Industrial and Engineering Chemistry : analytical edition, Vol. 6, No. 5

A n a l y t i c a l E d i t i o n V o l . 6 ,

No.

Se p t e m b e r

1 5 , 1 9 3 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. 26, CONSECUTIVE NO. 31

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 . I Io 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 t o n , P a .

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

Room 706, M ills B uilding, W ashington, D . C.

T e l e p h o n e : N atio n al 0848

C a b l e : Jiechem (W ashington)

Ad v e r t i s i n g De p a r t m e n t:

332 W est 42nd St., New Y ork, N. Y.

T e l e p h o n e : B ry a n t 9-4430

C O N T E N T S

15,600 Copies of This Issue Printed Measurement of Quality in Rubber Goods by Physical Tests

... Arthur IK. Carpenter Chemical Studies of Wood Preservation:

I. The Problem and Plan of Attack ...

... Robert It. Williams II. Sampling Poles for Chemical A n a ly sis...

. . ' ...Robert E. Waterman ana Charles 0. Wells A p p e n d ix ... R. L. Peek, Jr.

Occlusion of Water by Potassium and Sodium Chlorides . ... G. Frederick Smith, F. M. Stubblefield, and E. 11. Middleton Determination of N i t r a t e s ...

...Jeliiel Davidson and Alexander Krasnitz Rapid Potentiometric Method for Quantitative Determina­

tion of Copper in A llo y s ... : ■ ■ ■ ...Henry B. Hope and Madeline Ross Combustion Method for the Determination of Iodine in Plant M a t e r i a l ...

. . . J . .S McIIargue, D. W. Young, and R. K. Calfee Estimation of Phytin P h o sp h o ru s...

... Robert S. Harris and L. Malcolm Mosher Improved Method for Determination of Percentage Acetyl in Organic Com pounds... Max Phillips Suction D evice...I^ouis Cohen Analysis of Dry Refinery Gases below Pcntane by Simple

Batch Distillation . . . J. Happel and D. W. Robertson Self-Filling Pipet for Dispensing H ot Caustic Solutions . . . . . Clifford J. B. Thor Preparation of Samples for Determination of Arsenic . . ...F. P. Carey, G. Blodgett, and II. S. Salterlee Sulfur Determination in Sulfite Waste Liquor and Organic

Compounds . . . . R. N. Pollock and A. M. Partansky Colorimetric Determination of Iodine by the Starch-Iodine

R e ac tio n... Helen Quincy Woodard Determination of Lead Soap in Oils and Greases . . . .

...Harry Levin The Microanalysis of Gases. I l l ...

...Francis E. Blacet and George D. MacDonald Anhydrous Sodium Carbonate for Standardization . . . . Louis Waldbauer, D. C. McCann, and Lawrence F. Tuleen Precise Method for Determining Ammoniacal Nitrogen in

E g g s... ...

. . Arthur W. Thomas and Marguerite A. Van Hauwaerl Spectral Determination of Fluorine in Water. A. W. Petrey Analytical Uses of 2-Propanol...

... G. W. Ferner and M. G. Mellon Colorimetric Standards for S i l i c a ...

...II. W. Swank and M. G. Mellon Identification of Amines as 2,4-Dinitrobenzoates . . . . ... C. A. Buehler and John D. Calfee

301

308 310 313

314 315

316

318 320 321 322 323 326 327 330 331 333 334 336

338 343 345 348 351

Determination of Organic Halogens . . . Fred E. Beamish Determination of Total Reducing Sugars, Dextrose, and

Levulose in Raw Cane S ugars...

...F. W. Zerban and M . II. Wiley Extraction of Gossypol from Cottonseed M e a l ...

...J. 0. Halverson and F. II. Smith Direct Simultaneous Microdetermination of Carbon,

Hydrogen, and Oxygen in Organic Substances. I . . . ...W .R .K irn e r Colorimetric Determination of Silica in Boiler Water . . . ... M . C. Schwartz A Microscope Cold Stage with Temperature Control . . . ... C. W. Mason and T. G. Rochow Sintered Glass Absorber for Determining Carbon by Wet C o m b u s tio n ...

... P. A. Wells, 0. E. May, and C. E. Sensernan A New Ultraviolet Microscope Illu m in a to r...

... Thomas Hill Daugherty and Elmer V. Iljort A Stillhead for Rapid Concentration in Vacuo ...

. Hubert Bradford Vickery and George W. Pucher Continuous Laboratory Topping Apparatus ...

... II. T. Rail and II. M. Smith Determination of Phosgene by the Soda Method . . . .

... Maryan P. Matuszak A Distillation Apparatus for Phenols in W a t e r ...

...Eldon A. Meanes and Edward L. Newman The T onom eter... L. A . Wetlaufer Nickel Microbomb for Microestimation of Organic Arsenic ...F. E. Beamish and II. L. Collins Removal of Samples of Oil from Oil-Impregnated Paper . . ... John D. Piper ter Meulen Method for Direct Determination of Oxygen in Organic Compoimds Containing N i t r o g e n ...

... IV. Walker Russell and Maurice E. Marks Identification of Common G lv c o s id e s ...

... Kirby E. Jackson and William M . Dehn Constant-Temperature High-Pressure Laboratory Auto­

clave ...Fred J. Dykstra arui George Calingaert An Improved Fat-Extraction A p p a r a tu s ...

... Arthur D. Holmes and Madeleine G. Pigolt Preventing Bumping in Vacuum D istillatio n s...

...Avery A. Morion Rubber Stopper Remolding for Reduced Pressure Filtration ... G. Frederick Smith and J . L. Gring A Differential Pressure Control Mechanism for Vacuum D is tilla tio n ...S. Palkin and 0. A. Nelson A Simple Absorption P i p e t ...

... Eldon A. Meanes and Edward L. Newman Agitator for Lamp-Method Sulfur Titrations . Lyle Dolan A Divided Titration F l a s k ...J . W . Young

352

354 356

358 364 367

369 370 372 373 374 375 376 379 380

381 382 383 38-4 384 385 386 387 388 388

Subscription to nonm em bers, 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, *7.50 per year. Foreign postage *2.10, except to countries accepting m ail a t Am erican dom estic rates. To C an ad a, 70 cents. A n a l y t i c a l E d i t i o n only, *2.00 per year, single copies 75 cents, to m em bers 60 cents. Foreign postage, 30 cen ts; C an ad a, 10 cents. N e w s E d i t i o n only, *1.50 per year. Foreign postage, 60 c e n ts ; C anada, 20 cents. Subscriptions, changes of address, and claim s for lost copies should be referred to C harles L. Parsons, Secretary, Mills B uilding, W ashington, D . C. T he Council has v o ted t h a t no claim s will be allowed for copies of jo u rn als lost in th e m ails, unless such claims are received w ithin 60 days of tn e d a te of issue, and no claim s will be allow ed fo r issues lost as a re su lt of insufficient notice of change of address. (T en d a y s’ advance notice required.) "M issin g from files" c a n n o t be accepted as th e reason for honoring a claim . If change of address im plies a change of position, please in d icate its n a tu re .

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.

4 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5

FOR THE PUREST WATER

U s e

V IT R E O S IL

Distillation Equip­

ment as designed by Prof. James

Kendall

Parts Price

3 Liter opaque still

_ Vltreosil

Ground-on air cooled parts

condenser on]y

T r a n s p a r e n t f u s e d

q u a r t z f l a s k 500cc

capacity

p H E large number of units sold is a reliable index that j | ¡1 scientists are fast realizing fused silica offers the best means

| JL || o f

producing the purest water. No other known material offers equal resistance to its solvent action. The apparatus will be found indispensable for conductivity water tests, starvation experiments on plants, etc. and wherever a pure water solvent is re- quired free from objectional impurities.

The illustration shows a suggested method for erecting the appara­

tus. A dust cap is provided on the condenser bend and if so desired a stoppered flask may be obtained for storage of water at slight additional cost.

Published by th e A m erican C hem ical Society, Publication Office, 20th & N o rth am p to n Sts., E asto n , Pa.

E n tered as second-class m a tte r a t th e Post-Office a t E asto n , Pa., under the act of M arch 3, 1879. as 42 tim es a year. In d u stria l E d itio n monthly on th e 1st; N ew s E dition on th e 10th a n d 2 0 th ; A nalytical Edition bim onthly on the 15th. Acceptance for m ailing a t special

ra te of postage provided for in Section 1103. A ct of O ctober 3, 1917, authorized Ju ly 13, 1918.

The THERMAL SYNDICATE, Ltd.

62

Schenectady Avenue Brooklyn, New York

y T ¥ T ? T 'T ‘T * rT T T •

T '

T

T

T '

T v T y T r T . __________

L e t us send you further p articu lars

September 15, 193*1 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 5

K l M B L E Blue-Line E x a x C e n trifu ge T ubes are m a d e with the sa m e e x actin g care a n d high qu ality o f w orkm ansh ip that ch aracte rize all K im ble scientific gla ssw a re .

S O M E N O T E W O R T H Y F E A T U R E S

1. T ub es c lo se ly so rted to h a v e the m a xim u m p ra c tic a l w a ll thickness.

2 . N e c k s re in fo rc e d with m a c h in e -to o le d finish much stro n g e r than the o r d in a r y flare.

3 . T a p e r s o n t u b e s w it h c o n i c a l e n d s a r e c a r e f u ll y s h a p e d . 4 . C a lib r a t io n lin es a re a c id etched a n d filled with a d u r a b le blue

g la ss , fu se d into the lines.

5. Every tub e is re te m p e re d (stra in -fre e ) in a sp e c ia l le hr o r oven.

6. In d iv id u a lly in sp e cte d to insure fre e d o m from d e fe c ts a n d re ­ tested to a ssu re accuracy.

For a ccu racy a n d assurance , sta n d a rd iz e on K im ble B lu e-Line E x a x G la ssw a re . It is stocked b y le a d in g Labo ratory S u p p ly Houses throughout the United Sta te s a n d C a n a d a .

KIMBLE 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 .

I

J

b y skille d operators, after all o p e ra tio n s h ave been completed.

The retesting m ethods em plo yed were a d o p te d o n ly after tho ro ugh study a n d p a in sta k in g in v e stig a ­ tion b y the K im ble Research Staff.

6 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5

7 ADVANTAGES IN THE NEW CONTAINERS OF MERCK LABORATORY CHEMICALS

M erck Laboratory C h em ica ls are n o w p a ck a g ed in sp ec ia lly -d e sig n ed co n ta in e rs w h ich offer th e se sev en im p o r ta n t ad van tages:

1. Amber Color Glass 2. Non-metaliic screw cap 3. W ill not corrode 4. Easy to open

5. Special liner ensures air-tight sealing 6. Dust-proof

7. Attractive appearance T h e am ber c o lo r g la ss b o ttle s afford m a x im u m p r o ­ te c tio n a g ain st lig h t and o th e r d eter io ra tin g agen ts.

T h e n o n -m e ta llic screw caps w er e d e sig n e d t o o v e r ­ c o m e c o r r o sio n r e su ltin g from u n fa v o ra b le a tm o s-

p h e ric c o n d itio n s an d from v a p o rs p r e se n t in th e lab oratory. T h e la rg e facets o n th e sid e o f th e cap m a k e it easy to o p e n th e b o ttle .

A sp ec ia l lin er, im p e r v io u s t o th e c h e m ic a l, e n ­ sures a ir -tig h t se a lin g w h e n t h e h an d y cap is rep laced . T h e cap e x te n d s o v e r th e lip o f th e b o ttle , th u s p r e v e n tin g an a cc u m u la tio n o f d ust.

M erck Laboratory C h e m ica ls in th e se n e w am b er g la s s b o ttle s , w ith th eir b lack cap s and b lu e an d w h ite la b els, w ill add to th e attractive ap p earan ce o f you r la b oratory o r sto ck r o o m .

Y o u r w h o le sa le r is ready to su p p ly you .

MERCK & CO . Inc.

R A H W AY, N. J.

September 15, 1934 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 7

I

I

4 +5 = 9

I t ’s all the ^{S a m e *}

R e g a r d l e s s of the source of a possible error in your pyrometer installation—whether in the meter, the couple, or the lead wire—it’s all the same, so far as inaccuracy of tempera­

ture readings is concerned. So, while you rightly demand accuracy in your meter and thermo-couple, it means little unless you demand equal accuracy in your lead wire. But you are not getting that accuracy if you use so-called “ com­

pensating” leads, instead of Chromel- Alumel Extension Leads with your Chromel-Alumel Couples. The two e.m.f.’s developed where these “ com­

pensating” leads join the couple are of

unequal value, do not cancel each other, and thereby introduce an error. But you avoid all chance of error at this point merely by using Chromel-Alumel Extension Leads. Such leads have the same composition as the Chromel- Alumel Couple and where the two join, obviously no disturbing e.m.f.’s can de­

velop. If you want to avail yourself of the fine accuracy of your meters and your couples, you can’t do it with “ com­

pensating” leads. But if you want that accuracy, we invite you to send for Folder-GY. Hoskins Manufacturing Co., Detroit, Mich.

LEADS CHROMEL-ALUMEL ^HOSKINS COUPLES

A N A L Y T I C A L E D I T I O N Vol. 6, No. 5

Acids, Bases, Cement, Drugs, Ether, Fertilizers, Gold, Hypochlorites, Iron, Jellies, Kelp, Lime stone, Manganese, N ick el O r e s , P h o s p h o r o u s , Quantitative Tests, Rea gents, Silica, T u n gsten : U r a n i u m , V a n a d i u m W a t e r , X t r a c t i o n s ; Yttrium, Zinc.

if J u st a few o f th e m an y uses for W H A T M A N F ilter Papers in analysis. N o m atter w hat you test, there is a grade o f W H A T M A N to m eet your requirem ents.

S a m p l e s o n r e q u e s t

H . REEV E A N G EL & C O ., IN C ., 7-11 S P R U C E s r . , N EW Y O R K , N . Y

N o. 9916

rjp iIE C c n c o v acuum d rying oven b rin g s te m p e ra tu re co n tro l a n d te m p e ra tu re d is trib u tio n in vacuo to its finest p rac tica l p o in t. I t m a in ta in s a n equally d is trib u te d te m p e ra tu re over all w orking p o sitio n s o n its sh e lf w ith in a variable o f p lu s o r m in u s 0.5 degrees C. S uch c o n tro l is accom plished by its th e rm o s ta tic p rin cip le o f design, w hereby its drying ch a m b e r is im m ersed in a c o n s ta n t te m p e ra tu re oil h a th w hich is its e lf precisely co n tro lled by th e w ell- know n C cnco-D eK hotinsky b im e ta llic th c rm o - re g u la to r w orking to g e th e r w ith Ccnco K nife Type h e a tin g elem e n ts. T h e Ccnco v ac u u m d rying oven No. 9916 com pletely equipped is priced a t §350.00.

F O R

C o n s is t e n t M o is t u r e V a lu e s

T

C

V

O

N o .10999A.

HPHE Cenco Ilyvac P u m p provides a m o s t s a tis ­ factory m e an s for ex h a u stin g th e Cenco V acuum D rying Oven. W hen th e m o to r is lit te d w ith a No. 9917 D ouble P ulley, th e p u m p m ay he operated a n d th e oven stirre d fro m th e sam e m o to r. A No. 9918 B elt is used for driving th e oven stirre r.

T h e m o to r-d riv en p u m p , No. 10999A for 110 volts, 60 cyclcs A. C. is priccd a t $90.00.

A sk f o r B u lle tin No. 7 F

La b o r a t o r y M iffi Su p p l i e s

•Apparatus gMJia Chemicals

Ne w Yo r k - B o s t o n - C H I C A G O -Toro nto-Lo s Angèles

September 15, 1934 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 9 - / /

MUL T I P L E UNIT

For O ver 2 0 Years

CRUCIBLE

FURNACES

"M U L T IP L E U N IT "

MUFFLE

FURNACES

"M U L T IP L E U N IT "

HOT PLATES

"M U L T IP L E U N IT "

TUBULAR

FURNACES

"M U L T IP L E U N IT "

O RG ANIC COMBUSTION

FURNACES

"M U L T IP L E U N IT "

USED AS STANDARD EQUIPMENT IN LABORATORIES Let your Job b er or Dealer, handling

laboratory apparatus, supply you with

"M U L T IP L E U N I T " electric Furnaces and H o t Plates. Catalog N o . 30 sent upon request.

H evi D uty E lectric C o m pan y

MILWAUKEE ~ WISCONSIN M A N U F A C T U R E R S O F—

I n d u s tr ia l H e a t T r e a tin g a n d L a b o r a to r y F u r n a c e s •

A. H. T. CO. SP E C IFIC A T IO N

E L E C T R I C

D R Y I N G O V E N

1934 M O D E L

7784-A.

ELECTRIC DRYING OVEN, A. H. T. Co. Specifica­

tio n , 1934 Model. With automatic temperature regulation.

Constructed of heavy asbestos board with Monel metal trim and cast metal legs. The gross inside dimensions are 10 inches high X 16 inches wide X 10 inches deep, with net working space of 10 inches high X 15 inches wide X 7% inches deep.

Twoshelves are provided, with four shelf positions each 2 inches apart. The highest of these positions is 4 inches below the in­

side top of the oven.

Ventilating holes are provided under the heaters in the bottom of the oven, also in the top, the latter being provided with rotating shutters that permit adjustment of their size.

Temperature regulation is by means of a special control mechanism, conveniently located at the upper right-hand side of the oven. It is operated by means of a knurled-edge wheel with the direction of motion required for either raising or lowering the temperature level indicated by arrows.

For operation up to 150°C. Heating units are wound for a total capacity of 1000 watts and the oven must, therefore, be connected directly to a line of this capacity.

7784-A. Electric D rying Oven, A. H . T . Co. Specification, Code 1934 M odel, as above described, com plete w ith W ord therm o m eter reading to 200°C, cord and plug for connection, and detailed operating directions.

F o r use on 110 volts, a.c...50.00 Losdn 7784-B. D itto, b u t for use on 110 volts, d .c ... 50.00 Losgh

D etails o f te s ts , show ing te m p e ra tu re d is tr ib u tio n , u n ifo r m ity , etc., are incorporated in directions

fo r use, copy o f w hich is se n t up o n req u est.

A R T H U R H . T H O M A S C O .

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 T O R Y APPAR ATU S AN D REAGENTS

W E S T W A S H I N G T O N S Q U A R E

PH ILA D ELPH IA , PA., U. S . A.

Cable A ddress: B A L A N C E , Philadelphia

10 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5

NHUC1 ( N H 4)2S 0 4

M AXIMUM LIM ITS O F IM PURITIES Insoluble in H2 O . . .005?»

N o n v o la t ile .0 1 0 % Neutrality . . . .P assesT est

N H

N O

MAXIMUM LIMITS O F IM PURITIES Insoluble in H2O . . .005?»

N o n v o la tile ... 0 1 0 % C l . ...0 0 0 5 %

MAXIMUM LIMITS O F IM PURITIES Insoluble in H jO . . .0 0 5 % N o n v o la t ile .0 1 5 % Neutrality . . . .P assesT est

M AXIMUM LIMITS O F IM PURITIES Insoluble in H jO . . .0 0 5 % N o n v o la t ile ... 0 1 0 % Free A cid . . . Passes Test Nitrite (as N O2 )

.0 0 2 % PC .0 0 0 5 % A s .0 0 0 5 % Fe re ... 0005/O

H. M. (os P b ) ... 0 0 0 5 %

R e a t j e n i r - C h e m i c a l s

Y o u r d e a l e r w ill s u p p ly you, o r w rite th e n e a re s t c o m p a n y o ffic e

G

C

C

♦ 40 Rector St., N ew York

B UFFALO • CH IC A G O ‘ CLEVELAND • DENVER • LO S A N G EL ES • PHILADELPHIA • PITTSBURGH • PROVIDEN CE • S A N FR A N CISCO • ST LO UIS ATLANTA • BALTIMORE • BO STO N • CHARLOTTE • K A N SA S CIT Y • M IN N EA PO LIS • SEATTLE

° " J C . p j c i d s wm

jaw ®

Simple Losñc

1 -G e n e r a l C h e m ic a l C o m p a n y is a p r in c ip a l producer o f chem ically Pure A cid s...

2 -F r o m its h eavy chem ical m anu- facture and resources, it provides the B & A plant w ith special qual­

ity raw m aterials...

3 - T H E R E F 0 R E th e u n i f o r m excellen ce o f Baker & A d ­ am son R eagent C hem icals.

B & A A M M O N I U M S A L T S a r e a c a s e in p o i n t ; th e g r o u p illu strated even m ore so. M a d e from our C. P. A c id s a n d B & A A n h y d r o u s A m ­ m o nia, their purities exceed A .C .S . sta n d a rd s.

Vo l u m e 6 N u m b e r 5

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 d 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 . I Io w e, Ed i t o r

Se p t e m b e r 1 5 , 1 9 3 4

Measurement of Quality in Rubber Goods by Physical Tests

A r t h u r W . C a r p e n t e r , B . F. G o o d r ic h C o m p a n y , A k r o n , O h io

T

m ent of quality” as ap­

plied to rubber goods seems a t first thought to be quite definite; unfortunately, it con­

veys to different persons widely divergent ideas. Engineers in dealing w ith various materials o f t e n i n t e r p r e t t h e w o rd

“ quality” as being synonymous w ith strength. Such usage is quite common in the rubber in­

dustry, and stocks possessing high tensile s t r e n g t h m ay be designated as high quality. A rubber compounder, on the other hand, m ay consider the quality of a rubber compound to be related to the percentage of pure rubber contained in the mixture. Thus, compounds having only small

P h ysical tests of rubber products m ay be classed in two groups— those which measure fundam ental ph ysica l properties an d those which determine service value. Performance tests of the latter class present m any difficulties in their proper design an d in the interpretation an d correlation of the results. Often the value of a performance lest is lost because of careless an d incomplete mechanical analysis o f the factors involved in the test an d in (he service of the article. Some of these factors are discussed an d a number of performance tests are described. D ata are p re ­ sented showing the effect of the dual p la stic and elastic nature of vulcanized rubber on the test­

ing of indentation hardness. A tim e stu dy is given of actual rate of strelching dumb-bell speci­

mens in standard tensile testing.

am ounts o f o t h e r m a t e r i a l s

added to the rubber would be considered high grade though they m ight be inferior in strength. Purchasers of rubber products have in the p ast shared both of these viewpoints, but today the more enlightened consumers understand the expres­

sion “ high quality” to indicate th e relative excellence of an article in perform ance of the intended service. This seems a more rational interpretation since, in the last analysis, satis­

factory service is the prime objective and m ay or m ay not be affected b y either great strength or high rubber content.

While quality of rubber articles in term s of strength or rubber content is com paratively easy to measure in the laboratory, and fairly satisfactory methods have long been more or less standardized, adequate laboratory evaluation of service behavior is quite another m atter. Definition of quality on the basis of performance in service has therefore necessitated the development of new test methods. The older tests for particular properties which are still indis­

pensable for th e control of uniform ity have been supplanted in product evaluation to a considerable degree by tests di­

rectly related to the service conditions. Ju st as the varieties of articles and types of service cover a tremendous field, so too these performance tests are exceedingly diverse and m ay

be quite simple for some prod­

ucts or highly specialized and c o m p le x f o r o t h e r s . S o m e rubber articles are really struc­

tures requiring as complicated engineering as the building of a skyscraper, and th e play of forces within them in service m ay be more complex and less capable of complete analysis th a n th e stresses in the skyscraper. T est- ing such products involves more th a n merely the m easurem ent of quality of the rubber compounds.

Careful and complete analysis of b o th t h e s t r u c t u r e and the service is necessary, after which development of a suitable test is w orthy of the very best engi­

neering thought.

Ty p e s o f Ph y s i c a l Te s t s

The physical tests ordinarily m ade on rubber products m ay be considered as being in one of two classes, the first consisting of those which are designed to measure fundam ental physical properties, and the second, those tests which aim to determ ine service value. Obviously no such classification can be rigid, for in m any cases a certain particular physical property m ay govern the fitness of an article for service.

T he first class would include measurem ent of dimensions, of specific gravity, of tensile strength and ultim ate elongation or th e stress-strain relationship, of compressive strength and the relation between load and deflection, of hardness and re­

silience, of perm anent set, color, dielectric strength, coefficient of friction, and th e like. In the second class would be in­

cluded tests for aging, adhesion, resistance to abrasive wear including tearing and cutting, fatigue tests of various kinds involving repeated applications of stress producing either extension, compression, or flexure, as well as a countless variety of service tests which represent attem p ts to im itate the actual service under laboratory conditions in such a way th a t accelerated results m ay be secured.

The need for laboratory teste capable of giving inform ation rapidly from which the behavior in service of rubber articles 301

302 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5

Fi g u r e 1 . Ra t e o p St r e t c h i n g o f Du m b- Be l l Sp e c i m e n s b e t w e e n

On e- In c h Be n c h Ma r k s

can be reliably predicted and the difficulties which have arisen in such use of present tests have been frequently em­

phasized. Bierer and Davis (1) pointed out the failure of t e s t s of t h e first class to fulfill the r e q u i r e m e n t s of purchase specifica­

tions and discussed t h e v a l u e of per­

formance tests in t h i s c o n n e c t io n . They dealt particu­

larly with the vari­

ous tests for abra­

sive w e a r, acceler­

ated aging tests, and a f le x in g t e s t . W h ile t h e w e a k ­ nesses of these per­

formance tests are f u lly appreciated, they are neverthe­

less c o n s id e r e d to represent a d v a n c e over the older tests. Dinsmore (2) has given a number of instructive examples showing the inadequacy and unrelia­

bility of the usual laboratory methods for the prediction of service performance. He selected stress-strain data, abra­

sion test results, and certain flexing tests, and referred to aging tests although various other tests might also, as he observed, have been included. He cited the variety of performance testing devices which have been developed in recent years as evidence th a t th e need for b etter tests is well recognized and pointed out th a t such modifications as th e work of Somerville and Russell (6)^on testing rubber a t higher

tem peratures and th a t of Somerville, Ball, and Edland (5) on autographic stress- strain curves of rubber a t low elongations, are steps in th e right direction. Dins­

more further suggests that, s in c e r u b b e r is p a r t l y plastic and partly e l a s t i c slow deformation em pha­

sizes its plastic properties while fast deformation de­

velops m o re e l a s t i c i t y . High tem peratures appear to i n c r e a s e the plasticity effect a t slo w s p e e d a n d elasticity effect a t higher speeds. Degree of vulcani­

zation is also an im portant factor. H e c o n s id e r s i t likely th a t this dual nature of rubber is im portant in many tests, mentioning par­

ticularly stress-strain, fa­

tigue, adhesion, and possibly abrasion. Finally, he ex­

presses another t h o u g h t which seems especially w orthy of elaboration and emphasis:

“ More effective laboratory methods m ay result from careful mechanical analysis of th e behavior of rubber products in service. Rubber chemists have naturally failed to appreciate the full value of mechanical studies b u t they m ust tu rn to the physicist for aid in their difficulties. A sound theoretical basis may serve m aterially to shorten the tedious search for

ORIGINAL STRETCHED

Fi g u r e 2 . Ef f e c to f Du m b- Be l l En d s o n Ra t e o f St r e t c h i n g b e t w e e n Ma r k s

Ba s e, ¿ o n 0UND Cu r ea t2 0 $ T.

lO m in.

30 ml1

50 mi\.

Ba5 L R tC IP E R ubb « r 100

» , J f -

ulphur 15 peKifeftwdfr 1 P

- B USE PlUs2<v<x s. G isBLACK ^A

• lO nin.

—

- }

I 1

; 50 min.—

1 1

laboratory and service correlation. Certainly the haphazard development of new tests m ust lead b u t slowly to progress.”

I t would ordinarily be supposed th a t th e oldest tests used for rubber products would have been thoroughly investi­

gated and completely analyzed from a mechanical point of view. Two of these tests which were probably carried over from the field of the testing of m etals are the measure­

m ent of tensile strength and elongation and the determ ination of hardness. B oth of these have been used for more than a quarter of a century by rubber men and have been studied extensively. The lack of completeness of these studies can be illustrated by some d ata which were recently secured. In measuring tensile strength and elongation, it has usually been agreed th a t either

a uniform rate of application of load or a uniform rate of stretching is de­

sirable for produc­

ing duplicable test conditions. Since machines for ap­

p ly in g lo a d uni­

formly would be considerably more complicated than those designed for u n if o r m ra te of jaw separation, the la tte r have quite g e n e r a l l y b e e n used. How serious a n y d e p a r t u r e from uniform load­

in g o r u n if o r m stretching m ight be in its effect on

the final results is irrelevant in connection w ith th e present question of mechanical analysis. Presumably, the tensile testing machines were intended to give uniform stretching since care has been taken in all specifications to require a uni­

form and standard rate of jaw separation. A study was made of the actual rate of the stretching of dumb-bell rubber samples between one-inch bench m arks when tested in a type L -6 S cott tester. The machine was first carefully checked under load to be certain th a t the speed of lower jaw travel was uniform and independent of load. Stop-watch measure­

m ents of the tim e required for each 100 per cent elongation between the m arks were m ade by two observers. The d ata are shown in Figure 1. T he tim e for 100 per cent increments of extension between th e bench m arks is not uniform for a high-rubber stock having low modulus b u t increases from 0.08 m inute a t th e s ta rt to a maximum of 0.29 minute. In the case of a high-modulus tread stock, th e rate is very much more uniform. Evidently, then, the rate of elongation measured w ith bench m arks and dumb-bell samples is in ­ fluenced b y the modulus of th e sample. I t is believed th a t the explanation rests in the stretching of th e enlarged ends outside of the bench m arks. When under sufficient stress these also yield, relieving th e elongation of the portion be­

tween the marks. This effect is illustrated in Figure 2.

While A increases to A ', B and C do not increase to B ' and C’

in the same ratio, and the extension of C lowers the ra te of extension of B .

A simple study of two instrum ents for m easuring indenta­

tion hardness again illustrates the lack of complete analysis in the case of even this very old test. I t also adds w eight to D insmore’s view of the im portance of th e dual plastic and elastic nature of vulcanized rubber. Differences in relative

TIME IN MINUTES

Fi g u r e 3 . Ef f e c t o f Du r a t i o n o f Lo a d i n g o n In d e n t a t i o n Ha r d n e s s

(Pusey and Jones plastometer)

September 15, 1934 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

Fi g u r e 4 ( Ri g h t- Ha n d Co r n e r) . Au t o g r a p h i c Ma c h i n e f o r Me a s u r­

i n g Ad h e s i o n

Fi g u r e 5 ( To p Ce n t e r) . Co m p r e s- s i o n- De f l e c t i o n Te s t o f a Ru b b e r

Be a r i n g

Fi g u r e 6 ( Ri g h t Ce n t e r) . La i s o i i a- t o r y Te s t o f Tr e a d We a r

Fi g u r e 7 ( Le f t Ce n t e r) . Sp r a g u e Dy n a m o m e t e r f o r Ti r e Te s t i n g

Fi g u r e 8 ( Le f t- Ha n d Co r n e r) .

“ Gu i l l o t i n e” Te s t o f a Ti r e

Fi g u r e 9 ( Bo t t o m Ce n t e r) . Dr o p Ha m m e r f o h Im p a c t Te s t s

304 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5 hardness values were noted in an investigation of certain com­

pounds when using the Shore duroraeter and the A. S. T. M.

hardness tester. The results with three of these compounds are shown in Table I. I t m ust be remembered that, in the A. S. T. M. instrum ent, the indenting point operates under a dead-weight load, and readings are not taken until after a t least 30 seconds of weight application. The durometer, on the other hand, is a spring instrum ent, and the quickest possible and highest reading is taken. The scales of the two instrum ents read in reverse; th a t is, the higher durometer readings represent harder stock while the higher readings of the A. S. T. M. instrum ent show softer stock. Thus, the results on the 30-minute cures using the A. S. T. M. test show stocks A and B to be of substantially the same hardness while stock C appears decidedly more hard. The durometer

as direct data, m ust be assembled if the final estim ate is to be a good one.

Di f f i c u l t i e s i n Co r r e l a t i n g La b o r a t o r y a n d Se r v i c e Re s u l t s

The difficulties which are experienced in correlating labora­

tory test results with service performance m ust be a ttrib u ted to one or both of two causes. E ither the tests themselves are improperly designed or the results secured from the tests are not correctly interpreted. Im proper design is a frequent consequence of hasty, unsound analysis of the service which fails to give full knowledge and appreciation of all th e condi­

tions and forces th a t are involved. A fundam ental require­

m ent of good testing is th a t the service to be m easured shall be first completely and accurately defined before attem pting

T a b l e I. C o m p a r i s o n o f A. S .T . Mi a n d D u r o m e t e r H a r d n e s s

St o c k

Tensile stren g th Lb./sq. in.

2650 1570 1070

- Sa m p l e s a t Be s t Co r e-

hardness

B e s t C o r e a t 280° F.

M in.

A* 15

B c 45

C d 30

° SO p e r cent of ultim ate.

& Stock A (p a rts by weight): rubber, 36.5; inner tu b e reclaim, 36.5; zinc oxide, 6.5; m ineral ru b b er, 11.0; palm oil, 1.3 to ta l, 100.0 .

c Stock B : 100 p arts A -f 82.5 G eorgia clay.

d Stock C: 100 p a rts A -f- 82.5 M issouri clay.

U ltim ate M odulus a t 300% A. S. T . M.

elongation elongation hardness Lb./sq. in.

600 125

950 69

650 69

% 660 400 425

D urom eter hardness

39 59 56

C u r b , 30 m i n . a t 280° F.

A. S. T . M. D u ro m eter P e rm a n e n t hardness set, stretched®

78 7565

50 57 58

34 60 25 sulfur, 3.2; accelerator, 5.0;

test, however, indicates th a t stocks B and C are of the same hardness and th a t both are harder than stock A. If we bear in mind th a t undercures, such as the 30-minute cure of stock B, should be more plastic than correct or overcures, such as those of stocks C and A, the differences with the two instru­

m ents can be readily explained on the basis of plastic flow of stock B which affects the A. S. T. M. measurem ent b u t not the durometer reading. This is confirmed by the readings a t the best cures. A further check (§) was made using a high- rubber stock and a 20-volume gas black compound in three cures, measuring hardness w ith a Pusey and Jones plastometer which is also a dead-weight indentation instrum ent. Read­

ings were taken over a somewhat extended period. The results are shown in Figure 3. The curves for the under­

cured stocks (10 minutes a t 285° F.) show plainly the effect of plastic flow, some of which persists even in the over­

cures (50 minutes a t 285° F.) as sl\own by the slopes of these curves. Hardness of vulcanized rubber compounds thus appears to consist of two parts, one of which is due to resist­

ance to resilient deformation and the other to resistance to plastic deformation. Some methods of m easurem ent in­

clude both in the indentation hardness result, and other methods show only the resilient hardness depending on the duration of the application of the load.

The significance of this kind of analysis in making possible better correlation with service has been intentionally om itted from the discussion because much more work will be neces­

sary before it can be fully evaluated. Surely, however, such analysis cannot help b u t give us b etter appreciation of the value of the tests which are made and a more accurate under­

standing of how to use the test data. We m ust not fail to realize the indirect nature of all laboratory tests nor should we underestim ate their value for com parative purposes, even though direct correlation with service is n o t always clear.

Certainly, direct interpretation in term s of service value is not possible for tests such as determ inations of stress-strain relationships, perm anent set, and adhesion, except in some special instances. Yet, w hat rubber technologist would be willing to have such useful tools taken from him and would be content to rely on imitations of service and on simple hand tests alone? Service evaluation or prediction repre­

sents a judgm ent on the p a rt of the technologist, and all of the information possible, comparative and indirect, as well

the design of a test. A good example of the lack of such definition is found in the case of abrasive wear, particularly as applied to tread wear of tires. T he various conditions and forces involved are so numerous and complex th a t we frankly adm it our shortcomings in respect to their analysis. Y et we attem p t to design laboratory abrasion tests and we carry on extensive road testing a t enormous expense w ithout really knowing w hat it is we are trying to measure. Possibly more tim e and money spent in determ ining ju s t w hat road wear consists of and in establishing the relative im portance of the various service factors m ight pay more dividends in th e end than all of these expensive test programs. Proof of th e seri­

ous inadequacy of present analyses of road wear factors is evidenced by the difficulties which different tire m anufacturers have in checking one another’s road tests, and by the fact th a t each m anufacturer has elaborate sets of road test d ata which show th a t his tires are the best of all com petitive brands.

I t is w orthy of note th a t laboratory abrasion tests do cor­

relate fairly well w ith service wear when th e la tte r is simple enough to be readily analyzed or capable of being closely duplicated under laboratory conditions.

Im proper design of laboratory tests m ay result also from failure to carry over into th e te st apparatus a proper balance of the conditions and forces known to exist in the service.

This is often caused by th e necessity of accelerating the investigation. Performance te sts would fall short of their purpose if they required as long a tim e as the service life of th e article. The acceleration of failure is secured usually in one or more of the following ways: (1) by increasing the severity and intensity of forces on th e sample (higher pres­

sures or loads, harsher abrasive surfaces, etc.); (2) by in­

creasing th e tem perature; and (3) by increasing speeds.

Through emphasizing certain of these individual factors, the normal balance of service conditions m ay be upset, both directly and, as is often not realized, indirectly, since change in one condition m ay cause resultant changes in others.

Obviously, w ithout such emphasis the te st would n o t be accelerated. If th e emphasized conditions are those which are principally responsible for the ultim ate failure of the article and if the other factors which are involved are not im portant in contributing to the cause of failure even though they m ay be indirectly affected, reasonable success m ay be anticipated with respect to correlation of such te sts with

September 15, 1934 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 305

F i g u r e 12 ( L e f t C e n t e r ) . F l e x i n g T e s t o f G a s o ­ l i n e H o s e W h i l e C o n t a i n i n g L i q u i d

F i g u r e 13 ( A b o v e ) . F l e x i n g T e s t o f G r e a s e - G u n H o s e u n d e r 2500 P o u n d s p e r S q u a r e I n c h G r e a s e

P r e s s u r e

F i g u r e 14 ( L e f t ) . P e r f o r m a n c e T e s t i n g o f S t e a m - H o s e T o r s i o n a l F l e x i n g u n d e r 250 P o u n d s p e r

S q u a r e I n c h S t e a m P r e s s u r e

F i g u r e 10 ( L e f t ) . F a t i g u e T e s t i n g i n F l e x u r e

F i g u r e 1 1 ( B e l o w ) . F l e x i n g T e s t f o r S o l i n g

Vol. 6, No. 5

Fi g u r e 1 7 ( Ab o v e) . Hi g h- Sp e e d, 2 5 - I Io r s e- p o w e r Dy n a m o m e t e r f o r Te s t i n g Sm a l l

Be l t s

Fi g u r e 1 8 ( Le f t) . On e- Hu n d r e d- Ho r s e- p o w e r Sp r a g u e Dy n a m o m e t e r f o r Te s t i n g

Po w e r- Tr a n s m i s s i o n Be l t i n g

service. On the other hand, when the balance of the service factors is seriously disturbed in the te st conditions, it is unlikely th a t good correlation can be obtained. The only alternative which remains then is to analyze the service completely and emphasize all factors in the same propor­

tion.

In regard to interpretation of laboratory tests, it is not infrequent th a t attem pts are made to apply te st d ata to services th a t involve differences in conditions which are significant b u t not fully appreciated. Here, again, the solution of the difficulties which arise m ust reside in more careful analysis of both the test and th e service. I t is also quite usual to encounter lack of understanding of the limits in precision of engineering d ata secured by test. Almost any of the performance tests serves to eliminate products which are radically unfit for the intended services. I t is only when finer distinctions are involved th a t serious re­

versals are encountered. For instance, several of the better abrasion resistance tests will distinguish between first grade

and second grade treads when the actual service differences in the treads are fairly wide and when the treads have similar degrees of hardness. I t is only when close comparisons between treads of dissimilar hardness characteristics are required th a t serious reversals occur. While such accurate m easurem ent and correlation are extremely desirable and m ay some d ay be possible when we have learned to analyze all of the conditions closely enough, it m ust be adm itted th a t as yet we are somewhat in th e position of trying to weigh a d u st particle with ordinary counter scales.

La b o r a t o r y Te s t s

Some pictures of laboratory testing which follow are shown, n o t w ith any idea th a t they m ay serve as shining examples of perfect mechanical analysis or as the last word in quality measurement, b u t merely th a t they m ay be sug­

gestive'as to th e m odern trend of te st development and may illustrate th e simplicity of th e mechanical movements a t present utilized in developing performance tests. As has

Fi g u r e 1 5 ( Ri g h t) . Co m p a r a t i v e Pe r f o r m' a n c e Te s t o f Pn e u m a t i c To o l Ho s e

Fi g u r e 1 6 ( Be l o w) . Pe r f o r m a n c e Te s t o f St e a m Va l v e Di s k s

September 15, 1934 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 307 already been suggested, th e details of such tests are ex­

trem ely varied b u t th e fundam ental mechanical principles are not nearly so diverse as appears a t first glance. Figure 4 shows a machine test for adhesion or “friction pull.” The specimen in this case is a strip of transmission belting one inch in width. This test involves simply the measurement, by means of a pendulum dynam ometer head, of the force required to separate plies of the specimen under standardized conditions. As has been frequently pointed out in the literature, th e correlation of such tests as this with sendee performance is extremely unsatisfactory'. Figure 5, how­

ever, shows a test in which the service correlation is very positive. In this case the deflection of a rubber bearing is being measured under various compressive loads applied to a shaft by means of a universal testing machine.

As has been suggested, performance tests which appear to be very good im itations of service conditions often fail to give satisfactory service correlation, probably because of failure to include in the test the essential characteristics of the actual service. Figure 6 illustrates such a case. This machine was designed to test tread wear, using as te st speci­

men a small pneum atic tire which is run on a rotating track made of standard road concrete. The test is of the angle- slip type and provision is made for control of th e angle. The speed can be varied as well as the dead-weight load supported by the tire. T he road wheel is the driven member and in turn, through contact, rotates the tire wheel which is mounted as an idler on ball bearings. The am ount of tread wear is measured by accurately calipering the depth of th e nonskid grooves. For a tim e it appeared th a t this te st would correlate very reliably w ith actual road sendee, but, as often happens, it was necessary only to continue testing on a sufficient num ber of tires to encounter serious reversals.

In Figure 7 is s h o w a view of tire testing on Sprague dynam ometers. In such tests a generator is driven by a m otor through controlled contact of tire and road wheel.

The actual horsepower expended on th e road wheel is meas­

ured by weighing the generator torque and measuring the speed, using th e Prony brake formula for the calculation.

These tests have been quite reliably correlated with actual service for the evaluation of tire carcass performance. Figure 8 shows a rath er obvious b u t useful im pact te st known as the

“ guillotine te st.” This has given valuable information concerning the ability of tires to w ithstand service conditions.

In this case the im pact member is dropped between guides from controlled heights in an elevator shaft, striking a blow of known force on an inflated full-sized tire, properly mounted.

Another device for im pact testing, as shown in Figure 9, has been successfully used for the testing of rubber-covered m etal plates, such as are used in lining chutes, grinding mills, etc. In this device a chain elevator raises a 50-pound weight carrying a hemispherical im pact surface to a pre­

determined height a t which the weight is tripped from the elevator. The heavy body falling freely between nearly frictionless guides strikes a blow of known force on the specimen placed below on a suitable solid support. A very interesting result was observed w ith this apparatus while testing sheets of rubber which had been bonded firmly to m etal backing (S). C ertain specimens, when tested dry, required approxim ately one hundred blows before complete failure, which was taken as the num ber of im pacts necessary to cause the rubber to tear a p a rt sufficiently to expose the m etal base. In appearance th e failed sample showed a very roughened surface over a circular area of diam eter about equal to th a t of th e im pact ball. A t the center of this area a circular hole of small diam eter extended down through the rubber to th e m etal. W hen the experiment w as repeated, with th e difference th a t the surface of the rubber was kept w et with water, failure took place after three or four blows.

Irregular radial cracks extended from the center of percussion outward, and there was no appreciable roughening of the surface. A pparently the w ater acted as a lubricant, con­

centrating the full force of the blow a t the center of per­

cussion rather than perm itting th e energy of the blow to be dissipated through a larger volume of rubber by means of friction.

Figures 10 to 14 show applications of flexing tests to various rubber products. Such tests can seldom be corre­

lated directly w ith service performance, b u t they are ex­

tremely useful for com parative purposes. The m achine illustrated in Figure 10 is used with rubber strips or dum b­

bell specimens and is similar to the D eM attia flexing machine (4). A crosshead is driven by an eccentric a t controlled variable speed. By using suitable settings of the clamps, it is possible to flex the rubber samples in bending only, as shown, or in extension. In either case th e first sign of failure will be the development of small cracks which finally lead to a complete rupture of the specimen. Figure 11 shows a bending fatigue te st on soling stock. This differs from th e previous te s t in th a t the specimens are under slight tension produced b y th e w eight of th e driving arm s which are supported by th e specimens. In .Figure 12 the perform ance relationship is more clearly defined, for in this case a speci­

men of gasoline hose full of th e liquid is bent back and forth until the tube fails and the gasoline penetrates into the body of the hose. Figure 13 shows specimens of grease-gun hose filled with grease under high pressure, which are flexed with a reciprocating m otion un til failure and consequent release of th e pressure take place. Figure 14 shows a recent per­

formance te st for steam hose. In this case th e lower p la t­

form moves w ith an eccentric motion, causing th e lower end of the hose specimen to be rotated in a circle about 4 inches in diam eter. D uring te st th e hose is subjected to internal steam pressure of 250 pounds per square inch and external action of the w eather. I t is thus q uite typically a perform­

ance te st im itating actual sendee conditions as encountered by railway steam hose.

A nother perform ance test, in which a rath e r elaborate a t­

tem pt is m ade to duplicate on a laboratory scale, a compli­

cated set of service conditions, is show'n in Figure 15. In this case, service life of four samples of pneum atic tool hose is being compared. T he ap p aratu s consists of an air com­

pressor which discharges into a receiver through equipm ent arranged to give constant tem perature and pressure in the receiver. T he compressed air from th e receiver flows through th e hose specimens after having received a known addition of lubricating oil a t th e receiver outlet. T he com­

pressed air is released from th e hose through a valve mecha­

nism which duplicates th e impulse action of a pneum atic ham m er. T he te st m ay be accelerated by raising the tem ­ perature and pressure of th e compressed air. Figure 15 also shows a steam rack and a digester which are used for h eat deterioration tests of hose specimens. In Figure 16 equip­

m ent for testing steam valve disks is shown. A valve in­

stalled in a high-pressure steam line contains th e disk under test, and mechanical arrangem ents are provided w hereby th e valve is opened by a m otor which raises a w eight a t the same tim e. The mechanism th e n trip s and th e falling weight closes th e valve, assuring duplicate force conditions a t each closure.

Figures 17 and 18 show dynam om eter equipm ent for te st­

ing belts. B oth of these sets are so arranged th a t very com­

plete inform ation can be secured. In each case one dynam o is m ounted on a track which perm its control and m easure­

m en t of the to ta l tension on the te s t belt. In each set both dynam os are cradled and equipped for torque and speed m easurem ent so th a t th e actual pulley horsepowers can be calculated excluding the dynam o losses. In each case one