN 170 us DEPT OF JH~RICQli1URE c

In Oldinary xoutinesuspensions from eight soilsamples are placed

in a set ofsedimentation cylinders which arecov~red to prevent evaporation and are allowed to stand until aCQnvenient time fQr pipettin~ Each suspensiQn is stirred and the first aliqUQt taken at once Ii Qr the secQnd aliqUQt the suspensiQns are stirred at6-minute intervals and samples taken at the end Qfthe required time interval as xead frQm the time-temperature chart (Fig 2) FQr the third aliquQt the suspensions are stirxed early in the day and the samples taken after sh and Qne-half hQurs at the CQrrect depth as read frQm the depth-temperature chart (Fig 2) If desiredJgtQth charts may be prepared fQrpipetting at CQnstant time intervals or at CQnstant depth It is essential that the pipette be dried el(htime before filling and

that the entire CQntents be emptied into the wElighing dish The pipette is calibrated fQr total v91ume and nOt fQr delivery The alishyqUQts are evapQrated to dryness Qn a steam bath dried at 105deg0 for 16 hours (Qvernight) cOQled in a desiccatQr and weighed Since any

V110 liD

~ 2~

i- ~ - 1

~

1 1

I-1- ~

~ ~ aDV ~ ~

V 1-I--

50 7J ~ 10 JQ IS

Z5 TevnoltrIfrurlt (lt0 FlOURamp 2-Sedimentntlon velocity graphs used in the pipctting of clay and colloid

lQss of material Qr errQr in weighing is magnified nearly fQrtyfQld in the final result it is necessary tQ use care in the determmatiQnQf the pipetted fractiQns Weighings are carried to 01 mg and the weight of the dishes is determined each time they are used

If the rQom temperature changes rapidly the cylinders are cQvered with bakelite jackets but in general rQQm-temperaturechanges prQshyduce Qnly negligible variations If there is a temperature difference between QPPQsite sides Qf the cylinder there will be a circulatQry mQveshyment of the suspension a conditiQntQ be aVQided

OccasiQnally sets of separates are submitted to William H Fry Qf this laboratQry fQr micrQscopic examination by his methQds (10) He usually finds the sands practically free from adhering collQid and the silt relatively free frQm cQllQidal aggregates

CALCULATIoN OF RESULTS

FrQm the mQisture determinatiQn Qf the 5-gm sample the dry weight Qf the sample fQr analysis is cQmputed After perQxide treatshyment and acid treatment if used fQllQwed by wRshingthe sample is

17 A PIPETTE METHOD OF ANALYSIS OF SOILS

and time as abscissae At the time shown on the graph for the tempemture as read from a thermometer hanging in air near the cylinder the suspension is again pipetted for clay This time the pIpette clamped vertically to a SUppOlt (fi~ 1) and with stopcock closed is carefully lowered by a rnek and pInion until the tip is just 10 cm below the liquid surface as shown by a pointer moving over a poundied scale In case pipetting can not be done at the correct time the additional depth required for any delny can easily be computecJ time

FIGCIlI J-It Jell motor lind propeller used to stir suspensions at right pipette and stand

and depth being directly proportional This time the pipette is filled with an eyen suction in about 40 seconds and the entire contents run into a weighing dish The pipette is washed two or three times and tho washings added to the dish

Pipetting of the colloid is similar to that of clay except in this case settling time is fixed at six and a half hours and a graph (fig 2) comshyputed from Stokess law giving the relation of depth to temperature is used

18 ffECHNICAL RwwETlN 170 us DEPT OF JH~RICQli1URE c

In Oldinary xoutinesuspensions from eight soilsamples are placed

in a set ofsedimentation cylinders which arecov~red to prevent evaporation and are allowed to stand until aCQnvenient time fQr pipettin~ Each suspensiQn is stirred and the first aliqUQt taken at once Ii Qr the secQnd aliqUQt the suspensiQns are stirred at6-minute intervals and samples taken at the end Qfthe required time interval as xead frQm the time-temperature chart (Fig 2) FQr the third aliquQt the suspensions are stirxed early in the day and the samples taken after sh and Qne-half hQurs at the CQrrect depth as read frQm the depth-temperature chart (Fig 2) If desiredJgtQth charts may be prepared fQrpipetting at CQnstant time intervals or at CQnstant depth It is essential that the pipette be dried el(htime before filling and

that the entire CQntents be emptied into the wElighing dish The pipette is calibrated fQr total v91ume and nOt fQr delivery The alishyqUQts are evapQrated to dryness Qn a steam bath dried at 105deg0 for 16 hours (Qvernight) cOQled in a desiccatQr and weighed Since any

V110 liD

~ 2~

i- ~ - 1

~

1 1

I-1- ~

~ ~ aDV ~ ~

V 1-I--

50 7J ~ 10 JQ IS

Z5 TevnoltrIfrurlt (lt0 FlOURamp 2-Sedimentntlon velocity graphs used in the pipctting of clay and colloid

lQss of material Qr errQr in weighing is magnified nearly fQrtyfQld in the final result it is necessary tQ use care in the determmatiQnQf the pipetted fractiQns Weighings are carried to 01 mg and the weight of the dishes is determined each time they are used

If the rQom temperature changes rapidly the cylinders are cQvered with bakelite jackets but in general rQQm-temperaturechanges prQshyduce Qnly negligible variations If there is a temperature difference between QPPQsite sides Qf the cylinder there will be a circulatQry mQveshyment of the suspension a conditiQntQ be aVQided

OccasiQnally sets of separates are submitted to William H Fry Qf this laboratQry fQr micrQscopic examination by his methQds (10) He usually finds the sands practically free from adhering collQid and the silt relatively free frQm cQllQidal aggregates

CALCULATIoN OF RESULTS

FrQm the mQisture determinatiQn Qf the 5-gm sample the dry weight Qf the sample fQr analysis is cQmputed After perQxide treatshyment and acid treatment if used fQllQwed by wRshingthe sample is

18 ffECHNICAL RwwETlN 170 us DEPT OF JH~RICQli1URE c

In Oldinary xoutinesuspensions from eight soilsamples are placed

in a set ofsedimentation cylinders which arecov~red to prevent evaporation and are allowed to stand until aCQnvenient time fQr pipettin~ Each suspensiQn is stirred and the first aliqUQt taken at once Ii Qr the secQnd aliqUQt the suspensiQns are stirred at6-minute intervals and samples taken at the end Qfthe required time interval as xead frQm the time-temperature chart (Fig 2) FQr the third aliquQt the suspensions are stirxed early in the day and the samples taken after sh and Qne-half hQurs at the CQrrect depth as read frQm the depth-temperature chart (Fig 2) If desiredJgtQth charts may be prepared fQrpipetting at CQnstant time intervals or at CQnstant depth It is essential that the pipette be dried el(htime before filling and

that the entire CQntents be emptied into the wElighing dish The pipette is calibrated fQr total v91ume and nOt fQr delivery The alishyqUQts are evapQrated to dryness Qn a steam bath dried at 105deg0 for 16 hours (Qvernight) cOQled in a desiccatQr and weighed Since any

V110 liD

~ 2~

i- ~ - 1

~

1 1

I-1- ~

~ ~ aDV ~ ~

V 1-I--

50 7J ~ 10 JQ IS

Z5 TevnoltrIfrurlt (lt0 FlOURamp 2-Sedimentntlon velocity graphs used in the pipctting of clay and colloid

lQss of material Qr errQr in weighing is magnified nearly fQrtyfQld in the final result it is necessary tQ use care in the determmatiQnQf the pipetted fractiQns Weighings are carried to 01 mg and the weight of the dishes is determined each time they are used

If the rQom temperature changes rapidly the cylinders are cQvered with bakelite jackets but in general rQQm-temperaturechanges prQshyduce Qnly negligible variations If there is a temperature difference between QPPQsite sides Qf the cylinder there will be a circulatQry mQveshyment of the suspension a conditiQntQ be aVQided

OccasiQnally sets of separates are submitted to William H Fry Qf this laboratQry fQr micrQscopic examination by his methQds (10) He usually finds the sands practically free from adhering collQid and the silt relatively free frQm cQllQidal aggregates

CALCULATIoN OF RESULTS

FrQm the mQisture determinatiQn Qf the 5-gm sample the dry weight Qf the sample fQr analysis is cQmputed After perQxide treatshyment and acid treatment if used fQllQwed by wRshingthe sample is

19 APIPETrE METaOD OF ANALYSIS OF SOILS

dried and weighed The difference between the two weights is the hydrogen peroxide-solution loss The first dry weight which includes organic matter and solution loss is taken as the base for calculation of results except when the analysis is to be used for textural classific8shytion only In the latter case the d-y w6~ht aiter washing is taken as the base

From the weight of the first pipetted aliquot after deducting the weight of the dispersing agent the dry weight of silt and clay in the sedimentation chamber can be determined directly It can also be determined by taking the difference between the total weight of the sample before dispersion and the wei~ht of the dry sifted silt and sands These weights should check tmt in every case the weight directly determined by pipetting is slightly greater varying from a small fraction to as much as 1 per cent or more The reasoQ for this discrepancy has not yet been found In loutine analyses the dry weight of material in the sedimentation chamber is obtained by difshyference but the amolmt is also determined by pipetting and if the two results fail to check within 2 per cent the analysis isrejgteated

From the weight of the clay and colloid aliquots is deducted the weight of added sodium oxalate and the total amount of material smaller than 5p and 2p is computed No size class between these two limits is established If the weight of clay is deducted from the total dry weight in the sedimentation cylinder the difference is silt This is added to the amount of silt sifted from the sands to give total silt

Below are given the data obtained and the results computed from the analysis of a sample of soil Sample No 561860

Weight of sample air-dry 10 gm Moisture (determined on duplicate sample) =489 per cent Dry weight of sample at 1050 C=10000-0489=9511 gm Dry weight of sample (after pretreatment and washing) 9366 gm Solution loss=9511~9366=0145 gm=16 per cent Weight of sand lt+ some silt)=2U6 gm

Silt=0046 Size Weight Per

Sand 2070 gm mm

20 -10 10 -5

gm O 249 394

cent 2 7 42

5 - 25 312 33

25- 1 567 61

1-05 557 59 W~ht of silt+clay aliquot 01905 gm

Weight of clay aliquot 01127 gm Volume of pipette=2512 c c=1398 liter Weight of N8rC20~ in 2512 c c=00065 gmWeight of clay= (01127-00065) 398_____________ _________ 4227 451 Weight of silt=9356-(2070+4227) _____________________ 3059 327

Total except solution loss _____________________________ 9365 1000 Weight of colloid aliquot=00897Weight of colloid=(00897-00065) 398____________________ 3311 354

APPARATUS

A few special pieces of apparatus used in mechanical analysis that have not previously been described are the wei~hing dishes pipette stirrer sieves and shaker The pipette (fig 1) IS a Lowy automatic

j A determination of silt may be made os foUows Weight of silt aliquot=O1005-01127=O07i8 gm Weight o(silt=O07iSX398+OJI6=3H2 gm=336 per cent

ji20 TECHNICAIiBULLEThl t7() U S DEPT OF AGRICULTURE

equipped with a stopcock having an air vent When the pipette is full a 900 rotation of the stopper will close the stopcock and an addishytional 900 rotation will permit ddivery The house vacuum is conshyn~cUJd through a poundne capillarYl1id as~aJl sulphmic Bcid trap to ~c pIpette The capillary pernu~the deSIred slow andmiddot uniform filling of the pipette and the sulphuric acid trap keeps moisture from intershyfering with the air flow through the capillary The pipette has a delivery vobune of 25 c c but is calibrated with mercury for total ~olume

The stirrer shown in Figure 1 is a motor-driven 4-blade propeller ona sliding shaft which can be clamped at any height to the driving pul~ey The variable speed motor is run as fast as possible without whlWping air into the suspension Mter a suspension has stood for tWj or three days it is sometimes difficult with hand stirring to break up the flakes of silt and clay aggregates which have settle~ on the bottom of the chamber

The weighing dishes are of low flat form in two sizes one 65 mm in diameter and 30 mm high and the other 50 mm by 30 mm with correspondingly numbered glass lids ground to fit over the outside of the dish The small dish is used for the clay and colloid pipelting and the larger dish is used for the first or silt pipetting because of the extra washing required to remove the coarser particles from the pipette

The sieve frames mnde from 2~-inch extra heavy brass pipe are fitted with removable rings to permit the easy change of screens The two larger sieves have round holes of 1 and 05 mm respectively The next two screens conform to the Bureau of Standards specificashytions for 60-mesh and 140-mesh sieves They have square openings of 025 and 0105 mm respectively The finest sieve is 300 mesh and holds particles larOer than silt size The screen wire cloth on the 300-mesh sieve is frequently renewed as the wire is so fine that it is easily stretched worn or broken

SUMMARY

The method of mechanical soil analysis developed for use in the soil physics laboratory of the Bureau of Ohemistry and Soils is described In pretreatment the organic matter is removed with hydrogen peroxide but the hydrochloric acid treatment used in the international method ordinarily is omitted A method of removing organic matter in the presence of manganese dioxide is described Soluble matter is removed by washing and filtering with PasteurshyOhamberland suction filters The sample is dried and weighed and this weight is the basis of calculation of percentages of material in each size class when the results are for use in textural classification In all operations up to dispersion the sample remainsin an extra tall form beaker The sample is deflocculated by shaking in a dilute sodium oxalate solution The colloid clay and fine silt are separated from the sands by means of a 300-mesh sieve The clay and colloid are determined by sedimentation the pipette method being used The procedure is designed for accurate and rapid analysis

Investigation of dispersion aids incidental to this method discloses the fact that acid treatment introduces undesirable solution losses and is not necessary for dispersion even in calcareous soils particushylarly if sodium oxalate is used as the dispersing agent

A llPEllE MElHOl)OF ANALX~IS OF SOILS 21

LIlERATURE CITED

(1) ASSOCIAlION OF OFFICIAL AGRICULlURAL CHEBUSlS 1925 OFFICIAL AND TENTAlIVE MElHODS OF ANALYSIS COMPlLED JlY

lHECOMMIllEE ON EDIlING MElHODS OF ANALYEIS REVISED TO JULY i IOU Edbull2 535 p ilius Washington DC

(2) AllERBERG A ~908 SlUDIEN AUF DEM GEBlElE DER JlODENKUNDE Landw Verso

Sta 69 [93]-143 (3) BODMAN G B

1928 lHE HYDROGEN PEROXIDE-HYDROCHLORIC ACID lREATMENl 01 SOILS ASA MElHOD OF DlS~ERSION IN MECHANICAL ANALYSIS Soil Soi 26 459-470 illus

(4) BoUYoucos G B 1929 IHE ULTIMAC1l NATURAL SlRUCTURE OF THE SOIL Soil Soi 28

127-37 (5) BRIGGS L J MARlLN FO and PEARCE J R

1904 TlIE CENlRIFUGAL METHOD OF MECHANICAL SOIL ANALYSIS U S Dept Agr Bur Soils Bul 24 38 p illus

(6) DAVIS R O E 1925 COLLOIDAL DETERMINATION IN MECHANICAL ANALYSIS Jour

Amer Soo Agron17 275-279 (7) --- and BENNETT H H

1927 GROUPING OF SOILS ON THE BASIS OF MECHANICAL ANALYSIS U S Dept Agr Ciro 419 14 p illus

(8) --- and MIDDLETON H E 1927 DISPERSION OF SOIU3 FOR MECHANICAL ANALYSIS First Internatl

Congo Soil Soi 1 366-377 (9) FLETCHER C C andBRYAN H

1912 MQDIFICATION OF THE METHOD OF MECHANICAL SOIL ANALYSIS U S Dept Agr Bur Soils Bu 84 16 p illus

(10) FRY W H 1923 IHE MICROSCOPIC ESTIMATE OF COLLOIDS IN SOIL SEPARATES

bull Jour Agr Research 24 879-883 (11) HILGARD E W

1906 SOILS THEIR FORMATION PROPERTIES COMPOSITION AND REshyLATIONS IO CLIMATE AND PLANI GROWTH IN THE HUMID ANDmiddot ARID REGIONS 593 p illus New York and London

(12) HOPKINS C G 1899 A RAPID METHOD OF MECHANICAL SOIL ANALYSIS LlCLUDING THE

USE OF CENTRIFUGAL FOUCE U S Dept Agr Div Chern Bul 56 67-68

(13) JENNINGS D S THOMAS M D and GARDNER M 1922 A NEW METHOD OF MECHANICAL ANALYSIS OF SOILS Soil Soi 14~

485-499 illus (14) JOSEPH A F and SNOW O W

1929 THE DISPERSION AND MECHANICAL ANALYSIS OF HEAVY ALKALINE SOILS Jour AgrSoi 29 [106]-120 illus

(15) KOHN M 1928 BEIlRAGE ZUU IHEORIE UND PRAXIS DEU MECHANISCHEN BODEN-

ANALYSE Landw Jahrb 67 486-546 illus (16) KUAUS G

1923 ERGXNZENDER JlERICHI UBEU EINE DEM PBAGER BODENKUNDshyLICHEN JWNGRESS VORGETRAGENE NEUE METHODE DEU MECHshyANISCHEN BODENANALYSESOWIE EIN EINFACHESGRAPHJSCHES VERFAHREN ZUR BESTIMMUNG DER KORNOBERFLXCHE FERNER PRAKTISCHES GEMT ZUR PROBEENTNAllME ZWECKS ERMIllELUNG DER LAGERUNGSWISE Iuternatl Mitt Bodenk 13 147-160 illus

(17) MAllSON S 1926 ELECTRODIALYSIS OF THE COLLOIDAL SOIL MATERIAL AND TIlE

EXCHANGEABLE BASES Jour Agr Researoh 33 553-567 illus (18) MILLIKAN R A

[1924] THE ELECTRON IIS ISOLATION AND MEASUREMENT AND IHE DETERshyMINATION OF SOME OF ITS PUOPERTIES Ed 2 293 p illUB Chioago

A llPEllE MElHOl)OF ANALX~IS OF SOILS 21

LIlERATURE CITED

(1) ASSOCIAlION OF OFFICIAL AGRICULlURAL CHEBUSlS 1925 OFFICIAL AND TENTAlIVE MElHODS OF ANALYSIS COMPlLED JlY

lHECOMMIllEE ON EDIlING MElHODS OF ANALYEIS REVISED TO JULY i IOU Edbull2 535 p ilius Washington DC

(2) AllERBERG A ~908 SlUDIEN AUF DEM GEBlElE DER JlODENKUNDE Landw Verso

Sta 69 [93]-143 (3) BODMAN G B

1928 lHE HYDROGEN PEROXIDE-HYDROCHLORIC ACID lREATMENl 01 SOILS ASA MElHOD OF DlS~ERSION IN MECHANICAL ANALYSIS Soil Soi 26 459-470 illus

(4) BoUYoucos G B 1929 IHE ULTIMAC1l NATURAL SlRUCTURE OF THE SOIL Soil Soi 28

127-37 (5) BRIGGS L J MARlLN FO and PEARCE J R

1904 TlIE CENlRIFUGAL METHOD OF MECHANICAL SOIL ANALYSIS U S Dept Agr Bur Soils Bul 24 38 p illus

(6) DAVIS R O E 1925 COLLOIDAL DETERMINATION IN MECHANICAL ANALYSIS Jour

Amer Soo Agron17 275-279 (7) --- and BENNETT H H

1927 GROUPING OF SOILS ON THE BASIS OF MECHANICAL ANALYSIS U S Dept Agr Ciro 419 14 p illus

(8) --- and MIDDLETON H E 1927 DISPERSION OF SOIU3 FOR MECHANICAL ANALYSIS First Internatl

Congo Soil Soi 1 366-377 (9) FLETCHER C C andBRYAN H

1912 MQDIFICATION OF THE METHOD OF MECHANICAL SOIL ANALYSIS U S Dept Agr Bur Soils Bu 84 16 p illus

(10) FRY W H 1923 IHE MICROSCOPIC ESTIMATE OF COLLOIDS IN SOIL SEPARATES

bull Jour Agr Research 24 879-883 (11) HILGARD E W

1906 SOILS THEIR FORMATION PROPERTIES COMPOSITION AND REshyLATIONS IO CLIMATE AND PLANI GROWTH IN THE HUMID ANDmiddot ARID REGIONS 593 p illus New York and London

(12) HOPKINS C G 1899 A RAPID METHOD OF MECHANICAL SOIL ANALYSIS LlCLUDING THE

USE OF CENTRIFUGAL FOUCE U S Dept Agr Div Chern Bul 56 67-68

(13) JENNINGS D S THOMAS M D and GARDNER M 1922 A NEW METHOD OF MECHANICAL ANALYSIS OF SOILS Soil Soi 14~

485-499 illus (14) JOSEPH A F and SNOW O W

1929 THE DISPERSION AND MECHANICAL ANALYSIS OF HEAVY ALKALINE SOILS Jour AgrSoi 29 [106]-120 illus

(15) KOHN M 1928 BEIlRAGE ZUU IHEORIE UND PRAXIS DEU MECHANISCHEN BODEN-

ANALYSE Landw Jahrb 67 486-546 illus (16) KUAUS G

1923 ERGXNZENDER JlERICHI UBEU EINE DEM PBAGER BODENKUNDshyLICHEN JWNGRESS VORGETRAGENE NEUE METHODE DEU MECHshyANISCHEN BODENANALYSESOWIE EIN EINFACHESGRAPHJSCHES VERFAHREN ZUR BESTIMMUNG DER KORNOBERFLXCHE FERNER PRAKTISCHES GEMT ZUR PROBEENTNAllME ZWECKS ERMIllELUNG DER LAGERUNGSWISE Iuternatl Mitt Bodenk 13 147-160 illus

(17) MAllSON S 1926 ELECTRODIALYSIS OF THE COLLOIDAL SOIL MATERIAL AND TIlE

EXCHANGEABLE BASES Jour Agr Researoh 33 553-567 illus (18) MILLIKAN R A

[1924] THE ELECTRON IIS ISOLATION AND MEASUREMENT AND IHE DETERshyMINATION OF SOME OF ITS PUOPERTIES Ed 2 293 p illUB Chioago

TECHNICAL BUI4EllN 170U S DEPT OF AGRICULTURE

C(19) NovlK V

1927 CONCLUSIONS OF lHE FlRSl COMMISSION MEElING AT JlOTHAMshySTED llARPENDENl 926 Internatl SOC Soil Sci 16 p Brno Czechoslovakia [In English p 5--8 Germanp9-12 French

~p 13-161 (20) OSBO~NE T B

1886 THE METHODS OF MECHANICAL SOIL ANALYSIS Conn Agr Expt Sta Ann Rpt -- 141-158

(21) ROBINSONC S 1926 SOME FACTORS INFLUENCING SEDIMENTATION Jour lndus and

Engl Chern 18 869-871 iUus (22) ROBINSON G W

1922 NOTE ON THE MECHANICAL ANALYSIS OF HUMUS SOILS 1922 Jour Agr Sci 12 [287]-291

(23) 1~22~ A NEW ME~HOD FOR TRE MECHANICAL aNALYSIS OF SOlLS AND

OTHER DISpERSIONS JoUl Agr Sci 12[306]-321 lilus ~l--(24)

1927 THE GROUPlNG OF FRACTIONS IN MECHANICAL ANALYSIS First Internatl Congo Soil Sci 1 359-365

(25) ROBINSON WO 1927 THE DETERluNATION OF ORGANIC MATTER IN SOILS BY MEANS OF

HYDROGEN PEROXIDE Jour Agr Research 34 339-356 (26) --- and HOLMES R S

1924 THE CHEMICAL COMPOSITION OF SOIL COLLOIDS U S Dept Agr Bul 1311 42 p

(27) SNXDERH 1896 THE CHEMICAL AND MECHANICAL ANALYSIS OF SOILS Minn Agr

Expt Sta Ann Rpt 1895 [32]-63 lilus (28) STOKES C G

1856 ON TBE EFFECl OF THE INTERNAL FRICTION OF FLUIDS ON tlHE MOTION OF PENDULUMS Cambridge Phil Soc Trans (1851shy56) 9 (Pt ll) [8]-[106]

(29) WlEGNERG 1927 METHOD OFPREPARAtlION OF SOIL SUSPENSIONS AND DEGREE OF

DISPERSION AS MEASURED BY THE WlEGNER-GESSNER APPARATUS Soil Sci 23 377-390

QRGANIZATION OFlHE Ul1ITED STATES DEPARTMENT OFA~RICuLll1Rl)l

Decemlgtek-l2 1929

Becretaryoj Agri~lture___________________ MTHURId HY~E

ABsistant Secretary _______________________ iR W DUNLAP

DirectorgtojBcientific gtWor~_---------~----- A iF WOODS iDireclorof Regulatgtry 1firirk_ ___ ___ _____ __ _ WALTER G lAMPBELL

Direciorof Extension Work ________--_____ Q W WARBUllTON

J)ireclor of PerB01Inel and B18ineliB Admin-W W middotSTOCEBERGER istration

i(rectoroj Information ________________ --- M S EIIIENHOWER Weather Bur~u___________----- ________ CHARIiESF MARVIN Chief $ureau of Animal indu8try_______________ JOHN R MOHIiER middotChief BUrllau of Dairy Industry _________________ O E REED Chief BUTeau of Plant Industry________ _________ WILLIAM A TAlLOR Chief Forest Service ______ ______ ~----_________ R YSl1UART Chie Bureau of Chemi8try and BoiI8_____________ HG KNIGHTChief Bureau of Entomology____________________ C L MARLATT Chief Bureau of Biological Survey _______________ PAtL GREDINGrJOl Ohiej Burllau of Public Roads __________________ THOMAS H MACDONALD gtChief Bureau of Agricultural 8c9nomic8 __________ NILS A OLSENChief gt

BurealL of Home Economics _______________ LOmSESTAJlLEY middotChief Plant Quarantine and Control Administra- LEE ASTRQNGChief

tion -Grain FUture8 AdminiBtration _____________ J W T DuvEL Chief Food Drug and Jnsecticide Admini8tration __ WALTERGCAMPBELL Directorof

Regulatory Work in Charge Office of Experiment Station8_____________ Chief middotOffice of Cooperative Extension Work ________ C BSMITHChief Libra1I_________________ - ______________ gtCLAIDBEL R B~NETT Librarian

This bulletin is 8 cOlltribution from

Bureau of Chemi8try and Soil8 _____________ H G KNIGllTChief Soil Investigations ___________________ AG MCCALLmiddotChief

Division oj Soil Chemistry and H G BYERs Principal middotChemist Physics in Charge

23

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