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The determination of magnetite in metallurgicalproducts by an electromagnetic method
Item Type text; Thesis-Reproduction (electronic)
Authors Doan, Donald Jay, 1910-
Publisher The University of Arizona.
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THE DETERMINATION OF MAGNETITE IN METALLURGICAL PRODUCTS
BT AN ELECTROMAGNETIC METHOD
By
Donald J&y Doan
Submitted in p a r t i a l fu lf i l lm e n t of the
requirem ents f o r the degree of
Master of Soienoe in M etallurgy
in the College of Mines and Engineering of the
U niversity of Arizona
1 9 3 2
A
/ /
ACKNOWLEDGMENT
The au tho r wishes to acknowledge the a s s is ta n c e of
Dr. V. H, G ottsohalk and Mr. F. S. Wartman who, as
w ell as d ire c tin g the re se a rc h , made a l l of the chem
ic a l analyses p resen ted . The au thor a lso wishes to
express h is indebtedness to Dr. T. G. Chapman fo r
advice and cooperation in the p rep a ra tio n of th is
th e s is . This th e s is p resen ts the r e s u l ts of work
done under a cooperative agreement between the United
S ta te s Bureau of Mines and the U niversity of Arizona.
< 5
85739
OOTETOS
Page
In tro d u c tio n .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The B a l l i s t i c M ethod.............................................. 9
The D eterm ination of "Average Size" B a r t ic le . 23
M ateria ls U sed ....................................................... 27
The I& gnetic-Balanoe Method............ .. 30
S u m m a r y . . . . . . . . . . . . . . . . . . . . . . . . . . . .................. M
ILLUSTRATIONSFig .NO.
1 E lectr ica l diagram of the apparatus used fcy S tu tzer,Grozt and B o r n e a a n . 5
: ' . ■ -2 The magnetic balance used by Seaman................................. 6
2 Diagram of th e m agnetic f i e ld through a s o le n o id .. . . 10
4 Diagram of th e b a l l i s t i c a p p a r a tu s . . . .............................. IS
5 E ffec t of "average s iz e " p a r t i c le upon magnetica t t r a c t io n , using th e solenoid magnetic b a la n c e .. . 21
6 The e f f e c t of "average s iz e " o f p a r t i c le s upon magn e t ic a t t r a c t io n , u sing th e p o le-type magnetic b a lance ............................... 34
7 The e f fe c t of d i lu tin g m agnetite No. 11b, -356 mesh,and No. 11b, -100 +150 mesh, w ith q u artz , -350mesh and -100 +150 mesh, r e s p e c t i v e l y . . . . . . ............. 37
8 The e f f e c t of d i lu t in g m agnetite No. 4, -360 mesh(lower curve) and No. 4 , -100 mesh, w ith quartz ,-350 mesh and -100 +160 mesh, re sp e c tiv e ly ............... 37
9 Photograph of the "d en sito m ete r" .. . . . . . . . . . . . . . . . . . . 40
10 The r e la t io n between density and com position, usingm agnetite -quartz m ix tu res........................ 41
11 Photograph of the magnetic balance f in a l ly adopted*• 42
12 The e f f e c t of volume of m agnetite m ixtures upon magn e t ic a t t r a c t i o n . ....................... 43
13 The re la tio n between magnetite content and magnetic attract ion a t constan t volume.. . . . . . . . . . . . . . . . . . . 4 4
TABLES
Table Ho. : ...... .. .............. - • ■ Bilge
1 B eprofluo lb llity of the b a l l i s t i c instrum ent* . 19
Sa Grain s in e measurements u sing Sample Ho. 10,IBLnerille m a g n e tite .; ......... .... 26
8b Grain s iz e measurements u sing Sample Ho. 11a,M ineville m a g n e tite ...................... . 26
. S . Summary of the m a te ria ls u s e d .. . . . . . . . . . . . . . . 27
4 A com ^.risen of the m agnetite con ten ts o f a i z - ,.. tu re s as measured by th e balance method and as determined c h e m i c a l l y . . , . . . . . , . * . , . , . , , . ,47
6 . Comparative m agnetite co n ten ts of s la g s ........... .. 60
THE DETERMINATION OF MAGNETITE IN METALLURGICAL PRODUCTS
BY AN ELECTROMAGNETIC METHOD
INTRODUCTION
The presence of m agnetite (FegO^ In r e
verb era to ry and een v erte r s la g s r e s u l t in g from copper sm elt
ing operation i s g en e ra lly known. I t has been widely recog
n ised th a t th e presence- of th i s m agnetite caw ee c e r ta in
d i f f i c u l t i e s in copper sm elting o p e ra tio n s , among which the
fo llow ing are n o ted : increased lo s s of copper in th e s la g s ,
the g re a te r the m agnetite content th e h igher th i s lo s s ; th e
troublesom e "m agnetite mush" la y e r between the s la g and th e
m atte is a t t r ib u te d to th e presence of m agnetite; the b u ild
ing up of the re v e rb e ra to ry furnace bottom encountered a t some
p la n ts i s due to m agnetite . I t i s , th e re fo re , of th e utmost
im portance th a t an accu ra te and r e la t iv e ly simple method of
a n a ly s is be developed which can be used in sm elter co n tro l
work and to fu r th e r the study of s la g s . The ob jec t of th is
in v e s tig a tio n i s the study and development of a sim ple and
r e l ia b le method fo r the determ ination of m agnetite in re v e r
b e ra to ry and converter s lag s r e s u l t in g from copper sm elting
operations* :
This problem may be attem pted from e i th e r
the chemical s id e o r , since m agnetite la known to be m agnetic,
from a p hysica l view point. Inmerous papers on th e measurement
of e i th e r magnetic perm eab ility or s u s c e p t ib i l i ty have been
pub lished ; from th e se a few which a re ap p licab le to th is prob
lem a re no ted . The chemical method fo r th e determ ination of
m agnetite i s a lso described and d iscussed .
A method of measuring magnetic s u s c e p t ib i l
i t y which is based on th e p r in c ip le of a simple transform er i s1
advanced by S tu ts e r , Grog, and Bomeman. The magnitude of
the induced elec trom otive fo rce produced by a transfo rm er i s
a fu n c tio n of the magnetic perm eab ility of the eore th a t i s
used; i f an apparatus is s e t up in which the core may be in t e r
changed, the perm eab ility of the core can be determ ined. A
diagram of th e appara tus used i s shown in Figure 1. R eferring
to th i s F igure , two tran sfo rm ers , each being in th e form of
two concen tric so len o id s , a re arranged so th a t the induced
cu rren ts a re opposite ; i f both transfo rm ers a re id e n t ic a l ,
e l e c t r i c i t y w ill not flow through the secondary c i r c u i t when
an a l te rn a t in g cu rren t i s passed through the primary c i r c u i t .
S tu tze r p laced the sample of th e m a te ria l to be te s ted a t th e
cen te r of one tran sfo rm er, and th e perm eab ility of the core
was e i th e r increased or decreased , which in tu rn caused an
a l te rn a t in g cu rren t to flow in the secondary c i r c u i t . The
1S tu tz e r , F . , Groz, W., and Borneman, K ., Uber Magnetisohe E lgeneohaften der Zinkblende und e in ig e r anderer M ineralien : Me t a l l , und Erz, v o l. 15, 1918, pp. 1 -9 .
AMMETER GALVANOMETERAMMETER'
PRMARYCIRCUrr
SOLENOOS'
5ECOCARYCIRCUIT
COMMUTATNG
DEVICE
Figure 1 .—E le c tr ic a l diagram showing the appara tus used toy S tu tz e r , Groz, and Borneman.
a l te rn a t in g cu rren t in the primary c i r c u i t was produced toy a
ro ta t in g sw itch which co n tin u a lly reversed the d ire c tio n of
the c u r re n t, as may toe noted in Figure 1. This arrangement
y ielded a corresponding induced a l te rn a tin g cu rren t through
the secondary c i r c u i t . For the purpose of changing th is sec
ondary a l te rn a tin g cu rren t to d ire c t c u rre n t, a c i r c u i t Breaker
was placed on the sh a ft th a t operated the a l te rn a to r fo r the
primary c i r c u i t , thus p e rm ittin g only the cu rren t of one-half
a cycle to toe tran sm itted through the secondary c irc u it (see
Figure 1 ) . A D'Arsonval galvanometer was used to measure the
transform ed secondary c u r re n t. S tu tzer pointed out two main
e rro rs r e la t in g to th is work. The ncommutating device" was
operated toy a small e l e c t r ic motor which revolved a t a speed
of 1,200 r .p .m .; th e Inoenstaney of th e motor v/as +1.5 per c e n t.
The demagnetizing e f fe c t of the sample introdmeed considerab le
e rro rs th is e r ro r I s dependent upon the r a t io of le n g th to d ia - 2m eter of the sam ple, but i s only Im portant when ab so lu te meas
urements of the perm eab ility a re made, and i t need not be con
sidered when com parative s tu d ie s a re d e s ire d , provided the r a t io
o f le n g th to diam eter i s m aintained constant*
Wait used two methods fo r the determ ination
of ab so lu te p e rm e a b ilit ie s o f iro n and m agnetite . Aside from
the complexity of the ap p ara tu s , eaoh method has the disadvan
tage th a t th e samples to be te s te d must be worked in to wax and
a lso be made to assume d e f in i te shapes* Wait did not d iscuss
the percentage accuracy of these methods.
Mendenhall and Lent have advanced a method
fo r the determ ination of magnetic s u s c e p t ib i l i t i e s of diam agnetic
and param agnetic m a te r ia ls . The apparatus used i s very d e l i
c a te , and consequently i f placed in r e la t iv e ly u n sk ille d hands
the maximum e r ro r of 1 .5 per cen t obtained by Mendenhall and
le n t would be increased . A fu r th e r disadvantage of th i s method
is due to the fa c t th a t i t is not ap p lio ab le to m a te ria ls th a t
possess high magnetic p e rm e a b ilit ie s . * 3 *
S ta r l in g , S. G ., E le c t r ic i ty and magnetism: London, 1924, p . 2T03Wait, G. R ., Magnetic P erm eab ility of Iron and M agnetite in
High Frequency A lte rn a tin g F ie ld s : Phy. l e v . , vo l. 29, 1927, pp. 866—878. . ■
^M endenhall, C.B., and Lent, W. F . , A Method of Measuring the S u s c e p tib il i ty of Weakly Magnetic Substances: Phy. Rev., vo l.82, 1911, pp. 406-417.
6Wilson has m odified the Curie type of
instrum ent fo r th e determ ination of magnetic s u s c e p t ib i l i ty .
The general p r in c ip le of the l a t t e r type i s th a t th e fo rc e
exerted upon a sample of magnetic m a te ria l by a magnet i s
measured and the s u s c e p t ib i l i ty then ca lcu la ted from the r e -6
s u i t s ob tained . Soaman and H o s te tte r used a Ruepreeht
a n a ly tic a l balance fo r th e measurement of th is magnetic fe ra e ,
while Wilson used magnetic means to balance the fo rc e . The '
advantages and d isadvantages of th e Curie type of instrum ent
eq u a lly apply to bo th methods noted , and as the Sosman modi
f ic a t io n w ill be described in some d e ta i l , a d iscu ss io n of
the Wilson type i s om itted .
The Magnetic Balance Method
The p r in c ip a l exponent of the magnetic
balance method of app ly ing the Curie p r in c ip le fo r the d e te r
m ination of magnetic p e rm e a b ilitie s and s u s c e p t ib i l i t i e s has
been Robert B. Sosman. Seaman*s o r ig in a l procedure5 6 7 employed
an electrom agnet of the pole type; th is apparatus is shown in
F igure 2. I t consisted "simply of a Ruepreeht a n a ly t ic a l
5 :Wilson, E rn e s t, On the Measurement of lew S u s c e p tib il i ty by an Instrum ent of a Hew Type: F ree . Roy. So©, of London, (A), v o l. 98, 1931, pp. 274-284.
6Sosman, R. B ., and H o e te tte r , J . C ., The Ferrous Iron Content and Magnetic S u s c e p t ib i l i t ie s o f some A r t i f i c i a l and N atural Oxides of I re n i Trans. Am. I n s t . Min. Eng., v o l. 58, 1918, pp. 404-433.
7Sosman, R. B ., and H o s te tte r , J . C ., oj). o l t .
• 6 -
balanoe , from one pan of which was suspended a g la ss p latfo rm
on which the charge of oxide was p laced , a sho rt d is tance above
an electrom agnet. The oxide was contained in a small f l a t -
bottomed g lass pan; the p a r t ic le s a re kept from moving by a8
g la ss plunger which pressed down upon the powder." E rro rs
caused by ou tside d istu rbances such as the presence of s te e l
in the balance were remedied or computed m athem atically . In
using the method as described i t is obviously im possible to ob
ta in ab so lu te values fo r the s u s c e p t ib i l i ty because of many unde
term inable fa c to rs r e la t in g to the f i e ld , but as only comparative
r e s u l ts a re re q u ired , these fa c to rs are not im portant. Sosman
Figure 2 .--The magnetic balance used by Sosman*
3Sosman, R. B ., and H o s te tte r , J. C ., oj>. c l t .
l a t e r changed h is o r ig in a l apparatus by re p lac in g the pole type
electrom agnet by a se t of a d e n o id # , thus p e rm ittin g th e a t
tainm ent of ab so lu te r e s u l t s . The solenoid magnetic balance
has a maximum accuracy of 2 p e r cent fo r param agnetic su b stan ces ,
and "only somewhat crude comparative r e s u l t s a re ob tainab le9
w ith ferrom agnetic powders." The Sosman a p p a ra tu s , though
not of g re a t accuracy , has been in s ta l le d in th e la b o ra to r ie s
of two sm elting p la n ts (United Terde, CLarkdale, A r ia . , and
Copper Queen, Douglas, A r iz . ) fo r the comparative study of
rev erb e ra to ry and converte r s la g s . In Sosman*s and E e s te t te r 's 10o r ig in a l paper th e au th o rs have shown an approximate r e la t io n
sh ip between the magnetic s u s c e p t ib i l i ty and th e fe rro u s iro n
content in various oxides of Iron . The s u s c e p t ib i l i ty was de
term ined as the weight re q u ire d , in m illig ram s, per gram of
m a te ria l to balance the magnetic fo rc e . The idea of d e te r
mining the con ten t of a m agnetic substance in a given m a te ria l
by electrom agnetic measurements is th e re fo re not new. 9 10
9Sosman, R. B ., and Posnjak, E ., Ferrom agnetic F e rr ic Oxide, A r t i f i c i a l and n a tu r a l : J . Wash. Acad, of Science, v o l. 18, 1925, pp. 329-342.
10Sosman, R. B ., and H o s te tte r , J . C ., 0£. o i t .
Chemical Method f o r the Determ ination o f M agnetite
fhe most r e l ia b le chemical method fo r the
determ ination of m agnetite i s probably th a t advanced by Eawley1*
in 1919 and which Roberts and Hugent12 modified in 1901 w ith
improved r e s u l t s . The p r in c ip le involved in th is method i s the
s e le c tiv e d isso lv in g a c tio n of n i t r i c ac id and potassium ch lo r
a te so lu tio n , which sep a ra tes th e r e la t iv e ly in a c tiv e m agnetite
from the more r e a d i ly a ttacked iro n and sulphur compounds.
Roberts and Hugent l i s t the fo llow ing p o s s ib i l i t i e s of e r r o r ;
"1. The su lph ides may not be com pletely removed and
th e ir reducing a c tio n during the so lu tion of the sample cause
low r e s u l t s .
2. The ox id iz ing m ixture m y d isso lve m agnetite .
3 . The o x id is in g m ixture m y oxidize so lid fe rro u s
compounds in th e undissolved re s id u e ” to m agnetite , "g iv ing
h igh r e s u l t s .
4. Atmospheric oxidation may occur during th e so lu
tio n of the sample.
5. Traces of o ther elem ents may reduce iro n during
the so lu tio n of the sam ple, or may oxid ize the stannous chloride
in th e t i t r a t i o n ” of the iron from m agnetite .
TE ' ” 'Hawley, F. 0 . , D eterm ination of M agnetite in Matte and S lag;Eng. and Min. Jo u rn a l, vo l. 108, 1919, pp. 308-310.
12R oberts, L. E«, and Hugent, R. L . , D eterm ination of M agnetitein Copper Slags? Report of In v e s tig a tio n s , S e ria l 3180, U. S.Bureau of Mines, S e p t., 1931, 14 pp.
9
They estim ate the accuracy of the Improves
Hawley method to be about 2 per een t. The method i s q u ite
e lab o ra te and requires eonaiderable s k i l l in technique to ob
ta in eoneietent r e s u l t s . Roberts and liugent have compared the
chemical method with the magnetic balance f o r determ ining mag
n e t i t e in copper fu rnace s lag s and the re s u l ts agree "within
about 2 per e e n t." This l a t t e r r e f e r s to d iffe ren ce in p er
een t.
THE BALLISTIC MflOD
The b a l l i s t i c method, in so f a r as the
w riter could determ ine, has never been used to measure the
magnetic s u s c e p t ib i l i ty o r perm eability of pu lverized mate
r i a l s w ith . the d e f in i te o b jec t of determining magnetite con
te n t . The method has been ou tlined in several t r e a t i s e s on
e l e c t r i c i t y and m a g n e t i s m , b u t i t u su a lly is app lied to
the study of uniform so lid s such as s te e l s and iro n s . Y/elo16
and Baudisoh used the b a l l i s t i c method to determine the p e r
m eability of powdered m agnetite and o ther iron oxides. The
p resen t in v e s tig a tio n i s not concerned with th e ab so lu te value
13Spooner, T ., P ro p e rtie s and T esting of Magnetic M ateria ls : Hew York, p . 207, 1987.
14S ta r l in g , S. E le c t r ic i ty and Magnetism: London, 1924, p . 271.
Welo, L ., and Baudisoh, A ., The Two-Stage Transform ation of M agnetite in to Hem atite: P h il . Mag. (6 ), v o l. 50, 1926, pp. 599-408.
1 6
- 1 0 -
of the magnetic perm eab ility or s u s c e p t ib i l i ty of the m a te ria ls
u sed , but only w ith the comparative values which a re a func
tio n of the ab so lu te q u a n ti t ie s . The b a l l i s t i c instrum ent16
may, however, be c a lib ra te d by various means, and thus be
used to ob tain abso lu te r e s u l t s .
D iscussion of the B a l l i s t i c Method
The theory concerning th is method is not
new and is r e la t iv e ly sim ple. I f a uniform elec trom otive fo rce
is maintained through a so le n o id , a magnetic f ie ld w ill r e s u l t .
R eferring to Figure 3, th is magnetic f ie ld is denoted by l in e s
Figure 3. — Diagram of the magnetic f ie ld through a solenoid .
To "S ta r l in g , S. G ., Oj3. c i t . , p . 256
1 1 -
of fo rc e . I f a second so lenoid is in se rted in to th e f i r s t ,
th e term inals being connected to a galvanom eter, a momentary
cu rren t w ill be induced in th e secondary c o il when the cu rren t
in th e prim ary c i r c u i t i s in te rru p te d . S im ila rly , i f th e cu r
re n t i s "made" through the prim ary solenoid in the opposite
d ire c tio n , th e induced cu rren t in th e secondary solenoid w il l
be in the same d ire c tio n a s th e f i r s t induced secondary c u rre n t•
In th i s manner a double Induced cu rren t may be obtained by use
of a commutating sw itch , which sim ultaneously breaks the cu rren t
In the prim ary c i r c u i t and s t a r t s i t in the opposite d ire c tio n .
Thus:
. . . . ; . • ~ M # / . 1 7 .. . . , . ..
where e ia th e induced elec trom otive fo re # ,M ie the c o e f f ic ie n t of mutual inductance,£ i s th e cu rren t in the prim ary c i r c u i t .
This equation in d ic a te s th a t when th e cu rren t L i s constan t or
ae ro , the induced elec trom otive fo rc e i s ze ro ; the quan tity
of induced c u rren t produced i s a lso p ro p o rtio n a l to the ra te
of change of the prim ary c u rren t w ith tim e. In the p resen t
in v e s tig a tio n th i s r a te of change was kept constan t and no a t
tempt was made to determine i t .
S ta r l in g , S. G. , op. o i t . , p . m .
In any magnetio o ir e u it , eozjpeeponding to
Oto-a tow: u = e R 18 ' : ' ^
where u i s th e m agnetic p o te n t ia l in am pere-tarns, e i s the
magnetic f la x in wefcere, and R i s the to t a l magnetle re lu e tan ee
in am pere-tarns per weber# I f R*, R*,—— rs>-----a re the separa te
relaotam eea of the p a r ts o f th e magnet io c i r o u i t , then RA4- R&,+--+
, i f p ro v is io n is made in the wcomdary solenoid for
the p lacing of a c y lin d e r , which in turn serves to hold the sam
p le of magnetic substance to be te s te d , them
/ -/where A ,is th e c ro ss -se c tio n a l a rea of the sample, L*the depth
of the sam ple, and i s equal to 4 w l 0 when/t- i s the p e r-. ' 80
m eab ility of th e m a te ria l. S u b s titu tin g U* N,I where I
i s the cu rren t through th e prim ary and N pIs the number of
tu rn s of the prim ary, in equation 1 : 0 = , and d ifferen
t i a t in g :III .
The m utually induced elec trom otive fo rc e through the secondaryjh 21i s expressed by: * 19
Bennett, E, K ,, and Crother, H. M., Introductory E lec tro dynamics fo r E ngineers: Hew York, 1926, sec . 010, p. 644.
19 - ;Bennett and Crother, op. c i t . , sec . 314, p. 644.
80 -----Bennett and Crother, o£. c i t . , sec. 312, p. 642.
Bennett and C ro ther, 0£. c i t . , sec . 298-b, p. 577.
and, since th e t o t a l linked magnetic f l a x , A , i s equal to
the number of tu rn s on the seeen la ry , Ns , m u ltip lied hy the .22
t o t a l magnetic f lu x , 6 , e = .
S u b s titu tin g equation I I I in th is equation ,
6 = - ^ ^ • IV-
By Ohm’s Law e = 1 h # where r i s th e r e s is ta n c e .o f th e sec -
ondary so leno id , c i s the c u r re n t , and e i s the e lec trom otive
fo rc e . Then:
U t = _£U_Nfct[ T.
and since i d t — where d y i s the charge c irc u la te d through
the solenoid when a cu rren t t flows fo r a time d t . In te
g ra tin g th e equation V:>
> = - N r ‘ r, ^ ' = "r "since Ai, i s held co n stan t throughout th e in v e s tig a tio n , where
f" — Ns N»aI.r •
I f two se ts of id e n tic a l so leno ids a re oonneeted in
s e r ie s so th a t th e induoed c u rren ts a re opp o site , then :
v i i .
Bennett and C ro ther, 0£ . o l t . , s e e . 278, p . 481.82
•1 4 * '
K. does not e v m l ze ro , because of the d i f f i c u l ty in manufac
turing th e so len o id s , hut by a l te r in g th e re lu c ta n c e , Rz ,
of c e i l s Re. 2 the charge c i r c u la t in g through the secondary
c i r c u i t may be made sm all and equal to K. Solenoids l e . 2
a re not a l te re d a f t e r s e t t in g and therefore the re lu c ta n c e ,
Ra , i s a co n s tan t. The q u an tity fo r so lenoids Ho. 1 i s
a constan t when th e sample container of the secondary i s empty,
s ince th e reluctance does no t change; and th e re fo re the quan-
tityYtf,-$i) = K where K i s a co n stan t.
When th e sample of m a te ria l to be te s te d i s placed
in secondary c o i l Ho. 1 , thenz % — % = “ "r2
and su b tra c tin g equation VII (fs—%) — K = ^ ^ V III.
From t h i s equation the fo llow ing conclusion may be drawn:
(% -& ) “ K = FUNCTION (Rs)
A b a l l i s t i c galvanom eter la uael t . maaanr.
and a lso K, and s in ce 0 = fad where ^ i s charge put through
the galvanometer, ^ is the gal van easier constant and c t i s
the d e f le c tio n , and th e re fo re
Ad/ = FUNCTION (Rg) ' IX.
where A c/is th e difference between th e galvanometer d e f le c tio n
with and w ithout the sample in the c o i l . . Using equation l i t
Ac/ = FUNCTION (%) or Ad/ = FUNCTION X.
w h e re y ^ is . th e perm eab ility of the sample. ......
- 1 5 -
A lt hough I t may he considered obvious th a t
the magnetic perm eab ility is a fu n c tio n of the m agnetite content
of any p a r t ic u la r sample, a curve re p resen tin g th i s r e la t io n
is presented w ith the d e sc r ip tio n of the experim ental work.
VARIABLE RESISTANCE 7 KEY 7
Figure 4 .—Diagram of the b a l l i s t i c ap p a ra tu s .
F igure 4 rep resen ts a diagram of the appa
ra tu s used. R eferring to th i s f ig u r e , i t may be noted th a t
w ith both keys c lo sed , a snap of the commutating sw itch r e
verses the curren t in the primary c i r c u i t , thereby causing
the magnetic f ie ld to rev e rse in prim ary so leno id , which in
tu rn induces a corresponding instan taneous e le c t r ic cu rren t
through th e secondary c i r c u i t . This secondary charge is
me##mr#d by the b a l l i s t i c galvanom eter. The v a ria b le re s is ta n e e
ia connected in the prim ary c i r c u i t so th a t th e cu rren t may be
m aintained a t a given va lue . The m a te ria l to be te s te d i s
placed w ith in a b ra ss cy lin d e r and i s lowered in sid e a desig
nated secondary so leno id .
The B a l l i s t i c Apparatus
The galvanometer is a Leeds and ITorthrup
type which had a period of 5 .5 seconds, but because of th i s
r a p id i ty , a r o l l o f platinum f o i l was f ix ed upon the top of
moving c o i l ; th is improved galvanom eter has a period of 10.6
seconds and may now be convenien tly used as a b a l l i s t i c type
instrum ent. The so leno id se ts may each be subdivided in to p ri
mary and sooondary so len o id s . The prim ary c o ils a re r ig h t
cy lin d ers having an in s id e d iam eter of 2.2 cen tim ete rs , a
le n g th of 9 ce n tim e te rs , and approxim ately 40 tu rn s per cen
tim e te r of No. 12 enameled copper w ire . The secondary so len
oids a re a lso r ig h t cy lin d ers having an in sid e diam eter of
0.7-centim eter, a le n g th of 1 .7 cen tim ete rs , and approxim ately
1,600 tu rn s per cen tim eter of Ho. 38 enameled copper wire.
Each secondary c o i l f i t s r ig h t ly in to i t s prim ary so leno id .
The v a r ia b le re s is ta n c e i s a Genoo typo
having a maximum re s is ta n c e of 5 .8 ohms and cu rren t cap ac ity
o f 8*7 amperes. The commutating sw itch m s made from two
e le c t r ic l ig h t "snap" sw itches. These were mounted so th a t
a connecting bar of aluminum could be made to throw the two
- 1 7
sw itches sim ultaneously , which in tu rn reversed the cu rren t.
The ammeter i s a Weston d .o . ammeter, model 45, Ho* £0098.
I t i s equipped w ith an ap p ro p ria te shunt which i s in th is case
a 5 0 - a i l l i v e l t , f * 5-aapere shunt. th i s ammeter has the degree
of accuracy necessary to l im it the e r ro r of the f in a l galvan
ometer read ing to w ith in 1 p e r c e n t, the b a t te r ie s a re fo u r
Edison c e l l s arranged in s e r ie s , and they gave s a t is fa c to ry
se rv ice under the experim ental cond itions used.
P relim inary Knowledge R ela ting to th e A p p lic a b ility
of the B a l l i s t i c Method
Work was s ta r te d to in v e s tig a te th e p o ss i
b i l i t i e s of u t i l i z i n g th e b a l l i s t i c type of magnetic apparatus
fo r the determ ination of magnetic perm eab ility of m agnetite ,
m ainly because of the wide a p p lic a tio n of an instrum ent e f28
the same p r in c ip le fo r the t e s t in g of s te e ls and iro n s .
At th e s t a r t of th i s work i t was conceded th a t the method i s
sim ple, and as used w ith iro n and s te e ls i s f a i r l y accu ra te .
As no ted , the use of the b a l l i s t i c method
has been lim ited to homogenous s o l id s . I t was re a l is e d th a t
the a p p lic a tio n e f th i s m ethod.to f in e ly ground m a te ria l p re
sented serious; o b s ta c le s . From the work of Seamen and Hoe-'04
t e t t e r i t was p red ic ted th a t the "g rain s ize" of the m a te ria l
S U • I' ' • ■ , r r , r V ' T ' ' ' . . . . . . . . . . . . . . . - ; T ' r 1 T ' ’ r r i T 1 , T " ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . . ' * r " r n r ^ r ~ '
W all, T. F . , Applied Magnetism: Hew York, 1927, chape. IX and X, pp. 129-166.
24 . ■ . . . . . . . . . ■ : • . 'Seaman, R* B ;, and H o s te tte r , J . 0 . , The Ferrous Iron Conte n t and ISagnetle S u s c e p t ib i l i t ie s of Seme A r t i f i c i a l and n a tu ra l Oxides of I re n : Trans. Am. I n s t . Min. E ng ., vo l. 58, 1918, pp. 404-433.
to be te s te d would have a narked e f fe c t upon th e magnetlo p e r
m eab ility of th e l a t t e r . I t i s a ls o known th a t p rev ious mag
net io h is to ry , a s w ell as heat trea tm en t of magnet io m a te r ia ls ,
have some e f fe c t upon th e i r magnetic p ro p e r tie s .
In te rp re ta t io n of R esults
A bsolute values fo r the perm eab ility or
s u s c e p t ib i l i ty of m ate ria ls tested has not been determ ined.
I t i s , th e re fo re , im portant th a t an explanation be given th a t
w i l l enable the data presen ted to be in te rp re te d . The magnetic
p e r m e a b i l i t y ,^ , from equation X, page 14, i s a fu n c tio n of
the d iffe re n c e in galvanom eter d e f le c tio n s , and th i s read ing
i s recorded in cen tim eters f o r a given weight of sample.
Weight measure is used to determine the amount of m a te ria l to
be t r e a te d ra th e r than volume measure, because of the ease
and accuracy of weighing.
The Container
C onstruction and development of th e appa
ra tu s o ffe red many d i f f i c u l t i e s . Three s e ts of so leno ids were
construc ted of which the th i r d and l a s t s a t i s f i e d the re q u ire
ments of the method. The shape of the sample co n ta in er was
se lec ted a s long and narrow, to decrease the dem agnetization
e f f e c t . The l a t t e r does not e f fe c t the desired com parative 25
25S ta r l in g , 3. G ., E le c t r ic i ty and Magnetism: London, 1924,p. 270.
- 1 8 -
1 9
v a lu e s , tu t only le e re a se s the true magnetlo p erm eab ility
which f o r a c e r ta in perm eab ility i s ecn s tan t. Aluminum, g la s s ,
and brass co n ta in ers were t r i e d . These m a te ria ls a re non
magnetic w ith in the experim ental error. One very im portant
f a c t which was found ea rly in th e work i s th a t th e samples
must be of .th e , same id e n t ic a l s iz e and shape* The aluminum
being s o f t and the g la s s d i f f i c u l t to shape, the b rass was se
lected as the best a v a ila b le container m a te r ia l, s ince i t could
be. machined in a la th e to th e required s iz e w ith the desired
accuracy . Six b ra ss capsu les were made, but only th ree were
found to produce r e s u l t s to an accuracy w ith in 1 per cent.
The fo llow ing data shown in Table 1 give r e s u l ts which in d i
ca te th e fo re g o in g conclusions.
Table 1 .—R eprod u c ib ility of the B a l l i s t i c Instrum ent.
dapsule ; Galvanometer d e f le c tio n , cen tim eters50#
P C: %est So. I I : T e s tt io . 12 :1 l i s t i o . "1 8 1 Test lie. 14
i■ • r
: 21.19 : 21.08 ; 21.05 : 21.05
2:: 21.10 $ 21.11 \ 21.10 : 21.16
6«: 21.01 : 21.09 : 21.10 : 21.01
■ ■ i
A sample of fu rnace accretion m agnetite
produced in copper sm elting , weighing 1 .0 grams, was used in- ' . •' » % ' " , ' ' • - • - ' ' ■ • -
1 ■ I • • -.v ■ ' ' *1 '
these t e s t s , and a prim ary cu rren t of 2 amperes was employed.
The maximum percentage error i s 0 .9 .
Used to Control Volume of Sample
To ob ta in a volume f a c to r , uniform as poss
ib le , tapping of th e m ate ria l was p ra c tic e d . The tapping pro
cedure comprised (1 ) p lac in g th e sample in a capsule and tapping
the co n ta in er w ith a modified "b e ll buszer" which was arranged
so as to s t r ik e the capsule in such a way so as to ro ta te i t
and ja r the sample a t the same tim e. This process was continued
fo r about a 6-m inute p e rio d , a f te r which the capsule was removed
(2 ) The sample co n ta in e r was placed w ith in a so lenoid which
has approxim ately 80 tu rn s per cen tim eter of copper w ire . An
a l te rn a t in g c u r re n t , 5 amperes a t 60 c y c le s , was then caused
to pass th rough the so lenoid fo r th e purpose of p reparing the
sample so th a t constan t va lues could be ob tained . This proce
dure was continued fo r a period of approxim ately 3 minutes $
the capsule was then placed w ith in th e te s t in g solenoid and
the galvanom eter d e f le c tio n was read . /
Steps (1) and (2) were repeated fo r sh o rte r
time periods u n t i l successive galvanom eter d e f le c tio n s were
co n stan t. This c o n s ta n t:value was accepted as th e f in a l meas
u re of magnetic p e rm eab ility . .
The ob ject of p lac in g th e sample con ta iner
w ith in the a l te rn a t in g magnetic f i e ld i s not q u ite c le a r ly
e s ta b lish e d , but i t i s necessary from e i th e r a tapp ing in f lu
ence in a d d itio n to th a t obtained by the mechanical tapp ing
or the n e c e ss ity of dem agnetising o f the m a te ria l te s te d .
The p lac in g of the sample in th i s c o i l in creases the galvan
ometer d e f le c tio n ; th e re fo re the tapping in fluence appears to
be g re a te r than the dem agnetization e f f e c t , M eans# Shis l a t
t e r redmees the p e rm eab ility . Some m agnetite m ineral has an
app rec iab le h y s te re s is e f f e c t26 * and, provided the m agnetizing
f i e ld i s le s s th an th a t required to sa tu ra te th e m agnetite ,
demagnetizing would decrease the perm eab ility and th e re fo re
the galvanom eter d e f le c tio n . A marked disadvantage of th e
complete tapp ing procedure a s described is the len g th of time
re q u ire d . This am ounts 'to from 1 to 3 hours per th ree samples
in order to ob ta in f iv e to s ix constan t values of th e galvan
ometer d e f le c tio n s f o r each sample.
m ane t i e V iscosity
A co n d itio n which may or may not be p resen t
in m agnetite i s termed by Wall as "Magnetic V isc o s ity ." I t
i s conceivable th a t th e re v e rs a l of a magnetic f i e ld through
a magnetic m a te ria l would take a c e r ta in d e f in i te measurable
period of tim e. This period may prove to be so long th a t the
b a l l i s t i c method may be in v a lid a ted f o r perm eab ility measure
ments. 28 R eferring to the d e sc rip tio n of the theory as p re
sented on page 14, i t may be noted th a t in order to o b ta in a
W — 1 - ! 1 " 1 """"Seaman, R. B ., and Peanjak, E . , Ferrom agnetic F e rr ic Oxide, A r t i f i c i a l and n a tu ra l : Jour. Wash. Acad, o f S o l . , v e l. IS ,
, 1928, pp. 329-342.
W all, T. F , , Applied Magnetism* Bew York, 1927, pp. 90-91.
W all, T* F#, op. o i t ♦
tru e measurement of the charge, , by the b a l l i s t i c g a l-
vanometer, th e charge must be proameea p r a c t ic a l ly In s ta n ta
neously. I f th e value of th e magnetic f i e l d th rough the
m agnetite in c reases or decreases g ra d u a lly , th e re would be.a
"leakageM of the charge, which would not be f u l ly measured by
the f i r s t galvanom eter d e f le e tio n .
The e f f e c t of magnetic v ie e e e ity should be
determined or shown to be in e f f e c t iv e , but u n fo rtu n a te ly the
b a l l i s t i c method can not be used f o r th i s purpose and the w rite r
did not have the opportunity to develop any o ther means of
proving or d isprov ing th e e ffec t#89
%11 suggests th e magnetometer method
fo r "Magnetic V iscosity" measurements, but the apparatus used• ; .* .
in th is method i s qu ite d i f f i c u l t to co n stru c t and opera te .
Conclusions from th e Work on the B a l l i s t i c Method
Taking in to co n sid e ra tio n the leng thy
tapp ing time re q u ire d , the: "magnetic v is c o s ity " f a c to r , and
th a t the ammeter was found to be d e fec tiv e and was shipped to
the fa c to ry to be re c a lib ra te d and re p a ire d , work progressed
along two l i n e s —f i r s t , aeo u ra te determ inations of th e s iz e s
of p a r t ic le s were made on screen f r a c t i o n s s e c o n d , in v e s t i
g a tio n of the p o s s ib i l i t i e s of th e Sosman or magnetic balance
type of instrum ent was s ta rted * - -) ' . - . ;
Wall, T. P . Vo ^ . o i t . , chap. X llle pp. S01-814*
35PI ATION OF "AVERAOE SIZE" PARTICLETHE DE®
In any method f o r th e determ ination of mag
n e tic p erm eab ility of pu lverized m a te r ia l , th e e f fe c t of v ar
ia b le g ra in s iz e i s extrem ely im portan t. The general procedure. ' . — • ■- - - :; : ■ • r. '. : '
of p reparing s ized magnetic m a te ria l i s to crush or grind the
m a te ria l and then s iz e w ith Tyler standard s ie v e s . The average
s iz e of p a r t i c le fo r each sc reen f ra c t io n may not n ec e ssa rily
be the average o f the diam eter o f th e ho les of th e l im itin g
sc reen , and th e re fo re determ ination of the average g ra in s iz e
becomes necessary . Determ inations were made by th ree methods,
denoted "A", "B", and "0".
- ̂ Method "A"
A sample of a screen f r a c t io n was mixed
w ith some liq u id Canada Balsam on a g la ss s l id e ; a cover g la ss
was then pressed upon th e m ix ture. This s l id e was mounted upon
a mechanical stage o f a microscope equipped w ith a micrometer
ocu lar and th e g ra in diam eters were measured, u sing tran sm itted
l i g h t . From 50 to 160 g ra in s were measured in order to ob tain
a f a i r average , which n e c e s s i ta te s a system being adopted , using
the mechanical s tag e , whereby no p a r t ic le would be measured
tw ice. The "average s in e" p a r t i c l e , as used in th i s paper,
i s defined a s the num erical average of the measurements of 50- . - ■ • • • • • ‘ ' < •
to 150 g ra in s ; two measurements must be made on each p a r t i c le —
one along the g re a te s t and the o ther a long the sm a lle s t dimen
s io n v is ib le . A f a i r average was obtained by averag ing th e
f i r s t ana l a s t h a lf of the read ings and i f th ese two values
were co inc iden t w ith in the experim ental accuracy , the t o t a l
average was re p e rted as th e "average e ia e M p a r t i c le .
: ' ' ; - ; Method "B" : "
This method co n sis ted in the working of a
sm all m agnetite sample in to Canada Balsam on a cover s l i p .
A b rass r i n g .0 .26-inch long and 0 .50-inch diam eter was placed
around th e m ixture and the b rass contaizm r f i l l e d w ith Canada
Balsam. A g la ss s l id e was then placed on th e open end of the
r in g , the Canada Balsam adhering to th e g la s s . The m agnetite
sam ple, w ith the g la s s cover s l ip upperm ost, was examined by
tran sm itte d l i g h t . By u sing old Balsam, which i s r e la t iv e ly
viscous when cold but which becomes f a i r l y liq u id when warmed,
the s l id e specimen w as.made permanent. The method of measure
ment was the same as described under method "A".
..... -. . . -.......’ ' ' ;. Method "0" ■;..... :: ; . - . 7 . ... -.. ■;" ■; :■:. " . - . ■ , ■ " .. - ' ! ; v; **. -• -r
A sample of the m a te ria l was s t i r r e d in to
visooua C h asse r^ cement contained in a r in g of b rass tubing
approxim ately l /2 - i i i s h long . The m ixture i s allowed to see l
and harden, a f t e r which the su rface of the specimen i s ground
and p o lish ed . The " b r iq u e tte " i s then mounted fo r examine-
t io n w ith a m etallographio m icroscope. The measurementa were
c a rr ie d out the same as ou tlined under method "A".
Experiments were made with th e eb jee t of
determ ining which of the methods described o ffered th e g re a t
e s t promise of y ie ld in g th e " tru e" value of th e "average s iz e "
p a r t i c le . Tables 2-a and b p resen t the r e s u l t s of measure
ments u sing methods "A", and "G".
3ample- H°J
Screen s iz e , .mesh
O bjective ~ used .
Average Size1* of p a r t i c l e , m illim ete rs
Through : mm. : • t "B" : nC"
180 1 • 0.002 0*011i :
200 $ 380 0.002 0.088 $ :■ ■ 180 v t 200 0.000 0.144.
100 : 160 0.004 0.188 s 0.177 : 0.07416 t 100 0.0189 0.29148 $ 66 I> ' .. - . . '
Table 2 - t . —Grain Size Measurements Using Sample Ho.
. ./ .
11a. M ineville M agnetite.■ \ ' . : , .
Screen e ls e ,mesh
i Objee- % t t iv e i
"Average S ize" of p a r t i c l e , m illim e te rs Ratio
Through | On s used , $ »A» | "B" ; wCw i* * « rc*- : '
360 :J 0*0009)1t 0.002 )$
3 0.006)88 0.012)8 0.008 1 .6
200 i 360 - t 0*002 i 3 0.076 : 0.034 2 .2160 s 200 S 0.004 % 3 0.134 3 0.056 2 .4100 t 180 ; 0.004 $ 3 0.180 3 0.079 2 .3
66 t 100 8 0.0189 8 8 0.258 8 0.132* 1.9648 J
200 ! 250 $270 :
65260270860
s 0.0189 s : 0.002 $ 8 0.002 3 3 0.002 8 :
8 0.315 s3 0.098 8s 0.081 3 3 0.069 3
:
0.181 1 .74
*0b je e tiv e used was 0.004-mm.
The screens used as l is t® ! in the f i r s t
two columns, Tables 2-a and 2-b , a re Tyler standard sieves#
The s ig n if ic a n c e of th e f ig u re s l i s te d in the column "Objec
t iv e used" i s th e value of each sca le d iv is io n of the micro
meter d isc in the ocu lar o f th e microscope w ith the o b jec tiv e
used fo r th a t p a r t ic u la r screen f r a c t io n . .
I t i s th e w r i te r ’s opinion th a t of the
th re e methods t r i e d , method ”B" approaches the " tru e r value
of the "average s iz e " or p a r t ic le as defined above. The r e
s u l t s obtained by each method a re r e la t iv e ly c o rre c t, but the
ab so lu te values of "average size*! probably approach those of
method "B". The r e s u l t s obtained by employing method "B"
a re used throughout as th e "average s iz e " p a r t i c l e . The r e a
son fo r th is apparent v a r ia t io n of values f o r the "average
s iz e " in method "A" probably i s due to th e e f fe c t of fo rc in g
the cover s l ip down upon the g ra in s , thereby causing an a l ig n -i • !.ment p erp en d icu la r to the l in e s of force* In method .^C" th e i ; " “ ' ' i r | ■ •"read ings a re made by measuring sections; of p a r tic le s ^ which,
in the opinion of the w r ite r , tends to cause low r e s u l t s fo r
th e "average s iz e " p a r t i c le .
.MATERIALS USED
- ‘ - . Table S g ives a d e se r ip tio a in summary form of>
the m a te ria ls used . ; : -
Table 3 . . .Summary of the M ateria ls Used
M agnetiteeentent Den Methods of
Ho. B eslg- Source Per - Grams s i ty preparationn a tio n cent * *
0. 0.
10 Magne- Witherbee-Sherman Co., See page 28t i t * M inev ille , H.Y. - ■
11a do. " do. '■ • - ' • 90 See page 28l i b do. ... . do. 91.6 2,836 See page 28
2A Magne H o .lib , Ho. 3 73.8 2.255 80^ H o.libt i t e
m ixture2 # Ho. 3
SB do. do. -: ; ;z V- " 55.8. _ -*;*». . • • . .... -■
1.850 60=5 HO.lib 40̂ 5 Ho.3
■ " ; *20 do. do. . 27.7 1.455
■ .Ho. 11b
7 # He. 3
SD do. do. ' " - - - ' 46.2u v /• / •
0.787 1,704 SSS S:i". . . \ .2E do. 32.3 0,488 1.510 35^ H o .lib
. '■>. 665$ Ho.3
2F do. do. 25.0 0.3645 1.421 27J5 Ho. 11b• . 7356 Ho.3
EG do. do. • 12 .9 0,1680 1.298 145S Ho. 11b 86=5 Ho.3
2H do. '4@# 7 .4 O.OfSl 1.246 8.0% H o .lib 92% Ho.3
3 Quartz Ottawa, 111. 0 ' 0 1.186 See page 294 Magne Hevada Cons.Copper Go., See page 29
t i t e Hurley, II.M.5 do. Calumet & A ria . Copper
Co., Dou^lae, A ria .See page 29
6 R u tile 0 0 m u m ' See page 29
Kethoas of P reparing IS a teria ls
Ho. 10 :
The m ineral m agnetite was s ized as fo llow s: -65 +100^
-100 +150, -150 +500, -200 .*350, -550 mesh. A ll s iev es used
were Tyler standard s ie v e s . This m a te ria l was used only in
the pre lim inary work f o r the determ ination of "average s ize"
p a r t i c le and magnetic da ta were not obtained*
HQ. 11a :
The o r ig in a l specimen of m ineral m agnetite was ground
through 48 mesh, m agnetica lly concen tra ted , and s ized . The
f r a c t io n , minus 48 p lu s 65 mesh, was d igested in 10 per cent
so lu tio n of f e r r i c su lphate to remove the m e ta llic iro n , a f t e r
which i t was washed, d r ie d , and ground in an agate mortar to
secure th e fo llow ing sized fraction s: -48 +65, -65 +100,
-100 +150, -150 +200, -200 +250, -250 +270, -270 +550, -550
mesh. Each of these sized f r a c t io n s was analyzed fo r magne
t i t e content. The potassium dlehrornate and the potassium p er
manganate methods fo r fe rro u s iron were used fo r th ese analyses
The r e s u l t s of bo th methods were averaged to ob tain the magne
t i t e co n ten t. The value repo rted in Table 3 i s the average
value of m agnetite co n ten ts of a l l the fr a c tio n s .
Ho. 11b:
This m a te ria l i s th e o r ig in a l sized f r a c t io n minus 100
p lu s 150 mesh obtained as described under Ho. 11a. Half of
th i s f r a c t io n was ground through 350 mesh* These two s iz e s ,
-100+ 150 and -350 mesh, were se p a ra te ly d igested in a 10 per
cent copper su lpha te so lu tio n to remove m e ta llic iro n . They
were then washed, d r ie d , and resereened* The m agnetite een-
te n t of th e -100 t-150 meah was 90.8 per c e n t, and th a t of the
-880 meah 92.4 per c e n t. The d e n s ity a s used in Table 3 la
defined oh page 40.
Boa. 2A to 2H. in e lu a iv e :
The m agnetite con ten ts as rep o rted in Table 3 were ob
ta in ed by c a lc u la tio n from those known fo r the o r ig in a l sub-
etanoea. The d e n s i t ie s of m a te ria ls numbered SB to 2H, in
c lu s iv e , were ob tained from the curve shown in F igure 10.
Pure quartz was. ground through 350 meah, d i l a t e d in
d i lu te hydroohlerio a c id , w a s h # , ig n i te d , and resize#*
M ineral m agnetite was tre a te d to remove any m e ta llic
iro n p re se n tj i t was then ground to -100 *150 mesh s iz e in
an ag a te m ortar, and a p o rtio n of th e product was then ground
to -350 mesh.
Ho. 5 :
Furnace a c c re tio n m agnetite was ground through a 200-
mesh s ie v e , d igested in copper su lphate s o lu tio n , and re s iz ed
to -200 *350 meah. I t was then analyzed fo r m agnetite con
te n t and a p o rtio n was ground to -350 mesh in an ag a te m o rta r |
the l a t t e r was used fo r magnetic balance work.
Ho. 6 :
R u tile was ground through 350 mesh, d igested in d i lu te
hydroch lo ric a c id , washed, ig n i te d , and re s iz e d .
- 20 -
M&.6HETIC BALAJICI METHOD
On aooGnnt of the aforem entionea d i f f i c u l
t i e s concerning th e use o f th e b a l l i s t i c a p p a ra tu s , a study was
s ta r te d fo r th e purpose of in v e s tig a tin g th e p o s s ib i l i ty of
applying the-m agnetic balance method f o r th e com parative meas
urement of th e magnetic s u s c e p t ib i l i t i e s of magnetic m a te r ia ls .
The Curie p r in c ip le i s th e b a s is of a l l types of magnetic b a l
ances te s te d by th e w r i te r , th e only v a r ia t io n being th e means
of m agnetically a t t r a c t in g th e magnetic m a te r ia l. Two methods
of producing th e magnetic f ie ld s were used by Sosman; iro n -co reSO 31
elec tro -m agnetio p o le s , and a so lenoid magnetic f i e l d .
Instrum ents using both o f Sosman*s methods were assembled and
experim ents were ca rried out in order to determine which offered
the most prem ise.
The Solenoid Type of Magnetlo Balance
Figure 2 , page 6 , re p re se n ts a diagrammatic
view of the appara tus, w ith the exception th a t the pole p ieces
shown were rep laced by a so len o id , approxim ately 16 centim eters
long and 1 centim eter d iam eter. By allow ing a constant e l e c t r ic' V ' •
30 — — —Sosman, R. B ., and H o s te tte r , J . C ., op. c l t .
31Sosman, R, B ., and Poanjak, E . , op. p i t .
- 3 1 -
cu rren t to flow through th i s solenoid a magnetic f i e ld was pro
duced so th a t a capsule con tain ing magnetic m a te ria l would be
a t t r a c te d . The in te n s i ty of the a t t r a c t io n was measured by an
assay ba lance , accurate to 0, 02-m illig ram , and re s u l ts could be
reproduced w ith in 1 per c e n t.
The f i r s t experim ental work to be ca rried
out was to determine the e f fe c t of various s iz e s of p a r t ic le s
upon the magnetic a t t r a c t io n . The methods fo r determining the
"average s iz e " p a r t ic le have been described and the data a re
presented in Table 2-b. The r e s u l ts of the magnetic determ in
a tio n s on various p a r t ic le s iz e s , using the various sized f r a c
tio n s of m agnetite No. 11 -a , a re shown in Figure 5.
r i,3------------ -------------U______ L___________________ 1___
Figure 5 . —E ffec t of "average s ize " p a r t ic le upon the magnetic a t t r a c t io n , using the solenoid magnetic balance.
- 3 8 -
$he r e s u l t s o f measuring the magnetic a t t r a c
t io n of vario u s s iz e p a r t ic le s in d ic a te a d iffe re n c e of 2*7
m illig ram s between p a r t ic le s of average s iz e , 0.006 m illim ete rs
and 0.315 m illim e te rs . Expressing th ese re s u l ts in term s of
per eent based on the magnetic a t t r a c t io n of the la rg e r s iz e
p a r t i c l e , th e sm aller s iz e p a r t ic le s have a magnetic a t t r a c
t io n 21 per cen t l e s s than th e la r g e r . I t may be noted th a t
due to low in te n s i t i e s o f th e magnetic f ie ld s th a t th e d i f f e r
ences in a t t r a c t io n as measured in m illigram s a re sm all and
th e re fo re the balance must be s e n s i t iv e ; the balance used in
th i s work was ad ju sted fo r a high degree of s e n s i t iv i ty and
therefore n ec ess ita te d freq u en t checking of th e zero p o in t.
As p rev iously m entioned, m agnetite has an appreciab le h y s te re
s i s e f fe c t which n e c e s s i ta te s the use of a so lenoid having a
uniform magnetic f i e l d . Sue to th e d i f f i c u l t i e s mentioned sad
in view o f the f a c t th a t the po le -ty p e m agnetic balance de
creased these d i f f i c u l t i e s , th e so leno id-type instrum ent was
not f u r th e r used in th i s work.
The Pole-Type Magnetic Balance
R efe rrin g aga in to F igure 2, page 6 , the
po le-type apparatus used followed t h i s diagram w ith a few mod
i f i c a t io n s . The appara tu s used f o r t h i s work was a sm all
la b o ra to ry balance having an accuracy of approxim ately 1 to
2 m illig ram s, which req u ired the use of a correspondingly
greater magnetic f i e l d . The l a t t e r was obtained by means of
a s o f t iro n -co re p o le -ty p e electromagnet. The co n ta in e r f o r
the m a te ria l m s made of b rass and con sis ted of a cup 1 .35
cen tim eters in d iam eter and 1.26 cen tim eters h igh , w ith a
sm all screw on the s id e which served to hold a c lo s e - f i t t in g
p lunger, 2 .3 cen tim eters long , t ig h t ly once the plunger had
been ad ju sted . A sm all ey e le t was a ttach ed to the top of the
p lunger, to which th e balance arm was connected. When in use
th e co n ta in e r capsule was ad justed so as to r e s t d i r e c t ly upon
th e pole p ieces of th e magnet.
A constan t e le c t r ic c u rren t of approxim ately
0. 49-ampere was used to induce th e magnetic f i e l d , which in
tu rn produced an a t t r a c t in g fo rc e of th e o rder of 10 to 12
grams f o r pure m agnetite m a te ria l weighing 0.500-gram. This
fo rce was measured by a llow ing sand to slow ly r m upon the b a l
ance pan u n t i l the capsule was pu lled away from the pole p ie c e s ,
the capsule being f i r s t balanced without th e a t t r a c t in g f i e l d .
A fte r each sample was placed in th e co n ta in er th e l a t t e r was
tapped u n t i l successive determ inations y ie lded re s u l ts which
were ecn stan t w ith in an experim ental e r ro r of 1 per c e n t.
This co n stan t r e s u l t was the repo rted value of the magnetic
a t t r a c t io n f o r th a t p a r t ic u la r magnetic m a te ria ls
Using the method described, the e f fe c t of
"average g i s t ” p a r t ic le upon m agnetic a t t r a c t io n was determined
and is p resen ted in F igure 6.
- 3 4 -
Figure 6 . —The e f fe c t of "average s ize" of p a r t ic le s upon magnetic a t t r a c t io n , using th e po le-type
of magnetic balance.
By comparison of Figure 6 w ith Figure 5,
i t may he observed th a t the sen s itiv en ess of the po le-type
balance is not as great a s th a t of the so len o id -ty p e , the
v a r ia tio n of th e 0 .006-m illim eter m ateria l being only 6 per
cent as compared w ith la rg e r s iz e 0 .316-m illim eter m aterial
while th is amounts to 21 per cent fo r the so len o id -ty p e .
fhese curves dem onstrate the f a c t th a t v a r ia tio n in s ize of
p a r t ic le in flu en ces th e magnetic m a te ria ls and therefore i f
comparable r e s u l t s a re to be obtained on d i f f e r e n t magnetic
m a te ria ls the g ra in s iz e of th ese m a te ria ls must be id e n tic a l .
A fte r th e work upon e f fe c t of g ra in s ize
was completed the po le-type balance was improved. The pole
p ieces were moved f a r th e r a p a rt in o rder to e lim in a te the use
of sand to balance the p u l l , and th i s reduced th e a t t r a c t io n
to be measured from about 11 to 1 .5 grams, the s iz e of the
sample being a ls o reduced from 0.50 to 0 .25-gram. A marked
g la ss s l id e was a ttach ed to th e pole p ieces to f a c i l i t a t e th e
centering of th e container over the pole p io ees . The a t t r a c
t io n was th en measured d i r e c t ly w ith standard weights. The
procedure fo r th e p re p a ra tio n of th e m a te ria l was a lso modi
f ie d and comprised i
1 . In tim ate m ixing of th e m ate ria l in the capsu le .
2 . Demagnetization of the m ateria l in a decreasinga l te rn a t in g magnetic f i e ld , thus in su rin g the e f fe c ts due to h y s te re s is were absen t.
3 . The m ate ria l was aga in mixed.
4. The m a te ria l was leve led by g e n tle shaking andby f ix in g th e p lunger in p lace and then r o ta ting i t .
6. The co n ta in e r was tapped 10 to 20 tim es w ith hard blows upon a so lid p iece of wood while ho ld ing the p lunger f irm ly down upon the m a te ria l and then th e plunger was made f a s t by means of the screw. - •
The co n ta in e r was next placed over th e
polo p ieooe, the current turned on, the balance connected, and
weights added to th e balance pan u n t i l the magnetic p u l l was
ju s t enough, to hold the co n ta in e r . The weighings were d e te r -
mined to the order of 1 m illigram . Using th i s improved p o le -
type in strum en t, th e e f f e c t of d i lu t io n was stud ied using
q uarts as the d i lu tin g agen t.
The E ffec t of D ilu tio n of M agnetite w ith Quartz
The procedure fo r determ ining th e e f fe c t
of d i lu t io n upon magnetic a t t r a c t io n when u sin g m agnetite m s
as fo llo w s ;
1, The m agnetite and quartz were weighed d i r e c t ly
in to the sample co n ta in e r in the proper p roportion to make a
t o t a l weight of 0#2600-gram.
2. The m ixture was tre a te d and te s te d m agnetica lly
a s o u tlin ed on page 36. R esults were rep roducib le w ith in 1
p er cen t using th e same m agnetite m ixture j th i s dem onstrates
the la ck of segregation of th e components in the m ix tu re . The
m agnetite content was re p o rted as th a t determined by chemical
means in th e in te rp re ta t io n of these r e s u l t s . The r e s u l t s of
th i s work appear in th e form of cu rv es , which fo llow .
r - 3 7 -
L - - - " JFigure 7 .—The e f fe c t of d ilu tin g m agnetite H o .lib , -350 meah and H o .lib , -100 +150 meah, w ith q u a r tz , -350 mesh and -100
+150 mesh, re sp e c tiv e ly .
10 20 30 4090 80 70 60
COMPOSITION
Figure 8 .—The e f fe c t of d ilu tin g m agnetite Ho. 4 , -350 mesh (lower cu rve), and Ho. 4, -100 mesh, with quartz -350 mesh
and -100 mesh, re sp e c tiv e ly .
Several observations may be noted from a
co n sid e ra tio n of these cu rves. The most s ig n if ic a n t f a c t i s
th a t the curves a re not s t r a ig h t l in e s ; th i s variance from the
expected s t r a ig h t - l in e curves may be explained from th e type of
magnetic f i e ld which a t t r a c t s the m a te ria l and a lso from th e
v a r ia tio n of the d e n s it ie s of th e mixtures* The f ie ld becomes
weaker as the d is tan ce away from th e pole p ieces in c re a se s ,
and consequently , i f th e d en sity e f the p u lv e ru len t m a te r ia l
decreases o r , since th e d iam eter of th e co n ta in e r i s c o n s ta n t,
the heigh t in c re a se s , th u s producing a more than p ro p o rtio n a te
decrease in magnetic a t t r a c t i o n w ith d i lu t io n . The f a c t th a t
in Figure 7 the curves fo r th e -100 +i80-me#h and -3§0-mesh
m a te ria ls do net show a p ro p o rtio n a te decrease may a lso be
explained by th e v a r ia tio n in pulp d en sity . This d en sity is
not only a fu n c tio n of th e "massive d en sity " of the m a te r ia ls ,
but a lso r e l i e s upon the amount of v e ld s , which in tu rn de
pends upon packing of the mixed substances. I t was, th e re fo re ,
im portant th a t accura te knowledge be obtained oeneerning den
s i t i e s of the ground m agnetite and s i lu t lo n s of m agnetite , and
th e re su lta n t e f f e c t upon magnetic a t tra c tio n * I t i s known
th a t when a m ixture of m inerals i s ground the in d iv id u a l min
e r a ls a re not u su a lly d is tr ib u te d in the same r a t io in a l l th e
sized f ra c t io n s . Therefore in a l l the fo llow ing work i t was
decided to g rin d to minus 360-mesh in order to e lim in a te as
much a s p o ssib le the e f fe c t upon th e magnetic a t t r a c t io n caused
by th e v a r ia tio n s of m agnetite con ten ts fo r the d if fe re n t p a r
t i c l e s iz e s . That i s , a m ixture which produces a preponderance
of minus 360-mesh m agnetite when ground w ill have a le s s
a t t r a c t l e a than one which producea the m agnetite in th e ocareer
s iz e s , even though the two have equal m agnetite co n ten ts .
The Penalty of P u lveru len t M ateria ls
A photograph of the apparatus designed by
the w r i te r to measure th e d en sity of dry pu lverized m aterial®
i s p resen ted in Figure 9, and c o n s is ts of a c a p illa ry tu b e ,
closed a t one end by fu s in g . A sm all funnel was sealed to the
o ther end in order t e f a i i l t t a t e th e t r a n s f e r of m a te ria l to the
c a p il la ry . This tube f i t s in to a rack which has a s ta tio n a ry
s c a le , graduated in m illim e te rs along one edge. The m a te ria l
i s weighed in to th e funnel and tapped u n t i l the heigh t of the
column is eonstant as read w ith th e aid of a movable piece @f
paper w ith a f in e l in e drawn upon i t . The tube was c a lib ra te d■
by p lac in g v a ria b le amounts of mercury in i t and measuring the
heigh t of each mercury column and then weighing the tube te
ob ta in the weight of mercury contained by d if fe re n c e ; th e abso
lu te volume was ca lcu la ted and the d en sity of any m ate ria l c f
known weight and placed in the tube i s then o b ta in ab le . The
accuracy of the density determ ination was of the order of 1 per
-4 0
Figure 9•—Photograph of th e "densitom eter*"
From th i s d iscu ssio n i t fo llow s th a t th e
term "d e n s ity ” as app lied to pu lveru len t m a te ria l when used in
th i s paper i s the number of grams of m ate ria l which w ill occupy
a volume of 1 cubic centim eter when tapped u n t i l no fu r th e r
in crease in den sity is observed.
The d e n s itie s of m a te ria ls Ros. 2 , 2A, 2B,
2C, and 3 t which a re described in Table 3 , were determ ined and
the r e s u l ts a re in d ica ted in Figure 10.
•41
IF THEl a w o r
100-MAGNETITE NO 1^-350 MESH0 -Q U A RTZ, -3 5 0 MESH0 60 * 50 4 0 3(
COMPOSITION BY WEIGHT, PER CENT
Figure 10#--The r e la t io n between density and com position, using m agnetite -quartz mixtures*
I t is observed from Figure 10 th a t the
u sual law of m ixtures a s app lied to d en sity does not hold fo r
the m ixtures u sed , and the d ensity of a m agnetite -quartz mix
tu re is not the weighted average of th e component densities*
This is presumably due to the d iffe ren ce in r e la t iv e packing
of the quartz and m agnetite which in tu rn might be caused by
the d iffe ren ce in shape of t h e i r re sp e c tiv e g ra in s .
- 42 -
Development of a C a lib ra tio n Curve fo r Determining
the M agnetite Content of Substances
Magnetic measurements were made according
to the procedure ou tlined on page 55 w ith the exception th a t the
a t t r a c t in g c o ils and pole p ieces were changed in order to in
crease the s e n s i t iv i ty of the magnetic balance fo r dea ling w ith
m a te ria ls of small m agnetite co n ten ts . A photograph of th i s
f in a l apparatus i s shown in Figure 11.
Figure 1 1 .—Photograph of the Magnetic Balance f in a l ly adopted.
V aria tions In the d e n s it ie s of magnetic
m a te ria ls in fluence the magnetic r e s u l t s in two ways—f i r s t ,
the a c tu a l volume of the m ateria l taken to determine th e mag
n e tic a t t r a c t io n , and second, the amount of m agnetite (FegC^)
per u n it volume of m aterial# In order to study the f i r s t
e f f e c t , m a te ria ls Nos. 2d , 2E, 2F, 2G, and 2h, which a re de
scribed in Table 3, were used and the magnetic a t t r a c t io n of
various volumes of th ese m a te ria ls were determined and p lo tte d ,
as shown in Figure 12#
14 00
ooool OS 5? 5aVOLUME, CUBC CENTIMETERS
Figure 12 . —The e f fe c t of volume of m agnetite m ixtures uponmagnetic a t t r a c t io n .
- 4 4 -
In order to ob tain a s e r ie s of curves which
would account fo r both these e f fe c ts due to d en s ity , the degree
of magnetic a t t r a c t io n was obtained from Figure 11 where the con
s ta n t com position curves cut the volume o rd in a te s : 0.080, 0.120,
0 .170, and 0.210 cubic cen tim eters. The com positions of each of
these m a te ria ls being known in grams of m agnetite per cubic cen
tim e te r (see Table 3 ) , curves were drawn showing th e r e la t io n
between m agnetite (Fe^O^) content and magnetic a t t r a c t io n a t
sev e ra l constant volumes. These curves a re presented in Figure 13.
1.400
0.600
0.200
08000400 0.600
, P C O S * CENTIMETER Of MATERIAL0000
g ram s or m a o c t it c ,
Figure 1 3 .—The r e la t io n between m agnetite conten t and magnetica t t r a c t io n a t constan t volume.
To determ ine th e m agnetite con ten t of any
m a te r ia l , the d en sity of th e m a te ria l a f t e r g rin d in g through
350-mesh being known, a weight is se lec ted such th a t the volume
occupied i s th a t fo r which a curve has been p lo tte d as shown in
Figure 13, and the magnetic a t t r a c t io n fo r th i s volume is then
measure*$ th e eom peeition i s next obtained d i r e c t ly from the
proper curve. A fte r th e com position in grams of m agnetite per
cubic cen tim eter has been determ ines, the per cen t by weight
Is obtained by d iv id in g th e grama of m agnetite (FegO^) per
cubic cen tim eter by th e d en s ity and m u ltip ly ing by 100. The
reason fo r th e above curves being constan t-v e lu m curves ra th e r
than density i s th a t th i s procedure e lim in a tes the n ec ess ity
of in te rp o la t io n .
I t may be observed from th i s d iscu ssio n
th a t th e method i s dependent upon th e fo llow ing p o s tu la te :
That a constant amount of pure m agnetite w i l l show the same
magnetic a t t r a c t io n (or s u s o e p t ib i l i ty ) independent of what
th e composition of th e in term ediary components may be (except,
of cou rse , i f th e l a t t e r a re a lso m agnetic), provided th a t the
t o t a l volume of th e m a te ria l remains equal.
The TJae of th e C a lib ra tio n Curve
In order to t e s t th e v a l id i ty of th e fo re
going c a lib ra tio n curve i t was, of cou rse , necessary to d e te r
mine the m agnetite con ten ts by th e m agnetic-balance method of
substances of known chem ically determined m agnetite co n ten t.
From a eo n s ld e ra tio a of th e ea rv is shown In Figure 13 th e re a re
th z te measmrahle v a r ia b le s which f i x th e magnetic a t t r a c t io n —
namely, th e d en sity , the a c tu a l volume of th e m a te ria l used ,
and the m agnetite co n ten t. F u rth e r, the in d iv id u a l m agnetite
m a te r ia l s , , whether m ineral or fu rnace p roducts, m ight have some
e f fe c t upon the value fo r the m agnetite con ten t a s .determined by
th e magnetic balance method* The c a lib ra tio n curves {Figure 13)
were determined by u sin g m ineral m agnetite . As, i t i s planned'• i , ■ : ■ . • !
to use th ese curves fo r the determ ination of m ag n e tite -in furnaoe
products as w ell as in m inera ls , m agnetite contents o f m ixtures
of fu rnace m agnetite and a lso m ineral m agnetite w ith quartz
and r u t i l e of known chem ical m agnetite © intents were determined , - - ' :- ■ ; . . ■
Krith th e magnetic balanoe. I t i s noted th a t a l l the v a r ia b le s
which a f f e c t the determ ination of m agnetite by the balance methodf:.- : ' : ■' :. ;■ ' . : ■' !
have been a lte re d in order to te s t th e accuracy of th e c a lib ra -- : ■■ ; ; - ■ ■- . • - : • :t io n curves* The r e s u l t s of t h i s work a re shown in Table 4.
oh an lo a l l y .
Mixture cotnpositiewi, ’by weight nature of Density, Volume used for liagnetlte ise^eart. PercentageMat*- M agxeMte BllutjLog agent magnetite grama the magnetite per cent b: weight differenceH A5## Ho. Per cent Ho. Per cent
per o.o. determination,0. 0.
Oaloalated
chemloal
Magnetic H=HL V 100 71
i I I XII IV T VI VII f i l l
4A 4 27.00 8 78.## MSsma. 1.884 0.120 24.3 24.2 0.4
4B 4 sf.eo 6 73.00 * 8.874 0.120 24.3 24.0 1#8
40 4 13,50 3 86.60 1.883 @.170 38 OS 12.1 0.4
49 4 13.50 6 86.50 2.586 #•18# 12.15 11.8 2.9
4E 4 6.75 3 93.25 1.4fiL 0.210 6.08 5.75 w
4V 4 6.73 6 #8.87 2.587 0.120 4»#6 5.79 4.5
5A s 87.00 3 78.## Pumaoe 1.677 0.120 88.6 25.3 1.4
SB 6 87.00 6 73.00 * 2.667 0.120 25.6 25.3 1.4
50 5 13.50 3 86.50 1.676 0.170 12.80 12.2 4.7
5D 5 13.50 6 86.50 2.577 0.120 12.80 12.2 4.7
SB 5 6.75 3 93.25 1.464 ©.81# 6.41 5.98 6.7
5F 5 6.75 6 93.25 * 8 .m #.120 6.41 5.94 7.8
'It?-
•48
I t i s noted from Table 4 th a t th e magnetic
balance method need is capable of y ie ld in g co n s is te n t r e s u l ts
when compared to chem ically determined m agnetite con ten ts of
th e m ixtures used. R eferring aga in to Table 4 , columns I I I ,
IT, V, and VI rep resen t th e "v a riab le s" p rev iously d iscu ssed ,
and i t i s noted th a t th ese have been a l te re d w ith in wide l im i t s .
The percentage accuracy given in column T i l l v a r ie s from 0*4 in
the case of h ig i m agnetite con ten ts to 7 .3 fo r low m agnetite
co n ten ts . Those f ig u re s in d ic a te th e probable accu rac ie s of
the magnetic balance instrum ent by v ir tu e of th e f a c t th a t they
a re lim ited by th e accuracy of th e c a lib ra tio n curves. C ertain
e r ro rs in th e mechanical mixing of d ilu tin g substances combined
w ith the e r ro rs involved in th e chemical determ ination in d ic a te
th a t accu rac ies of th e m agnetic 'balance g re a te r than those noted
can not be expected. I t i s In te re s t in g to no te , however, th a t
the magnetto balance is capable of reproducing values fo r the
m agnetite content of m ixtures of th e same com position very
c lo se ly . Another very im portant conclusion which may be drawn
from the r e s u l t s presented in Table 4 i s the r e la t iv e magnetic
p ro p e rtie s of n a tu ra l m ineral m agnetite and th a t formed by
furnace reactions* These da ta show l i t t l e , i f any , v a r ia tio n
in m agnetite con ten t a s determined from t h e i r magnetio prop
e r t i e s u t i l i s e d by the m agnetic-balance method. I t i s f a r th e r
seen th a t the d i lu tin g medium does net have any e f fe c t upon
th e determ ination of m agnetite content when q u arts or r u t i l e
a re used.
- 4 9 -
The s lag s used hy Roberts and Hageat
In th e i r etufly o f th e Hawley chemical method fo r the d e te r
m ination of m agnetite were found to be a v a ila b le and were
te s te d by means of the magnetic balance as used by the w rite r .
The r e s u l ts of th i s work a re presented In Table 5, page 60.
I t i s noted from a co n s id e ra tio n of the
r e s u l t s presented in Table 5 th a t th e m agnetite co n ten ts of
s lag s nos, 11, 4 , and 8 a s obtained by the chemical method
(column I I ) agree w ith th o se determined by the magnetic b a l -
anee (column IT) w ith in the experim ental e rro r of both methods $
a l l o ther r e s u l t s do not show the requ ired agreement. I t i s ,
however, noted th a t both magnetic balance re s u l ts (columns I I I
and IV) show a marked consistency . The d iffe ren ce in m agnetic-
balance r e s u l ts obtained by th e w rite r from those repo rted by
Roberts and Nugent might p o ss ib ly be due to th e f a c t th a t th e
"d e n s ity ” of th e p u lveru len t m a te ria l was taken in to consider
a t io n . The probable experim ental percentage d iffe ren ce of
determ ining m agnetite con ten ts by th e m agnetio-balanoe method
as compared to chemical methods fo r converter s lag s i s l e s s
than 8 per cent and fo r re v e rb e ra to ry s la g s is le s s than 8
per c e n t. The v a r ia tio n of m agnetite con ten ts fo r the m ajo rity
of s la g s a s obtained by the eheaieal and magnetic balance
methods i s d i f f i c u l t to exp lain from th e b a s is of experim ental
e r ro r g iven . Several p o ss ib le exp lana tions of th i s marked
82 ...
52 • • .R oberts, L. E . , and Nugent, R, L ., op. p i t .
pQfefaiTable 5
I IX I I I 17 TSlag Ho.
(R.I.3120)
kagrotite content reported by Roberts and Hugent,
Magnetite oonteat from magnetic balance re-
Magnetite content from magnetic balance reported by writer,
per cent
Per cent differenceM t . 100
' \\- '18.2 17.7 . 11. . :''
25.78 26.2 24.6 4.6
2^48 22.8 22.0 18.25.12 25.8 24.0 4.5
9> 18.82 17.2 16.1 14.
11 28.05 *8.8 88.7 2.3IS 25.32 *6.* 84.4 5.6
2 4.48 4.0 3.88 . ;12.. .4 IMS 8.7 10.1 0.2
6 9.61 S.S W.4 8.5
• 1.79 1.5 1.80 0.6
10 5.76 ; s - 5 ■ .v : 4.56 21.
12 ' 4.94 2.0 .3.02 39.
-09-
-SI*
v a r ia tio n p resen t them selvess
1* The e f fe c t of s iz e of m agnetite g ra in
upon m agnetic a t t r a c t io n and th e re fo re on the determined magne
t i t e con ten t has been prev iously e s ta b lish e d , from which i t i s
seen th a t i f th e s iz e of m agnetite g ra in f a l l s app rec iab ly be
low 850-mesh, th e magnetic a t t r a c t io n w il l be reduced. This
e f fe c t may or may not be p resen t in s la g s , depending upon the
r a te of cooling of th e s la g . Thus, i f time is allowed fo r the
growth of m agnetite c ry s ta ls to such a s iz e th a t when the slhg
is ground, th e m agnetite g ra in s w il l be 350»®esh s i z e , the *
m agnetic-balance method r e s u l t s w il l not be a ffe c te d from th i s
cause. Some s la g s , however, a re ra p id ly cooled by pouring them
in to w ater, whieh p reven ts ap p rec iab le g ra in growth of the
m agnetite p a r t i c le s , th e g ra in size of which was undetermined
by th e w r i te r .
2, There i s a p o s s ib i l i ty of copper f e r r i t e
(CuO.PegOjj) being formed as a s id e re a c tio n in th e converter
and reverbera to ry fu rn a c e s . I f t h i s be the ease th e m agnetite
content determined by th e chemical method w ill probably include
the iro n p resen t as copper f e r r i t e , and so w il l be h igher than
th e tru e value . The magnetic perm eab ility of copper f e r r i t e
i s l e s s th an th a t of m agnetite and th e re fo re m agnetite con ten ts
as obtained by th e magnetic balance w ill be h igh , but w ill net
be as high a s th a t probably obtained by the- chemical method.
I t may be observed from Table 5 th a t th e re is a d e f in ite ten
dency fo r the m agnetite contents as determined by the m agnetic-
balance method to y ie ld lower r e s u l t s than these obtained by
- 52*»
aeans of th e chemical method. E ith e r the sm aller m agnetite
g ra in s iz e in th e s la g s or th e presence of copper f e r r i t e in
the s la g s , o r both , o ffe r two p o s s ib i l i t ie s fo r explain ing the
d iffe re n c e .
3. The p o s s ib i l i ty of the presence of mag
n e t ic substances o ther than Ire n o r i t s compounds i s u n lik e ly ,
s in ce i f t h i s %as the case th e magnetic balance r e s u l t s fo r
the m agnetite content would be c o n s is te n tly h igher than these
obtained from the use of th e chemical method u n less th is e f f e c t
m s obscured by the o ther p o s s ib i l i t i e s of e r ro r .
summer
Two methods fo r th e determ ination of magne
t i t e con ten t have been in v e s tig a te d . The b a l l i s t i c method was
deemed worthy of t r i a l , bat was shown to be lack in g in c e r ta in
fundamental c h a ra c te r is t ic s e s s e n t ia l f o r a sim ple and an aeon*
r a te method. The m agnetic-balance method w as.believed to show
promise fo r use in measuring m agnetite content and was used to
study the p ro p e r tie s of magnetic m a te ria ls which,might have
some in fluence on the determ ination of m agnetite . The r e s u l t s
of th ese s tu d ie s fo llow ;
1* Reproducible r e s u l t s fo r magnetic a t t r a c
tio n s were obtained by packing to a constan t volume to w ith in
1 per cen t.
2. The e f fe c t of g ra in s ize upon magnetic
perm eab ility was investigated and th e r e s u l t s dem onstrated th a t
uniform s iz e of m agnetite p a r t ic le i s neeessary fo r consisten t
magnetic a ttra ctio n . The s iz e of g rind ing was standard ized as
minus 250-mesh to avoid e r ro rs in too wide ranges of m agnetite
p a r t ic le s iz e s .
3* The v a r ia tio n of density of pulverulent
m a te ria l w ith com position was determ ined. With t h i s inform ation
the e f f e c t of volume of m a te ria l and density upon th e d e te r
m ination of m agnetite conten t was in v e s tig a te d . From th is
the ca lib ration curves expressing magnetic a t t r a c t io n , volume
of m a te r ia l , and grams of m agnetite (Fe30^) per cubic cen tim eter
o f m a te ria l were p lo t te d .
4» M agnetite conten t of m ixtures of chem
ic a l ly known m agnetite conten ts were determined by means' of
the c a lib ra tio n omrree ana a comparison of th e chemical and
magaetie-fcalanoe r e s u l t s has been given and shows th a t fo r
m agnetite con ten ts of about 25 per cen t th e v a r ia tio n is near
1 per c e n t, and fo r m agnetite contents of about 5 per cen t the
methods vary le s s than 8 per c e n t.
5* By determ ining the m agnetite con ten ts
of known m ixtures of fu rnace m agnetite w ith the c a lib ra tio n
ourve, i t was shown th a t the mode of form ation of th e m agnetite
did not have any e f fe c t upon the r e s u l t s of th e m agnetic-
balance determ ination .
t». M agnetite conten ts of s la g s , analyzed
chem ically by Roberts and Hugent, were determined by the mag
n e tic -b a la n ce method and very l i t t l e agreement was observed
between the r e s u l t s of th e modified Hawley chemical and the
m agnetic-balance methods. A discussion of the p o s s ib i l i t ie s
of e rro r between the two methods has been given.
fhe use of the magnetio balance for the
determination of m agnetite con ten ts of s la g s can not be re e -
ommended except when agreement w ith the r e s u l t s obtained by
the ohemloal method, such as those given in Table 5, a re de
s ire d . The writer b e lie v e s , however, th a t th e m agnetio-balanoe
method would be s a t is fa c to ry in general i f th e cond itions which
have been presen ted a re c lo se ly observed. Lacking tim e, the
- 8 8 -
w riter eonia not continue the work of d e fin ite ly estab lish
ing the reason fo r the lack of agreement "between magnetite
contents determined hy the magnetic-balance method and those
by means of the chemical method for s la g s .
BIBLIOGrRAPHT
BEME5I, E. E . , and CROWTHER, H. H ., In troduc to ry E le c tro dynamics fo r Engineers i Hew York, 1926.
HiWLEY, F. Q ., Determ ination of liagne tite in %&tte and Slags Eng. & m n . Jo u r ., vol» 108, 1919, pp. 308-310.
ROBERTS, L. 1 . , and HUGEHT, R. 1 . , Determination of M agnetite in Copper S la g s : Rent, of I n f . , Ser. 3120, tr. S. Bureau of Mines, S e p t . , 1931, 14 pp*
3P001BR, T ., P ro p e rtie s and T esting of Magnetic M ate ria ls :Hew York, 1927.
SOSMO, R. B . , and HOSTETTEH. J. C ., The Ferrous Iron Content and Magnetic S u s c e p t ib i l i t ie s of Some A r t i f i c i a l an# n a tu ra l Oxide# of Iro n : Trans. Am. In s t . Min. Eng., vo l. 5 8 , 1 9 1 8 , p p . 4 0 4 -4 3 3 .
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STARLIHC, S. G ., E le c t r ic i ty and Magnetism: London, 1924.
STUTZER, F . , GROZ, W., and BORKMU, E», Uber Magnetisohe E igensohaften der Zinkblenle i n i a n ie re r M ineralien:Me t a l l , und E rz, v o l. 15, 1918, pp. 1-9 .
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WAIT, 0. R ., Magnetic P erm eab ility of Iron and M agnetite in High Frequency A lte rn a tin g F ie ld s : Phy. R ev ., vo l. 29, 1927, pp. 666-578.
WALL, T. F . , Applied Magnetisms Hew York, 1927.
WELO, L ., and B AUDI SCI, A ., The Two-Stage Transformation of M agnetite in to Hem atite: P h il . Mag., (6 ) , v o l. 60, 1926, pp. 399-408.
WILSON, ERNEST, On th e Measurement of Low S u s c e p tib i l i ty by an Instrum ent of a Hew Type: proo. Roy. goo. o f London, (A), VOl. 98, 1931, pp. 274-284.
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