Industrial and Engineering Chemistry : analytical edition, Vol. 2, No. 2

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Analytical sss^a3^Hi©®5SBig Edition

Editorial Optics: kl M M ^ s Q j / Publication o p n c a : Easton, Pa.

Room 706, Milts Building, published by the yimeriean Chemical Society A dvbrtisino D epartm ent:

Washington, D. C. 419 Fourth Ave.,

TulSphonb: National 0848 New York, N. Y.

Cablb Addrbss: Jiechem (Washington) TBLBPHONB: Lexington 5608

Editor: H a r r i s o n E . H o w b Associate E ditor: E . P . P a r t r i d g e A ssista n t to E ditor: N . A. P a r k i n s o n (1440 East Eark Place, Ann Arbor, Mich.)

V o l u m e 2 A P R I L 15, 1930 N u m b e r 2

A. C. Wa l k e rand E . J . Er n st, Jr. 134 S ta n d a rd iz a tio n of T h io s u lfa te a g a in st S ta n d a rd P e rm a n g a n a te S o lu tio n . ,T . F . Bu e iir e r and C. Morgan Mason 138 M o istu re C o n ten t of C o m p resse d N itro g e n ...A. C. Wa l k e r and E . J . Er n st, Jr. 139 D e te rm in a tio n of C h ro m iu m a n d V an ad iu m a f te r O xidation w ith P o ta ssiu m B r o m a te ...

I. M . Ko lth o ffand Er n e s t B. Sa nd ell 140

T h e T e s tin g of A utom otive R u b b e r P a r ts A ssem b led u n d e r C om pression. P a r t I — D eflectio n u n d e r C om pression, 145;

P a r t n — C o m p ressio n -S e t a n d S om e S pecial T e s ts ...Franz D . Ab b o tt 153 C h o lestero l a s a M e a s u re of E gg Y olk in M ilk P r o d u c ts ...Lin c oln M . La m per t 159 C om parison of F u s e d Silica, G old, a n d P la tin u m L in in g s fo r C a lo rim eter B o m b s ... Oscar Ke n n e t h Ba tes 1G2 S e p a ratio n of N ick el a n d C obalt b y M e a n s of H y p o c h lo rite ...F . H . Rh o d esand H . J . Ho sk in g 164 Im p ro v ed M e th o d fo r D e te rm in in g V olatile H y d ro c a rb o n s in S o a p ...Cl a r e n c e T . N . Ma r sh 166 A S y ste m of P ro x im a te C h em ical A nalysis of P la n t M a te r ia ls Selm a n A. Waksm an and Ke n n e t h R . Ste v e n s 167 A pplication of M icroscopic A nalysis to M ix tu re s of M e ta ls a n d A lloys. .Wil l e t F . Wh itm o r e and Fr a n k Sc h n e id e r 173 S u b s titu te fo r A m alg am atio n in T e s tin g B itu m in o u s M a te ria ls for M e ltin g P o in t, D u ctility, a n d F lo a t T e s t. . Ha ns Eis n e r 176 D evice fo r R ap id E s tim a tio n of th e D e n sity of S m all A m ounts of S o lid s... Ea r le R . Ca lEy 177 R elay fo r U se in R e g u lato ry C irc u its... L. G. Wesso n 179 E lectro ly tic Cell fo r U se w ith th e M e rc u ry C a th o d e ... Ar t h u r D . Me l a v en 180 A cid N u m b e rs of D a rk -C o lo re d R e s in s ... Hayw ard H . Co b u r n 181 D u p lex W eig h in g T u b e ... ... ...W . E . Esk e wa nd Fr a n k C. Vilb r a n d t 181 T h e B a ro -B u ret— A N ew A ccu rate G as B u r e t ...Harold Simmons Booth 182 C o rrectio n s fo r S ta n d a rd S o lu tio n s of In co n v en ien t S tr e n g th s ... Selma Go ttl ieb 186 C o n v en ien t R eflu x R e g u la to r fo r L a b o ra to ry S tills ... Jo h a n n e s H . Br u u n 187 D e te rm in a tio n of A lu m in u m a n d M a g n e siu m in Z in c-B ase D ie-C astin g A llo y s... Ch a r l es M . Cr a ig h ea d 188 C o n firm ato ry T e s t fo r Z in c ... J . Stanton Pie r c eand Eth y l D . Na ve 190 D e te rm in a tio n of T otal N itro g en of P la n t E x tra c ts in P re s e n c e of N itr a te s ...

Ge o r g e W . Pu c h e r, Ch a r l es S. Le a v en w o r th, and Hu b e r t Bradford Vic k e r y 191 T itro m etric D e te rm in a tio n of M a g n e s iu m ... J . Stanton Pie r c e and M . B. Ge ig e r 193 M u ltip le S ta n d a rd C o lo rim eter fo r p H D e te rm in a tio n s ... S. L. Le ib o f f 194 M o d ified P e te rs o n -P a lm q u is t A p p aratu s for th e D e term in a tio n of C arb o n D ioxide in A ir... Ed w in P . Jo n e s 195 Som e Im p ro v em en ts in T h e rm o re g u la to rs ... Hen r y J . Win g 196 S a fe ty D evice to P ro te c t H e a tin g U n its ...F . H . Fis h 197 A R ap id B u lk -S am p le D r ie r ... T . H . Ho p p e r 198 Im p ro v ed L ab o ra to ry C o n d e n se r a n d I ts U se in th e C on stru ctio n of A p p a ra tu s...Edward S. We st 199 A M o d ified T h iele M e ltin g -P o in t A p p a ra tu s ...Er n e s t Co n te 200 D evice fo r F a ste n in g M e ltin g -P o in t T u b e s to T h e rm o m e te rs ...H . L. Lo c h te 200

E n te re d as second-class m a tte r a t th e P o st Office a t E a sto n , Pa., un d er th e A ct of M arch 3, 1879, a s 40 tim es a year. In d u stria l E d itio n m o n th ly on the- l s t ; N ew s E d itio n on th e 10th a n d 2 0 th ; A n aly tical E d itio n on th e 15th of J a n u a ry , A pril, Ju ly , a n d O ctober. A cceptance for m ailing a t special ra te of postage p rovided for in Section 1103, A ct of O ctober 3, 1917, a u th o rized Ju ly 13, 1918.

S u b s c r i p t i o n t o n o n m e m b e r s , 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 p e r y e a r . F o r e i g n p o s t a g e S I.50, e x c e p t t o c o u n t r i e s a c c e p t i n g m a i l a t A m e r i c a n d o m e s t i c r a t e s a n d t o C a n a d a . A n a l y t i c a l E d i t i o n o n l y , $1.50 p e r y e a r , s i n g l e c o p i e s 50 c e n t s , t o m e m b e r s 40 c e n t s . N e w s E d i t i o n o n l y ,

$1.50 p e r y e a r . S u b s c r i p t i o n s a n d c l a i m s f o r l o s t c o p i e s s h o u l d b e r e f e r r e d t o C h a r l e s I*. P a r s o n s , S e c r e t a r y , M i l l s B u i l d i n g , W a s h i n g t o n , D . C . T h e C o u n c i l h a s v o t e d t h a t n o c l a i m s w i l l b e a l l o w e d f o r c o p i e s o f j o u r n a l s l o s t i n t h e m a i l s , u n l e s s s u c h c l a i m s a r e r e c e i v e d w i t h i n s i x t y d a y s o f t h e d a t e o f i s s u e , a n d * n o c l a i m s w i l l b e a l l o w e d f o r i s s u e s l o s t a s a r e s u l t o f i n s u f f i c i e n t n o t i c e o f c h a n g e o f a d d r e s s . “ M i s s i n g f r o m f i l e s ” c a n n o t b e a c c e p t e d a s t h e r e a s o n f o r h o n o r i n g a c l a i m .

20,200 c o p ie s o f t h i s Is s u e p r i n t e d

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4 A N A L Y T I C A L E D I T I O N Vol. 2, N o. 2

A MORE UNIFORM PYREX TUBING

DIMENSIONS and PRICES

Sizeo.d. mm. Variation +o.d.mm. App. wall mm. App. lbs. per ft. App. lbs. per case Price per lb.

5 0.5 .8 0.0156 25 $1.00

6 _0.5 i. 0.0234 50 .90

7 0.5 i. 0.0284 50 .90

8 0.5 i. 0.0331 50 .90

9 0.5 i. 0.0378 50 .90

10 0.5 i . 0.0426 50 .80

1 1 0.5 i. 0.0472 50 .80

12 _0.5 i. 0.0520 50 .80

13 0.5 1.2 0.0669 50 .90

14 0.5 1.2 0.0727 50 .90

15 0.5 1.2 0.0783 50 .90

16 0.5 1.2 0.0840 50 .90

17 0.5 1.2 0.0891 50 .90

18 0.5 1.2 0.0953 50 .90

19 0.5 1.2 O . I O I O 50 .90

2.2. 1 .0 M 0.1454 50 .96

~5 1.0 1 . 5 0.1667 50 .96

28 1.0 M 0.1879 50 .96

32 i-5 1.8 0.2300 50 1 . 10

35 1-5 2. 0.1825 50 1 . 10

38 i-5 2. 0.3081 50 1.36

4 1 i-5 2. 0.3689 50 1.36

45 i-5 2 . 0.4065 50 1.36

48 i-5 2. _0.4349 50 1.36

51 i-5 2 . 0.4632 50 1.66

W / ’E are now prepared to furnish V V PYREX tubing w ith a closer se

lection than has heretofore been avail- able. The tubing is more uniform and the wall has been made lighter, w hich materially reduces the price because the user gets more feet per pound. The lighter wall makes an improved tubing for lamp working purposes. Further im

portant changes are,

1 . P acked in o rig in a l cases.

2. S u b ject to same con su m er d iscou n t as P Y R E X L a b o r a to ry G la s s w a re .

3. Stan d ard cases c o n tain in g tu b in g c u t in ap- p ro xim ate f iv e fo o t len g th s are n o w a v a il

able th ro u g h y o u r re g u la r d ealer.

T s jo te : L i g h t a n d I i c a v y w a l l t u b i n g f o r m e r l y l i s t e d w i l l h e d i s c o n t i n u e d, b u t m a y b e o b t a i n e d o n s p e c i a l o r d e r . P r i c e s o n a p p l i c a t i o n .

W e r e s e r v e t h e r i g h t t o s h i p t h r e e o r f i v e f o o t l e n g t h s w h e n le s s t h a n s t a n d a r d c a s e q u a n t i t i e s a r e o r d e r e d .

Industrial and Labor ato ry Division

CORNING G LA SS W ORKS, Corning, N. y.

N e w Y o r k O f f i c e : 501 Fifth A v e n u e

T . M . PY REX R eg. U . S. P a t. Off.

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April 15, 1930 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

NEW MODEL

VALENTINE REFRACTOMETERS

I n t e g r a l C o n s t r u c t i o n

E a sy M a n i p u l a t i o n

P ^{r e c is e} S e t t i n g

A c c u r a t e R e s u l t s

W a r r e n P. V a l e n t i n e , I n c .

BANKERS TRUST BUILDING

PHILADELPHIA, PA.

Valentine Precision Refractom eter w ith scale o f refractive indices divided to th e 3rd decim al and reading to th e 4th by estim a tin g te n th s o f the sm allest division.

F. O. B. Philadelphia . . . S200.00

A p a r t i a l lis t o f u s e r s i n c l u d e s t h e f o llo w in g :

U n iv e r s ity o f M in n e s o ta — D iv isio n o f A g ric u ltu ra l B io c h e m is try '

S o u th D a k o ta S ta te C ollege o f A g ric u ltu re a n d M e c h a n ic A rts — D iv isio n o f A g

r ic u ltu re

S t a t e o f M i c h i g a n — D e p a r t m e n t o f A g ric u ltu re

D e p a r t m e n t o f C o m m e rc e — B u re a u o f S ta n d a r d s

C h ica g o , B u r lin g to n & Q u in c y R . R .—

B u re a u o f T e s ts

U n iv e rs ity o f P e n n s y lv a n ia

U n iv e r s ity o f N e b r a s k a — D e p a r t m e n t o f A g ric u ltu re

I n d ia n a S t a t e T e a c h e rs ’ C ollege— T e r r e H a u te , In d .

Valentine Im proved Precision R e

fra cto m eter w ith scale divided to th e 4th decim al and reading to the 5 th decim al by estim a tin g te n th s o f th e sm allest division. F. O. B.

P h ila d e lp h ia ... S250.00

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6 A N A L Y T I C A L E D I T I O N Vol. 2, No. 2

PULVERIZING YOUR LABORATORY SAMPLES

W ITH SPEED IN THE

BRAUN Type UA Laboratory Pulverizer

I n d u s tr ia l a n d m e ta llu rg ic a l la b o ra to rie s fin d th e B R A U N T Y P E U A P U L V E R I Z E R e s s e n tia l fo r g rin d in g th e ir sa m p le s fro m M in c h to 100 m esh w ith on e o p e ra tio n . T h e m a c h in e is e q u ip p e d w ith 8-in. g rin d in g p la te s o f sp ecial allo y .

S tr a ig h t d riv e — n o g e a rs— re p la c e a b le b e a rin g s o f a n t i fric tio n m e ta l.

A ll p a r ts ea sily c le a n e d .

B R A U N P U L V E R I Z E R S h a v e re n d e re d efficient se rv ic e for m a n y y e a rs , a n d will be fo u n d in th e m o s t im p o r ta n t in d u s tr ia l a n d m e ta llu rg ic a l la b o ra to rie s th r o u g h o u t th e w o rld . S h ip p in g w e ig h t— 275 lb s.

P ric e F .O .B . F a c to ry , L o s A ng eles, $ 1 3 5 .0 0 .

Braun Laboratory Appliances

Standard the world over!

T H E B R A U N C O R P O R A T I O N

363 New High S c . LOS A N G EL E S, C A L IF O R N IA . U S. A.

San F ran cisco H ouse: B ra u n -K n e ch t-H eim an n Co.

B R A U N Products In clu d e:

Chipm unk Crusher, UA Pulverizer, Iron Ore and Coal Grinders, G-H Consistency Testers, Electrolytic Outfits, Furnaces—

Muffle Crucible and Com bination, F lo

tation T est M achines, R otarex A sphalt Tester, Oil Stills, E vaporators and Samplers.

B R A U N S ervice In clu d es:

Pyrex Glassware Coor’s Porcelain W are F ilter P aper—all

S tandard Brands Balances and W eights

H ydrom eters and Therm om eters Oil and A sphalt T est

ing Equipm ent.

CHEMICAL

^{a n d}

PHYSICAL l a b o r a t o r y s u p p l i e s

P Y R E X A N D S O F T G L A S S S T O P C O C K S G UA RA NTEED F O R H IG H VACUUM W O R K

S P E CI A L GLASS A P P A R A T U S

TRANSPARENT FUSED QUARTZ

T U B I N G A N D R O D I N S T O C K Q U A R T Z A P P A R A T U S T O O R D E R

Catalogue sent on request

M AC A L A S T E R B I C K N E L L COMP ANY

C A M B R ID G E M A SS.

HIGH SPEED BALANCE For your routine weighing THE MULTIWEIGHT CARRIER

c a rrie s all fra c tio n a l w e ig h ts w h ich b e in g u n its o f m a ss m a y a t a n y tim e be a d ju s te d a g a in s t y o u r la b o ra to r y s ta n d a r d s .

A sk fo r B ulletin A-36.

W M . A I N S W O R T H & S O N S , I N C . THE PR ECISIO N FACTOR'S'

2151 L a w re n c e S t. D en v er, Colo.

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

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NO._____________ IN S I DH D IM E N SIO N S______________________ W ATTAGE________________ _ P R IC E ________________________________ T E M P E R A T U R E R A N G E: 70° - 180° C.________________________________

601 12" X 1 2 ' X 12" 700 S250.00

621 1 8 ' X 18’ X 18" 1500 3.50.00

641 36" X I S ' X 2 4 ' 1900 450.00

T E M P E R A T U R E RAN GE: 150° - 260° C.

605 12" X 12" X 12" 1500 S275.00

625 18" X 18’ X 1 8 ' 2100 385.00

645 3 6 ' X 1 8 ' X 2 4 ' 2700 500.00

Also other models w ith various m odifications in design

T h e s e ovens are a radical departure fro m our fo rm e r models.

T h e air currents m o v in g th ro u g h ports o f varied p ro p o rtio n . in th e sides o f th e c h a m b e r have a u niform sw eeping m o v e m e n t over th e samples u n im p e d e d by th e presence o f n u m e ro u s samples on o th e r shelves.

T h e advantages o f forced air draft in th e drying o f samples are too w ell k n o w n to re q u ire c o m m e n t.

T h e ovens have passed th e e x p erim en tal stage, h av in g been m ade to ord er for m o re th a n two years, th irte e n o f th e m b eing in use in th e different laboratories o f a single purchaser.

T h e frames are o f w eld ed steel in place o f a lu m in u m , m a k in g a m u c h m o re rigid and d urable apparatus.

W e shall be pleased to answer such questions as m ay o c cu r to our friends.

P r i c e L i s t

FREAS’ ELECTRIC OVENS

w ith

Forced side draft

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STERLING’S

A N A LY SIS - C E R T IF IE D

Reagent Chem icals, C .P.

XT i u r» 0 » r e + S k i U = Q u a l i t >

Mol. W t. G r m s .

C E R T I F IC A T E O F A N A L Y S I S

A n alysis i s not enough—

i n s i s t on c e r t i f i c a t i o n . **Kach l o t o f S terlin g*“s A n a ly s is -C e r tifie d bears the sign atu re of the chem ist who made the a n a ly s is .**

Get t h i s added p r o te c tio n on your lab oratory s h e lv e s .

S T E R L I N G P R O D U C T S C O M P A N Y

A N A L Y T I C A L E D I T I O N Vol. 2, No. 2

IS YOUR LABORATORY NEAT?

It Can Be If T he

S C H W A R T Z E C T I O N A L Y S T E M

Is Installed

SAVES TIME, MONEY AND SPACE.

S u p p lie s a n d A p p a r a tu s A lw a y s K e p t in B e s t C o n d itio n

W r ite F o r O u r N E W B o o k le t

“ H o w to S to re a n d C a ta lo g C h e m ic a ls , R e -A g e n ts, S cie n ce M a te ria ls

a n d S a m p le s ”

SCHWARTZ SECTIONAL SYSTEM

INDIANAPOLIS, INDIANA

L ow est since 15 Years!

® P LA T IN U M

P la tin u m

now a v a ila b le a t p ric e s t h a t m a k e th e u se o f s u b s titu te s a d u b io u s ec o n o m y e s p e c ia lly w h en c o n sid erin g , in a d d itio n , th e long life a n d h ig h r e tu r n a b le v a lu e o f old w ares.

P la tin u m or P l a tin u m - R h o d iu m L a b o ra to ry Wares

a re m a d e o f p la tin u m refin ed fo r its specific p u rp o s e to a g ra d e o f p u r ity j u s t for th e c h e m is t a n d c o n fo rm in g w ith th e re q u ire m e n ts o f h ig h e s t c h e m ic al a u th o ritie s .

P la tin u m - R h o d iu m -A llo y

is p re fe rre d fo r g en eral ro u tin e w o rk fo r a d d e d m e c h a n ic a l s tr e n g th , low deg ree o f v o la tiliz a tio n a n d m in im u m ch em ical losses.

Exchange a n d R e m a k in g

o f y o u r o ld w o rn -o u t p la tin u m w ares will a d d to th e ir le n g th o f service a t a n o m in a l co st a n d will a lw a y s k ee p y o u r e n tir e sto c k a v a ila b le fo r in s t a n t u se.

W e supply P L A T IN U M and P L A T IN U M M ETA LS of every description an d for every purpose.

Ask fo r our Catalog E-15 describing our f u l l line o f apparatus.

THE AM ERICAN PLATINUM W O R K S

N . J . R . R . A V E . A T O L IV E R S T .

N E W A R K , N . J .

2Scc C ru c ib le

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Seventeen sizes. The very latest for laboratory and plant. Reduces laboratory expense and saves stock room space.

T h e in n e r a n d o u te r co n es o f e v e ry size are g ro u n d to g e th e r so t h a t th e y a r e c h a n g e a b le . S ingle p ie ce s c a n b e re p la c e d b y g iv in g th e size n u m b e r. C O N F U S IO N IS E L I M I N A T E D as e a c h in d iv id u a l p iece is n u m b e re d .

J o in t s a re m a d e to be in te rc h a n g e a b le w ith G e rm a n s ta n d a r d sizes.

F o r f u r th e r d a t a a n d p ric e s w rite fo r b o o k le t sh o w in g th e d iffe re n t a p p a r a tu s w h ic h w e are m a k in g w ith th e se jo in ts .

Expert Glass B low ing—Glass G rinding—Glass Engraving

/ \ Send us your sketch or blue p rin t fo r quotation.

S c i e n t i f i c Glass Apparatus Co.

L aboratory S u p p lie s & C hem icals

\ y 49 A c k e r m a n S t . , B l o o m f i e l d , N . J .

N ew ! ^I n t e r c h a n g e a b l e

Ground Glass Connections

M

a d e o f

E

i t h e r

P

y r e x o r

F

l i n t

G

l a s s

.

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A N A L Y T IC A L B A L A N C E

College Model for

Q uantitative Analysis and Research

455 BALANCE—A n a ly tic a l, a medium priced balance for ordinary analytical work. T he releasing mechanism is of th e fallaway type w ith three- point suspension for th e beam. A spirit level is fastened to the rear of the brass base of the column. The pan arrest is independent w ith autom atic stop and is of the self-locking type.

All brass p arts are heavily lacquered.

C a p a c ity — 100 grams.

S e n s ib ility — 1/20 milligram.

B e a m —Of rolled alum inum 6M inches long, graduated in white on black w ith 50 divisions on each side of the zero point. Used w ith a 5 milligram rider each division represents 1/io milligram.

R id e r C a rrie r— Consists of a sliding rod to which are attached patented rider hooks, so constructed as to m ake it impossible for the rider to slide back on th e shank of th e hook.

K n ife E dges a n d B e a rin g s —Of Russian agate perfectly ground.

P ans—2 )4 inches in diam eter.

B ow s—4Jij inches wide by 8 inches high.

C ase— M ahogany w ith the front door counter

poised. Dimensions, 16K inches long, 15 inches high, and 9 }{ inches wide.

P ric e —W ith slate b ase... 75.00 456 BALANCE— A n a ly tic a l, same as No. 455, but w ith plate glass b a s e ... 85.00

Im m ediate delivery fro m stock.

Refer to Catalog, “ C” fo r additional Laboratory Apparatus.

THE

CHEMICAL RUBBER COMPANY

L a b o ra to ry A p p a r a tu s a n d C h e m ic a ls W e s t 1 1 2 th S t r e e t a n d L o c u s t A v e .

C l e v e l a n d , O h i o

New Catalog Merck’s

Laboratory Chemicals

This Catalog contains a complete list o f our newly restandardized C. P. and Reagent Chemicals. They conform to or exceed in purity the well know n and widely recognized “Standards of M urray”

(1927 edition). The analysis o f each C. P.

and Reagent is given in the Catalog and shown on the container label.

W rite fo r Catalog

M E R C K & C O . I

n c

.

M A N U F A C T U R I N G C H E M I S T S R A H W A Y , N. J .

N o w Y o r k P h i l a d e l p h i a S t. L o u i s

I n C a n a d a : M E R C K & C O . L i m i t e d , M o n t r e a l

W H A T M A N N o. 42

For Obstinate Precipitates

Y o u k n o w th e m , th o se o b s tin a te , fine p r e c ip ita te s t h a t seep th ro u g h a n y b u t th e m o s t u n ifo rm ly close F ilte r P a p e rs.

F o r su c h b u g b e a rs, u se W H A T M A N F ilte r P a p e r N o . 42, close te x tu r e d , low a s h , id e a l for fre sh ly p r e c ip ita te d B a riu m S u lfa te , M e ta s ta n n ic A cid , e tc .

L e a d in g O il, C o a l, M e ta llu rg ic a l, F e rtiliz e r a n d o th e r L a b o r a to rie s r u n n in g S u lfu rs, T in s , e tc . re g u la rly h a v e lo n g been s ta n d a r d iz e d on N o . 42.

Let us send you sam ples H . REEVE A NG EL & CO., IN C . 7-11 S p ru c e S t. N ew Y o rk , N . Y.

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BECKER

A N A LY TIC A L BALAN C ES

IN OUR STOCK FOR IMMEDIATE SHIPMENT

1886-C.

C H R IS T IA N B E C K E R A N A L Y T IC A L B A L A N C E N O . 9, w ith sp e c ia l b e a m a r r e s t ( p a te n te d ) w h ic h n o t o n ly in s u r e s p o s itiv e a lig n m e n t of t h e a g a te ed g e s w ith th e ir re s p e c tiv e b e a rin g s , b u t is so d e s ig n e d t h a t th e c e n te r a g a te k n if e e d g e is d ir e c tly o v e r th e c e n te r o f th e c o lu m n . S in c e t h e b e a m a r r e s t a r m s a n d th e b e a m p iv o t a b o u t a c o m m o n ax is, t h e s u p p o r tin g p o in ts of th e a r r e s t a r m s m o v e th r o u g h th e s a m e a r c a s th e s u p p o r tin g p o in ts o f t h e b e a m , so t h a t c o n t a c t b e tw e e n e d g e s a n d b e a rin g s a lw a y s re m a in s th e sa m e a n d th e s h if tin g o f th e b e a m , w ith th e c o n s e q u e n t d u llin g of t h e a g a te e d g e s a n d b e a rin g s , is th e r e b y a v o id e d .

Sensitivity—Vioth mg w ith full load.

Capacity—200 gram s in each pan.

Case— Of polished m ahogany, w ith glass sides and top, front sliding frame counterpoised, rear frame rem ovable. W ith polished black plate glass base inside of the case. Outside dimensions, 19'/< inches long, 11®/* inches deep, 20 inches high. W ith vial levels and leveling screws.

Beam—Of hard rolled alum inum , of great tensile strength and uniform density; 7 inches long, graduated from 0 in center to 100 divisions on each side, each division corresponding to '/jo th m g when using a 5 mg rider.

Knife Edges and P lan es—Of agate throughout.

R elease and A rrest—Independent arrest for pans w ith autom atic stop.

P a n s—Of alum inum , 3 inches diam eter.

Arches—Of alum inum , 4 ‘/< inches wide by 8 V2 inches inside height.

1886-B. Balance, Analytical, Christian B ecker No. 9, as above described, with A uto-D ex attach m en t (see page 3) b u t w ithout weights. W ith three 10 mg riders... 195.00 Code W o rd ... Aolce 1886-C. Ditto, No. 9 b u t w ith Chainom atic feature in addition to Auto-Dex A ttach m en t... 235.00 C o d e W o rd ... Aolcg

ARTHUR H. T H O M A S COM PANY

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

LA BORA TO RY AP PA RA T US AND R E A G E N T S

W E S T WASHINGTON SQ UA RE PH ILA D ELPH IA , U. S. A.

Cable Address, “ B A LA NCE,” Philadelphia

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12 A N A L Y T I C A L E D IT IO N Vol. 2, No. 2

B ECK ER

ANALYTICAL BALAN C ES

1870. 1882. (See te x t on o p posite page.)

C H R IS T IA N B E C K E R A N A L Y T IC A L B A L A N C E N O . 8-A . A n A m e ric a n -m a d e b a la n c e of h ig h r e p u ta tio n , fo r y e a r s p o p u la r in e d u c a tio n a l, in d u s tr ia l a n d G o v e r n m e n t la b o ra to r ie s .

Sensitivity— »/so m illigram w ith full load.

Capacity— 200 gram s in each pan.

Case—p f polished m ahogany, w ith glass sides and to p and w ith fro n t sliding fram e counterpoised, and w ith a polished b lack p la te glass base inside of th e case. O utside dim ensions 161/* inches long, 181/* inches high, 9 inches deep; inside dim ensions 13 inches long, 13 inches high, 6*A inches deep.

B eam — Of h ard rolled alum inum alloy of g re a t d en sity and tensile stre n g th , 7 inches long w ith g rad u atio n s in black from 0 to 5 m g in l/jo th s on bo th sides of th e cen tral knife edge.

K nife E dges and P la n e s— Of ag ate th ro u g h o u t.

R elease and A rrest— In d ep en d en t a rre s t fo r p a n s w ith a u to m a tic stop.

P a n s — Of polished G erm an silver, 2*/8 inches d iam eter.

A rches— Of polished G erm an silver wire, w ith 4-inch spread.

R id ers— E ach balance is furnished w ith th re e 10-mg riders.

1870. Balance, Analytical, Christian Becker No. 8-A, as above described, w ithout weights, b u t with three 10-mg rid ers... 150.00 Code W o rd ... A oiuz C H R IS T IA N B E C K E R A N A L Y T IC A L B A L A N C E N O . 15. T h is is a h ig h - g ra d e a n a ly tic a l b a la n c e a t m o d e ra te p ric e , b u t w h ic h m e e ts all o r d in a r y n e e d s o f a n a ly tic a l w o rk .

Sensitivity— */io m illigram w ith full load.

Capacity— 200 gram s in each pan.

Case— Of polished m ahogany, w ith glass sides and to p and w ith fro n t sliding fram e counterpoised, and w ith a polished b lack p la te glass base inside of the case. O utside dim ensions 161/* inches long, 18l/ i inches high b y 9 inches deep; inside dim ensions 13 inches long, 13 inches high, 6*/< inches deep.

B eam — Of hard rolled alum inum alloy, oxidized black, 6 inches long, w ith w hite g rad u atio n s from 0 to 5 mg in 1/to th s on b o th sides of th e cen

tra l knife edge.

K nife E dges and P la n e s — Of ag ate th roughout.

R elease and A rrest— In d ep en d en t a rre st for p an s w ith a u to m a tic stop.

P a n s — Of polished G erm an silver, 2 '/# inches diam eter.

Arches— Of polished G erm an silver wire, w ith 4-inch spread.

R id ers— E ach balance is furnished w ith th ree 5-tng riders.

1872. Balance, Analytical, Christian Becker No. 15, as above described, w ithout weights, b u t w ith three 5-nig riders. 110.00 Code W ord... A o jp i C H R IS T IA N B E C K E R A N A L Y T IC A L B A L A N C E N O . 16. I d e n tic a l w ith C h r is tia n B e c k e r N o . 15 B a la n c e a s to c a p a c ity , s e n s itiv ity a n d all i m p o r t a n t sp e c ific a tio n s, b u t w ith s o m e w h a t sim p lifie d c o n s tru c tio n in o r d e r t o re d u c e c o s t, i. e., th e o m is sio n o f th e d r a w e r in th e m a h o g a n y b a s e , th e s u b s ti tu tio n of a b la c k s la te b a s e fo r th e p o lis h e d g la ss p la te , a n d a c e n tr a l p illa r fin ish e d in d u ll b la c k . R e c o m m e n d e d as a n u n u s u a l b a la n c e v a lu e .

1874. Balance, Analytical, Christian B ecker No. 16, as above described, w ithout weights, b u t with three 5-mg riders. 90.00 Code W o rd ... Aojsc

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

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April 15, 1930 I N D U S T R I A L A N D E N G I N E E R IN G C H E M I S T R Y 13

BE CKER

A N A LY TIC A L BALAN C ES

I885-F. I886-A.

C H A IN O M A T IC A N A L Y T IC A L B A L A N C E S , C h ris tia n B e c k e r. O f th e s a m e g e n e ra l c o n s tru c tio n a s t h e c o r r e s p o n d in g b a la n c e s d e s c rib e d o n o p p o s ite p a g e , b u t w ith C h a in o m a tic A t t a c h m e n t w h ic h e lim in a te s th e u se of rid e r s a n d sm a ll w e ig h ts u p t o 100 m illig ra m s . W e ig h in g is a c c o m p lis h e d b y m e a n s of a g o ld filled c h a in , w ith lin k s of u n ifo rm w e ig h t, s u s p e n d e d b e tw e e n t h e b e a m a n d a v e r n ie r s y s te m . T h e v e rn ie r, w h ic h r e a d s to 0.1 m illig ra m , is o p e r a te d b y a c r a n k o u ts id e th e ca se t o t h e rig h t.

Code 1880. B alance, A nalytical, C h ristian B eck er C hainom atic No. 8-A; identical w ith 8 -A described o n opposite page, b u t w ith W ord chain o m atic a tta c h m e n t. W ith o u t w e ig h ts... 190.00 A o kh y 1882. D itto, No. 15 C hainom atic... >50.00

1883. D itto , No. 16 C hainom atic... 130.00 Aolal

A U T O -D E X A T T A C H M E N T (M o v a b le I n d e x ) , P a t e n t e d , fo r C h r is tia n B e c k e r A n a ly tic a l B a la n c e s . T h e m o v a b le in d e x is c o n tro lle d b y a th u m b w h ee l s i t u a t e d a t th e le ft h a n d sid e of th e f r o n t o f t h e b a la n c e c a se a b o v e t h e d ra w e r. S ee illu s tr a tio n of N o . 1SS6-C o n p a g e 1. A s lig h t t u r n o f th e th u m b w heel m o v e s t h e in d e x p la te to th e le ft o r r ig h t, a s re q u ir e d , u n til th e in d ic a to r o r p o in te r is c o in c id e n t w ith z e ro of t h e in d ex .

T h is a t t a c h m e n t p ro v e s a g r e a t tim e sa v e r, a s i t o b v ia te s th e n e c e s s ity of to u c h in g th e a d j u s tin g n u t, o r o f re c o rd in g th e r e s t p o in t, sin c e th e r e s t p o in t a n d th e z e ro p o in t a r e a lw a y s c o in c id e n t. I t also p r o te c ts th e a g a te e d g e s fro m w e a r a s i t a v o id s th e n e c e s s ity of f r e q u e n t re le a se of t h e b a la n c e .

C ode W ord 1884. B alance, A nalytical, C h ristian B eck er No. 8-A, w ith A uto-D ex A tta c h m en t as above described, b u t w ith o u t w eights 160.00 Aolbe 1884-A. D itto , N o. 8-A C hainom atic, w ith A uto-D ex A tta c h m e n t... ^00.00 A o l b j 1885. D itto , N o. 15, w ith A uto-D ex A tta c h m e n t... ... , ? [ 1885-A. D itto, N o. 15 C hainom atic, w ith A uto-D ex A tta c h m e n t... Jo0*00 AolIbm 1885-B. D itto, N o. 16, w ith A uto-D ex A tta c h m e n t... *00.00 Ac>/oi 1885-C. D itto, N o. 16 C hainom atic, w ith A uto-D ex A tta c h m e n t. . . . ... 140.00 Aolbu

G R A D U A T E D N O T C H E D B E A M . C h r is tia n B e c k e r C h a in o m a tic B a la n c e s a r e f u rn is h e d w ith n o tc h e d b e a m g r a d u a te d fro m le ft t o r ig h t, 0 to 1 g ra m in 100 m g g r a d u a tio n s . T h is f e a tu r e , in c o m b in a tio n w ith t h e C h a in o m a tic A tta c h m e n t, r e s u lts in a b a la n c e in w h ic h t h e u se of a ll w e ig h ts f ro m 0.1 m g to 1.1 g ra m s a re e n tir e ly e lim in a te d . C o n s tr u c tio n is o th e rw is e id e n tic a l w ith N o s. 8-A , 15 a n d 16.

Code 1885-F. B alance, A nalytical, C h ristian B ec k e r C hainom atic No. 8-A, w^ith G ra d u a ted N o tch ed B eam , as above described, b u t W ord w ith o u t w eig h ts... 210,00 Aolby 1886. D itto, N o. 15 C hainom atic, w ith G ra d u a ted N o tch ed B e a m ... 170.00 Aolca 1886-A. D itto , No. 16 C hainom atic, w ith G ra d u a ted N o tch ed B e a m ... 150.00 A olcd

A R T H U R H. T H O M A S C O M P A N Y , P H I L A D E L P H I A , U. S. A.

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BECKER

A N A LY TIC A L BALANCES

1S86-D.

C H R IS T IA N B E C K E R A N A L Y T IC A L C H A IN O M A T IC B A L A N C E N O . 14, I m p ro v e d M o d e l.

S p e c ia lly a d a p te d fo r t h e c a lib r a tio n of v o lu m e tr ic flasks, th e a rc h e s h a v in g a n u n u s u a lly la rg e c le a ra n c e . T h is is a n ew e x e c u tio n of th e old N o . 14 B a la n c e re c o m m e n d e d fo r its la rg e c a p a c ity a n d h ig h s e n s itiv ity .

Sensitivity— '/s th milligram.

Capacity—2 kilos in each pan.

Case—Of polished mahogany, w ith glass sides and top, front sliding fram e counterpoised, rear fram e removable. W ith spirit level and leveling screws. Outside dimensions over all 30 inches long, 27’/j inches high, 14 inches deep.

Beam—Of bronze, of great tensile strength and uniform density; 14 inches long. G raduated on each side from l/ B mg to 20 mg. Will sustain full load w ithout flexure and m aintain adjustm ent through varying tem perature changes.

Chainomatic A ttachm ent—See discussion on page 3.

Knife Edges and P lanes—Of agate. All edges are entirely freed from the bearings when the balance is arrested.

P a n s—Of brass, 8 inches diameter.

P an A rrest—Independent arrest for pans w ith stop.

Arches—Of brass; inside dimensions 8 ‘/ i inches wide by 16 inches high.

1886-D. Balance, Analytical, Christian B ecker Chainom atic No. 14, as above described, w ithout w eights... 350.00 Code W o rd ... A olcl

ARTHUR H. T H O M A S COMPANY

R ETA IL —W H O LES A LE— EX PO RT

L ABO RA TORY A P P A R A T U S AND R E A G E N T S

W EST WASHINGTON SQ UA RE P H IL A D E LPH IA , U. S. A.

Cable Address, "B A LA N C E ,” Philadelphia

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Analytical ^W ⁱ ___________

Edition

Published h j the jinteriean Chemical Soeien/

V o l u m e 2 A P R I L 15, 1930

Number 2

A H ig h -S en sitiv ity A b so lu te-H u m id ity R e co rd er'

C ra n d a ll Z. R o se c ra n s

Le e d s & No r t i i r u p Co m p a n y, 4 0 0 1 St e n t o n Av e,, Pi i i i.a d e i.p h i a, Pa.

M e th o d s o f M e a s u rin g H u m id i ty

N

u m e r o u s devices have been used for the measurem ent of w ater vapor in th e atmosphere, each of which has certain advan

tages peculiar to itself and is adapted for use under particu

lar conditions.

T he wet-and-dry-bulb hy

grometer has been used to

measure atm ospheric hum idity since 1813, and in meteoro

logical and industrial work it is generally accepted as a stand

ard to the practical exclusion of all other methods. I t is well known, however, th a t the device is very inaccurate in its ele

m entary form, and th a t m any refinements m ust be m ade to render its readings reliable. In addition, it is unsuited for the determ ination of hum idities below about 20 per cent a t 25° C., while a t lower hum idities errors in w et-bulb tem peratures cause serious errors in readings of relative hum idity. On the other hand, th e w et-and-dry-bulb hygrom eter is also unsuited for observations a t high tem perature on account of th e dif

ficulties involved in keeping the wick wet. I t is, of course, completely useless above 100° C. U nder best conditions reproducible, results m ay be obtained, b u t an absolute error of less th a n ± 2 per cent cannot be assured. E rrors of =*=5 per cent or m ore m ay occur if the w et sack around the wet bulb is n o t in good condition, or either th e relative hum idity or th e tem perature is low; a t hum idities approaching satura

tion th e error m ay exceed 18 per cent (9). However, within the range of 20 to 100 per cent relative hum idity a t tem pera

tures ranging from 10 ° to 60° C., it fulfils a definite place in hum idity m easurem ents. T he device has only recently been m ade self-recording by the use of platinum resistance ther

mom eters and an ingenious com bination of electrical cir

cuits (1).

T he dew-point hygrom eter depends for its action on the determ ination of th e tem perature a t which dew forms on a polished m etal surface which is cooled by th e evaporation of ether or b y similar means. Reference to tab les or curves then gives th e relative hum idity for a given air tem perature and dew point. This ap p aratu s is evidently n o t adaptable for modification as a self-recording instrum ent. Moreover, it is difficult to a tta in th e low tem peratures necessary to ob

tain precipitation of m oisture in air originally a t 25° C. and with a relative hum idity of less th a n 10 per cent.

‘ R eceived D ecem ber 9, 1929.

A n a p p a r a t u s h a s b e e n dev elo p ed fo r m e a s u r in g a n d re c o r d in g t h e a m o u n t o f w a te r v a p o r in t h e a ir , w h ic h is s u ita b le fo r re c o rd in g h u m i d itie s f r o m zero u p to s a t u r a t i o n w ith in a te m p e r a tu r e r a n g e f r o m

— 100° to a b o u t 200° C. F ro m 0 to 10 p e r c e n t a t 25° C. its a c c u ra c y is ± 0 .0 5 p e r c e n t re la tiv e h u m i d it y . T h is a p p a r a t u s is b a se d o n t h e m e a s u r e m e n t o f th e t h e r m a l c o n d u c tiv ity of w a te r v a p o r a n d a ir m ix tu r e s , a n d is c o n tin u o u s re a d in g . A c o m m e rc ia l m o d ific a tio n of t h i s a p p a r a t u s is i n su c c e s s fu l o p e ra tio n , a lt h o u g h i t is n o t y e t p e rfe c te d fo r g e n e ra l p l a n t u se .

T he hair hygrom eter (3) shows a tendency to give higher and higher readings as tim e elapses, owing to the per

m anent elongation of the hair kept under tension. N o d ata are available regarding the accuracy a tta in a b le a t hum idi

ties below 10 per cent a t 25°

C., b u t Griffiths shows th a t when hair hygrom eters were subjected to hum idities of the order of 5 per cent a t abo u t 20° C. a perm anent change oc

curred, indicating th a t the hairs h ad stretched.

T he cotton hygrom eter described by Griffiths depends for its operation on the m aintenance of a water-soaked cotton winding around a resistance therm om eter. I t is therefore subject to th e same lim itations as th e wet-and-dry-bulb hygrometer.

If th e hum idity rem ains constant, it can be determined to w ithin ±0.1 per cent of its true value by absorbing the w ater vapor from a known volum e of air in a weighed absorption tube. Such accuracy is only m ade possible by the exercise of special precautions. U nder ordinary conditions, however, errors of 2 to 3 per cent m ay be expected w ith this m ethod, and w ith a rapidly varying hum idity it is practically useless, giving only an average value during th e tim e of observation.

H eretofore no commercial m ethod has been available for continuously measuring and recording the am ount of w ater v apor in air over a wide range of relative humidities, w ith an accuracy approxim ating th a t obtainable w ith th e absorption m ethod. A request was recently m ade by Bell System en

gineers for an ap p aratu s suitable for measuring and recording low hum idities w ithin a tem perature range of 25-50° C.

(77-122° F.) and sensitive to changes of ab o u t 0.05 per cent relative humidities. A fter consultation w ith the engineers of the Bell Telephone Laboratories, th e task of constructing a suitable ap paratus was undertaken, w ith th e understanding th a t A. C. W alker of th a t organization would calibrate the apparatus. D octor W alker’s work in this connection is pu b lished in a companion paper (10).

T he dew-point apparatus, cotton hygrom eter, and chemical absorption m ethods cannot a t present be m ade recording, a t least in satisfactory form. T he hair hygrom eter would oper

ate w ithin th e desired range of hum idity, b u t would certainly not m eet th e requirem ents of accuracy. D istinct possibilities were offered by th e therm al-conduetivity m ethod, and it is the purpose of this paper to show how th e unique character

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130 A N A L Y T I C A L E D I T I O N Vol. 2, No. 2 istics of this method are particularly adapted for th e m easure

m ent of extremely low humidities (0.1 to 10 per cent relative hum idity a t 25° C.). The adaptation has been carried far enough to dem onstrate its success as a semi-commercial plant installation. This m ethod can be adapted readily for re

cording continuously relative humidities from 0 up to satura-

tion; from 0 to 10 per cent a t 25° C. the accuracy approxi

m ates ± 0 .0 5 per cent relative hum idity. In general, it is capable of making determ inations a t tem peratures ranging from —100° C., or lower, to about 200° C., if all constituents of the m ixture being measured remain in the gaseous phase.

T h e r m a l- C o n d u c tiv ity M e th o d fo r G as A n a ly sis Koepsel (-5) in 1908 first described apparatus for determ in

ing concentrations of hydrogen in air by th e therm al-conduc- tiv ity method. Shakespear (8) made various improvements on the device of Koepsel, and with Daynes (2) made an elabo

ra te theoretical investigation of the m ethod. Palm er and W eaver (<?, IS) investigated various types of gas-analysis cells and electrical circuits and applied th e m ethod to the analysis of a variety of gaseous mixtures.

A brief description of th e gas-analysis circuit and cell will be repeated here.

Ga s-An a l y s i s Ci r c u i t—Two fine platinum wires are

placed axially in two tubes of metal, and are insulated from

the m etal. One tube is sealed w ith dry air in it. The other tube is connected so th a t the gas to be analyzed passes through i t and over th e wire. T he tw o wires are connected in a W heatstone bridge circuit as shown in Figure 1. S is the sealed wire, or standard, and X is th e wire exposed to the gas to be analyzed. A and B are the other arm s of th e W heat

stone bridge, and K is a slide wire for adjusting the bridge to a balanced condition as desired. If current from the b a t

tery, E, is passed through the bridge network, the fine plati

num wires are heated. Assume th a t d ry air is passed through the cell X , and th a t the bridge is balanced by an adjustm ent of th e slide wire. Now if a gas of higher therm al conductivity th a n air—-water vapor, for example— is passed through th e X cell, th e tem perature of the X wire will decrease, as the heat will be conducted aw ay from the wire a t a higher rate, owing to th e higher therm al conductivity of the w ater vapor. As th e tem perature of th e X wire decreases its resistance also decreases, and the bridge becomes unbalanced. The u n balanced potential across th e term inals M -N is measured by a recording potentiom eter. T hus it is evident th a t a calibra

tion of the ap p aratu s can be made, using the variation of the unbalanced potential as an index of th e percentage of the w ater vapor passing through th e cell X .

Ga s- An a l y s i s Ce l l—T he simple gas-analysis cell consists

essentially of two cylindrical tubes, through which th e plati

num wires are stretched. The cell as actually used is shown diagram m atically in Figure 2. The two tubes S and X are formed by drilling holes in a solid block of m etal, and are 0.375 inch (9.53 mm.) in diam eter and 4.5 inches (11.4 cm.) in length. T he wires are sealed into the tubes a t the top by glass-platinum seals. H eavy platinum is used as lead-in wire;

th e fine platinum wire, 0.002 inch (0.05 mm.) in diam eter, is gold-soldered to the lead-in wires.

P e rc e n t Hx0 in A i r

F ig u r e 3 —T h e r m a l C o n d u c t i v i t y o f M ix tu r e s o f W a t e r V a p o r a n d A ir. R e s u l t s o f G riis s a n d S c h m ic k

T he outstanding feature (7) of the cell, as shown in Figure 2, is the m ethod of adm itting gas to th e A' or analyzing wire.

T he gas sample is passed continuously downward through th e tu b e C. A small portion of the sample passes through the tube A into th e gas cell, X . Here it is heated by the fine plati

num wire, which attain s a tem perature of approxim ately 210° C., and consequently rises. I t passes out of th e cell a t th e top, through the diagonal tube, B, and reenters th e main gas-sample tube, C, a t a point opposite th e opening A , through which it entered the cell X . T he action of th e gas is th u s a by-passing of a small am ount of the sample flowing in th e tube C through th e analyzing cell X . This flow of gas is produced by th e difference in weight of the two columns of gas—one in the cell X a t high tem perature and one in the. tube B a t lower tem perature. The essential fact, however, is th a t the tubes A and B join th e main gas-sample tube, C, opposite each other. T hus there is practically no pressure difference between the inlet and th e exit of th e cell X , and th e flow through the cell X is dependent only on the platinum-wire

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April 15, 1930 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 131 tem perature, being practically independent of the velocity of

gas flow through the tube C.

T h e r m a l C o n d u c tiv ity of W a te r V apor

Values of the therm al conductivity of w ater vapor have been given from calculations based on th e specific h eat and viscosity. Recently, however, G russ an d Schmick (/¡) have determ ined th e conductivity of m ixtures of w ater vapor and air w ith considerable accuracy. Figure 3 shows the therm al conductivity of w ater vapor and air m ixtures, referred to air as unity, a t a m ean tem perature of 82.2° C., from the results

F ig u r e 4 —A c tu a l C i r c u i t o f A p p a r a t u s

of Gruss and Schmick. Based upon theoretical considera

tions, these investigators give for the equation of the curve of Figure 3:

/ X A j 1 0.85

\ L j ^j+ A j 3 5 - 1 + 0 4 g l P±

r i l ‘i

where Li and L\ are conductivities of two mixtures and Pi and Pi are the partial pressures of water vapor and air, respectively.

I t was desired to have the recorder accurate to ± 0.05 per cent relative hum idity over a range from 0 to 10 per cent rela

tive hum idity a t 25° C. C alculating the therm al conduc

tiv ity of a m ixture of w ater vapor and air a t tliis upper limit of 10 per cent a t 25° C. from the previous equation, we obtain 1.00116 referred to air as unity. The difference between 1.0000 and 1.00116 represents the limits within which the recording ap paratus should function. T his range is deter

mined, however, for th e gaseous m ixture a t 82.2° C., while in the therm al-conductivitjr cell described here th e m ean gas tem perature is about 100° C. Since th e tem perature coef

ficient of therm al conductivity of w ater vapor is n o t known, even approxim ately, it is possible only to estim ate the sensi

tiv ity of the gas-analysis cell from th e value derived from th e work of Griiss and Schmick. A sensitivity of ± 0.05 per cent relative hum idity is therefore equivalent to a change of th e order of 0.0000058 in the therm al conductivity of the gaseous mixture.

T h e r m a l- C o n d u c tiv ity A p p a r a tu s

The principal difficulty in designing an instrum ent of this type is to obtain sufficient sensitivity of th e gas-analysis cells to work satisfactorily over such narrow lim its of therm al- conductivity change. In order to increase th e degree of un balance of th e W heatstone bridge for a given change of cell- wire resistance, four cell tubes were used, arranged in the circuit as shown in Figure 4. Two cell wires, A'i and X», were

exposed to the air gas-w ater mixture, while th e other cell wires, S \ and iS2, were surrounded by d ry air. B y th e use of this device th e potential drop a t M -N , measured by th e potenti

ometer recorder, is twice th a t which would be obtained by the simple circuit of Figure 1. An a tte m p t was also m ade to in

crease the potential drop a t M -N (Figure 4) by increasing the cu rrent supplied to the bridge.-

Serious difficulties were soon found due to variable readings on constant-hum idity air, or on even dry air. The readings varied rapidly, sometimes increasing, sometim es decreasing.

Accordingly, a potentiom eter was connected across th e bridge to m easure th e unbalanced potentials, and an a tte m p t was m ade to measure the change of the reading per m inute, by tak

ing readings every 15 seconds. A constant-hum idity gas mix

ture was used during all this work. Since the unbalanced po

tentials are functions of the bridge current, th e finalresults of th e above tests as plotted in Figure 5 are shown in millivolts per m inute per milliampere of bridge current. In this w ay all values are strictly com parable in absolute m agnitude, since th e effect of the increase of the bridge current in increasing any unbalanced potential is elim inated by dividing th e drift in millivolts per m inute by th e bridge current.

Various values of bridge current were used, ranging from 500 to 800 milliamperes. T he curve of Figure 5 shows very strikingly th e sudden increase in the drift a t 650 milliamperes.

This increase represents a to ta l lack of reliability or reproduci

bility of the readings. As stated above, all readings were taken on a gas of constant hum idity. T he drifts took place in either a positive or negative direction. The sudden in

crease in the ra te of drift a t about 650 milliamperes is very probably due to the sudden setting u p of rapid and variable convection currents w ithin th e cell tubes themselves when the

B r i d g e C u r r e n t - m i l l i a m p e r e s F i g u r e 5—D r i f t o f R e a d in g s a t V a rio u s

C u r r e n t s

wire tem perature exceeds a certain critical value. T his theory seems reasonable, since all other known factors which vary w ith th e bridge current have been eliminated. T his critical value of tem perature is a function of th e cell diam eter also.

For th e final design, therefore, the current used was 600 milliamperes.

T he variation of sensitivity w ith current is based upon two facts.

(1) An increase of bridge current will obviously cause an increase in the potential measured across the terminals M -N (Figure 4) for a given degree of unbalance of the bridge. This effect is purely electrical.

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132 A N A L Y T I C A L E D I T I O N Vol. 2, No. 2 (2) If the curves of therm al conductivity versus tem perature

for w ater and air diverge w ith an increase of tem perature, the sensitivity of th e instrum ent will increase w ith higher bridge currents since th e difference of therm al conductivity of th e gases being analyzed will be greater. On the other hand, if th e curves of therm al conductivity converge w ith increasing tem perature, th e instrum ent will become less sensitive w ith increasing tem perature.

F ig u r e 6 —C ell U n it

T he effects m ay be additive or subtractive. From the results of W alker (10, Table II), which indicate an increase of sensitivity w ith increase of cell tem perature, it appears th a t th e curves of therm al conductivity for w ater and air diverge as the tem perature increases. No experim ental d ata are available on this point.

Three methods were used for securing a balance of the bridge circuit with dry air in all tubes. (This balance condi

tion is termed the “ dry-air zero.” )

Me t h o d 1 —Each of the four u nit cell tubes was equipped with

convection flow tu b e s; the air to be analyzed was passed through th e A' tubes, dried, and then passed through the standard tubes,

F ig u r e 7— R e c o r d e r C i r c u i t

in series. This m ethod gave the m ost satisfactory results, because the cell is practically independent of tem perature changes and is relatively insensitive to small changes in the current supplied to the bridge. More im portant, however, is the fact th a t changes in th e concentration of gaseous com ponents other th an w ater vapor which m ay be present in the m ixture

have no effect upon the readings, since such changes affect all four arm s of th e bridge equally. This is true, of course, only when w ater vapor is th e only constituent removed by the drying train interposed betw een the X and 5 tubes of th e cells.

Me t h o d 2—In this m ethod the two stan d ard tubes were

filled w ith purified, dried air and were sealed. T he X tubes were provided w ith convection flow tubes, and the air to be analyzed passed only through these in series. A change of 0.1° C. in th e cell tem perature (the cells being enclosed in a constant-tem perature b ath ) caused a bridge unbalance of 0.1 millivolt, equivalent to ab o u t 0.5 per cent relative hum idity a t 25° C. (This sensitivity to changes of cell tem perature was found to be of m inor im portance in a p lan t installation, since the controlled oil-bath tem perature rem ained constant to ± 0.01° C.

for several m onths.) A current change of 0.001 ampere caused a bridge unbalance of 0.05 millivolt. (The use of a direct-current trickle charger on th e storage batteries supplying the bridge completely elim inated any noticeable errors due to variations of bridge current.)

Me t h o d 3—In th is m ethod th e stan d ard tubes were filled

w ith dry air a t atm ospheric pressure, an d were protected w ith open-end drying tubes. These cells were less sensitive to tem p erature changes th an th e previous type, b u t were unsatis

factory owing to d rift of th e dry-air zero.

T he cell u n it is shown in Figure 6, which represents the set-up used according to M ethod 1. T he actual circuit em

ployed is shown in Figure 4. Si, X h and X* represent the standard and analyzing wires, respectively. IC is the zero balancing slide wire, which consisted of a 10-turn K ohlrausch slide wire of 6.5 ohms resistance shunted by a coil of 0.5 ohm.

F i g u r e 8 —R e c o rd e r (F r o n t)

E and F are coarse and fine battery-current rheostats;

the current was adjusted to th e proper value by balancing the potential drop across a coil, D, against th a t of a standard cell, H , using a small reflecting galvanom eter as an index of the balance point. F or convenience, all th e com ponent p a rts of the apparatus, except the b attery and the cells, were m ounted in a single control box.

R e c o rd e r

T he recording potentiom eter is connected to the term inals M-N.

T he instrum ent first used w as a standard potentiom eter- type recorder specially modified to cover a range of 0 to 2 millivolts. Its circuit is shown in Figure 7. T he attain m en t of this low range was made possible by the use of a recorder galvanom eter of much higher sensitivity than those usually produced. Figure 8 shows the front of the type of recorder used, and Figure 9 gives a view of its rear working parts.

The recorder constitutes in effect a galvanometer, a slide-

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April 15, 1930 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 133 wire resistance, and a mechanism set in motion by th e gal

vanom eter to shift a contact point along th e slide wire.

The balance point is determ ined by th e absence of current in the galvanom eter, a t which tim e th e self-balancing mechanism ceases to act.

T he disk on the rear of the recorder (Figure 9) carries the slide wire, S , of Figure 7. If th e potentiom eter is n o t bal

anced, current flows through th e galvanom eter, deflecting it and actuating th e balancing mechanism. T his mechanism turns th e slide-wire disk under the contact which m ay be noted a t th e to p of the disk. T he m ovem ent of th e disk produces an ad justm ent of the potentiom eter, and this autom atic ad-

F ig u r e 9— R e c o rd e r (R e a r)

justm ent continues until the potentiom eter voltage balances the voltage to be measured. A t this tim e the galvanometer returns to its zero position and th e balancing mechanism ceases to act. T hus the position of th e slide wire S, referred to its fixed contact slider, is a m easure of th e unknown voltage, in this case the unbalanced voltage of the gas-analysis bridge.

A small cable attach ed to a pulley on th e shaft carrying the slide wire moves a pen back an d forth across a chart. The position of the pen th u s indicates th e m agnitude of the un

known voltage. T he ch art is in rectangular coordinates, the hum idity scale being 10 inches (25.4 cm.) in width.

C a lib r a tio n

T he gas-analysis cells were connected to th e calibration ap

paratu s described by W alker (10) and air a t various constant known hum idities was passed through th e cells. Recorder readings taken for various hum idities furnish d a ta from which a calibration curve similar to th a t of Figure 10 can be plotted.

T his curve represents th e relation between millivolts as measured on the recording potentiom eter and per cent rela

tive hum idity a t 25° C. I t was tak en on a set of cells operated according to M ethod 1; they were placed in an oil bath a t 40.1° ± 0.01° C.

M e th o d fo r R e c o rd in g H ig h e r H u m id itie s

I t was desired to use th e range of th e recorder to m easure hum idities other th a n those included in th e narrow range of 0 to 10 per cent relative hum idity a t 25° C.

I t was a t first thought th a t a m ultiple-range recorder would be th e sim plest solution of the problem, b u t it was found pos

sible to calibrate the K ohlrausch slide wire, K , in term s of relative hum idity a t 25° C. T h a t is, by using th e recorder galvanom eter as an index of zero current condition (the re

corder being set a t zero on the scale), it was possible to plot a curve of slide-wire reading (K ) versus relative hum idity a t 25° C. W alker (10) describes this procedure in detail.

A m ultiple-range recorder was finally constructed, however, which enables the user to measure hum idity using a single gas-analysis cell and recorder, in th e following ranges: 0- 10 , 0-20, 0-50, and 48-98 millivolts. The first two ranges will cover from dry to saturated air a t 25° C. The last two ranges are useful for measurem ents of high hum idities a t higher tem peratures. The absolute precision and accuracy are, of course, reduced a t the higher ranges.

A ccu racy

On the 10 per cent range the recorder is sensitive to a change of ± 0.02 per cent relative hum idity a t 25° C. T he accuracy is ± 0.05 per cent relative hum idity a t 25° C. F or an instrum ent of such a low range this accuracy is far b etter th a n any heretofore obtained on a self-recording apparatus, and is sufficient for th e purpose for which it was designed.

F u rth e r work in progress bears promise of increasing th e accuracy by a considerable am ount.

F u r t h e r U ses o f t h e A p p a ra tu s

While the application of therm al-conductivity ap p a ratu s to the determ ination of w ater vapor is particularly successful in this case, where very low hum idities are to be measured, it also should have a considerable field in applications where greater ranges of hum idities are to be measured. T his is particularly true where it is desired to measure and record

R ec o rd e r R eading — M ill i v o l t s F ig u r e 10—C a l i b r a t i o n C u rv e

hum idities in an enclosure w ithout introducing any w ate r vapor by th e use of the measuring apparatus, as would be done if th e w et-and-dry-bulb therm om eter were used. T he greatest advantage of th e ap paratus is, of course, th a t it is continuous reading and no in te rm itte n t sampling is necessary.

F u rth er uses for the therm al-conductivity hum idity ap

paratu s are found where it is desired to m easure w ater-vapor content a t very high or very low' tem perature. Above th e boiling point of w ater th e usual forms of hum idity ap p aratu s cannot be used. For example, th e therm al-conductivity m ethod m ight wrell be applied to the determ ination of m oisture in dry kilns used in various processes. Likewise, even if th e tem perature of a gas m ixture is below the freezing point of water, the therm al-conductivity m ethod will still give reli

able indication of the am ount of w ater vapor present in the mixture. W alker and E rn s t (11) have given a m ethod of de

term ining the m oisture in high-pressure tanks of nitrogen, using the ap paratus described.