Industrial and Engineering Chemistry : analytical edition, Vol. 13, No. 6

INDUSTRIAL ^{a n d} ENGINEERING CHEMISTRY

A N A L Y T IC A L E D IT I O N

H A R R IS O N E . H O W E, E D IT O R m IS S U E D J U N E 16, 1941 ♦ V O L . 13, NO. 6 • C O N S E C U T IV E NO. 12

A n aly sis of C ellu lo se D e r i v a t i v e s ...

Leo B. G enung and Russell C. Mallatt 369 P h o to e le c tr ic V ita m in A P h o t o m e t e r ...

Beaumont Demarest 374 P r e c ip ita tio n o f Z in c S u lfid e fr o m S o lu tio n of

A m m o n iu m C it r a te a n d C itric A c i d ...

S. A. Coleman and G . B. L. Smith 377 D e te r m in a tio n o f T h ia m in b y T h io c h ro m e R e a c tio n

R. T. C onner and G. J. Straub 380 C o m b in e d D e te r m in a t io n o f R ib o fla v in a n d T h ia ­

m i n in F o o d P r o d u c t s ...

R. T. C onner and G . J. Straub 385 E th y le n e G lycol D e te r m in a tio n i n a n d R e m o v a l

tr o m C o m m e rc ia l A lkyl E th e r s o f D ie th y le n e G l y c o l ... M argaret K. Seikel 388 S a m p lin g a n d A n a ly sis of P h o s p h o r u s ...

I. W. H. A ldred 390 O x id a tio n of G r a p h ite in A n a ly sis of F e rr o u s M e ta ls

Ralph H. Steinberg and Fred W ilson Smith 392 S im p le S in te r e d - G la s s S a lt B rid g e . H. A. Laitinen 393 D e te r m in a tio n o f A n ilin e P o in t of D a rk P e tr o le u m

P ro d u c ts ...

Robert Matteson, E. H. Zeitfuchs, and K. R. Eldredge 394 T h e rm o e le c tr ic E ffects in P h o to m e tr y . . J. K. Berry 396 V isco sity of C h o c o l a t e ... Joseph Stanley 398 C o n tin u o u s W a te r R e m o v e r . . . . Jack H. Thelin 405 A n a ly se s o f S o d iu m M e ta -, P y ro -, a n d O r th o p h o s ­

p h a te s . . . . A rthur B. G erb er and Francis T. Miles 406

D e te r m in a t io n o f S u c c in ic A cid i n P l a n t T is s u e s . . G eorge W. Pucher and H ubert Bradford Vickery 412 U se of S ilic o m o ly b d ic A cid I n d i c a to r b e fo re V o lu ­

m e t r i c O x id a tio n o f I r o n ...

Albert C. Titus an d C laude W . Sill 416 P r e s s u r e - R e g u la tin g A p p a r a tu s fo r V a c u u m S y s­

te m s . ... Frederick M. Lewis 418 C o m p a ra tiv e T e s ts of C h e m ic a l G la ss w a re . . . .

Edward W ichers, A. N. Finn, an d W . Stanley C labaugh 419 S te a m - D is tilla tio n o f S m a ll Q u a n tit ie s o f V o la tile

O ils L ig h te r t h a n W a t e r ...Frank M. Biffen 422 H y d ro ly sis a n d C a ta ly tic O x id a tio n of C e llu lo sic

M a t e r i a l s ... R. F. Nickerson 423 A p p lic a to r fo r P r e p a r a ti o n o f U n ifo r m P a i n t F ilm s

E. J. Dunn, Jr., and C. H. Baier 427 G r a p h ite H e a tin g B a t h s ... Wm. I. H arber 429 M odified P h o to e le c tr ic P h o to m e te r fo r C o lo rim e tric

D e te r m in a tio n s in W a te r a n d S ew age L a b o ra to rie s William D. Hatfield and G eorge E. Phillips 430 M IC R O C H E M IS T R Y :

D e te r m in a tio n of E x c h a n g e a b le B ases in S o ils . . Michael Peech 436 D e te c tio n a n d T i t r a t i o n of C h r o m a te in B lood

Io d in e D e t e r m i n a t i o n s ...

O liver H. G aebler and M argaret Baty 442 M e th o d of M e a s u rin g C o n ta c t A n g l e s ...

J. J. Bikerman 443 W e t- C o m b u s tio n M ic ro m e th o d fo r D e te r m in a ­

ti o n of C a rb o n a n d H y d r o g e n ...

Bert E. Christensen an d Robert W ong 444

T h e A m erican C hem ical Society assum es no resp o n sib ility for th e s ta te m e n ts and opinions ad v an ced b y c o n trib u to rs to its p u b licatio n s.

25,200 copies of th is issue p rin ted . C o p y rig h t 1941 b y A m erican C hem ical Society.

P u b l i c a t i o n O f f ic e : E d i t o r i a l O f f ic e : 1 1 5 5 1 6 t h S t r e e t , N . W ., W a s h i n g t o n , D . C .

T e l e p h o n e : R e p u b l i c 5 3 0 1 . C a b l e : J i e c h e m ( W a s h i n g t o n )

P u b lish ed b y th e A m erican C hem ical Society, P u b licatio n Office, 2 0 th &

N o rth a m p to n Sts., E a sto n , P e n n a . 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 , P en n a., un d er th e A ct of M arch 3, 1879, as 24 tim es a year. In d u s tria l E d itio n m o n th ly on th e 1st; A nalytical E d itio n m o n th ly on th e 15th. A cceptance for m ailing a t special ra te of postage provided for in Section 1103, A ct of O ctober 3, 1917, au th o rized Ju ly 13, 1918.

A nnual su b scrip tio n ra te , In d u stria l E d itio n a n d A n aly tical E d itio n sold only as a u n it, m em bers $3.00, o thers $4.00. Foreign postage to countries n o t in th e P a n A m erican U nion, $2.25; C an ad ian postage, $0.75.

E a s t o n , P e n n a .

A d v e r t i s i n g D e p a r t m e n t : 3 3 2 W e s t 4 2 n d S t r e e t , N e w Y o r k , N . Y . T e l e p h o n e : B r y a n t 9 - 4 4 3 0

Single copies: In d u stria l E d itio n , $0.75; A n aly tical E d itio n , $0.50. Special ra te s to m em bers.

N o claim s can be allowed fo r copies of jo u rn a ls lo st in th e m ails unless such claim s are received w ithin 60 d ay s of th e d a te of issue, a n d no claim s will be allow ed for issues lost as a re su lt of insufficient notice of change of address. (T en d a y s’ ad v an ce notice req u ired .) “ M issing from files”

can n o t be accepted as th e reason fo r honoring a claim . A ddress claim s to C harles L. P arso n s, Business M anager, 1155 16th S t., N . W ., W ash in g to n , D . C ., U. S. A.

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

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

HEAT TREATI NG F U R NA CE S

mmmmm

E L E C T R I C E X C L U S I V E L Y

M I L W A U K E E , W I S C O N S I N

HEVI DUTY F U R N A C E S

One hundred and forty-five Years ago the first chemical laboratory in the world for undergraduates w as established at Nassau Hall by Dr, John Maclean. Nassau Hall still stands as g monument to this cradle of chemical education though the fine Frick Chemical Labo­

ratory now houses new modern laboratory eguipment. It is gratify­

ing to us to note that Princeton, like m any other leading universities,

uses Hevi Duty Laboratory Furnaces for chemical study and analysis.

lune 15, 1941 A N A L Y T I C A L E D I T I O N 5

i H B

M E R C I

LABORATORY C HE MI C A L S 1 9 4 I

M E R C K & C O . I

nc

.

RAHWAY, N. J.

N E W Y O R K ♦ P H IL A D E L P H IA • S T . LO U IS In C o nod «; M O N T R E A L * T O RO N TO

o V i 3 ^\V

CONTENT:

^ A com p reh en sive list o f M erck Laboratory C hem icals w hich are u sed in every branch o f industry

M olecular w eights C hem ical Form ulas

M axim um im p u rities o f M erck. R eagent C hem icals, in clu d in g th ose w h ich con ­ form to A.C.S. sp ecification s

P rop er storage o f fine ch em icals A tom ic w eights

M etric equivalents U seful con version ratios E q u ivalent o f d egrees B aum e.

W rite to d a y f o r a co p y o f this conven ient a n d h elpful cata lo g

M E R C K & C O . In c . iÀ îan u^actttK in ç, C€/cm iótá R A H W A Y , N. J .

P le a s e s e n d m e a c o p y o f th e n e w Me r c k La b o r a t o r y Ch e m ic a l s Ca t a l o g.

N A M E ... ...

C O M PA N Y ...

S T R E E T ...

C IT Y ... S T A T E ...

KEAdy FOR you NOW'

means Research in Glass

A NEW, ENLARGED AND COMPLETELY REVISED

PRESENTING 358 NEW ITEM S AND TWO HEW LIN ES ^

V Y C O R B R A N D L A B O R A T O R Y W A R E

P Y R E X B R A N D FRITTED W A R E

PYREX

• This new 160-page Catalog is the most comprehensive listing of laboratory glass­

ware we have yet published. I t lists approx­

imately 2700 items of which 358 are new\

Included is a complete listing of the items available in the new P Y R E X brand F ritted Ware, as well as the V YCO ll brand W are fabricated from the new 96% silica glass No. 790.

Prices have been reduced on a number of items. Consumer qu antity discounts apply to practically all items when ordered in full original packages, except for a few items which are packed one piece per pack­

age. F urther economies can be realized if

ware is pur- ' ... ■ - /

chased in assortments

of 20, 50, or 100 original pack­

ages. All items listed are available through your regular laboratory supply dealer.

C O R N I N G G L A S S W O R K S

Please forw ard to me a copy of the new “ P Y K E X ” L aboratory Glassw are Catalog, No. LP-21.

Name. Position.

Company or Institution.

Address __________

Please place ray name on your regular mailing list □ 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

June 15, 1941 A N A L Y T I C A L E D I T I O N 7

Practically-

I

Four Centrifuges in One!

M ICRO — ANGLE — H O RIZO N TA L — CHEM ICAL

INTERNATIONAL "Clinical M o d el"

ANGLE HEADS

The illustration at right shows a streamlined Conical Head for swinging 6 15 ml. glass tubes at an angle. Other Conical Heads with capacities up to 2 0 0 ml. are available.

H O RIZO NTA L HEADS

commonly known as "regular” heads, accommodate 4 15 ml. or 5 0 ml.

glass tubes or combination of both for horizontal sedimentation.

CHEM ICAL BA SK ET HEADS

A Basket Head and Draining Chamber may b e easily interchanged with the guard bowl and tube carrying heads to make a C h e m ic a l C en trifu g e . Baskets and Draining Chambers are available in m anganese bronze, Coors porcelain, monel metal, stainless steel and rubber covered steel.

O ne reason for the continued popularity of the International ''Clinical Model" Centrifuge is its wide range of usefulness due to the variety of interchangeable heads. Thus, at low cost, this small centri­

fuge offers the advantage of being practically four centrifuges in one. Maximum speeds range from 2 ,0 0 0 r.p.m. to 5 ,8 0 0 r.p.m. depending upon the type of head used and whether operated on A.C. or D.C.

M ICRO HEADS

for swinging .5, 1, 2, 3 and 5 ml. glass tubes either at an angle or in a horizontal position.

S en d for Bulletin

CC

or ask your D ealer

IN T ER N A T IO N A L EQ UIPM EN T CO .

352 WESTERN A V E N U E M akers o f Fine Centrifuges BO STO N , M ASS.

^ r c r- r r, ?

C o n g ress, under a Joint Resolution of Ju ly 27, 1866, provided that each o f the states be furnished w ith a com plete set o f w eig hts, running from 10 kilo g ram s to 1 m illigram . . . u n v aryin g stan d ard s of w eight throughout the states.

Unvarying Standards

E q u a lly as u n v a r y in g is th e c o n fo rm ity of M a llin c k ro d t A . R. C h e m ic a ls to th e ir p r e ­ d e te rm in e d s ta n d a r d s of p u r ity . W h e r e a b s o lu te a c c u r a c y in a n a ly tic a l w o r k is e sse n tia l, M a llin c k ro d t r e a g e n ts in s u re th e p u r ity t h a t f a c ilita te s p re c isio n in th e la b o ra to ry .

Send for new catalogue of M allinckrodt A n aly tical R e a g e n ts an d o th er chem icals for lab o rato ry use. C on­

tain s detailed descriptions of chem icals for every type of analytical w o rk . . . gravim etric, gasom etric, colori­

m etric or titrim etric.

M A L L I N C K R O D T C H E M I C A L W O R K S

ST. LOUIS • PHILADELPHIA * M ONTREAL

CH ICA G O • NEW YORK • TORONTO

June 15, 1941 A N A L Y T I C A L E D I T I O N

H O S K I N S P R O D U C T S

It’s not quite so sim p le , a s " a fe w tw ists of the w ris ts ” , to re n e w the C h ro m e l unit in o ur FD m uffle fu rn a ce . But it’s not fa r from it. The co iled w ir e is just w ra p p e d a ro u n d the g ro o ved su rfa ce . Further, w h e n the C h ro m el unit " b u rn s out” from sim p ly w e a r in g out, it d o e s not sp o il the m uffle, w h ic h can be u sed tim e a n d tim e a g a in , after re n e w in g the w ir e . W e u se a co nstructio n that per­

m its a o n e -p ie ce w ir e elem en t (so m e tim e s tw o - p iece) b e c a u s e w h e n the w ir e u ltim a te ly w e a r s out a n d f a ils at a g iv e n point, n o rm a lly the rest of the w ire is ab o u t in that sa m e co n d itio n , too. The fact that the m uffle so seld o m n eed s to be rep la ced (barring a ccid e n ts) o b v io u s ly points to the e c o n o m y of m a in te n a n c e of H o sk in s T y p e FD fu rn a c e s . A further e c o n o m y fa cto r is the re m a rk a b le d u ra ­ b ility of thé C h ro m e l w ir e , itself. Y o u m in im iz e tie -u p s, a n d thus s a v e both tim e a n d m o n e y , in u sin g H o sk in s T y p e FD fu rn a c e s. Fo r m ore in fo rm a ­ tio n, w rite to y o u r d e a le r or to u s. . . . H o sk in s M an u fa ctu rin g C o m p a n y , Detroit, M ic h ig a n .

T h e C h ro m e l h e lic a l unit is w ra p p e d a ro u n d the o n e- p ie ce g ro o v e d m u ffle, a n d is e a s y fo a p p ly .

n Th e in su la tio n is 3 * th ick in the F D - 2 0 2 , a n d in the L la rg e r F D - 2 0 4 , it’s 41/2".

Th e s lid in g d o o r m in im iz e s the h e a t lo s s , th at re s u lts from o p e n in g the d o o r. It s e ld o m n e e d s to be fu ll o p e n .

H e a v ie r C h ro m e l u n it ca n be u se d , b e c a u s e o n e fu rn a c e o p e ra te s on o n ly one v o lta g e .

T h e fu rn a ce o p e ra te s on lin e v o lta g e , w ith tem p e ra tu re co n tro l throu gh a rh e o sta t.

A s m a ll, in e x p e n s iv e pyrom eter/ g iv in g a p p ro x im a te tem p e ratu re m e a s u re m e n ts , is a v a ila b le fo r m o u n tin g on th is fu rn a c e .

E L E C T R I C H E A T T R E A T I N G F U R N A C E S • • H E A T I N G E L E M E N T A L L O Y S • • T H E R M O C O U P L E A N D L E A D W IR E • • P Y R O M E T E R S • • W E L D IN G W IR E • • H E A T R E S IS T A N T C A S T IN G S • • E N A M E L IN G F IX T U R E S • • S P A R K P L U G E L E C T R O D E W IR E • • S P E C I A L A L L O Y S O F N I C K E L • • P R O T E C T IO N T U B E S

10 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

A .H .T . C O . S P E C I F I C A T I O N

K R E B S E L E C T R I C S T I R R E R

A R T H U R H. T H O M A S C O M P A N Y

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

L A B O R A TO R Y A P P A R A T U S A N D R EAG EN TS

W E S T W A SH IN G T O N S Q U A R E , P H IL A D E L P H IA , U . S . A . C a b le A d d re s s , " B a l a n c e ,” P h il a d e lp h ia

Providing m a x im u m m otor ru n n in g to rq u e w ith heavy loads a t v a ria b le speeds

0242. F ig. 2 9242. Fig. 3

Showing stirrin g rod a t- Show ing stirrin g ro d a t ­ tach ed to “ In te rm ed ia te " ta c h ed to " H ig h " speed speed sh aft of m otor. sh aft of m otor.

9242. Fig. 1

Showing stirrin g rod a tta ch e d to “ Slow " speed sh aft of m otor.

STIRRING APPARATUS, KREBS ELECTRIC, A.H.T. Co. Specification.

C o n s is ti n g o f * /» h .p ., 8 0 0 0 r .p .m . s e r ie s w o u n d u n i v e r s a l m o t o r w i th t h r e e s h a f t e x te n s io n s , i n t e r c h a n g e a b l e , a d j u s t a b l e c h u c k w i t h M o n e l m e t a l s t i r r i n g r o d , a n d e n c lo s e d a n n u l a r r e s i s t a n c e , m o u n t e d o n h e a v y s u p p o r t .

T h e a p p a r a t u s is ru g g e d a n d q u i e t r u n n i n g a n d u tili z e s to b e s t a d v a n t a g e m a x im u m m o t o r r u n n i n g t o r q u e a t v a r i a b le s p e e d s b y u s e o f i n t e g r a l d o u b le r e d u c t io n w o r m g e a r , m o t o r s h a f t e x te n s io n s o p e r a t ­ in g a t th r e e d if f e r e n t s p e e d s , a n d r h e o s t a t a d j a c e n t t o m o t o r .

T h e in te r c h a n g e a b le , a d ju s t a b l e c h u c k is p r o v id e d w ith e x t r a lo n g b e a r i n g s u r f a c e a n d t a k e s s t i r r i n g ro d s y i o r f*6~ in c h d ia m e te r . I t is f u r n is h e d w ith M o n e l m e t a l s t i r r i n g r o d 12 in c h e s lo n g w ith f o u r - b la d e p r o p e l le r 2 in c h e s d ia m e te r , a n d l j ^ - i n c h p u ll e y fo r o p e r a t in g o t h e r a p p a r a t u s . G la s s s t i r r i n g r o d s -iV-inch d i a m e t e r c a n b e u s e d i n p la c e o f t h e M o n e l m e t a l s t i r r i n g ro d .

T he resistance in th e rheostat is sufficient to stop th e m otor so th a t, by changing th e chuck from one shaft to another, speeds are available w ithin th e following upper lim its: on low speed shaft, 500 r.p.m .; on interm ediate speed shaft, 2500 r.p.m .; and on high speed shaft, 5000 r.p.m . Speed rates were determ ined in a cylindrical bath, 12 inches diam eter X 12 inches high, containing approxim ately 5 gallons of w ater.

The stirrer can be tilted and ro tated through a wide range of angles and positions, w ithout moving th e support, by means of a modified ball and socket joint w ith th u m b screw locking device.

The stirrer support, which rests on four felt cushions, consists of a heavy and exceptionally stable base w ith crystal black lacquer finish, w ith clearance of approxim ately 16 inches between th e two front feet, and a cadm ium -plated steel rod 30 inches long X 3/t-inch diam eter. T he sem icircular shape of th e front feet perm its th e placing of cylindrical vessels up to 12 inches diam eter close to th e support rod.

9242. S tim n g Apparatus, Electric, K rebs, A.H.T. Co. Specification, as above described, w ith adjustable chuck, for stirring rods i/ t or Vit-inch diam eter, complete w ith M onel m etal stirring rod 12 inches long X Vi-inch diam eter w ith four-blade propeller 2 inches diam eter, support w ith 30-inch rod, toggle switch, cord and plug.

Power consumption approxim ately 0.49 amperes. F o r use on 110 volts, a.c. or d.c... 45.00 9242-A. Ditto, b u t for use on 220 volts, a.c. or d .c ... 48.75 9242-D. Support, only, with rod 30 inches high X 5/<-inch d iam eter... 4.50

INDUSTRIAL ^{a n d} ENGINEERING CHEMISTRY

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

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

A nalysis o f C ellulose D erivatives

Determination o f Total Combined A c y l in Cellulose O rganic Esters

LEO B . G E N U N G A N D R U S S E L L C . M A L L A T T 1 E a s tm a n K o d a k C o m p a n y , R o c h e s te r , N . Y.

M o s t o f t h e p u b lis h e d m e t h o d s fo r t h e d e te r ­ m i n a t i o n o f c o m b in e d acy l in c e llu lo s e d e riv a tiv e s h a v e b e e n r e s tr i c te d to a c e ty l in c e llu lo s e a c e t a te . T h e th r e e b e s t m e t h o d s , E b e r s t a d t, a lc o h o lic a l ­ k a li, a n d O s t a c id d is ti lla tio n , h a v e b e e n f u r t h e r in v e s tig a te d a s to t h e i r a p p lic a b ility fo r g e n e ra l ac y l a n a ly s is . T h e effe c ts o f th e i r m o r e im p o r t a n t v a ria b le s h a v e b e e n m e a s u r e d , a n d t h e p re c is io n , a c c u ra c y , a n d r a n g e o f a p p lic a b ility o f e a c h a r e r e p o r te d .

I n o rd e r to a v o id e r r o r s d u e to t h e h e te r o g e n e ity o f t h e r e a c t io n m i x tu r e a n d to excess a lk a lin ity o r a c id ity , te m p e r a t u r e , a n d ti m e , th e s e v a ria b le s m u s t b e c o n tr o lle d w ith i n d e fin ite li m i ts . I t w as

f o u n d t h a t s a p o n ific a tio n s by th e E b e r s ta d t m e t h o d a re b e s t r u n a t a n in i t i a l a lk a li c o n c e n tr a ­ ti o n o f 0.25 N fo r 48 h o u r s a t n o t h ig h e r t h a n 35° C.- T h is is t h e m o s t a c c u r a te m e th o d , h u t is a p p lic a b le to c e llu lo s e a c e ta te a n d o n ly c e r t a in o t h e r e s te rs . S a p o n ific a tio n m e t h o d s u s in g a lc o h o lic a lk a li a re a p p lic a b le to p ra c tic a lly a ll c e llu lo s e e s te rs , b u t a rc less a c c u r a te a n d re lia b le . T h e m o s t s a tis f a c to r y c o n d itio n s a re 0.25 iV in i ti a l c o n c e n tr a tio n fo r 21 h o u r s a t n o t h ig h e r t h a n 30° C. T h e a c id d is ti ll a ­ tio n m e t h o d o f O s t is r e s tr i c te d in i t s a p p lic a tio n , b u t i t h a s sp e c ia l u s e s d u e to s h o r te r e la p s e d ti m e r e q u ir e d fo r a n a n a ly s is a n d to t h e f a c t t h a t o n ly v o la tile a c id ity is m e a s u re d .

T

H E increasing stu d ie s of th e v ario u s esters of cellulose an d th e ever-w idening field of a p p lic a tio n of th ese esters to p ractical uses h a v e increased th e need for te s te d a n d reli­

able m e th o d s fo r th e a n aly sis of th ese p ro d u cts. I t is th e purpose of th is p a p e r to p re s e n t th e re su lts of a ccu m u lated experience a n d of special stu d ies m a d e on th e m o s t satisfac­

to ry an d generally ap p licab le of th e m eth o d s available.

T h e m e th o d s fo r th e d e te rm in a tio n of to ta l com bined acyl in cellulose organic e sters fall in to tw o g eneral classes: sa­

ponification w ith alk alin e rea g e n ts o r decom position a n d h y ­ drolysis b y acids. T h e m e th o d s in th e lite ra tu re , ap p ly in g principally to th e d e te rm in a tio n of ac e ty l o r com bined acetic acid in cellulose a c e ta te , h a v e b een w ell review ed b y K ru eg er (5) a n d b y M u rra y , S ta u d , a n d G ra y (11), a n d re c e n t a d d i­

tio n al references are given b y M a rsh a n d W ood (5).

Of th e saponification m ethods using aqueous alkali (8), th e one devised by E b erstad t (4) working w ith Knoevenagel (6, 7) and modified som ew hat by M urray, Staud, and G ray (11) has proved useful and reliable when applied to cellulose acetate and to cer­

tain sim ilar esters of low molecular w eight organic acids. I t breaks down, however, when applied to esters of th e ty p e of cellu­

lose stearate and even to certain cellulose butyrates. T his method involves swelling the sam ple w ith warm aqueous alcohol, followed by addition of aqueous alkali and a long saponification a t room tem perature.

The use of sodium ethylate was proposed by Cross and Bevan ($), and was successfully applied w ith modifications by Wood- bridge (16) and M ork (10). M ethyl or ethyl alcoholic alkali was

1 P rese n t address, D e p a rtm e n t of C h em istry , U n iv e rsity of R ochester, R ochester, N . Y.

used similarly by Green and Perkin (5). These m ethods are ca­

pable of yielding good results if conditions of tim e, tem perature, and alkali stren g th are carefully chosen. Furtherm ore, these alkalies atta c k a m uch wider range of cellulose esters th a n aque­

ous alkali. Zemplen (16) saponified cellulose acetate w ith traces of sodium m ethylate in refluxing absolute m ethyl alcohol, b u t his m ethod is not applicable to q u an titativ e analysis because the am ount of alkali consumed is not stoichiometric.

R apid m ethods involving solution of th e sam ple in pyridine have been described by B attegay and Penche (2) and also by M urray, Staud, and G ray (11). Aqueous alkali is added to th e solution and it is heated for a half hour a t n o t more th an a b o u t 55° C. Roeper (14) has tried various o th er solvents, including acetone, acetone-water, and acetone-alcohol mixtures w ith aque­

ous alkali a t various tim es and tem peratures. C oncordant and reasonable results were obtained w ith certain esters, b u t these m ethods are n o t generally applicable nor accurate.

The acid hydrolysis m ethod was proposed in 1906 by Ost (IS), who suggested th e use of strong sulfuric acid followed by steam - distillation of the liberated acetic acid, and also by Green and Perkin (5), who decomposed th e ester w ith sulfuric acid in th e presence of absolute ethyl alcohol and th en distilled off ethyl acetate and saponified this ester in the distillate. Various m odi­

fications of these methods have been reported (8), b u t nearly all th is work has been restricted to th e determ ination of combined acetic acid. A bribat (1) dissolved and degraded cellulose ace­

ta te w ith cold concentrated hydrochloric acid and then hydro­

lyzed of! the acetyl groups by diluting the acid. T he acetic acid liberated was titra te d potentiom etrically in th e presence of hydro­

chloric acid. Pilgrim (IS) used warm strong hydrochloric acid to degrade th e cellulose, and hydrolyzed th e acetyl groups by progressive dilution of th e acid under conditions mild enough to avoid charring. T he reaction m ixture was th en diluted to a known volume and a suitable aliquot titra te d . T he difference in tite r between the sam ple and a blank was taken as a measure of the acetic acid liberated.

369

370

T hese m eth o d s h av e th e following in h eren t difficulties or objections:

1. M ost of th e methods, and particularly the practical and widely applicable ones, involve heterogeneous conditions for the saponification or hydrolysis. The physical form of the solid ester is thus an im portant variable. I t is often necessary to powder or reprecipitate th e sample before reproducible and reliable results can be obtained. Since insoluble regenerated cellu­

lose is formed in all these m ethods except the strong acid proce­

dure, the final titration m ust be slow enough to allow for complete soaking out of the excess reagent. These factors may cause low results due to slow rate of penetration of the reagent and incomplete reaction, or high results due to slow soaking out of the excess reagent.

2. When this first difficulty is m et by dissolving the ester in a solvent, such as pyridine or acetone, the method is limited to esters soluble in such solvents and whose solutions will tolerate th e addition of a comparatively large volume of aqueous or alco­

holic alkali. N ot all the-esters of cellulose will m eet these re­

quirements. T he back-titration m ust still be made in the pres­

ence of regenerated cellulose.

3. Cellulose and its derivatives form acidic decomposition products when heated excessively w ith alkalies or acids in the presence of air. Strong alkalinities and elevated tem peratures m ust be avoided, and th e variables of time, tem perature, and re­

agent concentration m ust be balanced carefully if accurate re­

sults are to be obtained.

4. T he precision of these methods is, of course, easily meas­

urable, b u t the accuracy is very difficult to establish. The het­

erogeneous conditions m et in saponification and back-titration and the difficulty of complete distillation of acids after acid de­

composition tend to produce low results if the conditions are not vigorous enough, while too severe conditions of reagent concen­

trations and tem perature produce high results. Furtherm ore, it is extremely difficult to prepare a cellulose ester of known acyl con­

te n t to serve as a standard. Simpler esters, such as ethyl acetate or a glucose acetate, cannot be used for this purpose, since they do not duplicate th e heterogeneous conditions m et in th e analysis of cellulose esters.

T hese difficulties can be m e t b y using tested procedures w ith in lim its of reag en t concentration, tim e, a n d te m p e ra tu re w hich h av e been show n to be satisfacto ry . B y ta k in g these precautions, high resu lts can be avoided. Low resu lts are u sually caused b y lum py or h a rd san d y p recip itates w hich re­

sist p en etratio n b y th e reagent, a n d can be elim inated by pow dering th e sam ple, or preferably b y rep recip itatin g from su itab le solvents to g e t a so ft fluffy p ro d u ct.

The

^accuracy

o f a m ethod can be d eterm ined b y com paring th e b e st results from one m eth o d w ith those b y o th e r m eth o d s a fte r th e v a ri­

ab les a n d lim itatio n s of each h a v e been studied. Long expe­

rience wij;h sta n d a rd ty p es of cellulose esters, p a rtic u la rly th e ace ta te s, enables one to estab lish fairly acc u ra te acyl co n ten ts for each ty p e, an d th ese m aterials can th e n be used as refer­

ence sam ples, if n o t for p rim ary sta n d a rd s. B y com bining th is jhfoim atiori, p ractical lim its of accu racy can be s e t up.

i n t h e following sections^ th ree m ethods w hich h av e proved satisfactory, ¡are given in d etail w ith resu lts of stu d ies of th e effects of th e ir m o st im p o rta n t variables. T h e precision an d accu racy a tta in a b le a n d th e lim its of ap p licab ility a re also given for each m ethod.

E berstadt M ethod

Pr o c e d u r e. Accurately weighed 1-gram samples of the th o r­

oughly dried ester are placed in 250-ml. Erlenm eyer flasks, and 40 ml. of 75 per cent ethyl alcohol are added to each. Alcohol denatured by the 3-A formula m ay be diluted for this pur- j)ose. T he flasks are then heated loosely stoppered for 0.5 hour a t 50° to 60° C . (A double-walled b ath containing reflux- ing m ethyl alcohol in th e jacket provides the right am ount of heat for this purpose.) Then 40 ml. of 0.5 N sodium hydroxide solu­

tio n are added and th e flasks are heated for 15 m inutes a t 50° to C. Blanks containing alcohol and alkali are run w ith each set of samples or a t least on new reagents. T he flasks are stop­

pered tightly and allowed to stand a t room tem perature for 24, o r preferably 48, hours w ith occasional swirling. A t th e end of th is tim e th e excess alkali is back-titrated w ith standard 0.5 N hydrochloric acid, using phenolphthalein indicator, and an ex­

cess of about 1 ml. of acid is added. T he alkali is allowed to soak o ut from th e regenerated cellulose for several hours and more acid is added if necessary. Finally alkali o r acid is added to establish the exact neutral point, and the per cent acyl is calculated some­

w hat as follows:

[(ml. of acid for blank) — (ml. of acid for sample) ] X

(acid norm ality) = % aCyl

M o st of th e resu lts given in th e ta b le s w hich follow were calculated to acety l o r to “ a p p a re n t a c e ty l” (eq u iv alen t w eight 43) even th o u g h som e sam ples w ere k now n to contain o th e r acyl groups.

W hen a large n u m b er of sam ples is to be analyzed b y th is m eth o d , tim e a n d lab o r can be saved b y dispensing th e alkali from a dispensing p ip e t w hich delivers a p p ro x im a te ly 40 ml.

A lm ost all th e acid can be a d d ed from a dispensing p ip et w hich delivers ap p ro x im ately 20 m l., an d th e titr a tio n can be

A p p a re n t A cetyl for V arious T im es of Swelling N one 15 m in. 30 m in. 1 h o u r 3 ho u rs 5 hours Ta b l e I. Ef f e c t o f Ti m e o f Sw e l l i n g a t 50° t o 60° C.

Sam ple

Cellulose a c e ta te 1 Cellulose a ce ta te

pro p io n ate 1 Cellulose a c e ta te 3

Ta b l e II. Ef f e c t o f Al k a l i Co n c e n t r a t i o n Sam ple

% % % % % %

4 0 .5 4 0 .6 4 0 .7 4 0 .7 4 0 .9 4 0 .5

4 0 .0 4 0 .6 4 0 .7 4 0 .7 4 0 .9 4 0 .5

4 0 .5 4 0 .6 4 0 .5 4 0 .7 4 0 .9 4 0 .6

4 0 .5 4 0 .6 4 0 .5 40 .9 4 0 .6

4 3 .7 4 3 .6 4 3 .7 4 3 .6

4 3 .2 4 3 .5

Cellulose a ce ta te 1 (40.5% acetyl)

Cellulose a c e ta te 2 (40.5% acetyl)

Cellulose a ce ta te p ro p io n ate 1 (40.5% a p p a re n t acetyl)

Cellulose a ce ta te b u ty ra te 1 (35.5% a p p a re n t acetyl)

A lkali C o n cen tratio n s

Tim e 0.25 N 0.5 N 1 .V

H ours % % %

2 .5 2 8 .4 4 0 .3

3 3 .7 3 9.1

4 4 0 .0 4 0 .7

4 0 .2 4 0 .4

6 3 8 .9 3 9 .9 4 Ü 0

4 0 .7 40.1 4 0 .9

16 4 0 .5 4 0 .8 4 2 .3

4 0 .5 4 1 .0 4 2 .6

24 4 0 .5 4 0 .9 4 3 .4

4 0 .7 4 1 .0 4 3 .5

43 4 0 .5 4 1 .2 4 4 .9

4 0 .5 4 1 .2 4 5 .0

72 4 0 .5

4 0 .5

2 .5 2 7 .8 4 0 .5

2 9 .3 4 0 .5

4 3 8.4 4 0 .6

3 9 .5 3 8 .8

6 3 7 .6 4 0 .0 4 Ü 0

3 9 .9 40 .1 4 1 .5

16 3 8 .9 4 0 .8 4 1 .9

4 0 .7 4 1 .5

24 4 0 .5 4 0 .9 4 3 .4

4 0 .5 4 3 .0

48 4 0 .5 4 i ‘.2 4 4 .8

4 0 .5 4 1 .2

72 4 0 .5

4 0 .5

2 .5 3 4 .7 3 9 .4

3 5 .5 4 0 .2

4 40 .1 4 0 .5

4 0 .1 4 0 .5

6 3 9 .4 3 9 .9 40*8

3 8 .9 4 0.1

16 3 9 .8 39 .9 4 i * 3

4 0 .7 4 0 .5 4 1 .6

24 4 0 .6 4 0 .8 4 3 .4

4 0 .7 4 0 .9 4 3 .4

48 4 0 .4 4 1 .2 4 1 .2

4 0 .6 4 1 .2 4 1 .7

72 4 0 .4

4 0 .4

2 .5 2 4 .8 3 2 .3

2 8 .5 3 4 .5

4 34.1 3 5 .3

3 4 .7 3 5 .4

6 2 9 .8 3 2 .8 Z8.2

3 4 .0 3 8 .8

16 3 5 .0 3 5 .8 35.9

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

24 3 5 .5 3 5 .4 3 5 .9

3 5 .5 3 5 .4

48 3 5 .5 3 5 .5 3 9 16

3 5 .5 3 5 .5 3 7 .8

72 3 5 .7

3 5 .8

June 15, 1941 A N A L Y T I C A L E D I T I O N 371 finished using o rd in a ry b u re ts. O nly th e difference betw een

th e b u re t read in g s fo r th e b la n k a n d th e sam ple titr a tio n en­

ters in to th e calculation.

Ef f e c t o f Ti m e o f Sw e l l i n g. T h e effect of th e tim e of swelling a t 50° to 6 0° C . is show n in T a b le I . T h e ab o v e p ro ­ cedure w as followed a n d only th e tim e of sw elling w as v aried as in d icated .

T hese d a ta show t h a t th e tim e of sw elling is n o t im p o rta n t, and in m a n y cases th is p reso ak could be elim in ated . I t does n o t ad d m uch to th e m a n ip u la tio n an d does no h arm , how ever, so i t is a p recau tio n w ell w o rth ta k in g a n d is to be recom ­ m ended.

Ef f e c t o f Al k a l i Co n c e n t r a t i o n. T h e sam e procedure w as ag ain follow ed except th a t th e alk ali n o rm a lity a n d th e tim e of sta n d in g w ere v aried as in d ic a te d in T a b le I I . T h e solutions a d d ed wrere a c tu a lly 0.5, 1.0, a n d 2.0 N , b u t since th e y w ere d ilu te d w ith eq u al volum es of 75 p e r c e n t alcohol, th eir effective n o rm alities a t th e s t a r t of th e saponification were h alf th ese values.

T h e accep ted values fo r th e ac e ty l or a p p a re n t ac e ty l con­

te n ts—i. e., a ll th e a c id ity calc u lated to a c e ty l— of th e vario u s esters are given in th e first colum n. C o m p ariso n of these accepted v alu es w ith th e o th e r d a ta lead s to th e follow ing con­

clusions:

A t an effective norm ality of 0.25, the accepted acetyl value is reached in 16 to 24 hours’ reaction tim e, and this value is not raised even after 72 hours.

A t an effective norm ality of 0.5, th e accepted value is reached in about 16 hours, b u t after 24 hours th e value observed rises slowly above th is accepted figure.

At an effective norm ality of 1, abnorm ally high values are ob­

tained even a t short reaction times, and th e precision is poorer than a t lower alkalinities.

The m ost satisfactory conditions for use in this procedure are saponification a t an effective initial norm ality of 0.25 for n o t less than 24 hours and preferably for 48 hours. A set of 24 samples taken a t random was analyzed using these conditions; a 24-hour saponification was sufficient for 18 samples, b u t 4S hours was re­

quired to get acceptable results on th e other six. Consequently it is safest to allow 48 hours for all sam ples.

Ef f e c t o f Te m p e r a t u r e. T h e sam e sam ples w ere te ste d by th is m e th o d a t several d ifferen t te m p e ra tu re s a n d w ith v ary in g reactio n tim e s to m easure th e effect of te m p e ra tu re on th e accu racy of th e resu lts. In all cases 0.5 N alk ali w as added, m ak in g a re s u lta n t in itia l c o n cen tratio n of 0.25 N , an d th e 50° to 60° C. h e a t tr e a tm e n t w as o m itte d in th e reactio n s ru n a t 0 ° C. T h e d a ta o b ta in e d a re given in T a b le I I I .

T h e re su lts of th ese ex p erim en ts in d ic a te th e follow ing con­

clusions:

Saponifications a t 0° C. are incom plete and th e results erratic for reaction times of less th a n 24 hours. Acceptable results were obtained on three of these four sam ples using saponification times of 24, or preferably 48, hours.

Reactions run sm oothly a t room tem perature, and accurate values are obtained in from 24 to 72 hours. T here is apparently no tendency tow ard high results when the specified conditions of

Ta b l e I I I . Ef f e c t o f Te m p e r a t u r e

A p p a re n t A cetyl for V arious

tem perature and alkalinity are met.

When th e saponifications arcare run a t an elevated tem perature such as 60° C. very erratic results are obtained in short reaction times, and very high results are obtained after about 10 hours.

This result is th e same as is caused by too high alkalinity.

In the previous section it was shown th a t th e m ost satisfactory conditions of alkalinity and tim e were 0.25 N and 24 to 48 hours.

These experiments show th a t room tem perature (25° to 30° C.) is satisfactory, b u t tem peratures above about 35° C. are to be avoided.

Fo r m a t i o n o f Ac i d s Ot h e r Th a n Ac e t i c Ac i d. T h e a p p a re n t acety l v alu es in T ab les I I a n d I I I show t h a t too high v alu es a re o b tain ed w hen th e a lk a lin ity a n d te m p e ra ­ tu re exceed th e specified conditions. A special ex p erim en t was ru n to p ro v e t h a t th is e x tra a c id ity is d u e to acids o th e r th a n acetic.

Sam ple

Cellulose a c e ta te 1 (40.5% acetyl)

Cellulose a ce ta te 2 (40.5% acetyl)

Cellulose a c e ta te p ro p io n ate 1 (40.5% a p p a re n t acetyl)

Cellulose a c e ta te b u ty ra te 1 (35.5% a p p a re n t acetyl)

T im e R

0° C. eaction T e m p e ra tu re s 30° C. 40° C. 60° C.

IÎOUT8 % % % %

1 3 0 .4 2 8 .4 2 6 .0

3 3.1 2 6 .2 3 1 .9

2 .5 3 7 .8 2 8 .4 3 5 .5

3 6 .6 3 3 .7 3 5 .6

4 3 4 .0 4 0 .0 3 6.1

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

6 3 4 .0 4 0 .0 4 2 .0

34.1 4 0 .2 4 0 .4

18 3 4 .1 4 0 .5 4 (^5 4 2 .7

3 1.7 4 0 .5 4 0 .5 4 1 .8

24 4 0 .4 4 0 .5 4 0 .6 4 3 .4

4 0 .4 4 0 .7 4 0 .6 4 2 .9

48 4 0 .4 4 0 .5 4 0 .9 4 4 .9

4 0 .5 4 0 .7 4 0 .9 4 5 .6

72 4 0 .5 4 0 .9

4 0 .5 41 .1

1 3 1 .8 2 9 .7 3 1 .3

3 7 .4 2 9 .5 33.0-

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

2 9 .3 3 7 .7

4 38^5 3 8 .4 39.5-

39 .4 3 9 .5 38.5-

6 3 5 .2 3 9 .9 4 1 .1

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

18 3 2 .4 3 8 .9 4 0 .4 4 3 .0

3 7 .3 4 0 .7 4 0 .4 4 2 .7

24 4 0 .0 4 0 .5 4 0 .5 4 3 .5

4 0 .9 4 0 .5 4 0 .5 4 3 .5

48 4 0 .4 4 0 .5 4 0 .7 44 .1

4 0 .4 4 0 .5 4 0 .7 4 4 .2

72 4 0 .5 4 0 .8

4 0 .5 4 0 .8

1 31.1 3 3 .8 3 5 .4

3 3 .5 3 1 .0 3 6 .5

2 .5 3 2 .5 3 4 .7 3 8 .3

3 3 .8 3 5 .5 3 4 .8

4 3 6 .9 4 0 .0 3 9 .7

39.1 4 0 .1 39.1

6 3 3 .5 3 8 .9 4 0 .3

39 .4 4 1 .2

18 3 7 .5 40*. 7 4 0!2 4 1 .6

3 6 .9 3 9 .8 4 0 .6 4 1 .8

24 4 0.4 4 0 .6 4 0 .3 4 2 .2

4 0 .4 4 0 .7 4 0 .4 4 2 .0

48 4 0 .7 4 0 .4 4 0 .5 4 3 .7

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

72 4 0 .4

4 0 .4

1 17 .0 2 1 .9 31.1

17 .6 2 1 .6 2 4 .7

2 .5 2 5 .3 2 8 .5 3 2 .9

16.4 2 4 .8 3 5 .2

4 25.1 3 4 .7 36.1

2 3 .7 34.1 35 .8

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

3 4 .0 3 7 .2

18 24 ! 5 3 5 .0 3 5 .2 3 8 .7

3 5 .5 3 5 .3 38 .3

24 3 3 ’.0 3 5 .5 3 5 .5 3 8 .6

31 .1 3 5 .5 3 5 .5 3 8 .6

48 3 3 .3 3 5 .6 3 5 .6

..

3 3 .7 3 5 .6 3 5 .6

72 3 5 .7

3 5 .7

Cellulose acetate 1 (40.5 per cent acetyl content) was saponi­

fied w ith 1 Ar sodium hydroxide for 48 hours a t a tem perature of 55 to 60° C. resulting in an apparent acetyl value of 46.0. O ther samples which had received th is same heat treatm en t, together w ith samples saponified under norm al conditions to give an ap­

parent acetyl value of 40.5 per cent, were th en acidified with phosphoric acid, and th e volatile acids present were isolated by vacuum distillation. Isolation of the volatile acids b y th e tech­

nique used is known to be ab o u t 98 per cent q u an titativ e and, in order to elim inate errors in calculation resulting from incom plete distillation, th e volatile acids from a sam ple saponified under norm al conditions were distilled sim ultaneously w ith th e acids from the sample having a high acetyl value. A liquots of the distillates were titra te d and th e volatile acids were calculated to per cent apparent acetyl. T he acetyl values of th e samples saponified norm ally and under extrem e conditions averaged 39.4 and 40.7 per cent, respectively. T his difference represents vola­

tile acidity produced by th e strong conditions of heating and al­

kalinity.

Portions of the distillates were gently refluxed w ith yellow mercuric oxide, a reagent which does n o t decompose acetic acid.

T itratio n of the samples th u s treated resulted in ap p aren t acetyl values of 39.4 p r cent for both samples, indicating th a t th e ex­

cess volatile acids had been destroyed by gentle oxidation.

Form ic acid and o th er oxidizable acids in th e distillates were also m easured by th e reducing action of th e distillate on m ercuric chloride. The mercurous chloride precipitate formed by th e

Sam ple

C ellulose a ce ta te 1 (40.5% acetyl)

Cellulose a c e ta te b u ty ra te 1 (35.5% a p p a re n t acetyl)

Ta b l e I V . Ef f e c t o f Al k a l i Co n c e n t r a t i o n a t 2 5 ° C . A p p aren t A cetyl a t Various

A lkali C oncentrations A p p a re n t A cetyl a t Various

Alkali C on cen tratio n s

T im e 0.25 N 0.5 N 1 N Sam ple T im e 0.25 N 0.5 Ar 1 iV

Hours % % % Hours % % %

6 4 0 .1 4 0 .6 4 0 .5 Cellulose a ce ta te s te a ra te 6 2 5 .0 25 .1 2 4 .6

4 0 .2 4 0 .2 (25.6% a p p a re n t acetyl) 2 4 .6 25.1 2 4 .4

16 4 0 .5 40 ! 5 4 0 .6 16 2 5 .5 2 5 .3 2 5 .0

4 0 .5 4 0 .5 4 0 .6 2 5 .5 2 5 .4 2 4 .8

24 4 0 .5 4 0 .3 4 0 .7 24 2 5 .6 2 5 .4 2 5 .5

4 0 .5 4 0 .8 4 0 .7 2 5 .7 25 .3 2 5 .3

48 4 0 .6 4 0 .8 4 1 .2 48 2 6 .2 25 .7 2 5 .5

4 0 .6 4 1 .0 4 0 .9 2 6 .2 2 5 .6 2 5 .5

72 4 0 .8 4 1 .3 72 2 6 .0 2 6 .5

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

6 3 4 .8 3 5 .3 35! 2 Cellulose c ap rate 6 15 .0 22 .4 2 2 .0

3 4 .S 3 5 .3 35 .2 (2 3 .2 % a p p a re n t acetyl) 15 .4 22 .4 2 2 .0

16 3 5 .6 3 5 .5 3 5 .5 16 2 2 .0 2 2 .6 22 .7

3 5 .6 35 .6 22.1 2 2 .6 2 2 .6

24 3 5 .6 3 5 .7 3 5 ‘.6 24 2 3 .2 2 2 .7 2 3 .0

35 .7 3 5 .6 2 3 .2 2 2 .7 2 3 .0

48 35^6 3 5 .8 35 .7 48 2 3 .3 2 3 .2 2 3 .9

3 5 .6 3 5 .8 3 5 .6 2 3 .3 2 3 .2 2 3 .8

72 3 5 .6 3 6 .0 72 2 3 .3 23 .7

3 5 .6 3 7.8 2 3 .2 2 3 .3

sample saponified under normal conditions corresponded to 0.15 per cent acetyl and th a t detected in the sample saponified under extreme conditions corresponded to 0.88 per cent acetyl.

F ro m th is experim ent i t w as concluded t h a t a b o u t one fo u rth of th e excess a cid ity w as du e to volatile acids, a b o u t th ree fo u rth s w as due to th e form ation of nonvolatile acid groups, a n d th e excess a cid ity d u e to v o latile acids w as caused b y easily oxidizable acids, p ro b ab ly largely form ic acid. T h u s unless conditions of saponification a re controlled w ithin established lim its, acids o th e r th a n acetic acid m ay be form ed an d th e resu lts will be ab n o rm ally high.

Li m i t s o f Ap p l i c a b i l i t y. T h e m odified E b e rs ta d t m ethod, as described above, h as proved to b e th e m o st accu­

ra te , reliable, a n d satisfacto ry of all th e m eth o d s tested . I t is applicable to th e analysis of all cellulose a c e ta te s a n d o th e r cellulose e sters of relativ ely low m olecular w eig h t organic acids. W hen th is m eth o d is applied to esters of th e hom olo­

gous series of f a tty acids, i t is satisfacto ry fo r th e acetates, propionates, and som e of th e b u ty ra te s . I t is u n satisfacto ry a n d gives low’ results fo r th e valerates, caproates, cap rates, ste a ra te s, etc. I t is satisfacto ry fo r a c e ta te pro p io n ates an d for m o st a c e ta te b u ty ra te s, b u t is u n satisfacto ry fo r a c e ta te ste a ra te s. T h e lim its of ap p licab ility c a n n o t b e d raw n s h arp ly because th e physical condition of th e sam ple is v ery im p o rta n t.

Pr e c i s i o n a n d Ac c u r a c y. W hen all th e variables of th e m eth o d are p roperly controlled, resu lts m a y be expected h av ­ ing precision of =*=0.1 p er c e n t a p p a re n t a c e ty l or =*=0.25 per c e n t of th e num erical value, a n d accu racy of ± 0 .2 p er cen t a p p a re n t acetyl or ± 0 .5 p er cen t of th e num erical v alu e ob­

tain ed .

As a fu rth e r check on th e accu racy of th e m eth o d w hen it is in ev ery d ay use, i t is advisable to ru n a check b a tc h w ith ev ery se t of sam ples.

A lcoh olic A lkali M ethod

Pr o c e d u r e. Half-gram samples of the thoroughly dried ester are carefully weighed and transferred to 250-ml. Erlenm eyer flasks. F o rty milliliters of a 0.25 N solution of sodium hydroxide in 95 per cent ethyl alcohol are pipetted into each flask, and other flasks w ith reagent only are carried along as blanks and for stan d ­ ardizing the alkali. This also avoids errors due to changes in volume of th e alcoholic solution w ith tem perature. If desired th e reagent can be made up 0.5 N and 20-ml. aliquots used.

T hen 20 ml. of alcohol are added from a graduate to produce the sam e effective norm ality. The flasks are stoppered and set aside for from 16 to 24 hours a t not higher th an 30° C. A t the end of this tim e the excess alkali is back-titrated w ith standard 0.25 or 0.5 Ar hydrochloric acid, and a slight excess is added. After allowing about 4 hours for the alkali to soak out, th e excess acid is titra te d w ith 0.5 N sodium hydroxide to a phenolphthalein end point, taking the precautions required in th e E b erstad t procedure.

The am ount of acid added is corrected for the alkali required to establish the end point, and th e result is calculated by the equation used for th e E b erstad t procedure.

Ef f e c t o f Al k a l i Co n c e n t r a t i o n. A series of analyses w as ru n in w hich th e a b o v e procedure w as follow ed except t h a t th e stre n g th of th e alcoholic alkali an d tim e of reactio n w ere v a rie d as in d ic a te d in T a b le IV . T w en ty -m illiliter ali­

q u o ts of th e 1 N so lution w ere used to reduce th e b a c k -titra - tion.

T hese d a ta show t h a t th e saponification is com plete in from 16 to 24 h o u rs using 0.25 o r 0.5 N alkali. N o rm a l alkali te n d s

Fi g u r e 1. Ap p a r a t u s f o b Os t Di s t i l l a t i o n Me t h o d