Industrial and Engineering Chemistry : analytical edition, Vol. 7, No. 1

A n a l y t i c a l E d i t i o n V o l .

7 , N o . I

J A N U A R Y

15, 1 9 3 5

m

I

I n d u s t r i a l

A N D E N G I N E E R I N G

C h e m i s t r y

VOL. 27, CONSECUTIVE NO. 3

Pu b l i s h e d b y t h e Am e r i c a n Ch e m i c a l So c i e t y Ha r r i s o n E . Ho w e, Ed i t o r

Pu b l i c a t i o n Of f i c e: E a s to n , P a .

Ed i t o r i a l Of f i c e:

R o o m 706, M ills B u ild in g , W a sh in g to n , D . C . Te l e p h o n e: N a tio n a l 0S48 Ca b l e: Jie c h e m ( W a s h in g to n )

Ad v e r t i s i n g De p a r t m e n t: 332 W e st 4 2 n d S t.,

N ew Y o rk , N . Y . Te l e p h o n e: B r y a n t 9 -4 4 3 0

iW

C O N T E N T S P.

17,500 Copies of This Issue Printed Statement of Policy and N ote to A u th o r s ... 1

Microdetermination of L e a d ...

. Merle Randall and Marian N . Sarquis 2

Determination of Selenium . II. C. Dudley and II. G. Byers 3 An Inexpensive Vacuum Regulator . . . G .W . McConnell 4 Accelerated Tests of Paint Finishes on Aluminum . . . .

...Junius D. Edwards and Robert I. Wray 5 A Rapid Method for Dialyzing Large Quantities of Protein

S olu tion ... Gilbert C. II. Slone 8 Determination of Methane by Catalytic Oxidation . . . .

... I. F. Walker and B. E. Christensen 9 Molecular Weight of Cracked D i s t i l l a t e s ...

... Ogden FitzSimons and E. W. Thiele 11 Colorimetric Determination of Small Quantities of Chlorides

in W a t e r s ...II. B. Riffenburg I t Determination of Minute Amounts of Copper in Milk . .

Lillian W. Conn, Arnold II. Johnson, II. A . Trebler, and V. Karpenko 15 Determination of Fluorine in Drinking W a t e r ...

...II. V. Smith 23 Nomogram for Centrifugal F o r c e ...Herbert Shapiro 25 Critical Study of Cacotlieline for Detection of Tin . . . .

I. Laird Newell, Joseph B. Ficklen, and Lewis S. Maxfield 26 Spectropholometric Determination of Manganese in Steel .

...J. P. Mehlig 27 Determination of Free Silica . . II. L. Ross and F. W. Sehl 30 Determination o f Minute Amounts of Lead in Biological

M a te r ia ls ...E. S. Wilkins, Jr., C. E. Willoughby, E. 0 . Kraemer, and F. L. Smith, 2nd 33 Selenite-Phosphate Method for Determining Zirconium in

Ores . . . . Stephen G. Simpson with Walter C. Schumb 36 Confining Licjuids for Gas A n a ly sis ...

...Kenneth A. Kobe and John S. Williams 37 Determination of Chloride...

...lohn R. Caldwell and Harvey V. Moyer 38 Determination of P erch lorates... M. L. Nichols 39 Indicator Properties of Dinilroaniline Azo DvestufTs . . .

... Henry Wenker 40 Baume-Purity-Moisture Tables for Corn S ir u p ...

...W; R. Felzer and J. W. Evans 41 Determination of Available Chlorine in Hypochlorite Solu­

tions by Direct Titration with Sodium Thiosulfate . . . ... Virgil A . Willson 44

Precise Determination of Calcium, Magnesium, and Phos­

phorus in Evaporated M i l k ...

...C. II. Whitnah and II. L. Anderson Device for Holding Electrodes during Electrometric Titra- , t i o n s ... Milton L. Herzog

•New Method for Measuring Corrosion of M e t a l s ...

... W. R. van W ijk Making Clean Liquid Sodium Potassium A llo y ...

...I. F. Birmingham, Jr.

Oxidation of Hydrazine. IX ...

...A . G. iioupt, K . IF. Sherk, and A . W. Browne Standardization of Potassium D ich rom ate...

...Hobart II. Willard and Philena Young Estimation of Unsaturation in Aliphatic Hydrocarbons by Bromide-Bromate T it r a t io n ...

... Samuel P. Mulliken and Reginald L. Wakeman A New Laboratory Machine for Evaluating Breakdown Characteristics of Rubber C o m p o u n d s ...

... R. S. Itavenhill and W. B. MacBride Wash Bottle for Quantitative Work . . . Edwin J . deBeer Photronic Photoelectric Turbidimeter for Determining

Hydrocyanic Acid in S o lu tio n s...

... E .T . Bartholomew and E. C. Raby Apparatus for Control of Pressure in D istilla tio n ...

...G. W. Jacobs Application of the Glass Electrode to Dairy Products . . .

... L. R. Parks and C. R. Barnes Routine High-Vacuum Distillation of O i l s ...

. . . ... K . At. Watson and Charles Wirlh, II I Apparatus for Extraction o f Solids by Upward Flow of S o lv e n t ... F. E. Holmes Bapid Method for Making Standard Solutions of Specified

N orm ality... Otto Johnson A Ilot-W ater F u n n e l...John R. Caldwell Rapid Method for Quantitative Determination of Carbon in

Organic Compounds . C. B. Pollard and W. T. Forsee, Jr.

Effect of Asparagine on the Reducing Power of Levulose . . . . lone Weber, Edna J. Posen, and Nedda G. Ceboolsky Roulette Comparator for Colorimetric A n a l y s i s ...

... John II. Yoe and Thomas B. Crumpler Determination of the Phosphorus Fractions in Blood Serum

... R. R. Roepke 46 47 48 53 54 57

59

60 67

68

70 71 72 75 76 76 77 77 78 78

S u b acriD tio n to n o n m e m b e rs , I n d u s t r i a l a n d E n g i n e e r i n g C h e m i b t r t , * 7 .5 0 p e r y e a r. F o re ig n p o s ta g e $2 .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

\ m e r ic a n d o m e s tic r a te s . T o C a n a d a . " 0 c e n ts . A n a l y t i c a l E d i t i o n o n ly , * 2 .0 0 p e r y e a r, sin g le co p ies 7 5 c e n ts , to m e m b e rs 6 0 c e n ts . F o re ig n p o s ta g e ,

■in „ „ ( « ■ C a n a d a 10 c e n ts N e w s E d i t i o n o n ly , S I .60 p e r y e a r. F o re ig n p o s ta g e , 60 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 , c h a n g e s of a d d r e s s , a n d c la im ” t o l o s ? c o p i i s h o u fd b e re fe rre d to C h a r i « 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 sh in g to n , D . C . T h e C o u n c i 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 su c h claim 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 issu e, a n d n o c la im s w ill b e allo w e d fo r issu e s lo s t as a r e s u lt of in s u ffic ie n t n o tic e of c h a n g e of a d d re 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 issin g fro m files c a n n o t b e a c c e p te d a s th e re a s o n f o r h o n o r in g a c laim . If c h a n g e of a d d re s s im p lie s a c h a n g e o f p o s itio n , p le ase in d ic a te its n a tu r e .

The Am e r i c a n Ch e m i c a l So c i e t y a ls o publishes the Journal of the American Chemical Society a n d Chemical Abstracts.

4 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 7, No. 1

NEW DESIGN

P y R E X

PREVENTS /

CHIPPING /

C H IP P IN G is prevented by special reinforced rims on this new design of "PYR EX ” P etri Dish.

C a ta lo g Ite m N o . 1 3 4 5 Quantity Net

per Price N et Price Per Package

Code W ord Size trim. Package Each 1 Pkg. 25 Pigs. jo Pigs. 100 Pigs.

B E D O Z 1 0 0 x 10 (C o m p le te ) 7 2 $ .3 8 $2 4 .6 2 $2 3 .3 9 $ 2 2 .1 6 $ 2 0 .9 3 B E D IM i o o x1 5 (C o m p le te ) 7 2 .3 8 2 4 .6 2 2 3 .3 9 2 2 .1 6 2 0 .9 3

“P Y R E X ” is a trade-m ark anti indicates m anufacture by

C O R N I N G G L A S S W O R K S • C O R N I N G , N E W Y O R K

PyREXbrandLABORATORY GLASSWARE

B E S A F E See that this trade-m ari is reproduced on every piece of apparatus you buy!

PYREX

p a t

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 O ffice, 2 0 th & N o r th a m p to n S ts ., E a s to n , P a.

E n t e r e d as seco n d -c la s s m a tte r a t th e P o st-O ffice a t E a s to n , Pa_, u n d e r th e a c t of M a r c h 3 , 1S79, a s 42 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 lv o n th e 1 5 th . A c c e p ta 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 ro 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 ly 13, 1918.

C h i p p in g a r o u n d th e e d g e s is a c o m m o n c a u s e o f P e t r i d is h b r e a k a g e . R im s a r e c o n s ta n tly e x p o s e d to c h i p p in g in tr a n s p o r ta tio n , s to r a g e , a n d in a c tu a l se rv ic e . T h e n e w “ P Y R E X ” P e tr i d is h is d e s ig n e d to r e s is t b r e a k a g e . A s t r o n g ,r e i n f o r c i n g b e a d o f g la s s a r o u n d th e rim s s tr e n g t h e n s th e d is h a t its w e a k e s t p o i n t a n d e n a b le s it to w ith s ta n d r e p e a te d m e c h a n ic a l s h o c k s w ith little d a n g e r o f c h ip p in g .

T h e m a n y o th e r a d v a n ta g e s o f “ P Y R E X ” P e t r i D is h e s are:

C h e m ic a l s ta b ility w h ic h p e r m its re p ea te d s te riliz a tio n by h o t a i r o r ste am p r e s s u r e w ith o u t c lo u d in g . . . H e a t re s is ta n c e w h ic h re d u c e s b r e a k a g e s d u r in g s te riliz a tio n . . . T r a n s p a re n c y b e tte r th a n fine p la te g la s s — im p r o v in g v is io n a n d fo c u s in g . . . H a r d e r th a n o r d in a r y g la ss . . . S u rfa c e s r e m a in u n m a rr e d a fte r l o n g se rv ic e . . . T o p s a n d b o tto m s a r e in te r c h a n g e a b le .

N E W L O W P R I C E

“ P Y R E X ” P e tr i D is h e s th a t f o rm e rly s o ld a t 5 0 c p e r p a ir a re n o w p ric e d at 3 8 c, w ith c o r r e s p o n d i n g r e d u c tio n s f o r q u a n titie s , as fo llo w s:

! J. &, J. F R I C

« - • -

January 15, 1935 A N A L Y T I C A L E D I T I O N 5

P O L A R IM E T E R S ^ S A C C H A R IM E T E R S

The unvarying accuracy of the J. & J. Fri£ polarimetric instruments is guaranteed by the manufac­

turers and ourselves as distributors, and assurée! by the testimony of the most exacting laboratories in a ll parts of the world.

This is one of fourteen polarimetric instruments. It is an ultra precise saccharimeter manufac­

tured according to suggestions by Dr. Frederick Bates o f the N ational Bureau o f Standards, and is the standard instrument used at ports of entry of the U. S. Customs Department. It employs a Lippich polarizer w ith variable half shadow angle for adjustment of brightness.

Ask for the new illustrated catalog giving complete descriptions and specifications for all available models.

Sole D istributors for United States

S i H R G E R T

E . H . S H R G E f l T &• CO. C H I C R G O

L A B O R A T O R Y S U P P L I E S

1

R£TE5 T£t>

I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 7, No. 1

P L A C I N G C A L I B R A T I O N L I N E O N A KIMBLE V O L U M E T R IC PIPETTE, a c o o r d i n a ­ tio n of s k ille d h a n d a n d p r e c is io n m a c h in e .

An .T no lime in the produclion of Kimble Exax Blue Line Glassware is the skill of human hand and brain eliminated. In certain glass-making opera­

tions the "human equation" is vitally important, and is em ployed b y Kimble to do that w hich the hand can perform better than any mechanism.

At no time does Kimble sacrifice thoroughness and accu ra cy for sp eed . E very op eration is stu d ied and planned to fabricate only the best that brains and ma­

chinery can produce. It is this careful coordination of human ingenuity and mechanical perfection that places Kim ble S cientific G lassw are w h ere it is to d a y . . . the Standard for "Assured Accuracy" w herever labo­

ratory research, analysis, test and control work goes on.

Stocked by lea d in g Laboratory S u p p ly H ouses throughout the U n ite d S ta te s a n d C anada.

KIMBLE

<c~->

GLASS C O M P A N Y

V I N E L A N D , N E W J E R S E Y .

N E W Y O R K • P H IL A D E L P H IA - B O S T O N ■ C H IC A G O • D E T R O IT

January 15, 1935 A N A L Y T I C A L E D I T I O N

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 MERCK L A B O R A T O R Y C H E M I C A L S

M erck Laboratory C hem icals are n o w packaged in specially-designed containers w hich offer these seven im p ortan t advantages:

1. Amber C olor Glass 2. N on-m etallic screw cap 3. W ill not corrode 4. Easy to open

5. Special liner ensures air-tight scaling 6. D ust-proof

7. Attractive appearance T h e amber co lo r glass b ottles afford m axim um p ro­

tection against lig h t and other deteriorating agents.

T h e n on -m etallic screw caps w ere designed to over­

co m e corrosion resulting from unfavorable atm os­

pheric co n d itio n s and from vapors present in the laboratory. T h e large facets o n th e side o f the cap m ake it easy to op en the b ottle.

A special liner, im pervious to the chem ical, e n ­ sures air-tight sealin g w h en the handy cap is replaced.

T h e cap exten d s over the lip o f the b o ttle, thus p reven tin g an accum ulation o f dust.

M erck Laboratory C hem icals in these n ew am ber glass b ottles, w ith their black caps and blue and w h ite labels, w ill add to the attractive appearance o f your laboratory or stock room .

Y o u r w h olesaler is ready to supply you.

MERCK & CO. Inc.

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

RAHWAY, N. J.

8 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 7, No. 1

R e a s o n a b l e ...?

W ith y o u r C h ro m e l-A lu m el co u p les, if y o u a re u sin g lead w ire o f a n y c o m p o sitio n , o th e r th a n t h a t of th e couple, y o u r te m p e r a tu re re a d in g s v e r y lik e ly a re w ro n g . . . I f th e le a d w ire differs in c o m p o sitio n w ith th e couple, i t m e a n s t h a t w h ere th e y jo in , y o u h a v e tw o m o re th e rm o ­ co u p le ju n c tio n s . W h e n h e a te d , th e y g e n e ra te E .M .F .’s o f o p p o site , b u t u n e q u a l v a lu e . T h e ir differen ce in v a lu e is w h a t c a u se s th e e rro r. O n th e jo b , o f co u rse, th e s e ju n c tio n s a re h e a te d , b y ra d ia tio n fro m th e fu rn a c e . O fte n th e y a re v e r y h o t. I f th e ju n c tio n s h a p p e n to b e a t 200° F ., it u su a lly m e a n s a n e rro r o f m o re th a n 10° a t th e

L E A D S S S C O U P L E S

m e t e r ...Y o u e lim in a te th is so u rc e of e rro r b y u sin g C h ro m e l-A lu m e l L e a d s w ith y o u r C h ro m e l-A lu m el C o u p les. T h e n , y o u jo in C h ro m e l to C h ro m e l, a n d A lu m e l to A lu m e l. W h e re th e y jo in , n o d is tu rb in g E .M .F . ’s ex ist. T h is is w h y su c h co n c e rn s a s G e n e ra l M o to rs , F o r d a n d A m e ric a n R o llin g M ill u se C h ro m e l-A lu m e l L e a d s w ith C h ro m e l-A lu m e l C o u p les. I s n ’t i t re a so n a b le t h a t y o u d e m a n d , a n d g e t, t h a t sa m e a c c u r a c y in

■your p y r o m e te r sy s te m ? T h is s u b je c t is fu lly e x p la in e d in F o ld e r G .Y . o n a b a s is o f f a c tu a l te s ts a n d figures. S e n d fo r it. H o sk in s M a n u ­ fa c tu rin g C o., D e tro it, M ic h ig a n .

a

January 15, 1935 A N A L Y T I C A L E D I T I O N 9

A L L -A U T O M A T IC BURETTES

Patented

1950 1955 1970

T he B U R E T T E S illustrated are a few taken from our line o f A ll-A utom atic Burettes (booklet showing details and prices upon request) which we consider the finest on the m arket today.

These burettes can be obtained in schellbach or resistant glass, with resistant glass reservoir bottle and with interchangeable stopcocks and interchangeable ground glass jo in ts, elim inating the use o f rubber stoppers.

T he double arm leading to the stopcock is a m eans o f strengthening the burette as well as serving the purpose for which it was intended. A bove the P R E S S U R E B U L B there is an A IR V E N T which closes autom atically when pressure is applied, and m ay be released by pressing it with the finger when the burette has been filled. T h e m ost im portant fea­

ture o f the burette is that one meniscus reading is elim inated, because o f the autom atic zero point.

T he burette is controlled by the STOPCOCK. I t is filled from the bottle and also excess solution is returned to the bottle by means o f the stopcock m aking it unnecessary to take the apparatus apart.

T he G R A D U A T IO N S on the burette are in accordance w ith Bureau o f Standards specifications and are guaranteed to be accurate.

SCIENTIFIC G L A S S A P P A R A T U S CO M PA N Y

49 Ackerm an Street Bloomfield, N e w Jersey

10 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 7, No. 1

M ICRO -CH EM ICA L BALANCES

I N O U R S T O C K F O R I M M E D I A T E S H I P M E N T

1891

BALANCE, MICRO-CHEMICAL, Starke & Kammerer. Capacity 20 grams. With adjustment for two values, i.e. 0.1 mg or 0.01 mg for each scale division. With the latter, a sensitivity of 0.001 mg is obtainable by estimation—with the exercise of some care and under proper conditions.

The rider carrier is provided with a new device which prevents the rider from dropping, and also with a magnifier to facilitate the reading of the divisions on the beam and the setting of the rider. The beam is heavily platinum plated. Case is of well-seasoned mahogany, with base plate of black polished glass, and with magnifying mirror for the pointer scale.

This is the Micro-Chemical Balance mentioned on page 21 of Pregl, "Die Quantitative Organische Microanalyse," third edition (Berlin, 1930), and on page 18 of the second English edition (Philadelphia, 1930).

1890-A . B a la n c e , M ic ro -C h e m ic a l, S ta r k e & K a m m e r e r , a s a b o v e d e s c rib e d , c o m p le te w ith s e t of p la tin u m p la te d w e ig h ts 2 0 g ra m s, six t a r e flask s, filling tu b e , s u p p ly o f s h o t, e t c ... $ 4 2 5 .0 0

C o d e W o r d . . . . ... A o lla

N O T E — T h e a b o v e B a la n c e is n o t liste d in o u r c u r r e n t c a ta lo g u e b u t h a s b e e n a d d e d to o u r s to c k a n d lis tin g b e c a u se of th e s a tis f a c tio n ex p e rie n c e d w ith i t in th e la b o r a to r ie s o f so m e m ic r o - a n a ly s ts in th e U , S.

MICRO-CHEMICAL BALANCE, Kuhlmann. A new model of the balance recommended by the late Prof. Dr. Fritz Pregl as the most satisfactory balance for the work intended. This is the balance—with some improvements— illustrated, described and recommended in his, “ Die Quantitative Organische Microanalyse,” third edition (Berlin, 1930) pp. 7-21, and on pp. 7-18 of the second English edition (Philadelphia, 1930).

Capacity 20 grams, with a sensitivity of one scale division equal 0.01 mg, permitting reading—-with care—-to 0.1 of a division or 0.001 mg. With bearings and arresting contacts of agate, counterpoised door, sensitivity adjustment for zero point, and support for absorption apparatus.

The latest model, as shown above, is furnished with case removable from base for convenient cleaning, as suggested by Emich, and a hook underneath the base with which to make ground connection for discharge of static.

The new model is also furnished with an adjustable telescopic reading device, in place of the magnifying mirror shown in illustration on page 69 of our catalogue, by means of which the index scale can be read by interpolation to 0.001 mg.

This is preferred to the concave mirror, especially by those who are markedly ametropic.

1891. M ic ro -C h e m ic a l B a la n c e , K u h lm a n n , a s above^ d e s c rib e d , n ew m o d el w ith r e m o v a b le c a se w ith h o o k u n d e r n e a th f o r d is c h a r g e of s t a t i c a n d w ith a d j u s t a b le te le sc o p ic r e a d in g d e v ic e . C o m p le te w ith s e t o f sp e c ia l w e ig h ts in ca se , six ta r e fla sk s, tw o t u b e s f o r fillin g fla sk a n d a s m a ll p a c k a g e o f s h o t ... 2 7 5 .0 0 C o d e W o r d ... A ollp

P ric e s s u b j e c t t o c h a n g e w i t h o u t n o t ic e .

ARTHUR H. THOM AS COMPANY

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

LA B O R A TO R Y A PPA RA TU S AND R EA G EN TS

W EST W ASHINGTON SQUARE P H ILA D ELPH 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

VoLUiME 7

N u m b e r 1

A N A L Y T I C A L E D I T I O N

I n d u s t r i a l

A N D E N G I N E E R I N G

C h e m i s t r y

Pu b l i s h e d b y t h e Am e r i c a n Ch e m i c a l So c i e t y Ha r r i s o n E . Ho w e, Ed i t o r

J a n u a r y

15, 1935

[POLITECHNIKI

Statement of Policy and Note to Authors

T

H E A N A LYTICAL E D IT IO N has now com­

pleted six years of service, and those responsible for it have been pleased with its reception and w ith the realization that it has afforded encourage­

m ent to those working in this special field, at the same tim e placing a unique tool in their hands. W ith the record as a guide, we have formulated plans for fur­

ther improving the edition. T o that end a special Board of Associate Editors has been approved by the Directors of the So c i e t y, and six men have accepted service. The initial terms will be those indicated, at the expiration of which associate editors will be ap­

pointed for three-year periods. The following have been appointed:

B. L. Clarke, Bell Telephone Laboratories, 1 year

T . R. Cunningham, Union Carbide and Carbon Research Laboratories, 1 year

N. PI. Furm an, Princeton University, 2 years I. M . KolthofT, U niversity of M innesota, 2 years G. E . F. Lundell, Bureau of Standards, 3 years H . H . W illard, U niversity of Michigan, 3 years

The board will assist in the formulation of policies, in the general improvement and usefulness of the publication, and will serve frequently as final referees in the critical examination of subm itted manuscripts.

Po l i c y

T he An a l y t i c a l Ed i t i o n is primarily a journal for chemists specializing in analysis. In it M ill appear articles dealing with applications of methods of chemi­

cal analysis to problems primarily in industrial and en­

gineering chemistry, though worthy papers in other fields m ay be accepted. Such articles will properly include apparatus and physical tests th at are em­

ployed by the analytical chemist— for example, x-ray, colorimetry, chemical spectroscopy, calorimetry, and the like. Articles dealing more with the fundamental or theoretical considerations o f no im m ediate appli­

cation to chemical analysis belong more properly in the Journal of the American Chemical Society.

No t e t o Au t h o r s

In the preparation o f manuscripts authors should address them selves to specialists in their particular fields, rather than to the general reader. If the article describes a new method, the author should endeavor to tell the complete story, so that the reader will not have to wait for succeeding contributions or duplicate the unpublished tests in order to find out whether he can apply the method in bis own work.

T he following is suggested as a general outline to be followed in preparing analytical methods for this edition:

1. Prelim inary statem ent or introduction, in which the need for the m ethod should be stated, brief reference to other methods or literature given, etc.

2. Experimental

Outline of proposed method

Description of apparatus and reagents Procedure

D ata

Interfering substances or conditions

Concentration range tlirough which the m ethod is applicable

Accuracy of the m ethod Precision of th e m ethod 3. Discussion and sum m ary

The author should state a t the outset w hy he thinks the paper is worth publishing. If it deals w ith a method of analysis, he should give some comparison with established methods in point o f speed, applicability, accuracy, and cost. Extensive reviews o f the litera­

ture should not be given and such references as are cited should be carefully checked. Incorrect refer­

ences are inexcusable and cast doubts on the author’s reliability. The theoretical considerations on which the m ethod is based should be clearly set forth.

In the experimental part, previously published or well-known procedures which have been followed should only be designated or references given to them.

If, however, the method is new, the data upon which it is based should be presented but in no greater de­

i

2 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 7, No. 1 tail than is necessary to prove its soundness. N ew

procedures should be clearly described, that readers can easily duplicate the work. Loose directions should be avoided, unless the author knows that no possible harm can result from the m ost liberal interpretation that can be made of such expressions as “ to the faintly acid solution,” “wash the precipitate,” “ignite,” etc.

I f new or uncommon reagents are needed, the author should state their probable cost, where they can be purchased if rare, or how they can be prepared, if not on the market.

The author should distinguish carefully between pre­

cision and accuracy. Briefly but somewhat roughly stated, accuracy is a measure of degree o f correctness;

precision is a measure of reproducibility. T he pre­

cision of a result does n ot necessarily have anything to do with its accuracy; it serves merely as a measure of the duplicability of the procedure in the hands o f a given operator. N o claim for accuracy should be made unless the author believes that he has satisfactorily established the correct result.

T he author should be frank and define the lim itations of the method. T ests dealing w ith the effects of foreign compounds should be m ade on mixtures in

which the ratios of the compounds sought to the foreign compounds are varied and simulate conditions that are likely to be encountered in practice. If the author has made no such tests, he should state that he has no knowledge of the effects of foreign substances.

I t is desirable that possible applications of methods should be stated.

A summary or prefatory abstract should acquaint the reader w ith the main points of the article. This should give concisely where possible the substances determined, nature of material to which determination is applicable, interfering substances, range o f concen­

tration to which method is applicable, whether or not a sensible constant error is involved— th at is, the ac­

curacy of the m ethod— and its precision. Either the summary or the prefatory abstract is so often used by abstractors th at the author m ay well spend consider­

able tim e in their preparation, in order to be certain that proper emphasis is given to the main features of the contribution.

Our “Suggestions to Authors” is available to those unfamiliar w ith the form of manuscript and illustra­

tions preferred b y 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.

Microdetermination of Lead

Electrolytic-Colorimetric Method

Me r l e Ba n d a l l a n d Ma r i a n N . Sa r q u i s, Chemical Laboratory, University of California, Berkeley, Calif.

I

N A study of th e solubility of lead sulfate in aqueous solutions of acetic acid it was necessary to determine accurately small am ounts, 2 to 15 mg., of lead. From 95 to 99 per cent of th e lead in solution was precipitated electrolytically as lead peroxide and the rem ainder was determ ined colorimetrically

in th e form of lead sulfide. 0.10 The solution to be ana­

lyzed was measured into an e l e c t r o l y t i c beaker (9cm.

high, 3.8 cm. diameter) and 4 ml. of nitric acid (sp. gr. 1.42), 8 drops of 3 M sulfuric acid, and enough water to make the volume 35 ml. were added.

The anode w a s a s m a l l cylinder (4.5 cm. high, 1 cm.

diameter) of fine platinum gauze, 40 mesh per inch (16 mesh per cm.) with a piece of platinum wire attached, and the cathode a spiral of platinum wire wound on a thin glass rod. The anode was secured by means of a gold-plated clamp, instead of the usual holder in which the end of a screw engages the electrode used for the cath­

ode. It was f o u n d t h a t t h e a c t i o n o f t h e screw against the electrodes caused a loss in weight of as much as 0.05 mg.

g -O.IO

I

Ï iij-0.20£

- 0 . 3 0

- 0 4 0

The solution was electrolyzed for 12 to 18 hours at approxi­

mately 10 volts with a current of 0.05 ampere. Enough water was added so that, without breaking the circuit, the cathode could be lifted from the center of the anode and placed to one side of it. The current was short-circuited through the cathode and simultaneously the anode was taken out of the solution and

r i n s e d well, first with dis­

tilled water, and second with absolute alcohol. The rinse l i q u i d s were collected in a c a s s e r o l e placed below the anode. The anode with its deposit of lead peroxide was then placed for 2 hours in an oven maintained at 180° C., after which it was allowed to c o m e t o equilibrium w i t h r e s p e c t to the temperature and moisture content of the balance case, and carefully weighed on a microchemical balance with a sensitivity of 0.005 mg. Tares were used, so thnt the rider alone was sufficient to weigh the de­

posit. The theoretical factor w a s u s e d t o calculate the amount of lead precipitated.

T he procedure followed for the c o l o r i m e t r i c d e ­ t e r m i n a t i o n was a com­

b i n a t i o n of th e m ethods e m p lo y e d b y F r a n c i s , H a r v e y , a n d Buchan (2)

-

•

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•

• •

r

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•

• • • • \ S T * .

• •

•

9 k • • •

• • •

• •

0

• • •

-fc • • • .

o * ° •

w • • • o

• •

o •

•

•

< °

° © • °o

0 O o » ° ° o 0 0 ° o° O O

o

o

o O °o o

0 o

• 0

OO o o o

o 0

_ o ° o O o

0 o

o o oo o

o 0

o

El sc trotytic alone

Electrolytic and color ¡metric o o

- ® No acetic acid added

o

2 5 0 3 .0 0 3 .5 0 4 0 0 4 .5 0 9 .0 0 9 5 0 lOOO 12.50 1 5 0 0 Millitrams of lead In sample (net to scale) Fi g u r e 1 . Er r o r i n Mi c r o d e t e r m i n a t i o n o p Le a d

January 15, 1935 A N A L Y T I C A L E D I T I O N and A llport and Skrimshire (1). The reagents and m aterials

were tested to prove the absence of lead and sulfide. The sodium sulfide solution was m ade as suggested b y Francis, H arvey, and Buchan (2).

The solution remaining in the electrolytic beaker was poured into the casserole containing the liquids used in washing the anode, and the beaker and cathode were well rinsed. The solu­

tion in the casserole was then evaporated to a volume of 10 ml.

over a steam bath. Any particles of lead peroxide which might have been present dissolved during the process. In the mean­

while, 2 ml. of 10 per cent potassium cyanide solution, 5 ml. of 6 N ammonium hydroxide, and 2 grams of ammonium acetate were

Ç

laced in each of two exactly similar tall 50-ml. Nessler cylinders, he solution in the casserole was neutralized with G N am­

monium hydroxide and transferred to one of the cylinders.

Water to the 50-ml. graduation and 3 drops of sodium sulfide solu­

tion were added. Finally, the cylinder was shaken repeatedly until the ammonium acetate was dissolved and the solution was uniform. The other cylinder was treated similarly, except that a known amount of a lead nitrate solution, containing 0.01 mg. of lead per ml., was added instead of the solution from the casserole.

After a little practice, it was easy to determine within 0.05 mg.

the number of milligrams of lead present in the unknown solu­

tion by noticing the color intensity, and this quantity of lead was added to the standard cylinder for best comparison. The solu­

tions were compared in a Leitz colorimeter.

T he colorimetric value of the lead left in solution after electrolysis was in error from 5 to 20 per cent, b u t since this value was a small addition to th e value determined elec- trolytically, th e result was a considerable lowering of the total percentage error, which w ithout the colorimetric correc­

tion was from 2 to 10 per cent.

T he m ethod was tested by analyzing measured volumes of a solution of lead n itra te containing 0.5 mg. of lead per ml., prepared by dissolving a weighed am ount of pure te st lead in nitric acid and diluting w ith w ater to the proper volume.

Since the m ethod was developed for determining the lead

content of solutions containing a small am ount of acetic acid (left after several hours’ boiling) a drop of glacial acetic acid was added to the known te st solutions. A few of th e solutions did not contain acetic acid (indicated in Figure 1) and it is readily seen th a t the presence of acetic acid in such small quantities did not affect th e electrolytic precipitation of lead peroxide. W ith samples containing from 2.5 to 15 mg. of lead the deposit of lead peroxide adhered strongly to the anode and did n o t drop off even under vigorous shaking.

T he results of the various te st analyses are summ arized in Table I, and in Figure 1 the absolute error in milligrams of the individual analyses is indicated. The vertical sections of th e chart show the total am ount of lead in the various test solutions. T he accuracy in th e m ost unfavorable cases was ab o u t 1.5 per cent, and in the m ajority of cases it lay well below 1 per cent.

T a b l e I. M i c b o d e t e r m i n a t i o n o f L e a d b y a n E l e c t r o l y t i c - C o l o r i m e t r i c M e t h o d

Av e r a g e Le a d

N o . OF Fo u n d — Er r o r—

---

Le a d Ex p e r i­ E le c tro - C o lo ri- M a x i- M in i­

Ta k e n m e n t s ly tic a lly m e tric a lly m u m m u m A v e ra g e

M g . M o . M o. Mq. M o . %

1 5 .0 0 12 1 4 .8 3 6 0 .1 3 0 .1 4 9 0 .0 0 3 0 .2 9

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

1 0 .0 0 12 9 .8 2 1 0 .1 3 0 .0 9 0 0 .0 0 0 0 .3 4

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

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

4 .5 0 3 4 .3 2 4 0 .1 5 0 .0 4 3 0 .'0 i7 0 .6 8

4 .0 0 21 3 .8 8 2 0 .1 2 0 .0 7 1 0 .0 0 2 0 .7 2

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

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

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

Li t e r a t u r e Ci t e d

(1) AUport and Skrimshire, A n a l y s t , 57,440 (1932).

(2) Francis, H arvey, and Buchan, Ibid., 54, 725 (1929).

Re c e i v e s N o v e m b e r 8 , 1934.

Determination of Selenium

Quantitative Determination on Animal M atter and Clinical Test in Urine

H . C. D u d l e y a n d H . G. B y e r s , Bureau o f Chemistry and Soils, W ashington, D . C.

R

OBINSON, Dudley, Williams, and Byers (1) report procedures for th e determ ination of selenium and arsenic in a variety of m aterials. These methods were developed in response to th e necessities of an investi­

gation of th e selenium content of minerals, shales, soils, vegetation, and anim al tissues and products.

Selenium has been found in the tissues and in th e blood, feces, and urine of all animals which have ingested seleniferous food, and also in the milk of selenized cows, w hether the cows have been fed seleniferous vegetation or have been given inorganic compounds of selenium. Selenium has also been dem onstrated in eggs from selenized hens. The development of an accurate m ethod of determ ination of selenium in these m aterials is essential for satisfactory work and a clinical test as an aid to diagnosis of selenium poisoning is urgently re­

quired. T he procedures detailed in this paper are believed to be an advance upon those previously reported.

Qu a n t i t a t i v e De t e r m i n a t i o n i n An i m a l Ti s s u e s a n d Pr o d u c t s

1. F o r blood, eggs, flesh, hair, bones, or hoofs, the q uantity of m aterial required is from 50 to 100 grams.

The material in a suitable state of subdivision is placed in a beaker (400 to 600 cc. capacity), covered with 150 to 200 cc. of

concentrated nitric acid (sp. gr. 1.42), and allowed to stand at room temperature for from 2 to 3 hours, during which period it is stirred vigorously at intervals. Fifty cubic centimeters of hydrogen peroxide (30 per cent by weight) are added and the mixture is allowed to stand overnight. If frothing occurs on addition of the hydrogen peroxide, foaming over is prevented by vigorous stirring of the foam. The foaming is particularly in­

tense with blood, liver, and spleen. After standing overnight, the mixture is warmed slowly on the steam bath until frothing ceases, after which 50 cc. more of hydrogen peroxide are added, together with 20 cc. of concentrated sulfuric acid. The mixture is then taken to essentially complete dryness on the steam bath or hot plate. The cooled black paste is treated with 100 cc. of hydrobromic acid (45 per cent HBr) to which has been added sufficient bromine to make it deep yellow in color. The ma­

terial is then transferred to a distilling flask and 50 to 75 cc. of distillate are collected. Further procedure is as directed by Robinson et al.

2. F or milk, the procedure is essentially as for other ani­

m al m aterial, except th a t a q u an tity of from 500 to 1000 cc.

is advised. T he final evaporation should be carried o u t on a hot plate as soon as th e fa tty m aterial has separated o u t as a clear yellow layer on th e surface of th e m ixture. This fa tty layer, which also appears w ith egg yolk and other fa tty tissues, makes necessary th e use of a hot plate for th e complete evaporation.

3. The procedure for urine is sim ilar to th a t for milk, ex-

4 I N D U S T I t I A I, A N D E N G I N E E R I N G C H E M I S T R Y Vol. 7, No. 1 ccpt th a t the sample m ay be as large as desired. The residual

pasty m aterial, if highly colored, m ay be decolorized by a third treatm ent with hydrogen peroxide.

An example of the application of these procedures is given in Table I, which illustrates th e range of values ob­

tained.

T a b l e I. S e l e n i u m C o n t e x t o f V a r i o u s M a t e r i a l s o f A n i m a l O um iN

La b. N o . Ma t e r i a l S E L E N i d m C o n t e s t

P . p . m .

B 13724 M ilk 0 .0 2

13767 M ilk 3 . 0

11814 M ilk 0 . 5

13760 M ilk 2 . 0

4327 N o rm a l b lo o d of p ig 0 . 0

4 3 2 8 B lo o d of p ig 0 .5

4328 H o o f of p ig 2 . 0

7 7 1 0 L iv e r of r a t 4 .7

7710 K id n e y of r a t 1 .2

12347 N o rm a l liv e r 0 . 0

13727 H e a r t of ca lf 1 6 .0

13727 | B lo o d of calf 2 7 .0

13727 L iv e r of ca lf 2 5 .0

13727 Lungfl of calf 8 . 0

13726 U rin e of cow 5 . 0

5796 U r in e of p ig 0 .1

11813 E g g w h ite 6 . 0

11813 E g g y o lk 1 .0

11813 E g g sh ell 3 . 0

Xo sample of seleniferous hum an urine was available, b u t a normal sample to which was added 0.05 mg. of selenium in 100 cc., as sodium selenite, gave a somewhat doubtful test in 24 hours. A very satisfactory te st resulted when 0.1 mg.

of selenium was used w ith 1()0 cc. of urine, and became clearly defined in 12 hours.

A cow which had been selenized furnished urine for the following tests: Ten cubic centim eters of urine containing 0.04 mg. of selenium gave a positive te s t after standing 12 hours. A 100-cc. sample, containing 0.40 mg., gave a clearly defined positive test in 1 hour.

I t is unfortunate th a t no te st directly applicable to u n ­ treated urine is available. 'When th e a tte m p t is m ade to apply the foregoing te st w ithout treatm en t w ith nitric acid and hydrogen peroxide, no satisfactory results wrere obtained, even by filtering and reprecipitation.

Li t e r a t u r e Ci t e d

(1) Robinson, W . O., Dudley, H . C., Williams, K . T „ and Byers, H . G., Ind. Eno. Ch em., Anal. E d., 6, 274 (1934).

Re c e i v e d D e c e m b e r 4 , 1934.

Cl in ic a l Te s t f o r Se l e n iu m i n Ur i n e

Since selenium always appears in the urine of animals fed w ith seleniferous vegetation, a clinical te st sufficiently ac­

curate for detection of m inute quantities and sufficiently simple to be used in a doctor’s office or in a drugstore would be of great benefit as an aid to diagnosis in areas known to be affected by a selenium soil. T he procedure outlined is relatively simple and is th e best th e authors have as y et been able to devise.

A quantity of urine ranging between 100 and 500 cc. is placed in a large beaker and treated with 25 cc. of concentrated nitric acid and 30 cc. of hydrogen peroxide (30 per cent by weight). If seleniferous vegetation has been consumed, normally 100 cc. is a sufficiently large sample. The mixture is slowly warmed, and if rapid evolution of gases threatens loss, the bubbles are broken by vigorous stirring of the foam. After foaming ceases, the mixture is evaporated to dryness on the steam bath or hot plate. If the residue is darker than a very light yellow, it is treated with 10 cc.

of hydrogen peroxide and again evaporated to dryness. The dry residue is treated with 10 cc. of hydrobromic acid (20 to 25 per cent HBr) which is colored yellow with half a drop of bromine.

Without warming, the solution is filtered through an asbestos felt filter into a test tube of colorless glass. To the filtrate is added 0,25 to 0.5 gram of sodium bisulfite (N aH S03) and it is then gently warmed for 15 minutes, and allowed to stand for from 1 to 3 days.

A pink precipitate indicates the presence of selenium. If the coloration is but slight, it may be brought into sharper relief by examination in the sunlight by looking vertically into the tube.

The time required for the formation of the precipitate is much less if hydroxylamine hydrochloride or hydrazine sulfate is avail­

able for reducing the selenium.

If any doubt exists as to the source of any color observed, it may be resolved by filtering the material through a fine asbestos filter, washing with water, and redissolving the pink coloration on the filter in from 3 to 5 cc. of hydrobromic acid which is ren­

dered yellow by addition of bromine. The filtrate is reprecipi­

tated with from 0.1 to 0.2 gram of sodium bisulfite (or with hydroxylamine hydrochloride). No pink color will be observed in the absence of selenium.

T o te st th e validity of the m ethod as outlined, 50 cc. of urine from a norm al horse, which gave no te st for selenium, were treated w ith 0.05 mg, of selenium as sodium selenate.

N o visible te st was obtained on th e first precipitation w ith sodium sulfite, b u t on addition of hydroxylam ine hydro­

chloride a fain t coloration appeared after standing 24 hours. Using 0.1 mg., however, th e te st was very pro­

nounced, and reprecipitation as described recovered 0.08 mg.

H orse urine is very highly colored and probably offers the maximum degree of difficulty in the application of the m ethod.

An Inexpensive Vacuum Regulator

C . W. M c C o n n e l l , H yvis Oils, Inc., Warren, Pa.

T

H E au th o r’s m ethod of setting u p an ap p aratu s for w h at m ight be called a 100-mm. Engler fractionation m ay be of interest to lubrication engineers.

In the line is a glass T, one arm of which, A, is a small capillary used as a leak. This T joins the rest of the apparatus to a mer­

cury gage, B. The leak on the T is covered by a piece of rubber or other suitable material mounted on a flexible steel spring, C, which acts as the armature for the small doorbell magnet, D.

The bell or switch for the magnet is the mercury gage which is

pierced by two platinum wires, E ,E '. When the apparatus is exhausted to the desired vacuum, stopcock F on the mercury gage is closed, the mercury rises, touches contact E ’, and closes the magnetic circuit. Armature C is pulled dowm and opens the capillary leak, and the pressure within the apparatus is kept constant to within at least the accuracy of a mercury manometer.

Obviously, gage B is so adjusted that contact E ' just fails to touch the mercury when stopcock F is open.

T he ap paratus is inexpensive— a couple of dry cells, the glass T , some wire, a doorbell, and an alarm clock spring are easily obtainable and leave th e cost of th e m ercury gage th e only expense.

T he Petroleum Research L aboratory a t th e Pennsylvania S tate College is, so far as th e au th o r knows, the originator of th e apparatus, b u t he believes th a t only his laboratory has fully utilized its really rem arkable flexibility.

Received September 24, 1934

Accelerated Tests of Paint Finishes on Aluminum

Ju n i u s D . Ed w a r d s a n d Ro b e r t I. Wr a y, Aluminum Company of America, New Kensington, Pa.

T

H E d i f f i c u l t i e s in the w ay of developing satis­

factory accelerated tests for paint finishes are generally recognized. Nevertheless, the need is so urgent t h a t t h e i r use is justified, providing the results bear some r e a s o n a b l e relation to service performance.

In th e use of thin aluminum alloy sheet on s e a p l a n e s , par­

ticularly on p o n t o o n s , service

■conditions are m et which may require paint p r o t e c t i o n . In a n d o u t of sea water, alternately w et and dried, paints on sea­

planes are p u t to a searching trial. In examining paints for th is service, a te st has been de­

veloped which gives good results a n d has yielded valuable infor­

m ation. A description of this te st, w h ic h h a s b e e n in u se since 1926, and some of the in­

f o r m a t i o n gained from it are p r e s e n t e d b e c a u s e it seems generally applicable to paints for m etal which is subject to w etting a n d drying in service.

A n accelerated test of paint finishes on alumi­

num, which includes periodic immersion in salt water followed by atmospheric exposure in pre­

determined cycles, has been found useful in in­

vestigating painting practice on seaplanes. The apparatus consists of large wooden tanks which are automatically filled with salt u'ater at definite intervals. Boxlike structures of the aluminum alloy 17S-T were used as lest specimens, exposed in the tank in such a manner as lo be completely wet, inside and outside, when the tanks were filled. The results secured closely parallel the

lypes of failure experienced in service.

A n investigation of various surface prepara­

tions showed the following order of excellence:

anodic coatings, oxide coatings produced by means of chemical dips, treatment with phosphoric acid solutions, treatment with phosphate solu­

tions, and cleaning with solvents.

Investigations of types of painting systems in­

dicate that the best finishing system found to dale involves the use of an anodic coating and a phe­

nolic resin-base zinc chromale prim er applied and dried before assembly, followed by aluminum paint made with the same type of vehicle.

th e t a n k f i l l s , a similar float rises until it trips a valve in this tank, the water flowing to the next tank and so on to the last tank, from which it is discharged into the river. It u s u a l l y r e q u i r e s a b o u t 40 m i n u t e s t o f i l l t h e supply tank and about 10 minutes to drain it. The specimens are t h u s i m m e r s e d f or a b o u t 10 minutes and are out of the water until s u b s t a n t i a l l y dry during each cycle. A n ew s u p p l y of water is used in each cycle, since the old water is returned to the river.

D e s c r i p t i o n o f Ap p a r a t u s

The te st consists of immersion in salt w ater for a set period, followed by ex­

posure to th e atmosphere and drying;

the two conditions are repeated in cycles.

T h e te st apparatus, shown in Figure 1, is located on the roof of a factory build­

ing a t Edgewater, N . J.

Three large open wooden tanks approxi­

m ately 12 feet long, 4.5 feet wide, and 18 inches deep contain the test specimens. A large water-supply tank located at the side and above the first t a n k f u r n i s h e s t h e water for filling the test tanks. Water from the Hudson River is pumped directly into the supply tank. A typical analysis of this water, m a d e in A u g u s t , 1932, w a s a s follows:

Clso<

C O . pH

O./l.

1 0 . 4 1 . 4 0 . 0 6 5

The water contains approximately 1.7 per cent of sodium chloride, about half the con­

centration found in sea water.

When the water reaches a predetermined level in the supply tank, a large float trips a valve, permitting the water to flow into the uppermost test tank and fill it to a level

about 3 inches above the specimens. As ^{Fi g u r e 1 . Te s t A}p p a r a t u s

This apparatus can, of course, be o p e r a t e d only during the m o n t h s w h e n t h e r e is n o danger of freezing, n o r m a l l y from about th e middle of April until the l a s t o f N o v e m b e r . For m any coatings this period has been sufficient to produce substantial breakdown. Speci­

mens which successfully w ith­

stand one season’s e x p o s u r e are returned to th e tanks the following year and th e test is re­

peated until failure occurs or the answer is obtained to th e prob­

lem under investigation. The te st specimens are g e n e r a l l y stored indoors between exposure periods. In a few instances specimens have been continued in the te st for 5 years.

Various types of specimens can bo ex­

posed in these tanks, b u t experience has shown th a t the m ost comprehensive in­

formation can be secured by the use of a fabricated specimen containing riveted or welded joints and parts never exposed to th e sun, sim ulating conditions inside a pontoon. In th e earlier tests a fairly c o m p l i c a t e d specimen was employed (Figure 2) which embodied joints of dis­

similar m etals, metal-to-wood, etc., such as m ight be used in aircraft construction, Although much valuable inform ation was secured through its use, the num ber of tests which could be m ade a t one tim e was lim ited because of its size and design.

Consequently a much sim pler specimen was adopted, consisting of a boxlike struc­

ture w i t h r i v e t e d s id e s , open a t the bottom and vented a t th e top. T his box was 10 inches high, 10 inches long, and 7 inches wide, and was fabricated from Alu­

m inum Com pany of America's alloy 17S-T sheet; this is a heat-treated alloy similar to duralum in in composition and proper- 5