D,PoH0

Pis infectants9

The following are qualitative tests for some of the commoner disinfeobantso These tests, if positive are to be regarded as suggestive only and confirmatory tests would have to be employed in most instances.Formalin, Formo1 (a 40 per cent, solution of formaldehyde - H.CHO -

in water).(a) Distinctive smell in strong solution particularly on

warming, •*-'(b) Add a few drops of 57° phenol end then do a ring test with

strong H/5SG4 . Purple colour.,./ SPhenol. Carbolic acid - C^H.SaOH.

( \ TP V i , . . , _ - ^(a) F e m e chloride solution gives a purple colour(b) Bromine water - a white precipitate of tribromophenol.

Mercuric chloride - corrosive sublimate.(a) KI solution gives a yellow precipitate of mercuric iodide

soluble in excess*Cooper salts and 2,inc salts„

Same tests as in v/ater analysis.Sulphur ous acid, /

\ Cj. J CxliO _l_ —. .L G0£ (add acid if a sulphite).(b) AgNOj - white ppte soluble in strong HNO3,

Chlorine„(a) KI - iodine is set free. f\ 4-£o^,

(b) Ortho - tolidine testc

Quantitative Methodse(l) Determination of available chlorine in bleaching powder.(a) Make a suspension - solution by weighing otbt about 1 gram (accurately) of the powder and grinding it up in water. Make upto 100 cc0 in a volumetric flask,

Tako out 10 cc3 with a pipette,,Titrate with 0olN sodium arsenite solution. To determine the

approximate chi point, a drop is taker, out by means of a small glassIf free chlorine is still paper owing to the libera-

poiht is not very sharp a slight excess of the arsenito will have to be added before the test paper gives no colour. The amount of the excess added can now be determined by

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titrating the mixture of bleach and arsenite with 0.1N iodine solution using starch as an indicator.

Supposing that X cc, of the OelN arsenite were Qdded originally and y cc. of 0.1N iodine are needed to produce a blue colour on back titration then (X - y) cc„ of 0.1N arsenite solution have been required to use up the amount of available chlorine in 10 cc.' of the original dilution of bleach.

Calculate first to a normality and then express your result as a percentage of available chlorine by weight in the original powder.

A newly-prepared bleaching powder contains about 33 per cent, of available chlorine„

Rationale of the process:-2Ca(0C1)C1 + As203 = 2CaCl2 + As205

(b) An alternate method which however gives results which are too high in the presence of chlorates in the bleaching powder, is to take 10 cc. of the suspension-solution, acidify with acetic acid and then add KI. The free chlorine set3 free iodine which is then estimated by the usual thiosulphate titration method.(2) Determination of the amount of phenol in a solution.

To a 200 cc, flask add 50 cc, of water, 5 cc.. strong HC1, ‘ ‘ ” -« . . , - i n _ - i -in _____ J 1___________ f n t Z ~ ~ -P - i 4 > .25 cc. of the phenol solution followed by an excess (25 cc. for

given phenol solution) of 0.1N sodium bromide-bromate solution.*? S~*f . Shake and allow to stand for 15 minutes. Add 5 cc. KI when iodine will be liberated and can then be titrated with thiosulphate.This titration determines the excess of bromide-bromate solution which has not been used up by the phenol.

The rationale of the process.is, in the first place acid added to a mixture of bromide and brcmate yields free bromine

5NaBr + HaBrOg + S HC1 = 6NaCl + 3Br2 + 3Hg0

The free bromine then unites with the phenol:~C6H50H + 3Br2 5 OgHgBrgOH + 3HBr

The excess bromine is then determined as stated by means of KI and thiosulphate titration.

In the calculation note that:-C6H50H = 3Br2

and therefore a normal solution of phenol contains M.W., grams per6 litre

Calculation.Supposing 5 cco of 0.1N thiosulphate are required to neutralize

the iodine liberated by the residual bromine. . 25 - 5 cc. 0.1N bromide-bromate = 25 cc. of the phenol

solution ^Then the normality of the phenol solution = 20 x 0.1 = 0,09 N

25Prom this calculate the percentage strength,.

D.P.H.Adsorption,

Previously, in the lecture on colloida, the importance of electric charges and certain other physical properties of surfaces have been discussed,'without considering the actual make up of the surface.Today we wish to extend our study to a consideration of the molecules present at a surface. .We immediately find that even in many simple

Q) solutions the acfa al.-cona-ti fcutinrL_c.ilth&_siir£aiia„ layers--of -the solutlon \ .q different from that in the body pf the fluid, e.g. if air is blown through an aqueous solution of amyl alcohol so that a deep froth is formed, then on removing the froth and determining the amount of alcohol present in the fluid that makes up the froth, it is found that the concentration is much greater than is the concentration of alcohol in t,he underlying solution. The only difference between the froth and the underlying solution is that the .former has a much greater surface or interface between the solution and air makin'g up the froth.' It is clear then that the concentration of alcohol present at the air-liquid interface is greater than that in the body of the fluid. This inorease in concentration of a solution at a surface is due to the phenomenon known as adsorption.

Glbbjs Adsorption Theorem states that a dissolved substance must increase "its concentration at the surface if it tends to lower the surface tension. Or vice versa, a-solute must decrease its con­centration at a surface if it tends to raise the surface tension.♦

As adsorption does not depend solely upon the property of surface tension the theorem is best amplified thus:

Any substance in solution in a liquid in contact with the surface of another phase will increase its concentration at that surface, if by so doing the free energy (mechanical, ^Lectrical, chemical, etc.) present there is decreased.;

Adsorption may be roughly defined as a loose fixation of a I substance at an interface. it is not a true chcifflcal combination.

Adsorption may take place at an interface between any two phases, e.g. a solid and a liquid, a solid and a gas, a liquid and another liquid, or a liquid and a gas. Ab a simple example we may take the ‘'adsorption of the dye, methylene blue, from solution by the solid, powdered charcoal. If the dye solution be shaken with charcoal then on filtering the filtrate is found;fco be colourless. In this experiment we have a loose combination between the dye (the adsorptive) and the charcoal (the adsorbent). This combination of adsorptive with adsorbent is termed the adsorbate.

Gaseous Adsorption.„ * * ►

Similarly charcoal will adsorb many gases, e.g. it will remove NH3 from a mixture of this gas with air.

* *With gases it is usually found that the more easily a gas may be

liquefied the more readily will it be rdsorbed.Generally speaking a rise in temperature decreases the amount of

substance adsorbed. It follows, that when adsorption takes place heat is given out, e.g. the apparent temperature of a patient is higher if the thermometer is wrapped in flannel. This is duo to the heat of adsorption of the moisture on the flannel.

If the temperature is kept constant it is found that the amount of gas adsorbed increases at first rapidly with increase in its pressure, but that the increase gradually falls off until a further rise in pressure does not lead to any further increase in the amount adsorbed. This result can be shwn as a curve - an adsorption isotherm - if the amount of a gas adsorbed by unit area of an adsorbent when the system has reached equilibrium, is plotted against the concentration or pressure

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of the gas at that equilibrium. This result can be expressed mathematically (Freundlich): «% f. v

* * I = aC' n or l0g i = l0ga + n log C• '

wherex = the amount »f gas adsorbed by a surface of area m from a gaseous system in which the final concentration or pressure »f the gas is C. If the logarithmic equation be plotted instead then a straight line is obtained, the line cutting the x axis at the point log a above the zero point. y f

ASLSorbent^^^Exam^S^f good adsorbents are charcoal, silicic acid gel,’ infusorial earth, kaolin, alumina, etc.

Examples of gaseous adsorption.4 v

1. Charcoal respirators used to adsorb poisonous gases from *inhaled air.

2. The recovery of benzene from the waste fumes of many chemicalfactories by passing the flue gases over charcoal,, *

3. The attainment of very high vacua by adsorbing Hg vapour bycharcoal.

Adsorptl«n in solution. ,w I %.The laws governing gaseous adsorption apply equally to adsorption

from dilute solutions. If the concentration be increased beyond the value giving maximum adsorption then the adsorption generally diminishes, v . » . - .* *

Catalan-It is believed that adsorption is generally a preliminary stage in

catalytic and enzymatic reactions, that is, in those reactions whose rate is increased immensely by the addition «f some substance, e.g. finely divided platinum, which however appears fco be unchanged at the end of the reaction. Par example:

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(2) 3H2 + n2

(3) \CO ' + Cl2

Fe alloy> 2S03

2NH3 *

-> C0C12 (phosgene)

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It has actually "boon shown that the rate of many homogeneous reactions in-solution depends upon the nature of the containing vessel.

V

Theories of Adsorption. f

(1) Non-polar adsorption. Adsorption is due to the lowering of^ , surface tension by the concentration ef the adsorptive at the .surface. Called non-polar because many substances that lower surface tens ionise little in solution, e.g. the group of substances known as fatty acids increase in both- their power of being adsorbed and their power of lowering surface tension as the acid becomes more complex.19.) Polar adsorption. Adsorption is due to the partial or complete neutralisation of '£Ee electric charge of a surface by the deposition of oppositely charged particles at that surface, e.g. by oppositely 'charged colloidal jsarticles or ions.

• * .For example - negatively charged charcoal'-.particles adsorb positively charged FeToH)3 particles or positively charged ions suchas H*, K*, Na*, etc.

± • A *- (S) Chemical or Electro-chemical adsorption. ^

Neither (1 ) nor (2 ) can explain all examples of adsorption.For instance why-should negative OH ions be adsorbed more readily by charcoal than positive Na* ions? As we investigate further, and especially in biological fields.it becomes more and more obvious that a specificity *f-adsorption exiits, which can only be explained *>7 the view that certain groupings present in the surface have a specific affinity fer certain other groupings in the adsorbed molecule. mat is to say, that adsorption is really based on chemical attraction.•# ‘ , . \

Examples of Adsorption of Interest in _Bi<plogy_.(1) The power possessed by the humus ef the s«il to retain soluble salts, thereby preventing them from being washed away by rain.(2) In sewage disposal works nitrifying erganisms develop in the lower part of the contact filters. These organisms only develop, however, if certain organic impurities of.sewage are removed from the liquors by adsorption on the upper layers of the filter.

\

(3 ) The permutit water softening system depends upon the exchange of the Na ions of the zeolite fer Ca and Mg ions of the water. This exchange may be an adsorption process.(4)" Catalytic and enzymatic reactions are probably dependent upjn an initial adserption of the reactants at the surface ef the catalystor enzyme.(5 ) The actien of certain poisons en micro-organisms has been shown to be proportional to the amount deposited on their stir faces.

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A* It is better to speak of the ‘Colloidal Condition* than simply of •Colloids', since so many substances which are accepted as being crystalline, can be obtained in a colloidal condition by suitable

"methods. * •, , | The cclloidal condition is assumed by many substances when their

particles [in some other medium] have a diameter which is too small for them to be observed by ordinary methods of microscopy, *[i.e* the particles are sub-micrescopic], and yet are considerably larger than their constituent molecules. When the molecules as separate molecules can dissolve in a solvent, then we have a true molecular solution of a substance. The colloidal range of particle size is of 1-ZOOuu (|4 = .0 0 1 m.m.) in diameter. T/

Particles in true colloidal solution do not tend to settle out at the bottom cf a vessel - but remain indefinitely in a statf of' almost even dispersion.

Vv-A • v • • . * *The particles can be observed by means of a Tyndale Beam appliedsuitably. This beam of light does not enable the eye to detect theactual particles,;,but it can observe light scattered from them. With

* actual molecules rho such scattering is possible. a

B. The t*Xloid£UL condition is characterized by the following!*-(1) The Tyndale Beam effect.(2) The particles can be centrifuged down: not so in true molecular

solutions. ' ’(3) (a) The particles are extremely slow to diffuse.• (b) The particles cannot pass through animal membranes, parchment,

aoll^dion, etc., i.e. qannot 'dialyse*.(4) Brownian movement is observed - by means of the Tyndale Beam.**' ‘ \ ■. ‘

C. The total surface area ef all the particles in a colloidal solution is enormous. A piece of matter in the form of a cube whose sides are each 1 cm* in length has an area ff 6 cmsj . If this cube be split up into 1 0 29 cubes, each having a length now of only 0 .0 1 u . for each of its sides, the total surface area of all the cubes is oy this time 6 x 109 cms.2, which is equal t* 0,25 square mile. It c'an be Imagined that any chemical or physical reactions which c^n occur at the surfaces of such particles will prtgress to a far extent at the innumerable surfaces presented by colloidal particles. This feature is one of

- great importance in many serum reactions and in clarification processes used in water and sewage purification,

• * v ■ <

D.Methods of Making Colloids.t(a) By Dispersion, i.e. by reduction of^the sizes of 30lids.

(i) By grinding and milling a solid. *(11)’By-electrical dispersion, using a Bredig Arc. *(ill) By use mt Peptizing Agents. . ♦(iv) By ’weathering*, as in clays and rocks, *

ff(b) By Condensation, i.e. by condensing molecules 1 to frrm onlloidal

agglomerates. This is usually performed by methods of chemlgal reduction, i.e. by reducing agents. „ ., . _ .;

t ... . . . . V *♦ * ** ** *E. The colloidal conditions of chief interest in biology are *f two classes, SOLS and GELS.

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SOLS are liquid colloidal solutions; GELS are rigid colloidal ^a i M i i S . . * \

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* #F (a) Colloidal solutions are such that there is a boundary wftii or

•interface' between the colloidal particles and the surrounding medium. The colloidal particles form the DISPERSED PHASE, and the medium in which they are ! dissolved- or dispersed is the CONTINUOUS PHASE. For instance, in a colloidal gold gold particles form the Dispersed Phase, and water the ContinuousPhase. • *

(b) DISPERSED PHASE is one of two kinds:-(i) Emulsold, or (il)-Suspensoid. - ^EMULSOIDS: are colloidal solutions, which Ape more viscous £han water ("or other solvent), and which are hut little affected by precipitating action of added electrolytes, D J L *Example - proteins, starch solution, gums, etc

* <rr 4/ * < cMfM.Ut, Jwv Tiv^ ^ - SUSPENS6IDS: are colloidal solutions, whose viscosities are muc the' s'a S T as that of water: their particles are easily precipita­ted by added electrolytes. *Example - N/5 NaCl precipitates a red colloidal gold suspensoid as a blue precipitate of extremely small agglomerates of gold.

•Av(c) The viscosity is high in emulsoids,* because emulsoid particles

1bina! a considerable amount of the water c£ the continuous phase to themselves, leaving proportionately les^ ’free' water. Suspensoid particles have but little power of ‘binding’ water, and hence the viscosity of p suspensoid sol is almost that of water itself.

0 ELECTRICAL PROPERTIES of Colloidal Solutions.• •« >— ■ ’ ■In media having pH values of greater than '3-4, almost all

colloidal particles have a negative electrical charge. The sign of the charge is demohstrated bytBe migration of colloidal particles towards a charged electrode, I.e. a positively charged electrode will attract negatively charged colloidal particles a n d Increase their con­centration in its vicinity, or will repel positively charged particles and decrease their concentration in its vicinity. Vice versa for a negatively charged electrode. Hence knowledge of a change of ..centration of colloidal particles at an electrode of known electrical sign determines the sign of charge on colloidal particles. This ■ process is known as Cataphoresis. , .

H.(fa) PREGIPITATING POWERS of IONS.« The negative, charge on a colloidal, particle is neutralized th»positively charged ion, e.g. Na , Ba , A1 of ionized salts such as

1 * NaCl, BaClo, *nd AlClg respectively. The negative charges on thecolloidal particles repel the particles one from another and thus help to maintain stability of a colloidal solution. The repulsive charges being removed by addition of a'salt, allow tho colloidal partioles to

4 join together and later, precipitate out. Negative ions of an added salt will remove the charge from*a positively charged colloidal particle - with the s ame result.

» * *(b) MUTUAL PRECIPITATION of COLLOIDAL PARTICLES.1 1 ■ “• " 1 1 - ---

Negatively charged colloidal particles, e.g. colloidal organic matter in sewage will be flocculated by a positively charged colloid such, as A1(0H)3 (at pH >8.0). This is the basis of most processes »f chemical clarification of water and sewage.

* *♦« •

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- ' In'serum reactions, although at the pH of blood serum both antigen and antibody are negatively charged, the positive ions of electrolytes present [or added] tend to flocculate the, for instance, precipitinogen- precipitation complex. •%(c) Divalent ions are more effective in precipitating colloidal particles than are monovalent ions, and trivalent ions are much more effective than either.

For maximum precipitation of colloidal particles, a definite quantity of an ion of opposite charge is required. * More or less is not so efficient.

. » %♦I. PROTECTION. Particles of a suspensold sol may be protected from the precipitating action of ionized salts b^-having an emulaoid sol, such as gelatin sol, added to the suspension. The protective action of such an emulsoid appears to be due to its forming a coating round suspensold particles, and in some manner preventing the charges of the

_ suspensold particles from being neutralized by the oppositely charged ions of an added salt. 'Colloidal Metals* such as colloidalmangane’se, iron...... etc. , are protected from the precipitatingaction of the electrolytes in blood, etc., by the addition of emulsoid colloidi ^ ctheir P^^P^tion.

GELS: are two-phased systems like sols, but are rigid at ordinary temperatures. GELS may be changed into SOLS by warming; somewhat like the melting of a chemical compound. Cooling again may result in reforming the original GEL, e.g. agar, gelatin. Crystalloidal substances diffuse through gels almost as fast as they do through water, but ether colloidal particles diffuse through gels only very slowly.

9

References to Literature.Bayliss - General Physiology.Freundlich - * The Elements of Colloidal Chemistry. \ ;v

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D.P.H.Air.

‘ rn m amf XtUr® °f Nitl*°een [78.07^], Oxygen [30.95$] and C02LU.U3 - 0,04%]. Those gases account for about 99$ of the total theT; ! _ f inS \ A CCrnist of Hydrogen, Ammonia and the rare gases Neon,'Argon and luyp.on. ; ater rapour is el30 present to an e.xtent of about li on theaverage. '

Oxygen varies in ammount only slightly under normal conditions, but in nines _t. nay oe as low as 18%. When at rest, an individual feels little1 ^ df oxy«en» and consciousness can be retained at 7ti,P-. though '.onbuution is not supported much below 17$.

^ rrit .,1TV‘e C02 content of badly ventilated rooms frequently attains to 0.4#-5-10% -ill cause discomfort in human beings. 7 ’Cage.? of Polluted Air,

or Methane. CH^. Called 'marsh-gas’ since it is genera.en in stagnant marshy pools as a result of gradual decay of vegetablera*„oerr _n s limited supply of oxygen [i.e. partially anaerobic].

Aie g£'_ is often occluded by coal, sometimes under considerable procure. ".Hen e new face is cut. a continuous stream of methane may be: nce ^QT-hana is common in the atmospheres of coal-mines. 5-13$is iuxlejjiuaole in air.,

Methane has no definite physiological action.

2 Gsses in factories, etc. is notifiable.

, Gases. Ferro-silicon is used in the preparation of‘ ‘ ---ospnorus and arsenic are often present as impurities, and combined >-.posure jO moisture results in formation of the poisonous gases Phospheoe3- i.JTwineo

ii/22I°oj3?_^l^hideJ!_H2S. Found in sower gas and in chemical works g8C! v7, s- Tt ls ffiore dangerous than is usually thought; 0.2 to 0.4#

ay prrve .'.axal, and with larger percentages sudden death can occur. Thesame remarks apply to rNFAlo.S.ft-

, . Carbonbisulphide. CSo. Is a liquid solvent for rubber, and isProces3es and in "the artificial silk industry ( ’viscose*).

t BLj J-n--erm:i -J-3 ana very poisonous. An advanced degree of poisoningserious cons a quenci e s. Recovery is usual,, but slow.

B m z ene?-0j6jB6 . Benzene vapour is used in dry cleaning, and is icuaa -in^p'jorox vapour. Causes anaemia and haemorrhage under the skin •CU eiesding fVom the gums. Chronic benzene poisoning is a notifiable’ liiuUfr ,riax disease, but acu’ie poisoning is classed as an accident.

_ p0issn:'.ng is usually by direct absorption of intermediateprouuo.s of tho aye industries by way of the skin, but fumes of such products; ^ eV Q9 ? r th3 r3Spiratory and digestive tracts. The general action -- ana i s derivatives is to dissolve red blood corpuscles.'

I •

i-3-— ix^i°£®J^iane, nitrobenzene, chloroform and trinitrotolueneccca3t0nslly cause toxic jaundice.

rnori 1 emmonia, nitric acid, hydrochloric acid and phosgeneLCJClr J p.re all dengerous irritants.

Monoxide. An extremely dangerous gas. It combines withC : ? n J° T O m C0'haeaoelpbin, a compound which is sufficiently stable '« S' j cofv^rsi“n back to oxyhaemoglobin difficult.

Besides being so" poisonous it Is unfortunately colourless and(as it occurs/ Is o-Iourleas. It is inflammable.tout C-oS % Co

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M ^ r j p h & z ^ z x & & ? z 2 ^ u # s £ ^ , ^ w ^4T -T’ occurs in several gases used for fuels in industry. Coal gas

contains about 7.0$, but in some places as much as 12$. Anthracite stoves are sometimes a source of danger if the shaft is not quite inta#t.

•Producer gas1 - much used in heavy industry - is made by passing air, or air mixed with steam, through a deep bed of coke. The following reaction occurs:-

40 + 3 02 ---- > 2 CO + 2 C02The gas containing CO is now led away in pipes to any desired site and then is combusted. Any leakage from pipe lines may be dangerous.

I?§^®?L6as* Steam is passed over red-hot coke, causing "gasification" of the carbon:-

C + h20 ------- > CO + h2Here again the CO containing gas is led to its required site.

Blast-furnace gases always contain CO.

Other sources of CO are:-

Exhaust gases from motor cars. After explosions in coal mines CO may occur in the mine atmosphere. Brick and cement kilns. Coke ovens are possible sources. Carbon-arcs (as in cinamas). Patent water heaters, etc.

The smell of coal gas is not due, as some think, to the CO which it contains, but to the hydrocarbons of the gas.

Tests for Carbon Monoxide.

(a) The detection of CO is not easy. A piece of white filter paper moistened with palladium chloride - PdCl2 - is turned pink^ green, or black according to the amount of CO present in the atmosphere. But other organic substances produce the sane reaction, and H2S or NH3 must be removed from the atmosphere.

(b) Vogels blood tests. If ordinary blood be diluted- with 200 times its volume of water, a yellowish-red solution is obtained, but with blood containing CO, the solution is distinctly pink.

(c) Tannic acid test. Normal blood diluted 1 ; 4 with water is shaken with equal volume of 1 fo tannic anid solution and allowed to stand 24 hours. A grey suspension results. Normal blood solution shaken in aCO containing atmosphere and treated as above gives a camine red colour, ,

(cl) NHa - CuCl test. The reagent is NH4CI, CuCl, cone, NHg.The air suspected of containing CO must be free from COg and 0g by passing it through KOH and alkaline hydrosulphite. The CO then, on passing through the above reagent, forms a typical crystalline compound, which is probably CuC1.C0.2H20.

NOTE; KOH will absorb (i.e. react with) C02, but it has no chemical reaction with CO.

(e) Spectroscopic test.- will detect CO when as little as 0.25$.If normal blood solution is placed so that the sun’s rays pass through it before being admitted to a spectroscope, two dark bands [between the D and E lines] will be apparent, due to oxyhaemoglobin. A solution of blood containing CO-haemoglobin shows a very similar spectrum. But after adding a drop or two of (NH4 )2S and warming a little, and allowing to stand for 1/4 hour, the two bands persist, whereas with oxyhaemoglfbin the original bands merge together [due to the (NH.)rs reducing oxyhaemoglobin to haemoglobin].

- 3 - i *

Test for CO with small animal»

Introduced by Haldane in 1896 as a test for CO in dangerous concentrations in mine air. It depends upon the fact that small warm­blooded animals react far more quickly to CO than large animals, including man, and therefore act as safe indicators of CO.

9 "A small bird, such as a linnet or canary, may be used; it becomes

unsteady on its perch and falls off. But a bird is likely to die suddenly in a dangerous atmosphere and thus becomes useless as a further guide, A bxrd^or-.mousR i a fiffnofrftti within one-tenth nf tha time required to affect a man, and if a bird or mouse is affected, it will show ^j+hin .10minutes, depending on the CO concentration. The bird will probably die (unless promptly removed) with anything more than 0*2$ CO, while a mouse will only be disabled at' this concentration and may live at 0.4$ to 0.5$, It appears that a concentration of more than 0.2$ for a sufficient time is very dangerous to man, and a concentration of more than 0.02$ will cause headache and partial disablement.headache

(Jl/'r ftuantita'

\

Quantitative determination of CO.

(1) Carmine Titration. Small percentages of CO in air can be determined with considerable accuracy by a blood solution, of which the percentage saturation of haemoglobin with CO is titrated by means of a standard solution of Carmine,

Procedure. a solution consisting of 1 part of normal blood diluted to 100 parts with water is used. 5 cc.s of this normal blood solution is shaken up thoroughly with 200 to 300 cc.s of the air to be examined. This procedure brings the CO from the air sample into equilibrium with the haemoglobin. Call this solution A.

A further 5 cc.s of normal blood solution is saturated with CO by passing coal gas. The whole of the haemoglobin of this 5 ce, will then be combined with CO, Solution B.

•To a third 5 cc.s of normal blood is added standard carmine

solution from a burette until;-

(1) The colour matches tube A - say 2.2 cc.s and the titration then continued until:-

(ii) The colour matches tube B - say 6,2 cc.s.

From these two readings the ’percentage saturation1 X, of the blood solution in equilibrium with the sample of air can be deduced from the formula:-

2 . 6.2 v------------ - ; . X ; 100.2.2 + 5.0 6,2 + 5,0

Haldane has publiaHed curves correlating X the percentage saturation of haemoglobin with CO, with the percentage of CO in air. From these curves, therefore, we can determine the concentration of CO in an atmosphere.

This colorimetric titration is a peculiar one, since 'quality' and not 'depth' of colour is being estimated. The carmine has a bluer tint than blood solution saturated with CO, and the mixture of the carmine colour with the yellow of normal blood solution reproduces accurately the tint of the blood containing CO. The two solutions are not spectrally identical, ..... the equality of tint is physiological only.

(2) Estimation of CO by Iodine Pentoxide." 1 rThe a^r is £reed from C02, unsaturated hydrocarbon and aaueousvapour, and conducted through a U-tube containing 60-70 grams of pure I2OJ

heated to 160 C.: by this means the CO alone is oxidised and iodin$ liberatedaccording to the equation:- 5C0 + I205---- > 5 C02 + IP. If the gas is nowpassed through two tubes containing KI solution, the iodine will be absorbed, ahd can be titrated with standard Na2S203 solution.

Collection Number: AD843

XUMA, A.B., Papers

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