Industrial and Engineering Chemistry : analytical edition, Vol. 9, No. 7

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Analytical Edition Vol. 9, No. 7

IN D U S T R IA L andEJVGOJEERIlVG C H E M I S T R Y

V ol. 29, C o n s e c u tiv e N o . 27

P u b lis h e d b y th e A m e ric a n C h e m ic a l S o cie ty H a r ris o n E . H o w e, E d ito r

Ju ly 15, 1937

Publication Office: Easton, Pa. . Editorial Office: Room 706, Mills Building, Washington, D. C. . Telephone: National 0848 Cable: Jiechem (Washington) . Advertising Department: 332 West 42nd Street, New York, N. Y. . Telephone: B ryant 9-4430

C O N T E N T S

19,300 Copies of This Issue Printed.

Determining Ash in High-Carbonate Coals . . 0. W. Rees 307 Scattering in the Near I n f r a r e d ...

... D. L. Gamble and C. E. Barnett 310 The Use of an Electric Heater for the Lane and Eynon

T itration of Reducing S u g a r s ...

.D. T. Englis and E. G. Lynn 314

Determination of Unsaponifiable M atter in Rosin . . . ...I . E . Knapp 315 Analysis of Mixtures of Furfural and Methylfurfural . .

.Elizabeth E. Hughes and S. F. Acree 318

Small Chemical Changes in an Insulating Oil Associated with Oxidation . . . /?. N. Evans and J. E. Davenport 321 A New Photoelectric Method for Measuring Vitamin A .

... Ronald L. McFarlan, J . Wallace Reddie, and Edward C. Merrill 324 Determination of Carbon and Hydrogen in Gasoline and

Other Volatile Liquids . . Harry Levin and Karl Uhrig 326 A New Qualitative Test for Selenium. I. . I L A . Ljung 328 Feeding Device for Boiler Compound . . . J. L. Smith 330 Determination of Barium, Sulfur, and S ulfates...

...Stephen J. Kochor 331 A Simple Gas Thermoregulator. . . . R. M. Kingsbury 333 2,4-Dihydroxyacetophenone as a Qualitative Reagent for

Ferric I r o n ...S. R. Cooper 334 A Sloping M anom eter...Milton Burton 335 Rapid Analysis of Barite Ores Containing Calcium

Fluoride, without the Use of Fusions . Ellis S. Ilertiog 336 A Kjeldalil Digestion Apparatus . . . Wesley M . Clark 338

Diphenylguanidine as a Standard in Neutralization P ro cesses...

. . . . William iVi. Thornton, Jr., and Charles L. Christ 339 A Modification of the Berl-Kullmann Melting Point

B lo c k ...F. W. Bergstrom 340 Quantitative Determination of Oil in Fish Flesh . . . .

...Maurice E. Stansby and Janies M. Lemon 341 The Determination of Dissolved Nitrogen in W ater . . .

...Norris W. Rakeslraw and Victor M . Emmel 344 An Improved Salt Bridge for Electrometric Measure

ments . . . . Willard M. Bright and Elmer L. Miller 316 A Pressure Regulator for Vacuum D istillation...

...R. L. Emerson and R. B. Woodward 347 MlCROClIEMISTRY:

Separation and Determination of Impurities in Lead.

I. T i n ... Beverly L. Clarke, Iceland A. Woolen, and J. D. Struthers 349 A Semimicro Qualitative Test for the Nitro Group in

Organic C o m p o u n d s...

...W. M . Hearon and R. G. Gustavson 352 An Improved Reaction M icroapparatus...

...D. S. Binnington 353 Operation of Analytical Microbalances Highly Sensitive

to Temperature C h a n g e s ...Fritz Breuer 354 Modified Micro-Dumas Nitrogen Determination with

Readily Available, Air-Free Carbon Dioxide . . . . ... Fritz Breuer 354

Ralph E. Dunljar 355 A Macro- or Micro-Gooch Filter .

A Manometer for Carbon and Hydrogen Pressure R e g u la tio n ...William II. Hamill 355 A M icrocentrifuge... W. MacNevin 356

T h e A m e ric a n C h e m ic a l S o c ie ty a s s u m e s n o re s p o n s ib ility fo r th e s ta t e m e n ts a n d o p in io n s a d v a n c e d b y c o n t r ib u to r s to i t s p u b lic a tio n s .

P u b lis h e d b y th e A m e ric a n C h e m ic a l S o c ie ty , P u b lic a tio n Office, 2 0 th &

N o r th a m p to n S ts ., E a s t o n , P a . E n t e r e d as se c o n d -c la ss m a tte r a t th e P o s t O ffice a t E a s t o n , P a . , u n d e r th e A c t of M a r c h 3 , 1879, as 48 tim e s a y e a r.

I n d u s tr ia l E d i tio n m o n th ly on th e 1 s t; A n a ly tic a l E d itio n m o n th ly o n th e 1 5 th ; N e w s E d i tio n o n th e 1 0 th a n d 2 0 th . A c c e p t a n c e fo r m a ilin g a t sp ecial r a t e of p o s ta g e p r o v id e d fo r in S e c tio n 1 103, A c t of O c to b e r 3, 1917, a u t h o r iz ed J u ly 13, 1918.

A n n u a l s u b s c r ip tio n r a t e s : ( a ) In d u s t r i a l Ed i t i o n- $ 5 .0 0 ; (i>) An a l y t i c a l Ed i t i o n $ 2 .0 0 ; (c) N e w s Ed i t i o n $ 1 .5 0 ; fa) a n d (6) to g e th e r , $ 6.00;

(a ) , (6 ), a n d (c) c o m p le te , $7 .5 0 . F o re ig n p o s ta g e t o c o u n tr ie s n o t in th e P a n A m e ric a n U n io n , (a) $ 1 .2 0 ; (6) $ 0 .3 0 ; (c) $ 0 .6 0 ; to C a n a d a o n e - th ir d th e se r a te s . S in g le c o p ies: (a) $ 0 .7 5 ; (6) $ 0 .5 0 ; (c) $ 0 .1 0 . S p e c ia l r a te s to m e m b e rs.

C la im s f o r co p ies lo s t in m a ils to b e h o n o re d m u s t b e r e c e iv e d w ith in 60 d a y s of d a t e of issu e a n d b a s e d o n re a s o n s o th e r t h a n “ m issin g f ro m file s ."

T e n d a y s ’ a d v a n c e n o tic e o f c h a n g e of a d d r e s s is r e q u ir e d . A d d re s s C h a rle s L . P a r s o n s , B u sin ess M a n a g e r , M ills B u ild in g , W a s h in g to n , D . C . U . S. A.

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INDUSTRIAL AND E N G IN E ER IN G CHEM ISTRY VOL. 9, NO. 7

Th e W i r e t h a t M a d e E l ec t ri ca l H e a t P o s s ib le

A n n o u n c i n g

) HIGH TEMPERATURE COMBUSTION FURNACES

T h e s e f u r n a c e s a r e e q u i p p e d w i t h H o s k i n s N o . 10 e l e m e n t s , a n d c a n b e r u n a t 2300° - 2400° F . T h e t e m p e r a t u r e is c l o s e l y c o n t r o l l e d t h r o u g h a r e g u l a t i n g t r a n s f o r m e r , h a v i n g 16 s t e p s . T h e f u r n a c e s a r e m a d e i n S i n g l e a n d D o u b l e - B o r e . F o r m o r e i n f o r m a t i o n , w r i t e t o y o u r d e a l e r . H o s k i n s M a n u f a c -

C .o m p a n y , D e t r o i t , M i c h i g a n .

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JULY 15, 1937 ANALYTICAL ED ITION

M O D E L 3D with A U T O M A T IC

T E M P E R A T U R E C O M P E N S A T O R

Only Those Features Included Which Have Proved To Be ACCURATE, RELIABLE, RUGGED

R u g g e d and S im p le — O p e ra te d anyw here by

2 __ F le x ib le — w ide V a rie ty of S E A L E D E L E C - T R O D E A s se m b lie s availab le.

3

A ssy m e try correctors on all m odels. A u t o  m atic Temperature C orrector for sp ecia l conditio ns.

4

^Buffer standardization insures consistent ac

curacy b ecause the Instrument is corrected to A C  T U A L operating co nditio ns.

P O R T A B L E — Co m p act and Fu lly S e lf Contained.

" M E A S U R I N G p H u 'ith th e G L A S S E L E C T R O D E , '

"M e asu rin g p H with the G la s s E le ctro d e " an 18 page original work b y one of A m e rica 's lea d  ing authorities. Covers a discussion o f the theory of the glass electrod e and factors that must be co n  sidered In Its practical a p p lica tio n . Includ e s a b ib lio g ra p h y of 1 3 0 s c i

entific articles bearing on the subject.

M a i l e d o n R e q u e t i

Coleman Glass Electrodes are Factory Sealed and do not require periodic refilling, because the usual unstable solu

tions are replaced with a stable chloride in which is immersed a stabilized silver- silver chloride electrode. The whole is hermetically sealed at the factory, pre

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The New Coleman Glass Electrode is small, and adaptable to measuring the p H of nearly any material that is capable of wetting the surface of the bulb. The Glass Electrode is com pletely insulated from G rid Current— b y the original True Impulse Am plifier.

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O n ly the latest electronic developments are incorporated in the self-contained M odel 3 Coleman Electrometer. Cap ab ility of accurate and rapid measurements of p H and R E D O X under any and all conditions...positive and reproducible re

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6 INDUSTRIAL AND E N G IN E ER IN G CHEM ISTRY VOL. 9, NO. 7

Ask your laboratory su p p ly d e a le r or send for Bulletins HD735 an d HD123S

H E V I D U T Y E L E C T R I C C O M P A N Y

LABORATORY FURNACES MULTIPLE UNIT ELECTRIC EXCLUSIVELY M I L W A U K E E , W I S C O N S I N

In th e e x p e r im e n t a l la b o r a to r ie s of m a n y l a r g e u n iv e r s itie s H e v i D u ty 's l a b o r a t o r y f u r n a c e s a r e s t a n d a r d e q u ip m e n t. T h e illu s tr a tio n s h o w s a ty p i c a l o r g a n ic c o m b u s tio n

tr a i n a t C o lu m b ia .

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JULY 15, 1937 ANALYTICAL ED ITION 7

KIMBLE GLASS COMPANY • • • • v i n e l a n d , n. J.

N E W Y O R K * - C H I C A G O • ' P H I L A D E L P H I A » » D E T R O I T - * B O S T O N

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and. CONCRETE

T h e m a g ic o f in d u s tr ia l c o n s t r u c t i o n c r e a te s a s te a d y c a ll f o r c o n c r e te . M a m m o th d a m s s p r in g in to b e in g — g r e a t a q u e d u c t s h o n e y c o m b t h e m o u n ta in s — e n d le s s r ib b o n s o f r o a d s t h r e a d t h e n a tio n .

1 1 1 ,6 1 5 ,0 0 0 b a r r e ls o f P o r tl a n d c e m e n t w e re p r o d u c e d in 1 9 3 6 — a n d b a c k in g th is t r e m e n d o u s p r o d u c ti o n is a c c u r a t e q u a l ity c o n t r o l in th o u s a n d s o f m o d e rn , w e ll- e q u ip p e d la b o r a to r ie s f o r r e s e a r c h a n d e x p e rim e n t.

K im b le B lue L in e E x a x G la s s w a r e h a s a lw a y s b e e n c lo s e ly a s s o c ia te d w ith t h e c e m e n t a n d allie d in d u s trie s . Its r e lia b ility in a n a ly s is a n d c o n t r o l p r o t e c t s v a s t in v e s tm e n ts in c r u d e m a te r ia ls a n d a s s u re s a fin ish e d p r o d u c t o f g r e a t s e r v i c e t o i n d u s t r y . B lu e L i n e E x a x w a r e is r e t e s t e d a n d a n n e a le d ( s tr a in - f r e e ) . Its b rillia n t B L U E L IN E S a r e f u s e d - in f o r d u r a b ility .

W h e r e v e r c o n t r o l a n d r e s e a r c h a re i n v o lv e d — in c h e m i

cal field s, in c lin ic a l o r m e d ic a l in s t itu ti o n s , in b io lo g ic a l a n d b a c te rio lo g ic a l w o r k — B lue L in e E x a x G la s s w a re is th e la b o r a t o r y s t a n d a r d f o r a c c u r a c y , s e rv ic e a n d a s su ra n c e .

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JULY 15, 1937 ANALYTICAL EDITION 9

THE PUDDLER and

S E T T I N G T H E P A C E I N C H E M I C A L P U R I T Y S I N C E 1 8 8 2 “ J O

B ^{a k e r} A d a m s o n ^

Division of G E N E R A L C H E M IC A L COMPANY, 40 Rector St., New York L. H f\cUC(S

Afionra . Boitimore • Boslon • Buffalo • Charlolte*Chico9o • Cleveland • Denver • H o u s to n • Kansas CitY* los AnBeles • Minneooolis • P h ila d e '^ o • P iltsb u rg h • Providence • San Francisco • St. lo u is

O f th e ch aracters w ho m ake u p th e story o f iro n , one, the p u d d le r, sta n d s a p a rt. H e w as th e m an w ho once

"m a d e th e ir o n .” H is stro n g arm s a g ita te d th e m olten m etal a n d sla g in th e b a th . H is keen eye, by observing the co lo r o f b u rn in g gases, d eterm in e d th e iro n ’s chem i

cal c o n ten t. H is sk ill w as th e key to q u a lity p ro d u ctio n . B ut no tw o p u d d le rs p ro d u c e d iro n th a t was chem i

cally a n d physically th e sam e. A n d , m oreover, th e lim it o f a m a n ’s s tre n g th placed lim its o n q u an tity .

T h e in tro d u c tio n o f n ew a n d la rg e r types o f furnaces changed th e scene. T h e chem ist w ith his

exact m e th o d s o f analysis was ca lle d u p o n to rep la ce th e p u d d le r ’s less re lia b le m e th o d s o f ju d g m e n t. N o w , iro n and steel are p ro d u ce d to specification.

B aker & A dam son re a g e n t chem icals have lo n g con

trib u te d to advancing th e q u ality o f iro n an d steel.

B & A A n h y d ro u s C alcium C h lo rid e , as o n e im p o rta n t exam ple, is used in alm o st every iro n a n d steel te stin g lab o ra to ry as th e d ry in g a g e n t in th e carb o n d e te rm in a tio n test. W ith o u t th is exact test, m ost iro n s a n d steels do n o t leave th e p la n t.

B aker & A dam son A n h y d ro u s C alcium C h lo rid e is o f th e h ig h e st quality . I t is m a n u fa ctu re d u n d e r th e m ost rig id o f specifications, and is in te n d e d fo r use in th e la b o ra to ry w h ere u n ifo rm ity an d extrem e p u rity are c o n stan t requisites. C hem ists everyw here, w h en an efficient d ry er is req u ired , th in k im m ediately o f B & A A n h y d ro u s C alcium C hloride.

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NEW M O D EL

W I L E Y L A B O R A T O R Y M I L L

W IT H SEVERAL IM PRO VEM EN TS REDUCING T H E P O S S IB IL IT Y OF LOSS, EVAPORATION OR C O N T A M IN A TIO N OF SAMPLE

■4275

W I L E Y L A B O R A T O R Y M I L L , N e w M o d e l . F o r th e p r e p a ra tio n , w ith o u t loss o f m o is tu re fro m h e a tin g , o f c e rta in c o m m e rc ia l m a te ria ls fo r la b o r a to r y a n a ly sis. O rig in a lly d esig n e d fo r u se w ith f e r ti

liz er m a te ria ls b u t n o w w id e ly u se d fo r a g r e a t v a r ie ty o f o th e r m a te ria ls su c h a s : Agar

Animal Hair, Fur, Hoofs, Horn, etc.

Bakelite Barks

Chicken Feathers Com Stalks and Grain

Cotton Seed, Cake and Meal Crab Shells

Drugs, Organic Fish Scales Gelatine Grass Licorice Roots

Leather, incl. chrome tanned Oats

Shavings coated with resi

dues of impurities in coke oven and water gas Straw

Tankage

Tanning Materials (valonia cups, myrobalans, wattle bark, etc.)

Tobacco Stalks Wheat

F o u r k n iv e s o n a re v o lv in g s h a f t w o rk w ith a s h e a rin g a c tio n a g a in s t six s e t in th e fra m e . T h e sc re en is d o v e ta ile d in to th is fra m e so t h a t n o n e o f th e m a te r ia l co m es o u t o f th e g rin d in g c h a m b e r u n til it is fine e n o u g h to p a s s th r o u g h th e m e sh . H in g e d f r o n t p e r m its e a s y c lea n in g .

M ill is 21 in c h e s h ig h a n d re q u ire s floor sp a c e 14 X 20 in ch es. G rin d in g c h a m b e r 8 in c h e s in sid e d i

a m e te r. S h o u ld be o p e r a te d a t fro m 400 to 800 r.p .m . a n d re q u ire s l/ i to 1 h .p . m o to r . R e c e n t im p r o v e  m e n t« in t h e s h a p e o f th e b o d y c a s tin g a t b o tto m a n d sie v e fra m e , w ith lid o n h o p p e r , e tc ., re d u c e p o ssi

b ility o f loss, e v a p o ra tio n o r c o n ta m in a tio n o f sa m p le . B ib lio g rap h y Samuel W. Wiley, Ind. $ Eng. Chem., Mar., 1925, p. 30b.

Samuel W. Wiley, The American Fertilizer, Feb. 7, 1925.

K. Maiwald, Die Landwirlschaftlichen Versuchs-Slationen des Deulschen Reiches, 1928, p. 15.

I. D. Clarke and R. W. Frey, The Journal of the American Leather Chemists Association, Vol. X X I I I , No. 9 (Sept., 1928), p.

412.

Carl R. Blomstedt, Paper Trade Journal, Vol. X C II, No. 18 (Apr. 30, 1931), p. 43.

4275. W iley L ab o ra to ry M ill, New M odel, as above described, with three sieves of 1/ i mm, 1 mm and 2 mm mesh, respec

tively. With tight and loose pulleys for belt drive, but without m otor... 195.00 Code W ord... Elnfc F or m o r e d e ta ile d d e s c r ip tio n o f th e Wile,y M ill, to g e th e r w it h a m o d e l f o r d ir e c t m o to r d r iv e a n d a s m a ll

m o d e l f o r p r e p a r in g s a m p le s f o r M ic r o -a n a ly s is , see p a g e s 277 a n d 278 o f o u r c u r r e n t c a ta lo g u e .

ARTHUR H. T H O M A S COMPANY

R E T A IL — W H O L E S A L E — E X P O R T

LA BO RATO RY APPARATUS AND REAGENTS

W E S T W A SH IN G TO N SQUARE PH IL A D E L P H IA , U .S.A.

C a b le A d d re ss, “ B a la n c e ,” P h ila d e lp h ia

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IN D U S T R IA L

a i E N G I N E E R I N G

C H E M I S T R Y

H a r r i s o n E . H o w e , E d i t o r A N A L Y T IC A L E D IT IO N

D eterm ining A sh in High-Carbonate Coals

A Study o f the M odified M ethod

O . \V. R E E S , Illin o is S ta te G eological Survey, U rb a n a, 111.

T

H IS paper presents th e results of an investigation of a modified procedure for determ ining ash and mineral m at

te r in coals high in pyrite and calcium carbonate, first pro

posed by S. W. P arr. T his investigation was carried on to determ ine th e causes of difficulties encountered in attem pting to use this m ethod as described, and, if possible, to find a way of elim inating them . Since th e m ethod has received wide

spread distribution in textbooks (2) and as a recommended optional procedure of th e American Society for Testing M a

terials for determ ining th e m ineral m a tte r content of high- sulfur, high-carbonate coals for classification purposes (1), it was deemed desirable to call th e atten tio n of th e coal analyst to th e fallacies involved in th e procedure outlined and to recommended changes which would m ake it more reliable.

Samples which contain com paratively large am ounts of both p yrite and carbonate are frequently encountered in coal analysis. These two minerals m ay undergo various reactions in th e course of th e regular determ ination of ash. P yrite is mainly burned to ferric oxide and sulfur dioxide, b u t some m ay be oxidized to ferric sulfate, which on further heating will be decomposed to give ferric oxide w ith the loss of sulfur trioxide. Calcium carbonate m ay decompose to some extent to give calcium oxide and carbon dioxide and m ay react with pyrite to give calcium sulfide and ferric oxide w ith loss of carbon dioxide. T he calcium sulfide so formed m ay be par

tially oxidized to calcium sulfate, while th e calcium carbonate and oxide m ay react w ith sulfur dioxide and oxygen or with sulfur trioxide to form calcium sulfate. I t is apparent th a t no definite composition will be reached b y th e usual ashing procedure and th a t some special procedure is necessary for samples containing high am ounts of pyrite and carbonate.

As early as 1916 P a rr (8), realizing these facts, published a special m ethod for use in such cases. H is m ethod was based on

the idea th a t if th e sample was first ashed as usual and then treated w ith a few drops of sulfuric acid all calcium sulfide, calcium oxide, and calcium carbonate would be converted to calcium sulfate and could be weighed as such, after careful re

moval of th e excess sulfuric acid by heating a t a definite tem perature for a definite tim e. If the mineral carbon dioxide con

te n t of the sample was determ ined and if it was assumed th a t all mineral carbon dioxide was present as calcium carbonate, an as

sum ption for which there is proof, it would be possible to cal

culate back to th e calcium carbonate basis by subtracting three times the equivalent of carbon present as carbon dioxide from the ash as weighed. P arr (3) described his m ethod as follows:

For coals whose mineral carbon dioxide values are large enough to call for correction, say up to 1 per cent or greater, the ash, after the preliminary burning off of the carbon and cooling, is moistened with a few drops of sulfuric acid (diluted 1 to 1) and again after drying brought up to 750° C. and retained a t th a t temperature for 3 to 5 minutes. The capsule is cooled in a desiccator and weighed.

In the course of regular coal analysis in this laboratory the author encountered a series of samples having large am ounts of both carbonate and pyrite. As it was evident th a t a special procedure was necessary, he attem pted to use P a rr’s special m ethod. Disconcerting d iscrepancies were found in the results obtained. In some cases these unit coal values b y P a rr’s modi

fied m ethod differed to an unexpected degree from those calcu

lated using regular ash values as bases for calculated mineral m a tte r values. Furtherm ore, a comparison of these values w ith appropriate county average u n it coal values showed them to be entirely too high.

Table I shows th a t the mineral m a tte r values obtained by calculation (1.08 ash + 0.55 sulfur) from regularly determ ined ash values v ary considerably from the values obtained by

Ta b l e I. Co m p a r a t i v e Va l u e s (W o o d fo rd C o u n ty N o . 2 C o a l)

- M i n e r a l M a t t e r --- C a lc u la te d

f ro m r o u tin e a s h

L a b . N o . A sh S u lfu r C Oj d e te r m in a

C -993 1 9 .4 2 .2 4 1 .6 3 2 2 .1 8

C -9 9 4 1 1 .0 1 .6 8 0 .4 8 1 2 .8 0

C -9 9 5 1 4 .3 1 .7 7 0 .5 9 1 6 .4 2

C -9 9 6 1 9 .7 1 .9 7 1 .8 1 2 2 .3 6

C -997 3 0 . 5 2 .8 7 4 .4 9 3 4 .5 2

C -9 9 8 3 6 .5 3 .9 5 3 .9 3 4 1 .5 9

° R o u ti n e a s h to m in e r a l m a tte r . b C O i c o r r e c tio n .

D e te rm in e d )y P a r r ra e th c

2 2 .7 6 1 3 .2 2 1 6 .6 0 2 3 .1 9 3 6 .0 2 4 1 .7 9

F r o m c a lc u la te d m in e r a l m a tte r

v a lu e a,b 14744 14742 14786 14443 1 4515 14957

- U n i t C o al V a lu e - F r o m P a r r m in e r a l m a tte r d e te r m i n a tio n &

14854 14814 14818 14599 14855 15008

C o u n ty A v e ra g e U n it

C o a l V alu es 14690 14690 14690 14690 14690 1 4690

307

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Ta b l e II. Co m p a r i s o n o f Va l u e s Ob t a i n e d b y Tw o Di f f e r e n t An a l y s t s

U n i t C o a l V alu e s M in e r a l M a t t e r V alu e s (C O j C o rre c tio n )

1 st 2 n d 1 st 2 n d

L a b . N o . a n a ly s t a n a ly s t a n a ly s t a n a ly s t

C -993 2 2 .7 6 2 1 .9 4 14854 14700

•C-994 1 3 .2 2 1 2 .7 1 14814 14727

C -9 9 5 1 6 .6 0 1 7 .1 3 14818 14912

C -9 9 6 2 3 .1 9 2 2 .3 0 14599 14431

C -9 9 7 3 6 .0 2 3 6 .6 8 14855 15010

C -9 9 8 4 1 .7 9 4 2 .1 9 15008 15112

F u r t h e r R e s u lts o n S a m p le s C -9 9 7 a n d C -9 9 8

C -9 9 7 3 6 .2 1 3 6 .2 9 14899 1 4918

C -9 9 8 4 1 .9 8 4 2 .0 1 15057 15065

P a r r ’s modified m ethod. T his is especially true in sam ple C-997 a n d to a lesser extent in sample C-998, b oth of which are high in sulfur and carbon dioxide. U n it coal values cal

culated from th e m ineral m a tte r values differ considerably.

By use of th e regular A. S. T . M . ash m ethod, widely varying results were obtained on duplicate portions of the same sam ples.

110

100

9 0

£ 70

I “

«0 a SO

u.o

u i 5 0

0

1 4 0

uo

u 30 CL

20

10 0600

/

Fi g u r e 1 .

700 8 0 0 9 0 0 1000 1100

T E M P E R A T U R E - DEGREES C.

Di s s o c i a t i o n Cu r v e f o r Ca l c i u m Su l f a t e

Because of these discrepancies a second analyst was asked to check these determ inations, using th e modified ash deter

m ination m ethod. T able I I shows a comparison of these two sets of values, together w ith a com parison of unit coal values in whose calculation these two sets of m ineral m a tte r values were used. D eviations which are greater than desirable are noted in this table.

Because of these discrepancies it seemed advisable to stu d y further th e m ethod recommended by P arr. Samples C-997 and C-998, which have th e highest am ounts of sulfur and m ineral carbon dioxide, seemed to be best suited to such study.

In m aking u n it coal calculations

, , B .t.u . - 50/S w

Parr form ula^: 77^ ;---^ --- ¡7^{— r X} 100 1 100 — (1.08 ash + 0.5d sulfur)

three values are used— nam ely, calorific, sulfur, and m ineral m a tte r values. The m ineral m a tte r value is obtained either b y calculation from th e usual ash value (A. S. T . M . stan d ard m ethod) and sulfur value or b y P a rr’s modified m ethod of ash determ ination described above. T he u nit coal values in whose calculation mineral m a tte r values obtained b y th e modified m ethod had been used appeared to be too high. Since th e determ ination of calorific and sulfur values is well standardized, th e au th o r suspected th a t this modified m ethod of ash deter

m ination was giving high results.

In P a rr’s m ethod as described above, th e sulfuric acid which is added converts any calcium oxide or calcium sulfide to calcium sulfate, in which form it is weighed, and also con-

v erts iron and alum inum oxides a t least partially to sulfates.

However, these should be quan titativ ely decomposed upon ignition to th e oxides if th e m ethod is to give dependable re

sults. Therefore, a t the tim e of weighing the sample after the ignition following th e acid treatm ent, the sulfate present should be exactly equivalent to th e calcium present.

In order to see if the above condition held, two 1-gram sam ples of coal C-997 were trea ted b y th e P a rr modified proce

dure and weighed. T he ash was then extracted w ith hot 1 to 1 hydrochloric acid and determ inations of calcium oxide and sulfate were m ade. T he q u a n tity of sulfate present was far in excess of th a t required for calcium sulfate by the calcium oxide found present.

This fact suggested th a t th e heating period of 3 to 5 m inutes was n o t sufficient to expel th e excess sulfuric acid or to con

v e rt any iron and alum inum sulfates completely to th e oxides.

A longer heating period a t 750° C. or a higher tem perature should be used. However, in order to use either of these safely it is necessary to know th eir effect on th e decomposition of calcium sulfate. If the procedure is to be usable a t all, calcium sulfate m u st n o t be decomposed during th e actual procedure and all other sulfates m ust be quan titativ ely de

composed. In this connection P arr (8) published some d ata on the decomposition of calcium sulfate a t different tem pera

tures, according to which the decomposition of calcium sul

fate begins a t abo u t 700° C. and increases rapidly from 900°

to 1100° C. H e shows th a t calcium sulfate is decomposed to th e extent of ab o u t 3.5 per cent a t 750° C., while a t 1050° C.

th e decomposition is abo u t 48 per cent. P a rr sta te s th a t there were no values available on th e vapor pressures a t dif

ferent tem peratures for the decomposition of calcium sulfate, and th a t “from the decrease in the w eight of ash and th e cor

responding decrease in sulfur trioxide a dissociation curve m ay be constructed” which he assumes to be th e dissociation curve for calcium sulfate (Figure 1). F rom these d a ta and th e decomposition d a ta for calcium carbonate P arr concluded th a t th e sulfated ash should be heated above 700° C. b u t th a t

Ta b l e III. Ef f e c t o f He a t i n g Ca l c i u m Su l f a t e a t Di f f e r e n t Te m p e r a t u r e s f o r 4 - a n d 0 0 - Mi n u t e Pe r i o d s

T e m p e r a tu r e

0C.

550 600 650 700 750 800 8 50 9 00 950 1000 1050 1100

4 - M in u te P e rio d s S a m p le S a m p le

1 2

%

14

».00 M 9 14 1.37

.3 2 1.37

».37 1.37

».37 ,2 8

».85

- L o s s in W e ig h t—

0.000.00

0 .4 3 0 . 1 6 0 .4 6 0 .2 5 0 .4 2 0 .3 7 0 .4 2 0 .3 8 0 .1 9 0 .8 9

% 0.0.

0.0.

0.:0.

Av.

%

0 .0 7

0.00

0 .3 1 0 .1 5 0 .4 2 0 .2 9 0 .4 0 0 .3 7 0 .4 0 0 . 3 8 0 .2 4 0 .8 7

6 0 - M in u te P e r io d s S a m p le S a m p le

1

%

0 . 1 0 0 .2 5 0.22 0 . 2 8 0 .3 7 0 .3 3 0 .3 5 0 .3 7 0 .3 3 0 .3 7 0 .5 8 1 .3 2

2

% 0 .1 0 0 .4 1 0 .4 5 0 .2 2 0 .3 7 0 .4 1 0 . 4 0 0 . 3 8 0 .4 6 0 .5 4 0 .5 3 1 .4 1

A v .

% 0 .1 0 0 .3 3 0 .3 4 0 .2 5 0 . 3 7 0 .3 7 0 . 3 8 0 . 3 8 0 .4 0 0 .4 6 0 .5 6 1 .3 7

C aS O * D eco m p o sed ® 4 m in . 60 m in .

a A ssu m in g losses C o n v e rs io n f a c to r 1.'

in w e ig h t b y h e a tin g d u e to lo s s of SOa 7 0 05.

% .0012

53 26 71

.6849 63 68 65 41 48 fro m

0 . 1 7 0 .5 6 0 . 5 8 0 .4 3 0 .6 3 0 .6 3 0 . 6 5 0 .6 5 0 . 6 8 0 . 7 8 0 . 9 5 2 . 3 3 C aSO *.

Ta b l e IV. Ef f e c t o f He a t i n g Ca l c i u m Su l f a t e a t 7 5 0 ° f o r Di f f e r e n t Pe r i o d s o f Ti m e

C aSO * T im e of

H e a tin g

---L o ss in W e ig h t--- S a m p le 1 S a m p le 2 A v .

D e c o m p o se d , A v e r a g e “

M in . % % % %

4 0 .3 3 0 .4 3 0 .3 8 0 .6 5

8 0 .5 7 0 .4 3 0 .5 0 0 .8 5

12 0 .5 1 0 .4 7 0 .4 9 0 .8 3

16 0 .5 2 0 .4 2 0 .4 7 0 .8 0

20 0 .5 2 0 .4 2 0 .4 7 0 .8 0

24 0 .3 7 0 .3 8 0 .3 8 0 .6 5

2 8 0 .4 2 0 .3 7 0 .4 0 0 .6 8

32 0 .4 7 0 .3 8 0 .4 2 0 .7 1

3 6 0 .4 7 0 .4 2 0 .4 5 0 .7 7

60 0 .4 7 0 .3 7 0 .4 2 0 .7 1

80 0 .6 9 0 .5 7 0 .6 3 1 .0 7

110 0 .3 6 0 .4 3 0 .4 0 0 .6 8

a A ss u m in g lo sses in we ig h t b y h e a tin g d u e t o lo ss of S O i f r o m C aS O « . C o n v e rs io n f a c to r 1 .7005.

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JULY 15, 1937 ANALYTICAL ED ITIO N 309

Ta b l e V. Ef f e c t o f He a t (750° C.) o n Su l f a t e d As h

✓— P e r C e n t S u lf a te d A sh —- , P e r C e n t S O a * P e r C e n t C a O *

T im e D u p lic a te D u p lic a te D u p lic a te SOa, C aO , S O a /C a O M in e ra l U n it

H e a t e d d e t e r m i n a tio n s D iffe re n c e d e te r m i n a tio n s D iffe re n c e d e te r m in a tio n s D iffe re n c e M o le % M o le % M o le R a tio M a tt e r C o al M i n .

4 4 8 .0 6 . 4 3 .7 2 4 .3 4 2 0 .4 5 , 2 1 .2 0 0 .7 5 5 .3 5 , 5 .3 2 0 .0 3 0 .2 6 0 2 0 .0 9 5 2 2 .7 3 3 2 4 7 .2 6 17,872

A v . 4 5 .8 9 2 0 .8 3 5 .3 4

8 3 6 .3 4 , 3 7 .1 7 0 .8 3 8 .4 9 , 8 .9 9 0 .5 0 5 .6 4 , 5 .5 4 0 . 1 0 0 .1 0 9 2 0 .0 9 9 7 1 .0 9 5 3 3 7 .4 0 15,057

A v . 3 6 .7 6 8 .7 4 5 .5 9

12 3 6 .4 0 , 3 6 . 3 0 0 . 1 0 8 .3 4 , 8 .2 9 0 .0 5 5 .7 2 , 5 . 7 0 0 .0 2 0 .1 0 3 9 0 .1 0 1 8 1 .0 2 0 6 3 6 .9 6 14,951

A v . 3 6 .3 5 8 .3 2 5 .7 1

16 3 6 .2 1 , 3 6 .4 6 0 .2 5 8 .2 9 , 8 .3 4 0 .0 5 5 .2 8 , 5 .8 4 0 .5 6 0 .1 0 3 9 0 .0 9 9 1 1 .0 4 8 4 3 6 .9 5 14,949

A v . 3 6 .3 4 8 .3 2 5 .5 6

20 3 6 .1 9 , 3 5 .4 3 0 .7 6 8 . 1 9 , 7 .6 4 0 .5 5 5 .3 0 , 6 .0 0 0 .7 0 0 .0 9 8 9 0 .1 0 0 7 0 .9 8 2 1 3 6 .3 7 14,813

A v . 3 5 .8 1 7 .9 2 5 .6 5

3 0 3 6 .2 7 , 3 6 .2 5 0 .0 2 7 .8 4 , 7 .9 9 0 . 1 5 5 .5 0 , 4 .9 8 0 .5 2 0 .0 9 8 9 0 .0 9 3 4 1 .0 5 8 9 3 6 .8 6 14,928

A v . 3 6 .2 6 7 .9 2 5 .2 4

40 7 . 7 4 , . . . 5 .4 0 , . . 0 .0 9 6 7 0 .0 9 6 3 1 .0 0 4 2

A v . “ ’ . . . * * * 7 .7 4 5 .4 0

60 3 6 .1 1 , 3 6 .3 4 0 .2 3 7 . 8 4 , 7 .8 4 0 .0 0 5 .3 6 , 5 .2 0 0 .1 6 0 .0 9 7 9 0 .0 9 4 1 1 .0 4 0 4 3 6 .8 3 14,921

A v . 3 6 .2 3 7 .8 4 5 .2 8

it should n o t be heated too h o t or too long because of the pos

sibility of decomposing calcium sulfate. Therefore, he chose th e a rb itra ry tem perature of 750° C. and a heating period of 3 to 5 m inutes.

T his short heating period is evidently n o t sufficient to effect rem oval of excess sulfur trioxide. Before using a longer heating period it seemed best to check th e effect of h eat on calcium sulfate, varying the tem perature and tim e of heating.

I n T able I I I are given d a ta for th e decomposition of cal

cium sulfate from 550° to 1100° C., heating for 4- and 60- m inute periods a t each tem perature. T he calcium sulfate used in these experim ents was M allinckrodt reagent quality C a S 0 4-2H20 which had been heated to 500° C. in platinum to rem ove the w ater of crystallization.

In T able IV will be found d a ta on the effect of heating pure calcium sulfate a t 750° C. for increasing periods of time.

Table I I I indicates th a t calcium sulfate is decomposed only slightly even a t tem peratures up to 1100° C. and with heating periods of 4 or 60 m inutes. W hen th e differences ob

tained in duplicate determ inations as shown in Table I I I are taken into account, th e decomposition is small indeed. Ac

cording to P a rr’s curve, d a ta for which were obtained by heat

ing samples of sulfated ash, calcium sulfate is dissociated to the extent of ab o u t 34 per cent a t 1000° C. On the basis of th e evidence obtained from th e experiments on calcium sul

fate and a knowledge of th e composition of coal ash, th e author believes th a t P a rr’s curve is n o t a dissociation curve for calcium sulfate b u t rath e r indicates th e decomposition of iron and alum inum sulfates present in th e ash after trea tm e n t w ith sul

furic acid. This curve is in accordance w ith the known dis

sociation d a ta for iron sulfate.

In T able IV it will be noted th a t increasing the tim e of heating calcium sulfate does n o t result in m aterial increase of decomposition. F rom these d a ta it appears th a t increasing th e tem perature o r the tim e of heating th e sulfated ash would be perfectly safe and desirable. This is in accordance w ith the findings of Valdez and Camps-Campins (4), who studied th e restandardization of th e sulfated ash m ethod for determ in

ing ash in sugar products.

In view of the above facts, the effect of increased heating periods a t 750° C. on the sulfated ash of sample C-997 was studied. This coal had a moisture-free total sulfur value of 2.87 per cent, a moisture-free mineral-matter carbon dioxide value of 4.49 per cent, and a moisture-free calorific value of 9569 B. t. u. Eight 1-gram portions of this sample were ashed and treated with sulfuric acid in accordance with the procedure described by Parr. The first portion was heated ^ minutes, the second 8 minutes, and so on, up to 60 minutes. The samples so heated were first cooled and weighed to give sulfated ash values and then dissolved and analyzed for sulfur trioxide and calcium oxide. The molar ratios of these two constituents were cal

culated, as well as mineral m atter values and unit coal values, using the mineral m atter values so obtained.

In T able V th e duplicates of the portion heated for 4 min

utes show a large deviation, the m olar ratio of sulfur trioxide

to calcium oxide is alm ost 3 to 1 (2.7332) whereas it should be 1 to 1, and th e u n it coal value calculated from th e mineral m a tte r so obtained is unreasonably high. The portion heated for 8 m inutes shows a much smaller deviation between dupli

cates in per cent of sulfated ash, th e m olar ratio of sulfur trioxide to calcium oxide is only slightly greater th a n one (1.0953), and th e calculated unit coal value is much more rea

sonable although possibly a little high yet. T he portions which were heated 12 m inutes and more in general show small devia

tions between duplicates in per cent of sulfated ash, th e ratios of sulfur trioxide to calcium oxide are very close to one, and calculated unit coal values compare m uch m ore favorably with the county average value of 14,690 B. t. u. for this coal.

C o n c lu sio n s

The following facts have been brought o u t by this investi

gation:

1. A heating period of 3 to 5 m inutes a t 750 ° as described by P arr is not sufficient to expel all sulfur trioxide in excess of th a t in calcium sulfate.

2. T he so-called “ dissociation curve for calcium sulfate” as published by P a rr is not a dissociation curve for calcium sul

fate. The loss m ay very probably be due to decomposition of iron and alum inum sulfates.

3. The dissociation of calcium sulfate is n o t m aterially in

creased b y increased tem perature from 750° to 1000° C. or by increased heating periods up to 110 minutes.

4. In m aking modified ash determ inations on coal samples high in carbonate, P a rr’s procedure may be followed as far as the place where he directs th a t th e sulfated ash be heated 3 to 5 minutes. Instead of heating as directed, th e sulfated sam ples should be heated to constant weight, which should be reached in 15 to 20 m inutes. This will ensure com plete ex

pulsion of excess sulfur trioxide.

A c k n o w lc d g n ie n I

T he author wishes to express his appreciation to F. H . Reed and G. Thiessen for helpful suggestions in the preparation of this report and to C. S. W esterberg, J. W. Robinson, and L. D. McVicker for assistance in obtaining analytical results.

L ite r a tu r e C ited

(1) Am. Soc. T esting M aterials, S tandards on Coal and Coke, D esignation D38S-36T, p. 103.

(2) P arr, S. W ., “ Analysis of Fuel, Gas, W ater, and L u b rican ts,”

4 th ed., pp. 54 and 213, New York, M cGraw-Hill Book Co., 1932.

(3) P arr, S. W ., Illinois S tate Geol. Survey, Bull. 3, 35 (1916).

(4) Valdez, R.., and Cam ps-Cam pins, F., I n d . Eno. Ch em., Anal.

Ed., 9, 35 (1937).

Re c e iv e d M a r c h 2 7 , 1937. P u b lis h e d b y p e rm is sio n of th e C h ie f, Illin o is S ta t e G eo lo g ical S u r v e y , U r b a n a , 111.

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Scattering in the Near Infrared

A M easure o f P a r tic le S ize an d S ize D istrib u tio n

D. L. GAM BLE ^{A N D}C. E. BARNETT, T h e New Je rse y Z inc C o m p an y , P a lm e r to n , P a.

S

IN C E th e reinforcing characteristics of pigm ents in ru b ber depend to a large extent upon th eir degree of fineness, there lias been considerable interest in the m easurem ent of the particle size of these m aterials. T he principal m ethods which have been employed are:

(1) th e direct microscopic m eas

urem ent, (2) th e “ count” m ethod u s i n g t h e m i c r o s c o p e w i t h

“ dark field” illum ination, (3) the indirect turbidim etric methods, and (4) th e sedim entation rate and equilibrium sedim entation m ethods.

P r e s e n t M e th o d s o f M e a s

u r in g P a r tic le D ia m e te r s In th e first of these m ethods, a m inute am ount of the m ate

rial to be examined is dispersed in s o m e m o u n t i n g m e d iu m

such as a m elted gum or resin, on a microscope slide. A photograph m a y be m ade of the field and th e actual diam eter of each particle m easured on an enlargem ent, or projection of th e negative, or on a directly projected image. T he principal ad vantage in this direct m ethod of particle m easurem ent is th a t it yields a size distribution curve and, therefore, is not restricted to a single average diam eter. There are several ob

jections to th e m ethod:

1. To obtain a satisfactory field for projection or photography, the mount should not be more than a few particles thick. This requires pressure on the cover glass or some other method of rub

bing out the sample to a very thin layer and on such small amounts of m aterial the procedure may result in a greater degree of deaggregation than it is possible to attain by the usual methods of commercial dispersion. According to the pro

cedure of the individual investigator, all the aggregates in a sample may be broken up or only part of them. In most cases, the particle size as observed microscopically will be at consider

able variance with the effective particle sizes in an oil or rubber dispersion. The fume products such as zinc oxide which are relatively free of aggregation will show this difference to a lesser degree than precipitated materials.

2. In the case of nonuniform materials, difficulty is experi

enced in bringing both coarse and fine particles into focus a t the same time. The lack of uniformity experienced in m any pig

ments makes the method extremely laborious because of the necessity of measuring a large number of particles in order to ob

tain truly representative data.

T he dark-field count m easurem ent of particle size as exem

plified in the Goodyear m ethod (2) gets aw ay from th e v aria

tions in grinding between th e microscopic m ount and actual application, since a rubber com pound is used in m aking the counting suspension. However, this m ethod gives only the diam eter of th e particle of average volume, D, from which the num ber of particles per gram m ay be calculated, b u t since no inform ation as to size uniform ity is obtained, th e specific sur

face cannot be calculated. I ts application is restricted to relatively fine and uniform pigments. In th e case of samples which are relatively nonuniform , it has been shown (4) th a t th e D diam eter is of less significance in indicating the proper

ties of a pigm ent in rubber th a n th e diam eter from which specific surface m ay be calculated, d3, or th e diam eter of the particle of average weight, dt. This is because th e first

nam ed fails to evaluate th e coarse particles in th e degree to which they affect th e behavior of p ain t or rubber. T h e signifi

cance of th e several average diam eters has been covered extensively by Green (8).

Wells (9) has given a rdsumd of th e turbidim etric m ethods.

T he particle sizes of m any of th e pigm ents which are of in

terest in rubber and in p ain t are in th e range where th e tu r

bidity or opacity of th e suspen

sion to visible radiation is due to b o th ordinary reflection and scattering p h e n o m e n a . Since th e tw o phenom ena are affected b y particle size in different ways, it is difficult to apply these m ethods to m aterials lying in th e pigm ent range b e c a u s e of th e complexities i n v o l v e d . T heir application is restricted because of th e m arked influence of size distribution characteristics, and the particle size in

form ation obtainable is lim ited. In th e w riters’ laboratory, for example, one of these m ethods (7) has been used exten

sively on relatively fine zinc oxide b u t it has been possible to correlate th e results only w ith th e di or arithm etical m ean diam eter, which is probably th e least significant average di

am eter as far as rubber properties are concerned. Others working w ith coarser particles (1 micron or larger in average diam eter), where th e tu rb id ity is due to simple reflection and depends on th e projected area of th e particles, have been successful in correlating w ith specific surface. T he m ethods are indirect in th a t one of th e d irect m ethods m u st be used for standardization, and are lim ited to samples which are simi

lar to th e standards in th eir uniform ity of particle size distri

bution. Unless a practical dispersion is used in preparing th e suspension, it is open to th e same objections as th e microscopic m ethod in th a t the degree of dispersion of th e te st suspension is n o t necessarily th e same as obtained in actual com pounding.

U ltracentrifugal m ethods as developed b y Svedberg (5) and others (I) are a t present th e best of th e sedim entation schemes, b u t the necessary equipm ent is so expensive th a t it m ay be enjoyed by only a very few laboratories. However, recent work b y H auser an d Reed (5) using a cylindrical bowl supercentrifuge appears to be very promising.

From th e above discussion it is obvious th a t a fairly rapid m ethod of attain in g size distribution characteristics of pig

m ents in a sta te com parable w ith th a t prevailing in actual use is highly desirable.

P fund (6) has proposed the a d a p ta tio n of infrared scatter

ing to this purpose and th e present paper m erely represents th e application and extension of his work on scattering in th e near infrared region.

R a y le ig h ’s L aw o f S c a tte r in g a n d I n te r p r e  t a t io n o f E x p e r im e n ta l D a ta

T he extent to which radiation incident upon a suspension of particles in a tran sp a ren t m edium is tran sm itted is deter

m ined by th e optical constants of th e p articulate m aterial and th e m edium, th e size of the suspended particles, and the wave T h e p r e s e n t m e t h o d s o f m e a s u r in g t h e

p a r tic le s iz e a n d s iz e d is t r ib u t io n o f p o w d er s are rev iew ed a n d t h e n e e d o f a n e w m e t h o d is s h o w n . S u c h a m e t h o d , b a se d u p o n t h e t r a n s m is s io n o f s u s p e n s io n s a t v a r io u s w ave le n g t h s i n t h e v isib le a n d n e a r in fr a r e d r e g io n s , is d e sc r ib e d . F r o m t h e sh a p e o f t h e sp e c tr a l tr a n s m is s io n curve o b t a in e d , t h e r e la tiv e average s iz e a n d s iz e d is t r ib u t io n c h a r a c te r is tic s o f p o w d e rs c a n b e e s tim a te d .

310

(13)

JULY 15, 1937 ANALYTICAL ED ITION 311

Fi g u r e 1. Ag r e e m e n t b e t w e e n Ca l c u l a t e da n d Ob s e r v e d Tr a n s m i s s i o n

length of th e radiation. T he transparency of the suspension a,t various w ave lengths and th e degree to which transparency varies w ith th e w ave length yield inform ation as to the average size and size distribution characteristics of the m aterial.

Rayleigh has w orked o u t the form of th e wave length-transmission curve for the case in which all particles present are sm all in com parison w ith the short wave length lim it of the spectral range employed. This curve m ay be calculated from th e well-known Rayleigh scattering law. The Rayleigh for

m u la for th e transm ission of radiation through a scattering m edium according to W ien-Harm s (10) is:

r r rSirYn* - nos\ / 3n„s \ iV T J1

I = J 0 exp. - +

■where

I — intensity of the transm itted radiation la = intensity of the incident radiation n = refractive index of particle n0 = refractive index of medium Ar = number of particles per cc.

V = volume of each particle X = wave length

By assuming the refractive index term s in the above equa

tio n as constant, and since the mass per u n it volume or con

centration, c, is equal to N -V -p where p is the specific gravity o f th e particles, we m ay su b stitu te N -V - = - in the simplifiedC

P

N V 1 C V

exponent, K , and obtain jj- K . A t a constant concen

tra tio n of one single pigm ent and considering the volume V as proportional to d3, where d is th e diam eter of an equivalent

T K d 3 ' spherical particle, the equation becom es/ = h exp. — - ^ j - .

Thus th e intensity of th e transm itted radiation varies di

rectly as the fourth power of th e w ave length and inversely as th e th ird power of th e particle diameter.

Figure 1 shows th e experim ental w ave length-transm ission curve for a uniform , fine particle size zinc oxide (0.3 micron) com pared w ith th a t calculated from the above equation.

■Good agreem ent is obtained over the region in which the p ar

ticle size-wave length relationships fulfill Rayleigh’s assump

tions. In calculating this curve, the value for th e particle diam eter was taken from a direct microscopic determ ination using the D diam eter which is theoretically the diam eter in

volved in the Rayleigh law. The constant K was calculated from the observed transm ission a t a wave length of 1.0 micron, a point a t which the Rayleigh conditions should be fulfilled.

I t should be borne in m ind th a t in extending the curve into the near infrared no corrections have been m ade for possible changes in th e optical constants of the pigm ent and medium, and th a t the Rayleigh law should hold rigidly only when the ratio of th e indices of refraction of the particle and medium approaches one.

W hen the Rayleigh conditions are n o t fulfilled and the par

ticle size m ore closely approaches the wave length of th e radia

tion, the transm ission becomes less and less dependent upon the wave length, and when the particle becomes equal to or larger th a n th e wave length it is no longer selective in itfl transmission characteristics and its opacity depends only upon the optical constants and the projected area of the particle.

The m ethod employed here consists in m erely measuring the spectral transmission of th e pigm ent suspended in either oil or rubber from the visible blue to a wave length of about 4.0ju in the infrared. From the shape of this spectral trans

mission curve, the relative average size and size distribution characteristics can be estimated.

Typical transm ission curves are shown in Figure 2. Low transm ission in th e short wave length region is indicative of small particle size and the greater the selectivity (slope of the transmission curve tow ards longer wave lengths) accom pany

ing the low transmission the finer is the particle size. High transmission in the short wave length region w ithout selec

tivity is indicative of coarse particle size. Low transm ission in the long wave length region is also indicative of a large p ar

ticle size. The average particle size of th e pigm ent is roughly indicated by the point in the spectral transm ission curve a t which selectivity begins to develop. This occurs a t a point where the particle size approaches the m agnitude of th e wave length.

I 00

<s>

o 8 0

to<0

z <

trH 4 0

H

Z 111

o ' 2 0

UJ

Q .

0

0 1.0 ao 3.0 4.0

W A V E L E N G T H IN M I C R O N S

Fi g u r e 2 . Ty p i c a l In f r a r e d Tr a n s m i s s i o n Cu r v e s

Curve A of Figure 2 represents a uniform m aterial of ex

trem ely fine size, as indicated by th e m arked selectivity, high transm ission a t th e long wave lengths, and low transm ission a t the extremely short wave lengths, th e maximum opacity occurring a t wave lengths shorter th a n those included in th e illustration. Curve B represents a m aterial of fairly small