INDUSTRIAL a n d ENGINEERING CHEM JSJRY
( S % %
A N A L Y T IC A L E D IT IO N
H A R R I S O N E . H O W E , E D I T O R « I S S U E D N O V E M B E R 18, 1942 m V O L . 14, NO. 11 » C O N S E C U T I V E N O. 22
D e te r m in a tio n o f M o is tu r e i n S ta r c h a n d I t s M o d i
fic a tio n s ... L. Sair and W. R. Fetzer 843 In su la tio n fo r N e c k s o f W a sh B o t t le s . . . .
Jacob Mizroch 845 Ascorbic A cid . • . . H. J. Loeffler and J. D. Ponting 846 A gar-Agar a s C o a g u la n t fo r B a r iu m S u lfa te . . . .
Edgar J. Bogan and Harvey V. Moyer 849 D e te r m in a tio n o f B lo o d in P a c k in g -H o u s e B y -P ro d -
u c t s ...Raymond Reiser and G. S. Fraps o o l A n alysis o f E t h y le n e in P r e se n c e o f B u ta n e • • • •
James J. Eberl 853 S im p lified T e c h n iq u e in U s e o f L iq u id A m a lg a m
R e d u cto r s . . . G . Frederick Smith and L. T. Kurtz 854 E lim in a tio n o f F lu o r id e I n te r fe r e n c e in M olyb -
d e n u m B lu e R e a c t i o n ... L. T. Kurtz ooo R apid K je ld a h l D ig e s t io n M e th o d U s in g P er ch lo r ic
A c i d ... Leonard P. Pepkowitz, Arthur L. Prince, and Firman E. Bear 856 P ressure W a sh B o t t le fo r V o la tile S o lv e n ts . . . ■
Lowell W. Charkey and D. V. Zander 857 C o lo rim etric D e t e r m in a t io n o f C o b a lt . . . .
R. J. DeGray and E. P. Rittershausen 858 Use o f P h o s p h a te fo r S e p a r a tio n o f C o b a lt fr o m Iro n
Victor North and Roger C. W ells 859 C o lo r im etric D e t e r m in a t io n o f T r in itr o b e n z e n e in
D in itr o b e n z e n e . . M. L. Moss with M. G . Mellon 8bl C o lo rim e tric D e t e r m in a t io n o f Ir o n w it h 2,2 -B i-
p yrid yl a n d w it h 2 ,2 ',2 " -T erp yrid yl . . • • ; • • R„
M. L. Moss with M. G . Mellon 862 D e te r m in a tio n o f C op p er w it h 8 -Q u in o lin e c a r b o x -
y lic A c i d ... o m James R. Gilbreath and Helmut M. Haendler 866 P o larograp h ic D e t e r m in a t io n o f D ead in L ead -
B ea rin g S t e e ls . . . G . Haim and W. C. E. Barnes 8 6 7 M ea s u r em e n t o f T h ic k n e s s o f F ir e d -o n G o ld C o a t-
i n g s ... K. H. Ballard 868 S p e c tr o p h o to m e tr ic D e t e r m in a t io n o f Iro n w it h
o -P h e n a n th r o lin e a n d w it h N itr o -o -P h e n a n th r o - l i n e J. P. M ehlig and H. R. Hulett 869 D e tec tio n a n d S e m iq u a n t ita t iv e E s t im a t io n o f
G roup I C a t i o n s ... S. S. Le^nrá' Robert Maurmeyer, and Milton Cutler o / i R e fr a c to m etr ic D e t e r m in a t io n o f C a s ein i n S k im
M i l k ... John G. Brereton and Paul F. Sharp Ü U A n a ly tica l R e a c tio n s I n v o lv in g I g n it io n w it h M a n -
g a n o u s N i t r a t e ... .... • ~ * , ' o n c.
M. Joan Preising, Otto F. Slonek, and J. H. Reedy A n a ly sis o f P la n t E x tr a c ts for C h lo r o p h y lls a a n d b
U sin g C o m m e r c ia l S p e c tr o p h o to m e te r ^ • ^ g rjrj
D e te r m in a tio n o f U n s a tu r a te s in H y d r o ca r b o n G a ses . . . Richard F. Robey and Charles E. Morrell 8 8 0 C o n ta c t S u lfu r ic A cid M a n u f a c t u r e ...
Gerrit Dragt and K. W . G reenan 8 8 3 D e te r m in a tio n o f P y r o p h o s p h a te b y P r e c ip ita tio n
w it h C a d m iu m a n d P o la r o g ra p h ic M e a s u r e m e n t o f C a d m iu m in P r e c i p i t a t e ...
Gunther Cohn and I. M. Kolthoff 8 8 6 D e te r m in a tio n o f L ow C o n c e n tr a tio n s o f O x y g en in
G a s ... Joseph A. Shaw 891 P h o to m e tr ic D e t e r m in a t io n o f S ilic a in P re se n c e of
P h o s p h a t e s ...M. C. Schwartz 8 9 3 S p e c tr o p h o to m e tr ic D e t e r m in a t io n o f M a g n e s iu m
by T ita n Y e llo w . . E. E. Ludwig and C. R. Johnson 89S D e te r m in a tio n o f R o t e n o n e ... S. I. Gertler 8 9 7 L ab oratory B e llo w s P u m p ...
B. B. Corson and W . J. C erveny 8 9 9 D e te r m in a tio n o f S u lfu r in A c id -S o lu b le S u lfid e s .
H. C. Froelich 9 0 0 T iltin g Arc F lo w D iv id e r S u ita b le fo r R eflu x R a tio
C o n t r o l ...Samuel Palkin and S. A. Hall 901 L eak p roof S to p c o c k for R e g u la tio n o f T a k e -o ff
d u r in g D i s t i l l a t i o n ...Melvin S. Newman 9 0 2 S ta b ility o f C u p r ic -A m m o n ia C olor S y s te m . . . .
J. P. M ehlig 9 0 3 S im p le L a r g e-C a p a city E x tr a c tio n A p p a r a tu s . . .
Edward Smallwood 9 0 3 M IC R O C H E M IS T R Y :
M ic r o d e te r m in a tio n o f L ead b y D ith iz o n e w it h Im p ro v ed L e a d -B is m u th S e p a r a t i o n ...
Karl Bambach and Roland E. Burkey 9 0 4 S im p le A p p a r a tu s for S m a ll-S c a le C a ta ly tic H y
d r o g e n a tio n . . . C. R. Noller and M. R. Barusch 9 0 7 Q u a n tita tiv e D e c o m p o s itio n o f O rg a n ic B r o m in e
a n d Io d in e C o m p o u n d s b y L im e -F u s io n M e th o d William M. M acNevin and G lenn H. Brown 9 0 8 P re p a r a tio n o f S a m p le s fo r M ic r o b io lo g ic a l D e te r
m in a t io n o f R i b o f l a v i n ... ...
F. M. Strong and L. E. Carpenter 909
S y s te m a tic I d e n tific a tio n o f C o m m o n M e ta llic C o a tin g s . Howard Nechamkin and Alvin Sanders 913 K jeld a h l N itr o g e n D e t e r m in a t io n . . . . . . . .
L. P. Pepkowitz and J. W . Shive 914 D iffu sio n M ic r o m e th o d fo r N i t r o g e n ...
Roland C. Hawes and Edwin R. Skavinski 917 S p ec tr o g ra p h ic A n a ly s is o f R a t T is s u e s for I n
g e s te d V a n a d iu m . . . Esther Peterson Daniel, Elizabeth M. Hewston, and Marian W . Kies 921
' f™- th e statem en ts a n d opinions advanced by c o n trib u to rs to its publications.
T h e A m erican C hem ical Society assum es no responsibility tor C o p y rig h t 1942 by A m erican Chem ical Society.
26,000 copies of th is issue prin ted .
P u b lic a tio n O ffice:
Editorial O ffice! 1155 1 6 th S t r e e t , N . W ., W a s h in g to n , D. C.
T elep h o n e! R e p u b lic 5301. C a b le ! J ie c h e m (W a sh in g to n )
Published b y th e A m erican C hem ical Society. P ublication Office,^Oth &
N ortham pton S ts., E a s to n , P en n a. E n t e r e d as second-class « w e Post Office a t E a sto n , P en n a, u n d er th e A ct of M a r c h e r 1 ! mo nt hl y year In d u stria l E d itio n m o n th ly on th e ^ t : A n a l y t i c a l E d itio n m o n t^ y on the 15th. A cceptance for m ailing a t special ra te of postag p in Section 1103, A ct of O ctober 3, 1917 authorized Ju ly 13,. U l!E d itio n sold
Annual subscription ra te , In d u stria l ^ 1*lon1? ■ to countries only as a u n it, m em bers *3.00, o th ers *4.00. F o r e i g n postage to countries not in th e P a i A m erican U nion, »2.25; C an ad ian postage, $0.75. sm gie
E a s to 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 est 4 2 n d S t r e e t , N e w Y o rk , N . Y.
T e l e p h o n e : B r y a n t 9 - 4 4 3 0
copies: In d u s tria l E d itio n , S0.75; A nalytical E d itio n , *0.50. Special ra te s 10 No "claims can be allowed for copies of jo u rn a ls lo st in th e m ails unless such claim s a re received w ithin 60 days of th e d a te of issue, and no claim s iriU be allowed for issues lost as a re su lt of insufficient notice of change of address (T en d ays' advance notice required.) “ M issing from hies can n o t be accepted as th e reaso n for honoring a claim . A ddress claim s to C harles L Parsons, Business M anager, 1165 16th S tre e t, N . V , W ashington, 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 Vol. 14, No. II
ANALYTICAL WEIGHTS
A cco rd in g to N ational Bureau o f Standards Specifications Class S - 2
(IMMEDIATELY AVAILABLE)
8200 8210 -8 2 2 5
8200 W EIG H TS, Analytical, Lacquered, Class S-2, for use in routine analytical work in commercial and stu dent lab oratories. Constructed and adjusted according to th e requirements of the N ational Bureau of Standards for w eights of this classification.
T he gram weights are of lacquered brass and the fractionals from 500 to 50 m g are of nickel and from 20 to 1 m g, together w ith th e tw o 10 m g riders, are of alum inum . In velvet-lined m ahogany box w ith hinged lid, and removable com partm ent tray for th e fractionals. Com plete w ith nickel and aluminum fractionals and w h ite com position-tipped brass forceps, but without certificate.
N o ... A B Values, 1 mg to, grams... 50 100 P er s e t ... $10.00 $12.00
8210 W EIG H TS, Analytical, Lacquered, Chain and Gram R ider Balance, C lass S -2, same as N o. 8200 W eights, except th a t all fractionals, which are n ot required w ith chain balances having a notched beam and gram rider, are om itted. In velvet-lined m ahogany box w ith hinged lid. Com plete w ith com position-tipped forceps, but without fractionals or certificate.
N o ... A B Values, 1 gram to, gram s... 50 100 Per s e t ... $7.25 $9.25
8225 W EIG H TS, Analytical, Chromium P lated , Chain and Gram R ider B alance, C lass S -2, same as N o. 8210 W eights, but w ith gram w eights of chromium-plated brass. In velvet-lined m ahogany box w ith hinged lid.
C om plete w ith com position-tipped forceps, but without fractionals or certificate.
N o ... A B Values, 1 gram to, gram s... 50 100 P er s e t ... $8.75 $11.00
C H IC A G O 1700 Irving Pk. Road
Lakeview Station
S C I E N T I F I C I N S T R U M E N T S New York • Boston •
d l®
C H I C A G O
L A B O R A T O R Y A P P A R A T U S
• Toronto • San Francisco
BO STO N 79 Amherst St
Cambridge A Station
November 15, 1942 A N A L Y T I C A L E D I T I O N 5
The is Toda>
Shortage
An Item
From the Com prehensive K IM B L E LINE
2 9 0 5 0 - S T F u n n e l , S e p a r a t o r y , S q u ib b ’s, P ea r S h a p e d , K im b le B r a n d , w it h ? s to p p e r a n d s t o p c o ck .
29050-ST
S y n th e tic rubber is o n ly o n e o f th e a ch iev em en ts o f m od ern c h e m istr y in developing a ltern a tiv es to m e e t
cu rrent em ergen cy d em a n d s.
KIMBLE LABOBATOBY GLASSWABE fills req u irem en ts o f to d a y ’s c h e m i
cal w orkers in m a n y e ss e n tia l p rofes
sion s and in d u str ies. C o n su lt lea d in g laboratory su p p ly h o u se s th ro u g h o u t th e U n ited S ta te s and C anada for K im ble products to serve your ow n n eed s.
Y o u w ill b e h e a r t i l y w e l c o m e a t o u r B o o th ¡Wo. 1 4 2 a t t h e N a tio n a l C h e m ic a l E x p o s itio n, H o te l S h e r m a n , C h ic a g o, N o v e m b e r 24 t o 2 9 , 1942.
Capacity
ml. Stopcock Stopper SUe Size
(ÉV
Y o u r d e a le r w ill b e g la d to s u p p ly f u r t h e r d e t a i l s , a n d t o q u o t e q u a n t it y p r ice s.
$1.40 1.60 1.90 2.50 3.50
tSSff
1U l.f IÏ1 1 jftv jf w n R
6 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 11
PYREX C orning means---
Research in Glass
for speed and economy, Pyrex brand accurate 60° Fluted Funnels fit perfectly into today's accelerated labo
ratory work.
These precision-shaped fluted funnels practically d o u b le the effective filtering area— and hen ce the sp eed — of ordinary funnels. Their accurate 6 0 ° angle was deliberately chosen by Corning Research as the angle permitting a close paper fit over the entire supporting area with less tendency to tear. Fire-polished bead and tip and heavy wall stem add to the me
chanical strength of the "Balanced Glass"
construction— assure longer service at a time w hen durability is a premium quality.
Available both fluted and plain, "Pyrex” 60° Funnels are stocked by your regular labo
ratory supply dealer.
SPA C E 169
P Y R E X BRANDLABORATORY WARE
" P Y R E X ” a n d " V Y C O R " a r e r e g is t e r e d tra d e - m a rk s a n d in d ica te m a n u fa ctu re b y
C O R N I N G G L A S S W O R K S C O R N I N G , N E W Y O R K
Ô .W.rfKÀL pèçMntfi o
A G U A R A N T Y O F Q U A L IT Y
C h e m ic a l e x p e r ie n c e o f m a n y y ea rs h a s e n a b le d M e r c k & C o . I n c . t o p la n , d e s ig n a n d e q u ip th e n e w M e r c k A n a ly tic a l L a b o r a to r ie s , w h e r e in r ig id a n d c o n s t a n t c o n t r o l is e x e r c is e d o v er m o r e th a n 1 ,5 0 0 p r o d u c ts b e a r in g th e M er ck la b e l. T h e e x t e n s iv e fa c ilit ie s f o r p r e c is io n a n a l
y s e s a n d t e s t in g in c lu d e n o t o n ly c h e m ic a l m e th o d s , b u t p h y s ic a l a n d o p t ic a l p r o c e d u r e s a s w e ll. B e c a u s e o f t h e s e m o d e r n c o n t r o l fa c ili
tie s , th o u s a n d s o f in d u s tr ia l c h e m is ts , stu d e n ts, a n d r e s e a r c h w o r k e r s u s e M e r c k L a b o ra to ry
n
C hem icals w ith co m p lete confidence in th e ir p u rity an d uniform ity.F O R V I C T O R Y — B u y W a r
A P L E D G E O F S E R V I C E
A lth o u g h th e M e r c k f a c to r ie s a re n o w o p e r a t
i n g o n a 2 4 -h o u r d a y , 7 -d a y w e e k s c h e d u le in o r d e r t o s u p p ly th e n e e d s o f o u r a r m e d fo r c e s a n d c iv ilia n p o p u la tio n , it m a y n o t a lw a y s b e p o s s ib le t o s u p p ly y o u im m e d ia te ly w ith y o u r c o m p le te r e q u ir e m e n ts o f M e r c k C h e m ic a ls . B ut in s p ite o f th e d ifficu ltie s w h ic h c o n f r o n t u s, w e s h a ll c o n tin u e t o d o e v e r y th in g p o s s ib le to se r v e o u r c u s to m e r s t o th e lim it o f o u r a b ility . In f a c in g th e v ita l ta sk at h a n d , it is o u r h o p e th at w e m a y c o n t in u e t o h a v e th e u n d e r s ta n d in g c o o p e r a t io n o f o u r c u s to m e r s , w h ic h h a s h e lp e d us im m ea s u r a b ly in o u r e ffo r ts t o se r v e th e m .
S a v i n g s B o n d s a n d S t a m p s
M
e r c k& c o
New Y o rk . N. Y.
I n c . f^ ia n u J a ctu rJ n ç , (1 /c m i.iti R A H W A Y , N . J .
Los A ngeles, Cal.
P h ila d e lp h ia , P a. • St. L ouis, Mo. • E lk to n , Va. • C hicago, 111.
In C a n a d a : MERCK & CO. L im ited , M ontreal and T oron to
November IS, 1942 A N A L Y T I C A L E D I T I O N
8 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 11
Figures that m ean CONTROL/
T h e a n a ly sis o n th is b o ttl e o f R e a g e n t H y d ro flu o ric A c id is a n o t h e r e x a m p le o f th e h ig h p u r ity a c h ie v e d in t h e m a n u f a c tu r e o f B a k e r & A d a m s o n p ro d u c ts . N o te th e e x c e p tio n a lly lo w c o n te n t o f ir o n a n d n o n -v o la tile m a te r ia l!
W h e r e v e r th is H y d ro f lu o ric A c id is u se d . . . in m in in g , m e ta llu rg ic a l, o r c e m e n t la b o r a to r ie s — o r fo r t h e a n a ly sis o f glass a n d c e ra m ic m a te r i a l s —c h e m is ts d e p e n d u p o n it to h e lp th e m
m a in ta in a c c u ra te c o n tr o l in t h e i r ow n pro cesses.
B & A d e p e n d a b ility is d e riv e d fro m 60 y e a rs of e x p e r ie n c e i n t h e m a n u fa c tu r e o f r e a g e n t c h e m i
cals. C a re fu l a t te n t io n to a ll p r o d u c tio n d e ta ils a n d p a in s ta k in g la b o r a to r y c o n tro l a s su re u n i
fo rm h ig h q u a lity a n d p u r ity .
A c c u ra c y i n a n a ly tic a l d e te r m in a tio n s r e q u ire s th e b e s t o f la b o r a to r y c h e m ic a ls. A lw a y s s p e c ify B a k e r & A d a m s o n R e a g e n ts !
S E T T I N G T H E P A C E I N C H E M I C A L P U R I T Y S I N C E 1 8 8 2
T f c K x u u jx w T
B a k e r & A d a m s o n a™ **
D ivision o f GENERAL CHEMICAL COMPANY, 4 0 R ector St., N e w York C . P A c d s Technical Service Offices: Atlanta • Baltimore • Boston • Bridgeport (Conn.) • Buffalo • Charlotte (N . C.) Chicago • Cleveland • Denver • Detroit • Houston • Kansas City • Milwaukee • Minneapolis
New York • Philadelphia • Pittsburgh • Providence (R . I.) • St. Louis • Utica (N . Y.) Pacific Coast Technical Service Offices: San Francisco • Los Angeles Pacific Northtcest Technical Service Offices: Wenatchee (Wash.) • Yakima (Wash.) In Canada: The Nichols Chemical Compaoy, Limited • Montreal • Toronto • Vancouver
November 15, 1942 A N A L Y T I C A L E D I T I O N
IT’S THE
LONG-RUN COST
THAT COUNTS!
H O S K I N S P R O D U C T S
E L E C T R IC H E A T T R E A T IN G F U R N A C E S • • H E A T IN 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 LEAD W IR E • • PYRO M ETERS • . W E LD IN G W IR E . • H EAT R ESISTA N T C A ST IN G S • • EN AM ELIN G FIXTURES • • S P A R K P LU G ELECTRODE W IR E • • SP E C IA L A LLO Y S O F N IC K EL • • PRO TECTIO N TUBES
W h e n yo u b u y a H oskins combustion fu rn ace, you’ll find it lasts so long th a t its m ain ten a n ce cost p e r y e a r ap proaches a figure th a t’s triv ia l. N ot o n ly is yo u r se n se of thrift satisfied—your perform ance re q u ire m e n ts a r e also fully m et. • • • Hoskins M anufacturing C o ., D e tro it, M ichigan.
( L e ft ) To a p p ly a C h rom ai unit in the FD fu rn a ce i t a s . a t y a t w ra p p in g a r a p t a ro u n d a stic k.
(R ig h t) T yp e F H - 3 0 3 - A ; o p e ra te s on A .C . o n ly through a tra n sfo rm e r. H e a v y C h rom e! unit, g o o d fo r 2 0 0 0 ° F . Th« former 5 * O.D. o f the c a se is
now 7", w ith corresponding in
crease in heat-insulation .
A t2000°F .,form ercasetem perature of 3 9 3 ° Is n o w 1 3 5 ° cooler. Hold- ing w attage h as b een reduced 14%.
Heating unit, a sin g le Chromel coil, that very e a sily is w rap p ed around T * ^ the grooved tube.
A given furnace built for o n e given voltage permits a h ea v ier Chromel unit that lasts longer.
Recom mended m axim um operat
ing temperature is 1 8 0 0 ° F. for FD;
and 2 0 0 0 ° F. for FH (b elo w ).
Hoskins com bu stion fu rn aces are cheaper in the lon g run. Send for descriptive folder.
iR ig h t) O perates directly on the line w ithout transformer. Tempera
ture is controlled b y rheostat.
10 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 11
A . H . T . C O . S P E C I F I C A T I O N
B O E R N E R SH A K IN G A PPA RA TU S
For shaking flasks, test tubes, separatory funnels, etc.
Fig. 1
W ater undergoing sh ak in g in 500 m l flask a tta ch e d to v er
tical rod of B oerner Shaker.
From ph o to g rap h b y “ stop
a ctio n ” cam era. 8927.
Showing m ethod of shaking 500 ml flasks.
Fig. 2
M ercu ry undergoing shaking in 500 m l flask a tta c h e d to v ertical rod of B oerner Shaker.
From ph o to g rap h b y “sto p a ctio n ” cam era.
S H A K IN G A P P A R A T U S , B O E R N E R , A. H . T . Co. S p e c ific a tio n , o sc illa tin g p la tf o rm ty p e , w ith a u to m a tic tim e sw itc h . D e sig n e d e s p e c ia lly fo r s h a k in g flasks, t e s t tu b e s a n d m ic ro t e s t slid e s in th e B o e rn e r-J o n e s -L u k e n s flo c c u la tio n te s ts b u t u se fu l also for m a n y o th e r s h a k in g p ro c e d u re s in v o lv in g re la tiv e ly s m a ll c o n ta in e rs .
C o n s istin g of a flo a tin g p la tf o rm re s tin g o n ly o n f o u r v e r tic a l S ta in le s s s te e l coil sp rin g s w h ic h a re f a s te n e d to th e u n d e r s u rfa c e of th e p la tf o r m a n d to th e c o rn e rs of a s u p p o r tin g m e ta l b a s e . T h e b a s e is p r o v id e d w ith r u b b e r f e e t a n d en c lo se d in a m e ta l g u a rd .
Shaking is produced b y a double-ended ' / « h. p. motor bolted to the middle of the underside of the platform in such a manner that the axis of the shaft is horizontal. Eccentrically secured on the motor shaft are tw o w eights w ith aligned cen
ters so that, in operation, the platform oscillates in a generally elliptical path which, opposed b y the tension of the supporting springs, results in compound oscillations producing a violent shaking and swirling m otion.
The platform for slides, te st tube racks, etc., is 13 inches square and covered w ith sponge rubber. On it are m ounted, on opposite sides, tw o Stainless steel rods, 12 inches high X Vs-inch diameter, for attaching special heads above th e level of the platform for shaking separatory funnels, b ottles, flasks, etc.; or, b y means of th e usual laboratory clamps, flasks or bot
tles up to 500 ml capacity provided th e y can be securely clamped around the neck.
The upper ends of the shaking rods can be made to vibrate violently or gently, as desired, b y changing the height of the flasks, etc., on the rods and by adjusting their position above or beyond the platform; also, if necessary, b y adding a counter weight to the opposite rod a t m ost advantageous height.
Com plete w ith autom atic tim ing device which can be set for a maximum interval of 28 m inutes in step s of '/a m inute and sw itch for operation without timer. Overall height, 19L/s inches; power consum ption 40 w atts.
8927-M . Shaking Apparatus, Boerner, A. H . T. Co. Specification, as above described, com plete w ith cord and plug, but without flasks and clam ps shown in illustration. For 110 volts, 60 cycles, a. c . . . 47.50 8 9 2 7 -0 . D itto, but for 110 volts, d. c ... 55.00 S927-P. “ “ " 220 volts, 60 cycles, a. c... 53.00 8927-Q. “ “ “ 220 volts, d. c... 56.50
Code Word Ocrft Ocrfu Ocrfw Ocrfy 8929.
8929-B.
8929.
Show ing h ead for a tta c h m en t to v ertical rod for sh aking sm all bo ttles and
flasks.
M ultiple Shaking H ead , for attach m en t to vertical rods of Boerner Shaker for shaking four sm all flasks, bottles, etc., up to 125 m l capacity and w ith necks from 18 to 2S mm outside diameter. W ith four adjustable Spring-Grip Clamps of nickel plated bronze and clamp holder for attach m en t to rod 6.00 Code W ord... Ocrgi Separatory Funnel Shaking H ead , for attach m en t to vertical
rod of Boerner Shaker for shaking two separatory funnels, 60, 125 or 250 ml capacity, in inverted position. Suitable for use in the determ ination of fusel oil in distilled liquors in accord
ance w ith A. O. A. C. “ M ethods of A nalysis” , 5th ed., 1940, p. 175 ... 13.50 Code W ord... Ocrgn
S929-B.
Showing h ead for a tta c h m e n t to v ertical ro d for sh ak in g S ep arato ry F unnels.
ARTH U R H. TH 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
L A B O R A T O R Y A P PA R A TU S AND R E A G E N T S
W E S T W A S H I N G T O N S Q U A R E , P H I L A D E L P H I A , U. S . A.
C a b le A d d ress, “ B a la n c e ” P h ila d e lp h ia
INDUSTRIAL a n d ENGINEERING CHEMI
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
Determination of Moisture in Starch and Its Modifications
L O U IS S A IR 1, C orn I n d u s tr ie s R e se a rc h , F o u n d a tio n , A N D W . R . F E T Z E R , U n io n S ta r c h a n d R e fin in g C o ., G ra n ite C ity , 111.
M
ANY extensive investigations have been made on the determ ination of moisture in cereals, starch and its modifications, proteins, and other biological products. These studies have indicated th a t empirical or relative moisture is possible rath e r than tru e moisture (8, 9, 10, 12, 13, 15) and have led to th e general conclusion th a t p a rt of the water is so “bound” th a t it cannot be differentiated from water of constitution (7). Consequently, workers requiring a knowledge of the true dry substance in a cereal, or in its constituents, are a t loss to know which m oisture method, if any, to employ.
In the w heat milling industry, empirical or relative moisture methods have proved adequate in com putation of factory yields or losses, for any method suitable for ground wheat would be expected to be equally satisfactory for the milled products, since the milling process involves only the physical separation of w heat into flour, shorts, bran, and germ.
In the corn wet-milling industry an entirely different set of conditions arises. The corn is steeped with dilute sulfurous acid which produces changes in the character of the constitu
ents. The separation is then carried out in the wet state.
The final product, starch, is either dried or converted by acid hydrolysis to corn sirup or corn sugar. The starch may be modified before or during drying.
The industry has long recognized th a t no one moisture method is applicable to all products, and different methods have been developed by the laboratories of the individual companies. In order to unify and standardize these methods, the Corn Industries Research Foundation established a fellowship w ith the objective of developing methods which would give tru e m oisture for all products of the wet-milling industry. M oisture methods for corn, corn gluten meal, corn gluten feed, corn oil meal, steep water, corn sirup, and corn sugar have been developed and are fully discussed else
where (4, 6,1 4 ). Although the results of m any studies have been published on th e determ ination of moisture in starch, there is still apparently considerable question as to which method, if any, yields th e true value. Little attention has been paid to the determ ination of moisture in commercial modified starches.
Block (3) showed th a t under atmospheric conditions tem peratures as high as 160° C. are necessary for removing the moisture from starch. M aquenne (11) compared data obtained in dry air a t 120° C. to atmospheric air in an oven a t 110° C. The results indicated th a t the former procedure
P resen t address, N o rth e rn R egional L aboratories, Peoria, 111.
was capable of removing the total moisture. Zerewitinoff (16) applied the use of magnesium methyl iodide to the deter
mination of moisture in starch, and found th a t results from this method agreed with the values obtained in a vacuum oven a t 100° C. Other investigators (5) have m ade use of dis
tillation procedures.
E x p erim en ta l
To the average person, starch means pearl or pure-food starch, which includes not only corn b u t also tapioca, potato, sago, etc. Commercial starches include the wet modified starches, principally those in which the character of the original starch has changed by a treatm ent with acid. There is also a group of oxidized starches, chlorinated or hypo
chlorite-treated, with different properties. Finally, there is the group of roasted starches or dextrins whose properties vary over a considerable range. The purpose of this research was to determine methods for true moisture, since it was considered unlikely th a t all these products could be covered by a single method.
The study covered 22 different commercial starches. These samples, if lum py, were ground to pass a 40-mesh sieve. After thorough mixing, the starches were transferred to 120-ml. (4- ounce) screw-top bottles, and stored in the refrigerator.
Me t h o d s. Distillation. T he assem bly was a modified Bid- well Sterling, fully described elsewhere (2, 4). Tw enty-five to 35 grams of starch (depending on the moisture content) were weighed into the tared distillation flask, containing 5 to 8 grams of asbestos, both of which had been previously dried in an air oven at 100° C. The purpose of the asbestos is to prevent bum p
ing during distillation, ¡sufficient toluene (usually 100 m l.) is added to fill the traps and cover the sample. The flask is then placed in an oil bath, and distillation continued until an addi
tional 24 hours showed no increase in recovered water.
Vacuum-Oven Methods. A Weber vacuum oven and a H yvac pump were employed, w ith oven pressures ranging from 0.5 to 2.5 mm. and temperatures of 100° =*■ 1 ° C. Standard A. A. C. C.
moisture dishes, 55 X 15 mm., were used ( /) . T ests were in duplicate (3 to 5 grams), and included sampling error, since the samples for each determination were taken from different storage bottles. The oven vacuum was restored by air passing through a drying train w'hich included concentrated sulfuric acid, Dri- erite, and phosphorus pentoxide. The sam ples were cooled in desiccators over calcium carbide for 15 to 20 m inutes.
Air-Oven Methods. The air oven was an Elconap se t a t 100° =*=
1° C.
M o i s t u r e R e s u l t s . The d ata obtained for th e first sam
ples of pearl cornstarch are shown in Table I.
843
844 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 11
Ta b l e I. Mo i s t u r e o f Pe a r l Co r n s t a r c h D istilla tio n Methods®
th of D rying Air oven V acuum oven Benzene X ylene
Hours % % % %
2 7 .9 10 .0
5 8Í96 10 .5 0 9 .7 10.2
20 9 .1 9 10.52 10.33 10.34
40 9 .3 3 10.54 10.65 10.63
65 10.63 10.60
10.67 10.66
a All values except final a re a p p ro x im ate readings of trap s.
Ta b l e I I . Op e n Ve r s u s Pa r t i a l l t Cl o s e d Di s h e s (V acuum oven, 100° C .)
D ry in g C onditions M oisture
%
M o istu re C hange
% 24 hou rs, open dishes
P lu s 24 hou rs, p a rtia lly open lids P lu s 24 hours, open dishes
10.54 1 0 .6 6 10.64 10.52
+
0 .1 2- 0:12
T he difference between th e final values obtained b y th e air- and vacuum-oven methods is 1.21 per cent. This m ay be explained on the basis th a t th e values obtained from an air oven depend upon th e m oisture content of th e air passing through th e oven and upon th e hygroscopic properties of the m aterial being dried. T he difference between values employ
ing the vacuum oven and th e distillation methods am ounts to 0.10 per cent. I t was thought th a t this difference resulted from m oisture picked up during th e tim e th e lids were re
moved from the bottom of th e dish and placed on th e top.
This hypothesis was tested b y th e following experiment:
On placing the samples in the oven th e dishes were se t on the lids for the first 24-hour drying period, for the next two 24- hour periods the lids were tilted on th e dishes so th a t they were only slightly open, after
which for another 24 hours the dishes were again placed on the lids. The results are given in Table II.
The d ata on pearl starch were confirmed by m any other tests m ade in like maimer. T able I I I gives the r e s u l t s o n a n u m b e r of starches, natural and modi
fied. In these tests th e oven tem perature was raised to 135° C. after completing 101 hours a t 100° C., to see if any further moisture was lost.
A lth o u g h n o t in c lu d ed in th e table, eight other
s t a r c h v a r i e t i e s w e r e : . . r ...:
analyzed with results which g a v e s e t h e m a x i
m um 0.04 per cent between a vacuum oven a t 100° C. and a t 135° C. T he acid-modified starches—20, 40, and 60 fluidity—as well as British gum and chlorinated starch, can be treated as straight starch for determ ination of moisture.
However, in th e case of 90 fluidity starch and white and canary corn dextrins, a definite loss in weight of 0.12 to 0.08 per cent occurred a t the higher drying tem perature. W ith th e hypochlorite-oxidized starch, th e weight loss was 0.45 per cent and there was visual evidence of decomposition, in th a t th e starch changed to a dark brown color. T he distillation results were in agreement w ith vacuum-oven procedures.
R e v e r sib ility o f V a c u u m -D r ie d S ta r c h e s A full discussion of th e use of the reversibility method for the determ ination of moisture in cereals has been given in moisture studies covering corn and gluten meal (14). This procedure was applied to the vacuum -dried starches (135° C.) in order to determ ine w hether any volatiles had been lost along w ith th e adsorbed w ater. T he starch samples dried in vacuo a t 100° and 135° C. (Table I II) were allowed to readsorb m oisture a t room conditions. These samples, to
gether with unheated samples of the same starch, were then placed in desiccators which served as conditioning chambers.
Through the desiccators was passed a stream of air which had been passed previously through a large q u an tity of concen
trated sulfuric acid. Equilibrium required approximately 14 days. If no volatiles are lost during vacuum drying a t 135° C., the vacuum -heated and th e control starch samples should reach th e same equilibrium value, w ith respect to m oisture retained, provided th a t th e m oisture-retaining property of the starch has not been changed during heating.
T he results obtained are shown in Table IV. The data show th a t the weight loss which occurs upon transfer of the samples from th e desiccator over sulfuric acid to th e vacuum oven a t 135° C. is recovered in m ost cases when th e samples are replaced in their original condition. T he two samples which clearly do not regain the to ta l weight lost are th e white corn dextrin and th e hypochlorite-oxidized starch, and in both these cases it was found th a t the 135° C. vacuum-oven procedure removed volatiles other th a n w ater, as indicated by th e 100° C. vs. th e 135° C. vacuum -oven results and the toluene distillation data.
Of interest in these results is the am ount of w ater each product retains over concentrated sulfuric acid. Under these conditions, th e am ount of m oisture still held by the various products varied from 1.00 to 1.65 per cent. These results dem onstrate the danger inherent in empirical methods.
Ta b l eI I I . De t e r m i n a t i o no f Mo i s t u r ei n St a r c h Pr o d u c t s
Starch —V acuum O ven, 100° C .- V acuum
O ven, 135° C., A d d itio n a l
Loss a t D is tilla tio n w ith
Plus P lus P lu s P lu s 135° C. vs. T oluene,
P ro d u ct 5 ho u rs 16 hours 40 h ours 40 ho u rs 20 H ours 100° C. 48 H ours
% % % % % % %
C orn 9 .7 0 9 .7 6 9 .8 2 9 .8 0
9 .8 0 9 .8 5 + 0 . 0 5 9 .8 4
9 .8 0 Acid m odification,
60 fluidity 12.44 12.49 12.57 12.55
12.51 12.54 + 0 .0 1
Acid m odification,
90 fluidity 11.16 11 .2 2 11 .3 0 11.30
11.30 11.42 + 0 . 1 2 11.30
11.21
W h ite d e x trin 5 .6 0 5 .6 7 5 .6 9 5 .7 0
5 .6 9 5 .8 2 + 0 .1 2 5 .6 2
C an a ry d e x trin 2 .9 2 2 .9 6 3 .0 6 3 .0 4
3 .0 3 3 .1 3 + 0 .0 9
B ritish gum 3 .4 0 3 .4 4 3 .5 0 3 .4 8
3 .4 7 3 .5 0 + 0 .0 2
C h lo rin ated starch 7 .1 2 7 .2 2 7 .2 4 7 .2 2
7 .2 5 7 .2 5 + 0 .0 1
H y p o ch lo rite-treated
sta rc h 12.76 12.84 12.90 12.91
12.95 1 3 .3 8 + 0 . 4 5 12.85
12.91
T ap io ca 14.67 14.72 14.80 14.78
14.78 14.82 + 0 .0 4
T e n a c ity o f W ater R e te n tio n o f S ta r c h P r o d u c ts I t is well known th a t a t th e same hum idity different starch products retain different am ounts of water. L ittle thought has been given to th e possible significance of this fact, with respect to the properties of starches. A preliminary study was conducted for th e purpose of determ ining th e relation of degree of modification to the sorptive capacity of th e starches.
Vacuum-dried samples (100° C.) were allowed to readsorb m oisture under room conditions. The ra te of m oisture up
take and th e final equilibrium values obtained are given in Table V.
November 15, 1942 A N A L Y T I C
Ta b l e I V . We i g h t Lo s sa n d Ga i nb e t w e e n Va c u u m Dr y in g a t 1 3 5 ° C . a n d Dr y i n g o v e r Co n c e n t r a t e d Su l f u r i c Ac id
i n De s ic c a t o r s Loss in W eig h t on T ran sfe r of S ta rc h D ried over C oncen
tra te d IIiSO« to V acuum Oven a t
G ain in W eight on R eplacem ent of Vac-
uum -D ried Samples (135° C.) in Desicca
to rs over C oncentrated Loss in
P ro d u ct 135° C. HtSO« Recovery
% % %
Corn 1.43 1.36 0.0 7
Acid-m odification,
60 fluidity 1.40 1.49 0 .0 9 °
Acid-m odification,
90 fluidity 1.21 1.15 0.06
W hite corn d extrin 1.65 1.19 0.4 6
C anary d ex trin 1.03 1.01 0.0 2
B ritish gum 1.41 1.37 0.04
C hlorinated sta rc h 1.41 1.43 0.02«
H ypochlorite-
oxidized starch 1.05 0.8 4 0.81
T apioca 1 .00 0.9 9 0.01
° G ain.
Ta b l e V . Ad s o r p t io n o f Wa t e r b y Va c u u m- Dr i e d St a r c h Pr o d u c t's
M o istu re Adsorbed by V acuum -D ried Samples (W et Basis)
P ro d u c t 1 h o u r 2 hours 3 hours 6 hours 24 hours
% % % % %
C o rn starch 5 .4 7 .4 9 .0 10.8 11.8
90 fluidity starch 4 .5 6 .2 7 .7 9 .3 10.3
W h ite corn d e x trin 5 .1 6 .8 8 .0 9 .0 9 .8
C an ary dex trin 4 .5 5 .8 6 .8 7 .9 9 .2
W ith increasing modification th e sorptive capacity of starch decreases—th a t is, the modified products are less hygroscopic. As shown in Table VI, although the modified products retain less water, the w ater th a t is held is retained with equal or greater tenacity th a n the w ater held by the original cornstarch. These d ata show th a t canary dextrin holds th e least m oisture and retains it with the weakest tenacity. The white corn dextrin retains its moisture with the greatest tenacity. M ore critical studies are now under way to determ ine the relation of the sorptive capacity of starches to their properties.
Starch is extremely hygroscopic. For this reason, the air used to replace the vacuum in the oven should be passed through a train as follows:
Two 19-liter (5-gallon) bottles, in series, each containing 2.5 to 5 cm. (1 to 2 inches) of concentrated sulfuric acid; drying tower filled with glass wool; and preferably another tower filled with Drierite.
The A. O. A. C. oven tolerance of a pressure of 25 mm. or less of mercury is too great. The oven should have a well-seated door which will retain the vacuum for several hours after the pump is stopped. Otherwise, a slight leak of atmospherie air will occur, resulting in low moisture data.
The period of drying should be continued until constancy is obtained.
L E D I T I O N 845
A ck n o w le d g m e n t
The authors’ thanks are due to the Corn Industries Re
search Foundation for permission to publish the work.
L ite r a tu r e C ited
(1) Am. Assoc. Cereal Chemists, ‘‘Cereal Laboratory Methods”, p. 21, Lincoln, Ncbr., 1941.
(2) Bidwcll, G. L., and Sterling, W . F., In d. En o. Ch e m., 17, 147 (1925).
(3) Block, M., Compt. rend., 118, 140 (1894).
(4) C le la n d , J. E ., a n d F e tz e r , W. I t . , In d. En o. Ch e m., An a l. Ed., 13, 858-00 (1941); 14, 27-30, 124-7 (1942).
(5) Fairbrother, T. H., and Wood, It. J., Ind. Chemist, 6, 442 (1930).
(6) Fetzer, W. It., a n d E v a n s , J. \V., In d. En d. Ch e m., An a l. Ed„ 7,41 (1935).
(7) Gortnor, R. A., "Outlines of Biochemistry”, New York, John Wiley & Sons, 1938.
(8) Halvorson, II. A., J . Assoc. Official Agr. Chem., 20, 435 (1937).
(9) Hoffman, J. F., and Schulze, J. II., Wochschr. Brau., 20, 217 (1903).
(10) Kent-Jones, D. W., “Modern Cereal Chemistry”, Liverpool, Northern Publishing Co., 1939.
(11) Maqucnne, M. L., Compt. rend., 141, 609 (1905).
(12) Nelson, O. A., and Hulett, G. A., In d. En o. Ch e m., 12, 40 (1920).
(13) Nowak, G., and Enders, C., Chem. Zenlr., 11, 202 (1938).
(14) Sair, L., and Fetzer, W. R„ Cereal Chem., 19, 633 (1942).
(15) Snyder, H., and Sullivan, Betty, In d. En o. Ch e m., 18, 272 (1920).
(16) Zerewitinoff, T., Z. anal. Chem., 50, 680 (1911).
Ta b l eVI. Te n a c i t yw i t h Wh i c h St a r c h e s Re t a i n Mo i s t u r e M oisture R etain ed (V acuum a t 100° C. — 0% ) 24 hours, a ir oven. P lu s 24 hours, P lu s 100 hours, P ro d u c t 70° C. air oven, 100s C. 70" C . in d ry air
% % %
C o rn starch 3 2 .8 1 6 .6 7 .6
90 fluidity sta rc h 3 4 .8 17 .2
White corn dextrin
Canary dextrin 3 4 .83 0 .2
17.7 1 3 .8
8 .6 9 .1 6 .9
In su lation for N ecks o f W ash B ottles
C o n c lu sio n s
E ither of two moisture methods is suitable as a reference method for determ ining moisture in starch and its modifi
cations. These two methods are the toluene distillation procedure, and the vacuum-oven method a t 100° C. Rapid oven procedures using tem peratures as high as 140° C., based on these methods, should prove reliable for most starch products. Care m ust be exercised, however, in drying highly acid modified starch and th e hypochlorite-oxidized products a t tem peratures higher than 100° C.
The official Corn Industries Research Foundation toluene distillation m ethod for corn and its feed products (14) is equally suitable for starch products. The recommended official C. I. R . F. reference 100° C. vacuum method for starch products is essentially similar to the A. O. A. C.
vacuum-oven m ethod for w heat flour, with th e following modifications:
JA C O B M IZ R O C II
F ed era l W ork s A g e n c y , P u b lic R o a d s A d m in is tr a tio n , W a s h in g to n , D . C.
I
N T H E Subgradc Laboratory, Division of Tests, Public Roads Administration, necks of wash bottles containing hot liquids had been insulated by a wrapping of thin sheet asbestos. A serious drawback is the tendency of th e asbestos to crumble with use, leading to th e danger of asbestos p articles falling into precipitates being washed.
Bottlenecks insulated by th e following procedure have been used daily for over two years w ithout sign of deteriora
tion.
T he neck of th e wash bottle is snugly wound w ith a w etted thin asbestos strip about 2 inches wide, and the bottle is set aside to dry overnight. Bakelite lacquer (BL 3128, B 57) is then brushed on the dry asbestos, allowed to air-dry for an hour, and baked a t 110° C. for 4 hours.
Ascorbic Acid
R a p id D e te r m in a tio n in F r e sh , F r o z e n , o r D e h y d r a te d F r u its a n d V e g e ta b le s
H . J . L O E F F L E R a n d J . D . P O N T IN G
S . D e p a r tm e n t o f A g r ic u ltu r e , A lb a n y , C a lif.
W e ster n R e g io n a l R e se a rc h L a b o r a to r y , U .
P
LANT tissues m ust be finely divided and uniformly mixed as a prelim inary step in analysis. These objectives, formerly accomplished only b y laborious hand grinding after cutting up the sample or passing it through a food chopper, may now be attained easily by use of a commercial household food-preparing device described as a liquefier or blender. This was first pointed o u t by Davis in 1939 (2).
Morell (16) has found th a t in 3 per cent m etaphosphoric acid plant tissues m ay be disintegrated in these devices, such as the W aring Blendor (made by W aring Corporation, 1697 Broadway, New York, N . Y.), w ithout causing any loss of ascorbic acid. Davis (2) has also used such a blender for ascorbic determ ination using an extraction and titration mix
ture of trichloroacetic and m etaphosphoric acids.
MorelPs adaptation (16) of the photom etric m ethod for determ ining ascorbic acid by comparing photoelectric color
im eter readings on specially prepared plan t extracts with a standard curve obtained w ith regularly increasing mere- m ents of pure ascorbic acid is satisfactory where only one type of m aterial is to be tested, b u t the research programs on dehydrated and frozen foods under way in th e W estern R e
gional Research Laboratory have necessitated a method equally adaptable to m any kinds and varieties of fruits and vegetables th a t m ay be fresh, frozen, or dehydrated (partially or completely), and in some cases highly pigmented. This requirem ent is m et b y combining M orell’s technique of p re paring p lan t extracts with a modification of the E velyn et al.
(4) colorimetric m ethod for determining ascorbic acid. This combination m ethod is an extension of th a t used by Loeffler (1 0) for orange juice and utilizes a rate reaction in a photo
electric colorimeter. I t is somewhat simpler in operation than th e excellent Bessey (1) modification of th e M indlin and B utler technique (IS) which also utilizes th e photoelectric colorimeter.
S im p lifie d M e th o d
Blend 25 or 50 grams of fresh or frozen fruit or vegetable tissue w ith 350 ml. of 1 per cen t metaphosphoric acid in a blending machine operated for 5 m inutes at high speed. If the material is of high ascorbic acid content, such as leafy vegetables, rasp
berries, strawberries, or asparagus, use the smaller quantity.
F ifty grams are used w ith foods containing less ascorbic acid, such as stored potatoes, carrots, yam s, peaches, plums, and apricots. I f a dehydrated fruit or vegetable is being analyzed, 5 or 10 grams of sam ple are sufficient, depending upon this same classification. Som e thoroughly dehydrated vegetables, such as sw eet potatoes or carrots, m ay need 0.5 hour of soaking in the acid before blending. Frozen foods m ay be blended w ithout preliminary thawing.
Filter the extract through coarse, fluted filter paper. E x
tracts of starchy vegetables, such as potatoes and corn, filter better through a Buchner funnel. T h ey can also be cleared by centrifugation. M oderate turbidities do not interfere, since the instrum ent is calibrated w ith proper blanks.
P ip et 1-ml. portions of the filtrate into three m atched tubes from the E velyn photoelectric colorimeter.
Add 9 ml. of distilled water to one tube and adjust the colorime
ter to read 100 w ith this tube, using filter N o. 520.
T o each of the other tubes add 9 ml. of the previously stand
ardized indophcnol dye solution from a calibrated rapid delivery ipet. T ake a reading in the photoelectric colorimeter, using Iter N o. 520, 15 seconds after the start of the dye addition.
T his reading is Gt, from which the corresponding Li value is ob
tained, from the calibration table provided with the instrument, and substituted in the following equation of Evelyn:
Ascorbic acid, mg. per 100 ml. of filtrate = 10.8 (Li — Lj) T he equation for fruit and vegetable tissue becomes:
Ascorbic acid, mg. per 100 grams of tissue = 10.8 (In — Li) [ml. of acid extractant + (% liquid in sam ple) (wt. of sample)]
w t. of sample
T he authors use a reservoir-type autom atic pipet for the acid and nonreservoir typ es for the 1-ml. portions of filtrate and 9- ml. portions of dye, so th at th ey can achieve a rate of 20 samples per hour (two testers and a helper). Unlike E velyn , they have found it more suitable to add the dye to the tube outside the colorimeter and agitate the tube slightly before pu ttin g it in the instrum ent. T he autom atic 9-ml. pipet m ust extend to near the surface of the liquid in the tube to avoid splashing and must be calibrated to drain uniformly in less than 5 seconds.
S ta n d a r d iz a tio n o f D y e
The dye is standardized by noting the 15-second reading with filter 520 (when the instrum ent is calibrated to 100 with distilled water) given by a tube containing 1 ml. of 1 per cent metaphos
phoric acid and 9 ml. of the dye solution. T his value is Gi, from which Li is obtained on the calibration table. T his stand
ardization is very much easier and faster than titrim etric pro
cedures.
T he dye solution is prepared sim ply b y dissolving enough of the dye in water so that a Gi reading of about “ 3 0 ” is given with the Evelyn photoelectric colorimeter. T he concentration of dye to give such a reading is roughly 13 mg. per liter. The reaction between ascorbic acid and stronger dye solutions is not a linear relationship, so th at a calibration curve rather than a constant factor m ast be used w ith such solutions.
V o lu m e o f A cid a n d E x tr a c tio n C a lc u la tio n Because of the thorough disintegration of th e sample in th e blender, th e ascorbic acid is distributed uniformly through th e entire liquid phase present. B y determ ining th e ascorbic acid concentration in th e filtrate (per milliliter of liquid phase) and by knowing the to ta l volume of liquid, the am ount of ascorbic acid in a sample can be determined from a single ex
traction. Only a few milliliters of filtrate are necessary. The total am ount of liquid is simply th e sum of th e volume of metaphosphoric acid solution added plus th e liquid originally present in the sample.
T he authors have found a ratio of seven p arts of m eta
phosphoric acid solution to one of vegetable or fruit tissue satisfactory. U nder such circumstances th e liquid originally present in the sample (water plus soluble solids) m ay be ap
proximated from food tables, since a variation of 7 per cent causes less th a n 1 per cent variation in the ascorbic acid cal
culation. The results are more accurate and simpler to ob
tain th a n those after three or more extractions w ith small volumes of extractant (usually 1 to 1 ratio). M ost of the previous workers [Mack and Tressler (13), K irk and Tressler (7), M cHenry and G raham (1 2), and Rolf (IS)] have disin
tegrated th e tissue in a m ortar and then used such multiple extractions.
Bessey (1) uses b u t one extraction and suggests th a t the volume of the solids m ay be neglected. He recommends a sample of only 0.5 to 2.0 grams; b u t a much larger sample, 25 to 50 grams, is necessary with fruit and vegetable tissues to approach uniform ity. U nder such circumstances the re
sults approach th e accuracy of th e method, which is about 1 per cent.
