Industrial and Engineering Chemistry : analytical edition, Vol. 7, No. 4

Analytical Edition Vol. 7, No. 4

INDUSTRIAL

AND E N G I N E E R I N G

CHEMISTRY

Vol. 27, Consecutive No. 24 Published by the American Chemical Society

Harrison E. Howe, Editor

[ tA*

July 15, 1935

Publication Office: Easton, Pa. . Editorial Office: Room 706, Mills Building, Washington, D. C. . Telephone: National 08-18 Cable: Jiechein (Washington) . Advertising Department: 332 West 42nd Street, New York, N. Y. . Telephone: Bryant 9-1430

C O N T E N T S

16,300 Copies of This Issue Printed.

General M icrochem istry... A . A. Benedelii-Pichler 207 Catalytic and Induced Reactions in Microchemistry . . .

... I. M . KollhojJ and R. S. Livingston 209 Recent Advances in Applied M icrochem istry...

... Joseph B. Niederl 214 Role of Analytical Chemistry in Industrial Research. II.

... Beverly L. Clarke and II. W . Ilermance 218 An Efficient Vacuum Pump Check Valve . Roy L. Mobley 222 Photoelectric Colorimetry in M icroanalysis...

... Ralph II. Muller 223 Colorimetric Methods for the Determination of Phosphorus

...Ch. Zinzadze 227 Colorimetric Methods for Determination of Arsenic in

Phosphorus-Free S o lu tio n s ... Ch. Zinzadze 230 Analysis of Mixtures of the Monochlorides of n-Pentane

and I s o p e n ta n e ...II. B. Ilass and Paul Weber 231 Analytical Properties of Commercial Sulfated Alcohols . .

...Frank M. Bifjen and Foster Dee Snell 234 Effect of Pretreatments of Wood on Lignin Determination

... Geo. J. Ritter and James II. Barbour 238 Sampling and Analysis of Entrained M atter in Gases . . .

... Frank B. Varga and Roger II. Newton 240 A Rapid Method for the Determination of Sulfur in Ferro­

magnetic Alloys ...

. . Beverly L. Clarke, L. A. Wooten, and C. H. Pottenger 242 Sulfur Determination by the Combustion Method . . . .

... I I . A .K a r 244 Determination of Water in By-Product S u l f u r ...

...I^ouis Shnidman 246 Detection and Estimation of Orthophenylphenol . . . .

... William 0. Emery and Ilenry C. Fuller 248

Identification of Halides in the Presence of Thiocyanates . ... G. B. and L. K. Heisig 249 Determination of Diphenylamine in Smokeless Powders .

... Stanley G. Cook 250 A Modified Persulfate-Arsenite Method for Manganese

. . . . E. B. Sandell, I. M . Kolthoff, and J . J . Lingane 256 Determination of Ammoniacal and Urea Nitrogen . . . .

...J . Y. Yee and R. 0 . E. Davis 259 Turbidimetric Determination of Sulfate in W ater . . . .

... R. T. Sheen, II. L. Kahler, and E. M. Ross 262 Determination of L e a d ... 0. B. Winter,

Helen M. Robinson, Frances IK. Lamb, and E. J . Miller 265 Oxidation-Reduction Indicators. I ...

...L. A . Saner and Wm. von Fischer 271 Determination of Small Amounts of Potassium by Means

of Sodium C o b a ltin itrite ... II. W. Lohse 272 Determination of Molybdenum in Plants and Soils . . .

... Kenneth E. Stanfield 273 A Procedure for Classification of H y d ro carb o n s...

. . . . Samuel P. Mulliken and Reginald L. Wakernan 275 The Evap-O -R otor... J. Herbert Lowell 278 Photoelectric Photometers for Use in Colorimetry . . . .

... Ch. Zinzadze 280 A Photoelectric C o lo r im e te r...

...John II. Yoe and Thomas B. Crumpler 281 A Pressure Regulator for Vacuum Distillation ...

... 0. J . Schierholtz 284 Determination of L e a d ...

C. E. Willoughby, E. S. Wilkins, Jr., and E. 0. Kraemer 285 Permanent Aqueous Microscopic Mounts . . II. R. Smith 286

S u b s c r ip tio n to n o n m e m b e rs , In d u s t r i a l a n d En g i n e e r i n g Ch e m i s t r y, S7.50 p e r y e a r. _ F o re ig n p o s ta g e $ - .1 0 , e x c e p t to c o u n tr ie s a c c e p tin g m a il a t A m e ric a n d o m e s tic r a te s . T o C a n a d a , 70 c e n ts . An a l y t i c a l Ed i t i o n o n ly , $ 2 .0 0 p e r y e a r, s in g le co p ies <5 c e n ts , to m e m b e rs 6 0 c e n ts . 1 'o reig n p o s ta g e , 3 0 c e n ts ; C a n a d a , 10 c e n ts . Ne w s Ed i t i o n o n ly , $ 1 .5 0 p e r y e a r. F o re ig n p o s ta g e , 6 0 c e n ts ; C a n a d a , 2 0 c e n ts . S u b s c r ip tio n s , ch a n g e s of a d d r e s s , a n d c la im s fo r lo s t co p ies s h o u ld b e re f e r r e d t o C h a r le s L . P a r s o n s , S e c r e ta r y , M ills B u ild in g , W a s h in g to n , D . C . T h e C o u n c il h a s v o te d t h a t n o c la im s w ill b e allo w e d fo r co p ies of jo u r n a ls lo s t in th e m a ils , u n le ss s u c h c la im s a r e re c e iv e d w ith in 6 0 d a y s of th e d a t e of is s u e , a n d n o c la im s w ill b e allo w e d fo r issu es lo s t as a r e s u lt o f in s u ffic ie n t n o tic e of c h a n g e of a d d r e s s . ( T e n d a y s ' a d v a n c e n o tic e re q u ir e d .) . M is sin g fro m files c a n n o t b e a c c e p te d as tn e r e a s o n lo r h o n o r in g a cla im . I f c h a n g e of a d d r e s s im p lie s a c h a n g e of p o s itio n , p le a s e in d ic a te its n a tu r e .

The A m e r i c a n C h e m i c a l S o c i e t y also publishes the Journal of the American Chemical Society and Chemical Abstracts.

VOL. 7, NO. 4

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 t s . , E a s to n , P a .

E n te r e d a s se c o n d -c la ss m a tte r a t th e P o st-O ffice a t E a s to n , P a ., u n d e r th e a c t o f M a r c h 3, 1879. as 4 2 tim e s a y e a r. I n d u s tr ia l E d itio n m o n th ly o n th e 1 s t; N e w s E d itio n o n th e 1 0 th a n d 2 0 th ; A n a ly tic a l E d itio n b im o n th ly o n th e 1 5 th . A c c e p ta n c e f o r m a ilin g a t s p e c ia l

r a t e o f p o s ta g e p r o v id e d fo r in S e c tio n 1103, A c t o f O c to b e r 3, 1917, a u th o r iz e d J u lv 13, 1918.

A P o w e r f u l T ^{o o l o f} R e s e a r c h

T he resistance o f Transparent V itreosil (fused pure quartz) to severe tem perature conditions and chemical attack, w ith its non-porous structure and unusual optical characteristics, perm its th e use o f Vitreosil equipm ent under conditions where glass and porcelain are inadequate. E v en under less severe service it possesses advantages more than offsetting th e initial difference in cost.

Transparent Vitreosil is composed solely o f th e purest grades o f rock crystal elec­

trically fused and offers a product o f unexcelled uniform ity and unlim ited possibili­

ties, especially for researches where the presence o f foreign substances w ould be objectionable. N o form o f equipm ent has greater transparency to ultra-violet and infra-red radiations and it also possesses exceptional clarity in th e visible spectrum.

Literature fu lly describing the possibilities o f V itre o sil w ill be gladly sent upon request.

The THERMAL SYNDICATE, Ltd.

62 Schenectady Avenue Brooklyn, New York

JULY 15, 1935 ANALYTICAL EDITION 5

We are proud of their excellence, judged b y any standard. Examine the catalogued limits of im­

purities and you'll agree. Making, as we do, our own hydrofluoric acid it is only natural that our quality control can be held to exacting limits more easily. The Baker & Adamson plant and its products have given to the laboratory workers of America an outstanding demonstration of achievement in standardized reagent purity.

Y o u r d e a l e r w ill s u p p l y y o u , o r w r i t e t h e n e a r e s t c o m p a n y o f f ic e

G e n e r a l C h e m i c a l C o m p a n y ♦ 40 Rector St., New York

'H e a q e tij t—

C hem icals

*”dC .p J c id s

ATLANTA • BALTIMORE • BOSTON • BUFFALO • CHARLOTTE • CHICAGO • CLEVELAND * DENVER ■ KAN SAS CITY • LO S AN GELES * MINNEAPOLIS • PHILADELPHIA ■ PITTSBURGH • PROVIDENCE.* SAN FRANCISCO • SEATTLE • ST. LOUIS

‘"•"“ L A B O R A T O R Y G L A S S W A R E

it h e a t re sista n t? ” m a y w ell b e th e first th o u g h t o f th e c h e m ist in selecting h is la b o ra to ry glassw are.

T h e use o f L a b o ra to ry W a re w ith o u t go o d h e a t-re sistin g p ro p e rtie s is a serious h a n d ic a p in e v e ry d ay la b o ra to r y o p e ra tio n s— th e cau se o f b ro k e n glassw are, lost tim e, lost effort, a n d w asted m a te ria ls.

F u rth e rm o re , la b o ra to ry vessels m a d e fro m glasses w h ich a r e n o t h e a t-re sistin g m u s t b e blo w n w ith th in w alls to p ro v id e som e m e a su re o f resistan c e to h e a t a n d su d d e n te m p e ra tu re ch an g es. T h is sacrifices m e c h a n ic a l s tre n g th a n d w eakens th e w a re a g a in st th e m e c h a n ic a l shocks o f e v e ry d a y service.

“ Py r e x” b r a n d L a b o ra to ry W a re gives th e c h e m ist th e u tm o s t in s tre n g th a n d d e p e n d a b ility — m o re resistan ce to h e a t a n d to su d d e n te m p e r a tu re ch a n g es—

(because o f its low coefficient o f th e rm a l e x p a n sio n — o .ooooo32/° C .)— m o re r e ­ sistance to ch e m ic al a tta c k a n d m e c h a n ic a l shock; c o rre c t a n n e a lin g , a n d ac c u ra c y . B ecause th e good q u a litie s o f “ Py r e x” L a b o r a to ry W a re a r e u n iv e rsa l—a n d inexpensive— it is g e n e rally p re fe rre d fo r a ll ty p es o f la b o ra to ry w ork— rese arch , testing, a n d e d u c a tio n a l.

T h e w a re is sold th ro u g h le a d in g la b o ra to ry su p p ly d ea le rs in th e U n ite d S tate s a n d C a n a d a .

“P Y R E X " is the registered trade-m ark of

C O R N IN G GLASS W O R K S • C O R N IN G , N E W Y O R K

B E S A F E ! S ee th a t th i s tr a d e -m a r k is r e p r o d u c e d

PYREX

exactly o n ev e ry p ie c e o f a p p a ra tu s y o u b u y .

“ P Y R E X ” V O L U M E T R IC

F L A S K S

Accuracy, plus heat rcsistancc, chcm ical stability, and mechani­

cal strength.

JULY 15,1935 ANALYTICAL ED ITION 7

7 A D V A N T A G E S IN THE N E W C O N T A I N E R S O F M E R C K L A B O R A T O R Y C H E M I C A L S

M erck Laboratory Chemicals are now packaged in specially-designed containers which offer these seven im portant advantages:

1. Amber Color Glass 5. Special liner ensures 2. Non-m etallic screw cap air-tight sealing 3. W ill not corrode 6. D ust-proof

4. Easy to open 7. Attractive appearance

T he amber color glass bottles afford maximum pro ­ tection against light and other deteriorating agents.

The non-metallic screw caps were designed to over­

come corrosion resulting from unfavorable atm os­

pheric conditions and from vapors present in the laboratory. T he large facets on the side o f the cap make it easy to open the bottle.

A special liner, im pervious to the chemical, en­

sures air-tight sealing when the handy cap is replaced.

T he cap extends over the lip o f the bottle, thus preventing an accumulation o f dust.

Merck Laboratory Chemicals in these new am ber glass bottles, with their black caps and blue and white labels, will add to the attractive appearance o f your laboratory or stock room .

Y our wholesaler is ready to supply you.

M E R C K & C O . I n c .

M a n u f a c t u r i n g C h e m i s t s

R A H W A Y , N. J .

8 INDUSTRIAL AND EN GIN EER IN G CHEMISTRY

K KIMBLE GLASS C O M P A N Y . ^{. »} v i n e l a n d , n . j .

N E W Y O R K • P H I L A D E L P H I A • B O S T O N • C H I C A G O • D E T R O I T Placing ca li bra tio n lines on a K im ble Blue Line E x a x

Pipette — an o p e ra t io n re q u ir in g skill a n d a c c u r a c y .

S tan d ard ize on Blue Line Exax P pettes..for assurance. A full line of Kimble Exax glassw are is stocked by leading Laboratory Supply Houses throughout the United States and C a n a d a . Kimble Blue Line Exax P ip ettes..in addition

to their 'assured accu ra cy " and d epen d ­ ability . . have many v a lu a b le features of construction:

They are m ade of autom atic-m achine- m ade tubing . . straight, thick-w alled and o f very uniform bore. They a re retem pered (s tra in -fre e ) fo r m axim um stren g th . A ll

V o lu m e tric a n d O s tw a ld P ip e tte s

Size Tolerance Size Tolerance

1 ml. . . ± 0 .0 1 2 ml. . 15 ml. . . ± 0 .0 6 ml.

2 ml. . 0.012 ml. 20 ml. . 0.06 ml.

3 ml. . 0.02 ml. 25 ml. . 0.06 ml.

4 ml. . . 0.02 ml. . 50 ml. . 0.10 ml.

5 ml. . 0.02 ml. . 100 ml. . 0.16 ml.

10 ml. . . 0.04 ml. . 200 ml. . . 0.20 ml.

lines and numbers a re d eep ly acid etched and filled with a d u rab le blue g lass, fused- in. Expertly ca lib rated a t 2 0 ° C . Main division lines com pletely encircle tube. Tip openings deliver contents accu rately and at proper sp eed .

Every Blue Line E xax Pipette is r e t e s t e d to these to leran ces:

M easuring an d Se ro lo g ica l Pipettes I /10 ml...± 0.005 ml.

2/10 ml... 0.008 ml.

1 ml... 0.02 ml.

2 ml... 0.02 ml.

5 ml... 0.04 ml.

10 ml... 0.06 ml.

25 ml... 0.10 ml.

JULY 15, 1935 ANALYTICAL EDITION 9

T h e W i r e t h * t M a d e E le c tr ic a l H e a t P o s s ib le

♦ S e n d f o r o u r H a n d y H e a t i n e - U n i t C a l c u l a t o r .

free

A H an d y To o I

C hem ical ig n itio n s, lig h t h e a t- trc a lin g , a n d v itreous en a m e lin g o f sm a ll pieces as show n here, illu s tr a te th e varied uses o f th is sm a ll H oskins ele c tric fu rn a c e — w h ic h proves it a h a n d y tool. I t can he set tip w herever you can r u n a p a ir of w ires; provides precise c o n tro l o f te m p e ra ­

tu re , a n d h e a t t h a t is as clean and q u ie t as su n sh in e .

T his fu rn a c e is equipped w ith a one-piece grooved m uffle, a ro u n d w hich is w rapped th e helical C hro- m el lie a tin g -u n it. P la in ly , a new u n i t is very easy to in sta ll. T his c o n stru c tio n p e rm its c o n c e n tra t­

ing th e coiled w ire a t th e ends of th e

m uffle to co m p en sate for ra d ia tio n

losses. For m o re in fo rm a tio n

a b o u t H oskins F u rn a ce , w rite to

yo u r dealer. H oskins M a n u fa c ­

tu rin g Co., D e tro it, M ich.*

N EW 1935 M O D E L

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

W ith several im p ro vem ents reducing th e p o ssib ility of loss, evaporation or co n ta m in a tio n of sam p le

W ILEY LABORATORY M ILL, New 1935 M odel.

T h e follow ing a re th e m o re im p o r ta n t im ­ p ro v e m e n ts in c o rp o ra te d in th e new m odel, all o f w hich red u c e p o ssib ility o f loss, e v a p o r a tio n o r co n ­ ta m in a tio n o f sa m p le :

The body casting has been changed at the bottom and the shape of the sieve frame has also been changed to close completely the space heretofore existing between the sieve and the drawer for the collection of the sample. This drawer is now provided with a groove at top which permits it to slide in close proximity to the bottom of the sieve frame without loss of sample.

The hopper fits more tightly than heretofore and is provided with a close-fitting lid at top.

O rig in ally d esigned for th e p re 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 fe rtiliz e r m a te ria ls su c h as ta n k a g e , an im al h a ir, fu r, hoofs, h o rn s, e tc ., for la b o ra to r y a n a ly sis, b u t now s a tis f a c to r ily u s e d fo r a g re a t v a r ie ty o f o th e r m a te ria ls su c h as:

S traw C otto n seed cake C orn sta lk s C rab shells

Tobacco sta lk s C otto n seed m eal C hicken fe a th e rs D ried fish scales

Licorice ro o ts W heat B akelite Agar

G rass C orn L e a th e r G elatin e, etc.

C o tto n seed O ats

Four knives on a revolving shaft work with a shearing action against six which are set in the frame. The screen is dovetailed into this frame so that none of the material comes out of the grinding chamber until it is fine enough to pass through the mesh.

Three sieves with screen of mm, 1 mm and 2 mm mesh, respectively, are furnished with each mill. A hinged front permits easy cleaning.

The mill is 21 inches high and occupies a floor space about 14X20 inches. Grinding chamber is 8 inches inside diameter, with knives 3 inches wide. Drawer for ground sample'is 7X3X2J4 inches and holds 24 oz. liquid measure. Mill should be op­

erated at from 400 to 800 r.p.m. and requires from Vi to 1 h.p. Pulleys are 6 inches in diameter X V /i inches face. Knives should be run in counter-clockwise direction. Approximate shipping weight 210 lbs.

See Samuel W. Wiley, “ A New Laboratory Mill,” Industrial and Engineering Chemistry, March, 1923, p. 304 and The American Fertilizer, February 7, 1925: K- Maiwald, “Beobachtungen zur Methodik des Gefiissversuchs,” published in Die Landwirtschaftlichen V(rsuchs-Stationen des Deutschen Reiches, 1928, p. /? ; I. D. Clarke and R. W. Frey, “A Comparison of Four Machines in the Preparation of Leather Samples for Analysis,” The Journal of the American Leather Chemists Association, Vol. X X III, No. 9 {.September, 1928), p. 412; and Carl R. Blomstedt, “A Rapid Moisture Test for Wood,” Paper Trade Journal, Vol. XCII, No 18 (Apr. 30, 1931), p. 43.

4275. Wiley L aboratory M ill, New 1935 Model, as above described, with three sieves of mm, 1 mm and 2 mm mesh, respectively. With tight and loose pulleys for belt drive, but without motor... $165.00 C ode W o rd ... E ln fc F o r m o r e d e t a i l e d d e s c r i p t i o n o f t h e W i l e y M i l l , t o g e t h e r w i t h a m o d e l f o r d i r e c t m o t o r d r i v e a n d a s m a l l

m o d e l f o r m i c r o - a n a l y s i s , s e e p a g e s 2 7 7 a n d 278 o f o u r c u r r e n t c a t a l o g u e .

ARTH UR H. T H O M A S C O M P A N Y

R ETAIL—W H O LESA LE— E X P O R T

LA B O R A TO R Y A PPA R A TU S A N D REAG EN TS

W E S T W A S H IN G T O N SQ UARE P H IL A D E L P H IA , U .S.A.

Cable Address, “Balance,” Philadelphia

■Kr

ANALYTICAL EDITION

Vo l u m e 7 N u m b e r 4

INDUSTRIAL

AND E N G I N E E R I N G

CHEMISTRY

^{J u l y 1 9 3 51 5 ,}

Ha h m s o n E . Ho w e, Ed i t o r

=SH-

General Microchemistry

A. A. BEN ED ETTI-PIC H LER , W ash in g to n S quare College, New York U niversity, New Y ork, N. Y.

M

IC R O C H E M IST R Y m ay be defined as th e sys­

tem atic presentation of the technic involved in the perform ance of chemical experiments on an essen­

tially smaller scale th a n is usually employed in laboratory practice. In accordance w ith th e atom ic concept of m atter, th e chemical phenom ena and physical properties observed on th e smallest quantities of m a tte r handled up to th e pres­

en t tim e in microchemical experiments (10-9 gram or approxi­

m ately 1012 molecules) cannot be expected to differ essen­

tially from those observed on a large bulk of m aterial. (Phe­

nomena belonging to th e fields of colloid chem istry, the study of radioactive elements, etc., are n o t considered here.) I t is obvious, however, th a t the technic of working and th e m eth­

ods of observation m ust v ary w ith th e am ount of m aterial under consideration.

Field of M icrochem istry

General microchem istry (S) deals w ith th e development, testing, correlation, and system atization of m ethods for the handling of small quantities of materials, and for the obser­

vation and determ ination of their properties. I t has the task of supplying th e working technic used in applied micro­

chem istry, of which microanalysis represents up to th e pres­

e n t tim e th e m ost im p o rtan t branch. C ertainly more than nine-tenths of th e microchemical m ethods carried o u t are used in m icroanalytical procedures.

According to th e definition, th e upper lim it for the size of m aterial to be handled b y microchemical m ethods is rea­

sonably defined by statin g th a t the q u an tity of m aterial taken should be so small as to prohibit the use of traditional working m ethods. T he lower lim it is, of course, determined by th e sta te of advance of microtechnic. I t is obvious th a t both lim its of th e am ount of m aterial depend on th e nature of th e individual problem and will undergo changes in the course of tim e. If chemists should succeed, for example, in increasing th e sensitivity of an analytical procedure by in­

creasing th e molecular weight of the precipitate to such an extent th a t 1-mg. samples could be analyzed by the stand­

ard m ethods of today, then th e use of microtechnic as applied today to th e analysis of 1-mg. samples would probably per­

m it th e analysis of 0.01-mg. samples. Such an advance would sim ply effect a shift of both lim its of the range of micro­

analysis in favor of still smaller samples. T he example also illustrates th e relation between the sensitivity of tests and the necessity of using microchemical technic for their perform ­ ance: th e more sensitive the test, th e smaller the q u an tity

of m aterial which m ay be analyzed w ithout th e use of a m i­

crochemical technic. The simultaneous use of sensitive te sts and microchemical methods, however, promises th e a tta in ­ m ent of extremely low lim it of identification.

T he principal task of m ost chemical work (analytical a 3 well as preparative) is the isolation of th e com ponents con­

tained in a mixture, and their subsequent identification or estim ation. T he isolation itself usually comprises th e prepa­

ration of suitable compounds, followed by their separation and purification. Identification and estim ation are nearly always based upon the observation or m easurem ent of physical properties—states of aggregation, transition tem ­ peratures, shape, density, mass, volume, color, refraction and reflection of light, radiation, magnetic susceptibility, etc.—which can be directly or indirectly recognized by sen­

sory impressions. W hen the size of the specimen under in­

vestigation becomes very small, a refined m anipulative tech nic m ust be employed, and th e m anifestations of th e physical and chemical properties m ust be amplified b y suitable de­

vices in order to be registered by our sense organs. G eneral m icrochem istry provides these special technics.

M icrom ethods m u st be ra th e r closely correlated to th e am ount of m aterial available, and th e size of sample which m ay be taken for a microanalysis varies over a wide range.

In general, approxim ately 10 to 50 mg. constitute th e upper lim it of sample size for qualitative and quan titativ e micro­

analysis. T he sm allest sample m ay a t present be considered 0.1 microgram (0.1 gamma, 0.0001 m g.), since it is possible to collect and recognize quantities as small as 0.00003 y of hydrogen ion, 0.0002 y of hydroxyl ion, 0.0005 y of b orate ion, 0.0003 7 of cobalt or nickel ion, abo u t 0.001 y of an ti­

mony or silver ion, or about 0.01 y of sulfide, arsenic, cadm ium , copper, iron, lead, or m ercury ion (2). F urtherm ore, it is pos­

sible to collect and m easure such small quantities as 0.001 y of gold (5) and 0.01 y of m ercury (9). As little as 0.00001 y of thorianite should be sufficient to detect th e helium oc­

cluded in such m aterial (7), and only 0.005 y of air is required for a quantitative analysis by th e bubble m ethod of K rogh (6). Gravim etric residue determ inations w ith a few micro­

grams of sample have already been carried o u t in great num ­ bers a t Em ich’s in stitu te (10), and the use of microbalances of extreme sensibilities—0.0002 y and less—should m ake it possible to work w ith still smaller samples.

A variation in th e size of a microsample from 0.1 7 to 50 mg. corresponds to a variation in th e weight of a m acro­

sample from 1 gram to 500 kg. Consequently, th e m anipu­

207

VOL. 7, NO. 4 lative technic and methods of observation used in micro­

analysis m ust undergo vast changes as the am ount of material decreases. These changes m ust be even more radical than those taking place when reducing the quantity of the sample from 500 kg. to 1 gram, as the corresponding range in micro- analysis extends below the limit where the palpable proper­

ties of m atter can be directly observed by the hum an sense organs. This fact, together with th e observation th a t a re­

duction to one one-hundredth of the original mass manifests itself in a less obvious way when working on a small scale (compare the reduction of a mass from 10 to 0.1 mg. w ith the reduction from 100 to 1 kg.) necessitates a close correlation between mass and technic in microanalysis, a fact which is usually overlooked but which cannot be emphasized too much.

M icro technic

T he development of a system of microtechnic for chemical work was begun by Emich in 1900 and essentially completed by 1911, when the first edition of his Lehrbuch (S) appeared.

This p art of Emich’s work has not only contributed tow ard the rapid progress of microchemistry in the last two decades, b u t was actually the foundation of microchemistry (8).

The technic of quantitative analysis and of preparative work, and the methods for the observation of properties (physico-chemical work) have been developed w ith proper consideration of adaptability to certain size ranges of m atter.

Emich m ust have recognized this requirem ent a t a very early stage of his research, and he repeatedly emphasizes th e importance of its strict observation.

When a sample of a few centigrams is taken for analysis (semi-microanalysis, or centigram method), the use of centrifuge tubes of 3- to 15-cc. capacity is recommended. In most cases it will be possible to effect the separation of solid and liquid phases by simply pouring out the filtrate after centrifuging. Filtration through paper could be used, but is less efficient. Spot tests are suggested as confirmatory tests.

With samples of 0.5 to 1 mg., small centrifuge tubes (micro­

cones) of 0.7-cc. capacity are most efficient for the separation of solid and liquid phase. The use of a microscope is still not neces­

sary, as the presence and color of precipitates 5 to 10 y in weight, or of colorations caused by these amounts, can be observed with the unaided eye. Spot tests suggest themselves as confirmatory tests here; however, the certainty of identification is increased by the use of tests carried out with microscopic observation.

A complete scheme for the isolation, identification, and estimation of the commoner cations has been worked out, and will be presented soon in book form ( i). The results, which may be obtained w ithout difficulty, m ay be illustrated by the analysis of a 1-mg. “ unknown” sample: Al, 3 per cent found (3 per cent given); Fe, 0.1 (none); Cr, 1 (1.5); M n, 1 (1.5); Zn, 1.5 (1.5); Ni, 0.7 (1.5); Ca, 0.4 (1.5); PO<, not es­

tim ated (1.5). The iron found was introduced by th e re- reagents used. If th e purity of the reagents has not been tested, the detection of less th a n 2 y of iron, calcium, or so­

dium, which constitute very common impurities of the

Etching Stainless Steels. A new method for etching stainless steel, prior to microscopic study of grain structure, has been developed in the National Bureau of Standards.

AU metals are composed of small, imperfect crystals known as grains, the size, shape, and structure of which are of great im­

portance in the study of any metal and its application in service.

To reveal this grain structure it is necessary to etch the metal with a chemical reagent. The appearance is then studied under the metallurgical microscope at suitable magnifications.

Certain metals are difficult to etch satisfactorily because of their compositions. Stainless steels are among the most trouble­

some, since they resist all ordinary reagents. In the past it has been necessary to use strong, mixed acids to reveal the structures

“ pure” reagents, should never be taken as proof of their presence in the sample.

A technic of working in capillaries of 0.5- to 1-mm. bore has been developed (4) for the analysis of 0.05- to 0.5-ing.

samples (a centi-milligram procedure), whereby practically all the processes required in qualitative analysis can be car­

ried out with ease and certainty. A magnifying lens, or a low-power microscope becomes a necessary tool for the d e­

tection of precipitates and colorations.

The use of laboratory apparatus of the ordinary ty p e be­

comes absurd when the size of the sample decreases to a few micrograms or less, since the small quantities of precipitates or the tiny drops of solution cling to any surface. C ontinu­

ous control of all operations by means of the microscope be­

comes im perative, magnifications of 50 X to 100 X being necessary for th e observation of th e confirm atory tests.

Emich succeeded in handling such small quantities of m a tte r by absorbing them on the ends of textile fibers. Precipitates, formed by dipping the fiber into droplets of reagent solutions, cling to the fibers and can be transferred w ithout difficulty to other solutions which m ay serve for washing th e precipi­

tates, extracting parts of them , etc. A t th e same tim e, th e m aterial under investigation always rem ains concentrated in a very small area, thus preventing its loss and facilitating observation.

M icrotechnic has already contributed greatly to the prog­

ress of science, b u t one cannot expect it to realize its full potentialities in th a t direction until the great m ajority of research men—n o t only th e chemists b u t also biologists, geologists, archeologists, etc.—are informed as to th e possi­

bilities of microchemical work. Even Pregl would n o t have begun th e development of organic quan titativ e microanalysis had it not been for th e knowledge of th e previous work of Emich which indicated the feasibility of th e proposed task (S).

L ite ra tu re C ited

(1) Benedetti-Pichler, A. A., and Spikes, W. F., “Introduction to the Microtechnique of Inorganic Qualitative Analysis,”

Douglaston, L. I., Microchemical Service, 1935. (In press.) (2) Emich, F., Ann., 351, 426 (1907).

(3) Emich, F., “ Lehrbuch der Mikrochemie,” p. 3, Munich, Bergmann, 1926.

(4) Emich, F., Z. anal. Chern., 54, 489 (1915).

(5) Haber, F., Jaenicke, J., and Matthias, F., Z. anorg. Chern., 153, 177 (1926).

(6) Krogh, A., Skand. Archiv. Physiol., 20, 279 (1908).

(7) Paneth, F., and Peters, K., Z. phys. Chem., 134, 353 (1928).

(8) Pregl-Fylemann, F., “Quantitative Organic Microanalysis,”

p. 1, Philadelphia, P. Blakiston’s Son & Co., 1930.

(9) Stock, A., et al., Z. angew. Chem., 44, 200 (1931); 46, 62, 187 (1933).

(10) Wiesenberger, E., Mikrochemie, 10, 10 (1931).

Re c e i v e d M a y 25, 1935. P r e s e n te d , w ith d e m o n s tr a tio n s b y H . K . A lb e r, b e fo re th e D iv is io n of P h y s ic a l a n d I n o r g a n ic C h e m is tr y , S y m p o s iu m o n R e c e n t A d v a n c e s in M ic ro c h e m ic a l A n a ly s is , a t th e 8 9 th M e e tin g of th e A m e ric a n C h e m ic a l S o c ie ty , N e w Y o r k , N . Y -, A p ril 22 to 26, 1935.

of stainless steels, and these mixtures require great care in han­

dling and in disposing of them afterwards.

The new method was worked out in connection with a study of the changes induced in stainless steels by welding. The stain­

less steel is etched electrolytically in oxalic acid (10 grams dis­

solved in 100 milliliters of water), the specimen being the anode and a piece of platinum the cathode. Current is supplied from four dry cells in series or from a 6-volt storage battery. The carbides are revealed in from 15 to 30 seconds’ etching time, while an additional 30 to 45 seconds will reveal also the grain boundaries of the “ 18-8” (18 per cent chromium, 8 per cent nickel) type of stainless steel. The solution is relatively rapid in etching action and does not stain the specimen.

Catalytic and Induced Reactions in M icrochemistry

I. M . K O LTH O FF AND R. S. LIVINGSTON, U niversity o f M in n e so ta , M inneapolis, M in n .

A

LTHO U G H catalytic and induced r e a c t i o n s are widely used in th e detec­

tion and q u antitative estim a­

tion o f c e r t a i n ions or com­

pounds, n o t m uch theoretical w o rk h a s been done on the mechanism of m ost of these re­

actions. I t is rath e r deplorable th a t m ost of our knowledge in this field is empirical. If th e

theory underlying catalytic and induced reactions were known more explicitly, it m ight be expected th a t a system atic applica­

tion of th e theoretical fundam entals would result in th e dis­

covery of m any useful reactions for the qualitative detection and quan titativ e estim ation of m icroquantities of substances.

Homogeneous catalysis of oxidation-reduction reactions occurs when th e catalyst can exist in an oxidized and a re­

duced form and when these forms of th e catalyst are capable of reacting rapidly w ith th e reducing and oxidizing agents, respectively. A simple and well-known example of this type of reaction is th e catalysis by th e iodine-iodide couple of the oxidation of thiosulfate ion by hydrogen peroxide in slightly acid solution. T he kinetics and stoichiom etry of this reac­

tion m ay be summarized by th e following chemical equations:

T h e general theory o f catalysis an d in d u c ­ tio n in hom ogeneous system s is discussed.

In d u ce d an d catalyzed p rec ip ita tio n s arc m e n tio n e d briefly, followed by a general d iscussion of a n a ly tic a l a p p licatio n s. F i­

nally, th e c a ta ly tic a n d in d u cin g effects of silver a n d m erc u ry a n d som e new tests are d escrib ed .

h 2o 2 + i - - * i o - + h 2o IO - + H + ? iH IO

h i o + i - + h + ^ i 2 + h 2o Is- + 2S,0 3- — — s,0 r + 31- H20 2 + 2SiOj- + 2H+ = S ,0t-

(1, rate determining) (2, rapid, reversible) (3, rapid, reversible) (4, rapid, reversible) (5, rapid, probably complex) + 2H20 (6, stoichiometric) E quation 6, which represents th e stoichiometric reaction, is the sum of th e five preceding equations which represent the reaction steps. A lthough the specific reaction ra te of reac­

tion step 1 is very m uch smaller th a n th a t of reaction step 5, th e steady-state concentration of Is- is under ordinary con­

ditions so small th a t th e absolute rates of reactions 1 and 5 are equal. A ny one of a num ber of similar processes would serve equally well to illustrate this ty p e of catalysis. T ypi­

cal examples are th e decomposition of hydrogen peroxide catalyzed by th e iodine-iodide (1), the bromine-bromide (5), or th e chlorine-chloride (22) couples, and th e oxidation of chromic to dichrom ate ion or of ammonium ion to nitrogen (24) by peroxysulfate ion catalyzed by th e trivalent-m ono- valent silver couple. Acid-base catalysis has n o t been men­

tioned in th e foregoing discussion, only because it was felt th a t a discussion of th is phenomenon would n o t contribute any­

thing useful to the study of catalysis in analytical chemistry.

Of course (generalized) acid-base catalysis as well as kinetic salt and solvent effects (7) play im portant roles in determ in­

ing th e ra te of oxidation-reduction reactions.

Efficient catalysts for a given reaction can be selected (with­

o ut direct trial) whenever th e rates of th e reaction steps are known. F or example, in th e case ju st cited it is well known th a t th e ra te of oxidation of thiosulfate ion by iodine is ex­

trem ely rapid and th a t hydrogen peroxide oxidizes iodide ion more rapidly than it oxidizes thiosulfate ion. On th e basis of this evidence, we could predict w ith certainty th a t the io- dine-iodide couple would act as an efficient catalyst for the

oxidation of thiosulfate by hy­

drogen peroxide. On the other hand, we could predict th a t th e chlorine-chloride pair would n o t be an efficient catalyst for this reaction, since the ra te of oxida­

tion of chloride ion by hydrogen peroxide is known to be slow.

U nfortunately, such inform ation about th e rates of th e reaction steps involved is commonly not available and a consideration of th e free energies of the prob­

able reaction steps is th e only system atic guide which we can use in selecting catalysts. While this m ethod does not enable one to predict th a t any possible catalytic pair will be an efficient catalyst for a given reaction, it does greatly simplify the prob­

lem by excluding m any substances which m ight otherwise b e considered as possible catalysts.

As an example of this m ethod, let us consider th e oxidation of arsenious acid by eerie ion in an acid solution. Since th e free energy of a reaction is the algebraic sum of th e free ener­

gies of its constituent half-cell reactions, th e free energy d a ta m ay be conveniently summarized by plotting th e half-cell potentials (4) of reactants and possible catalysts against p H (Figure 1). I t should be emphasized th a t this plot is n o t intended to imply th a t any electrochemical m echanism of catalysis exists, it is merely a convenient m ethod of repre­

senting free energy or equilibrium data. In preparing th e plot no attem p t has been m ade to allow’ for secondary effects of pH —i. e., th e electrom otive force of the C e++++, C e++ +

C o '" +

B r O ; + 3 H i 0 * { B r e

Mn”

C r , 0 ; 7 H j , O ^ C r

H B r O +

JOj /

T !" i

/ —

__

Brj t 2 2 Br HIO * H i H eO +1 / H*

F e ’ " t — H \ F t "

H jA s O 4 1 f y - f y O * H jA sO s

p H

Fig u r e 1

half-cell a t pH = 1 is n o t th e e. m. f. which would be obtained in a half-cell prepared w ith equal am ounts of cerous and eerie salts dissolved in 0.1 N acid, b u t is th e potential which th e half-cell would have if th e activities of th e eerie and ce­

rous ions were equal.

209

210

When the half-cell potential of the catalytic pair lies be­

tween the half-cell potentials of the compounds taking part in the main (stoichiometric) reaction, the free energy of each of the two compensating catalytic reaction steps—steps 2 and 5 in the first case considered—will be negative, and th e pair in question is a possible catalyst. All oxidation-reduction couples which do not satisfy this condition cannot act as catalysts for the given reactions. For the eerie arsenite re­

action a number of catalytic couples satisfy this condition.

Of these, only compounds of iodine (17) and bromine are found to catalyze the reaction measurably, and th e effect of bromine is too small to be of any practical value. T he dia­

gram indicates th a t the iodine-iodide pair will probably not be effective, but th a t either the hypoiodous-iodide or th e io- date-iodine couple should be capable of acting as an efficient catalyst. I t is very probable th a t the hypoiodous-iodide pair is the active catalyst, since it is well established th a t hypoiodous acid is interm ediate in the oxidation of arsenite by triiodide ion. While the diagram does include as possi­

bilities a number of compounds which are not efficient cata­

lysts, it definitely excludes such, otherwise probable, couples as the manganic-manganous and eobaltic-cobaltous. The method is of greater practical value when the free energy of the main reaction has a smaller (negative) value—i. e., when the potentials of the corresponding half-cells are n o t so widely separated.

In d uccd R eactions

In some cases th e rate of an oxidation-reduction reaction is greatly increased when one of the reactants is simultaneously oxidizing or reducing some other substance. Such reactions are called induced or coupled reactions. The simultaneous oxidation of manganous ion and arsenious acid by chrom ate ion,

C rO r + HsASO, + Mn + + + CH+ =

H,AsO, + M n+++ + C r+++ + 3HsO is an example of a simple induced reaction. In th e absence of arsenious acid th e oxidation of manganous ion by chromate ion is extremely slow. B u t in the presence of arsenious oxide, and under favorable conditions, one mole (I equivalent) of manganous ion is oxidized for each mole (2 equivalents) of arsenious acid oxidized. This corresponds to a maximum induction factor—i. e., the ratio of the equivalents of th e in­

duced oxidation to the equivalents of th e prim ary oxidation—

of one-half. A possible, although by no means established mechanism of this process m ay be represented by the follow­

ing equations:

CrO<" + HjAsOj—► HjAsO< + CrO»” (7, relatively rapid) 2CrO," + HjAsO, + 10H+ — — H ,A s O , + 2Cr+++ + 5H ,0

(8, slow, probably complex) CrO," + Mn++ + 6H + — — M q+++ + C r+++ + 3HsO

(9, rapid, probably complex) The sum of Equation 8 and twice E quation 7 gives the stoichiometric equation for the prim ary reaction.

2 C rO r + 3HjAsOj 4- 10H+ = 3HjAsO, + 2Cr+++ + 5HsO (10, stoichiometric) When the reaction step represented by E quation 9 occurs very much more rapidly th a n th a t represented by E quation 8, an induction factor of 0.50 is realized and th e total stoichio­

m etric reaction is represented by E quation 11.

CrO, “ + HjAsOj + Mn + + + 6H + =

HjAsOi + Mn + f+ + Cr +++ + 3H20 (11, stoichiometric)

Tn m any of the practically im portant examples of this type of reaction, the oxidation of a reducing agent by atm ospheric oxygen is greatly accelerated by its sim ultaneous oxidation by some oxidizing reagents. T he oxidation of stannous chloride by dichrom ate in the presence of air is a well-known example of this type of induced reaction. T he value of the induction factor increases as the ratio of the concentration of dissolved oxygen to the concentration of the prim ary oxidant is increased. In practice this ratio depends on such factors as order of mixing, rate of stirring, etc. In some cases th e induction factor is also a function of th e concentration of hy­

drogen ion and even of the concentration of th e reducing agent. If a proper choice of conditions results in a value of the induction factor much greater th a n unity, the induced reaction is said to be an example of "induced catalysis” (6).

If on the other hand the induction factor cannot be m ade to exceed unity (or some other small num ber), th e reaction is considered to be an example of “ simple coupling.” For all practical purposes, reactions of th e “ induced catalysis” type are of greater im portance.

A possible mechanism for reactions of this type is catalysis (of the reduction of oxygen) due to a catalytic couple, one member of which is an interm ediate in the prim ary reaction.

When th e oxidation by oxygen is a chain reaction, “ induced catalysis” m ay be the result of th e starting of reaction chains by an interm ediate of the prim ary reaction. T his la tte r mechanism has been clearly dem onstrated for such reactions as the atmospheric oxidation of sulfite, induced b y its prim ary oxidation w ith hydrogen peroxide. F or this special class; th e induction factor will be greatly decreased by th e presence of a suitable inhibitor (3). In some cases even m icroquantities of an inhibitor produce a m arked decrease in the reaction rate.

This suggests th a t the inhibiting effect of a substance could be used to determ ine its concentration michrochemically.

U nfortunately, th e inhibiting effect is seldom very specific, which greatly reduces th e general utility of th e m ethod.

However, it m ight be used to determ ine the concentration of an inhibitor in a solution which was known to be free of all substances which could act either as an inhibitor or as an in­

ducing agent for the reaction.

In d u c e d a n d C atalyzed P re c ip ita tio n s

The theory underlying induced and catalyzed precipitations is different from induced and catalyzed reactions in homo­

geneous systems. Two different cases m ay be distinguished:

1. A constituent forms a slightly soluble crystalline com­

pound upon addition of a suitable reagent. If the constitu­

ent is present in extremely small quantities (microconstituent) no precipitate is noticed, either because th e am ount is too small to be visible or because of super- or undersaturation.

If in such a case a larger am ount of another constituent (macroconstituent) is added, forming a slightly soluble com­

pound w ith th e same reagent, th e m icroconstituent m ay be co-precipitated. Especially if th e micro- and macrocompo­

nents form mixed crystals, th e enrichm ent of the microcom­

ponent in th e precipitate m ay be very pronounced. T hus a very dilute solution of lead does n o t yield a precipitate upon addition of sulfuric acid. If barium is added to th e lead solution, mixed crystals of barium and lead sulfate are pre­

cipitated, th e la tte r containing all th e lead originally present in the solution.

D irect application of such “ induced” precipitations to microdetection can be m ade when th e microcomponent gives a colored precipitate w ith th e reagent whereas th e macro­

component which is added yields a colorless precipitate. F or example, nickel mercuric thiocyanate, which has a green- yellowish color, is precipitated by an alkali mercuric thio­

cyanate solution from relatively concentrated solutions

JULY 15, 1935 ANALYTICAL EDITION 211 only. However, when zinc is added to the solution the white

crystals of zinc mercuric thiocyanate are colored green if nickel is present. K orenm an (18) makes use of the same prin­

ciple for th e detection of cobalt. In the presence of small am ounts of cobalt the zinc mercuric thiocyanate has a blue color. M ontequi (25) found th a t copper mercuric thio­

cyanate, which normally has a green color, yields a violet precipitate when precipitated together w ith zinc. T he re­

action is applied as a sensitive m ethod for th e detection of copper.

2. H e t e r o g e n e o u s C a t a l y s i s . I t is beyond the scope of this paper to discuss th e theory of heterogeneous catalysis.

This has m any analytical applications b u t th e exact mecha­

nism involved in m ost of these reactions has not been investi­

gated yet. U pon treatm en t of various m etal solutions with suitable reducing agents no m etal is separated, although the reducing action of th e agent is great enough to cause reduction to th e metallic state. An alkaline stannite solution reduces th e bism uth salts to metallic bism uth (27). Use of this re­

action is made in the sensitive detection of bism uth. Lead salts are slowly reduced b y alkaline stannite, this reduction being strongly accelerated by traces of bism uth. By adding some lead salt to th e solution th e reaction for bism uth w ith alkaline stannite solution can be m ade 250 tim es more sensi­

tive (18). Various examples of induced reductions involving th e form ation of precipitates are given by Feigl (8). T he catalytic effect of m ercury in th e reduction of arsenic by stannous chloride or hypophosphite reagent is m entioned in th e practical p a rt of this paper.

A n aly tical A pplications

A substance is transform ed into a reaction product which is readily detected. If the speed of transform ation is slow, a suitable catalyst is added. T hus manganese is oxidized to perm anganate by potassium persulfate in the presence of silver as a catalyst.

M ore general use is m ade of the catalytic and inducing properties of substances, for the qualitative detection and q u an tita tiv e estim ation of th e catalyst.

Care should be observed in th e interpretation of th e results.

N either a positive nor a negative result as a rule is entirely conclusive regarding the presence or absence of a certain constituent (catalyst), for th e following reasons:

1. The specificity of th e catalytic or inducing action of the substance to be determ ined or detected m ust be considered.

From the considerations presented in th e theoretical p a rt of th is paper it m ay be inferred th a t in oxidation-reduction re­

actions various oxidizing or reducing substances, whose half­

cell potential is interm ediate between those of the two slowly reacting systems, m ay exert a catalytic effect. In m any cases these changes in free energy are n o t known exactly. There­

fore, after it has been found th a t a particular substance ex­

erts a catalytic effect, a great num ber of substances (which m ight possibly serve as catalysts) should be tested also, in order to find how specific th e catalytic effect is. E ven if it lias been found in an empirical w ay th a t th e catalytic effect is quite specific for a certain reaction, it is n o t permissible to conclude the presence of this particular catalyst if a positive catalytic effect has been observed. T he necessity for cau­

tious interpretation m ay be inferred from th e following ex­

am ple: I t is m entioned b y Feigl th a t traces of silver ion cata­

lyze the reduction of tri- and te trav alen t manganese in a hydrochloric acid solution. In testing the specific character of this te st for silver th e authors found th a t palladium exerts a similar effect, th e reaction being even more sensitive for palladium th a n for silver.

2. T he generality of the catalytic or inducing action m ust be considered. A fter it has been found th a t a substance exerts a catalytic effect, the question arises as to w hether

general use of this effect can be made for the detection and determ ination of the catalyst. I t should n o t be overlooked th a t other substances present m ay make th e catalyst ineffec­

tive. For example, silver and manganese can be detected by making use of the catalytic effect of silver upon th e oxidation of manganese to perm anganate by potassium persulfate in strongly acid medium. Halide ions interfere, because they either precipitate the silver or reduce the perm anganate formed. In a study of the catalytic effect of silver the authors found th a t in the presence of an excess of solid mag­

nesium oxide manganese is oxidized to perm anganate on boiling w ith persulfate in the presence of silver as a catalyst.

This effect is quite specific for silver, and traces of this element can be detected in this way (see below). However, in testing the lim itations of th is te st for silver it was found th a t cobalt and chloride make th e silver ineffective. In certain cases where two or more substances exert a similar catalytic effect i t should be possible to m ake advantageous use of the m ask­

ing effect, in order to m ake th e reaction more specific.

F or example, it was found th a t traces of iodine (or iodide, or iodate) and of osmium exert a trem endous catalytic effect upon th e reaction between eerie sulfate and arsenic trioxide in acid medium. In this case the iodide can be m ade ineffective by the addition of a small am ount of mercuric mercury.

In the quantitative estim ation of a catalyst use is m ade of th e relation between th e concentration of th e catalyst and th e ra te of th e catalyzed reaction. I t should be realized th a t quite generally indifferent electrolytes affect th e rate of a re­

action. Therefore, this relation between concentration of catalyst and reaction rate should be known for the particular m ixture in which the catalyst is to be determ ined. The difficulty as a rule can be elim inated in a practical way. The ra te of reaction is determ ined first by mixing a measured volume of th e solution in which the catalyst is to be deter­

m ined w ith a measured volume of the reacting components.

A fter th e approxim ate am ount of the catalyst is determ ined, ab o u t an equal b u t exactly known am ount is added to the same volume of th e solution originally taken, w ithout chang­

ing th e volume appreciably (additions w ith m icroburet or micropipet) and th e m easurem ent is repeated. If the ra te of reaction is proportional to the concentration of the catalyst, the am ount of th e catalyst is readily calculated from th e two sets of m easurem ents. Various modifications of this proce­

dure are possible. T he simplest procedures for measuring the ra te of reaction are found in those cases in which one of the reacting components is colored. T he tim e required for ob­

taining a colorless solution is measured. A reversal of this procedure is possible if a color develops after one of th e react­

ing components has been quantitatively oxidized or reduced.

In other cases the am ount of reaction p roduct formed is meas­

ured quantitatively. The catalytic effect of copper in th e oxidation of cysteine to cystine and th e subsequent m easure­

m ent of the oxygen evolved in a given tim e was used b y W ar­

burg (28) for the determ ination of m icroquantities of copper in blood and was applied to m ilk by Zondek and Bondm ann (29). G reat care, however, should be observed, since rela­

tively large and variable readings are obtained in blanks (2).

P ra c tic a l A pplications

Since th e catalytic or inducing effect is often exerted by extremely small traces of a substance, it is possible to m ake use of th e catalysts for th e microdetection and estim ation of th e particular substance. I t is beyond th e scope of this paper to give an exhaustive treatm en t of all catalytic and induced reactions which find application in qualitative and q u an tita­

tive microanalysis. Ajs examples, th e catalytic and inducing effects of silver and mercuric m ercury are discussed below and some new reactions are described.

C atalysis by Silver

1. The catalytic effect of silver ions in oxidation reactions is to be attributed to the interm ediate formation of a higher oxidation state, probably of trivalent silver ions. The latter have a high oxidation potential and are not stable as such in aqueous medium. The catalytic effect of silver ions in the oxidation of manganese to permanganate, of trivalent chro­

mium to chromate, and of trivalent cerium to eerie cerium in strongly acid medium by persulfate has been known for a long time. Use of it was made by M arshall (23) in th e de­

tection of traces of manganese. To the authors’ knowledge the reaction has never been used for the detection of silver, although it was found to be highly sensitive.

P r o c e d u r e . One milliliter of a manganous sulfate solution containing 0.1 mg. of manganese is diluted to 5 ml. with 4 N sulfuric acid and 1 ml. of the solution to be tested for silver is added. About 0.2 to 0.4 gram of potassium persulfate is then added and the tube is placed in a ooiling water bath. In the absence of silver the solution remains colorless, even after 5 minutes of heating. In the presence of 0.05 y ( = 0.00005 mg.) of silver a distinct violet color appeared after 2 minutes of heat­

ing. The test is therefore sensitive to one part of silver in 20,000,000 parts of solution when 1 ml. of the unknown is tested in the above way.

The reaction is specific for silver. Osmium tetroxide, auric gold, palladium, cobalt, copper, mercury, and various other cations did not catalyze the reaction.

Halide ions interfere. Even traces of chloride in the solution prevent the formation of permanganate or make the reaction for silver much less sensitive.

I t was found in this work th a t silver n ot only catalyzes oxi­

dations with persulfate in strongly acid medium, b u t also in weakly acid and in alkaline medium. Thus manganese is oxidized to perm anganate in sodium hydroxide, or sodium carbonate medium or in the presence of excess magnesium oxide. Silver also catalyzes the oxidation of lead to lead per­

oxide by persulfate in neutral or alkaline medium. Five milliliters of 0.1 per cent lead nitrate solution were treated with 5 ml. of 1 N sodium acetate and divided into two parts.

One drop of 0.1 per cent silver nitrate was added to one p art and 0.5 gram of potassium persulfate to both. T he tubes were placed in a boiling w ater bath. A reddish brown colloi­

dal precipitate of lead peroxide was formed in th e presence of silver, whereas th e blank remained clear, except for a slight white precipitate on cooling. This te st for lead is not very sensitive and of little analytical significance, since m any ions interfere with the silver catalysis. On the other hand the oxidation of manganese to perm anganate in alkaline medium in th e presence of silver as a catalyst is of analytical significance.

D e t e c t i o n o f M a n g a n e s e i n W e a k l y A l k a l i n e M e d i u m .

Fifty milligrams of magnesium oxide (manganese-free), 1 drop of 0.1 per cent silver nitrate, and 0.2 to 0.3 gram of potassium per­

sulfate are added to 10 ml. of the solution to be tested for man­

ganese. The tube is placed in a boiling water bath for 3 to 4 minutes, then removed and allowed to settle. ^A red-violet coloration in the supernatant liquid shows the presence of man­

ganese. Sensitivity: 0.3 mg. manganese per liter gave a dis- t inct pink color. It should be mentioned that the magnesium oxide should be tested in the same way for manganese. It was found that c. p. products of magnesium oxide contained traces of manganese. With large amounts of manganese (100 mg. per liter) a heavy precipitate of manganese dioxide is formed which masks the silver catalysis. The solution to be tested should not contain more than 10 mg. of manganese per liter. The reaction is specific for manganese, although cobalt and nickel interfere, giving black precipitates. The presence of 0.05 mg. of nickel did not affect the sens tivity of the reaction, but the same amount of cobalt decreased the sensitivity markedly. Chlorides interfere.

By working in strongly alkaline medium the interference by chlorides is eliminated.

D e t e c t i o n o f M a n g a n e s e i n S t r o n g l y A l k a l i n e M e d i u m i n P r e s e n c e o f C h l o r i d e . T o 10 ml. of solution are added 1 drop of 0.1 per cent silver nitrate, 0.5 to 1 ml. of 4 N sodium hydroxide, and 0.2 to 0.4 gram of potassium persulfate. The

mixture is heated to boiling for 30 seconds to 1 minute and al­

lowed to settle. A pink coloration of the supernatant liquid indicates the presence of manganese. The test is sensitive to 5 7 of manganese, corresponding to 0.5 mg. of manganese per liter. Cobalt interferes, but small amounts of nickel and coppcr may be present.

D e t e c t i o n o f S i l v e r i n W e a k l y A l k a l i n e M e d i u m .

To 10 ml. of the solution to be tested arc added 1 ml. of a man­

ganese chloride solution containing 100 mg. of manganese per liter, 50 mg. of magnesium oxide, and 0.2 to 0.3 gram of potas­

sium persulfate. The tube is heated in a boiling water bath for 3 to 4 minutes, removed, and allowed to settle. ^A red-violet color indicates the presence of silver. The test is sensitive to 3 7 of silver in 10 ml., corresponding to a concentration of 0.3 mg. of silver per liter.

The reaction is specific for silver. Nickel, cobalt, and chlo­

ride interfere. In strongly alkaline medium chloride does not interfere, but the reaction becomes slightly less sensitive.

D e t e c t i o n o f S i l v e r i n S t r o n g l y A l k a l i n e M e d i u m i n P r e s e n c e o f C h l o r i d e . T o 10 ml. of the solution arc added 0.2 ml. of manganous sulfate solution containing 0.1 gram of manganese per liter, 1 ml. of 4 N sodium hydroxide, and 0.2 to 0.4 gram of potassium persulfate. The mixture is boiled for 30 seconds to 1 minute and allowed to cool. ^A blank without silver is used for comparison. ^A pink coloration shows the presence of silver. The test is sensitive to 5 7 of silver, corresponding to 0.5 mg. of silver per liter.

Copper catalyzes the oxidation, but the reaction is not sensi­

tive for copper.

Palladium inhibits the silver catalysis; gold has a similar effect but not as pronounced as palladium. Cobalt interferes, but small amounts of nickel may be present.

2. .Silver chloride is m ore or less soluble in stronger chlo­

ride solutions w ith the form ation of a complex AgCli- ion.

I t was found by Lang (20) th a t brown solutions of manganic manganese (M nm and M nIV) are fairly stable in 2.5 N hydro­

chloric acid. Addition of a trace of silver catalyzes th e reac­

tion between th e higher-valent manganese and chloride and th e solution becomes colorless w ithin a short tim e. Feigl and F rankel (12) found th a t silver also catalyzes th e reaction between eerie cerium and hydrochloric acid. In using a suitable manganic chloride solution in 2.5 N hydrochloric acid as a reagent they could detect on a spot plate 0.4 7 of silver (1 drop of a solution containing 8 mg. of silver per liter).

T he authors found a sensitivity of 1 7 silver, b u t in testing the specific character of the reaction noticed th a t palladium has a stronger catalytic effect than silver. In a spot plate 0.2 7 of palladium can be detected. W ith a suitable m ixture of eerie n itra te and hydrochloric acid Feigl and F rankel could detect 0.05 7 of silver. However, the authors found th a t th e sensitivity was less than 1 7 . In addition it was found th a t palladium behaves like silver; the test, therefore, is n o t specific. Thallous thallium interfered badly w ith th e test, a yellow precipitate and a rapid decoloration being obtained.

3. Silver salts exert an inducing effect upon th e reduction of mercuric chloride b y phenylhydrazine (10). In the ab­

sence of silver the mercuric chloride is reduced to calom el and then slowly to metallic m ercury. In the presence of sil­

ver the black m ercury separates instantaneously. H ah n (14) found th a t traces of silver accelerate reduction of mercuric chloride to calomel by hypophosphite in a well-buffered solu­

tion and makes use of this fact in a sensitive detection of silver.

C atalysis by M ercury

1. K ing and Brown (16) found th a t mercuric m ercury strongly catalyzes th e reduction of arsenite or arsenate in hydrochloric acid m edium to brown arsenic by stannous chloride. T he addition of enough mercuric chloride to m ake its concentration 0.00001 M before th e addition of stannous chloride, hastens the appearance of th e coloration, increases the sensitivity of B ettendorf’s test 10- to 100-fold and enables th e test to be m ade in a lower concentration of hydrochloric acid. T he authors were able to confirm th e catalytic effect of mercury upon th e speed of reduction of th e arsenic, b u t