266
IV. .?. S O Y E d . \ X I 1 O T I I K R S ,
Uriefly tlescribeti, the methoti proposed ior the cletermiiiation o i gliadin h y the polariscope is nl; folloi~s: ‘,\7eigh I 3.97 grams of flour into a flask and add 100 cc. of 70 per cent. alcohol. Shake the flask moderately at inter\-als of a half hour for two or three hours. Ixave the alcohol in contact ivitli t h e 11our for from t i v c l ~ cto eighteen hours, at a temperature of about 20’ C. Filter the alcoholic solution antl polarize, using a 220 mm.tube. Alultiply the reatiiijg on the s i i ~ a r i l c 0 . 2 , wliicli Kives approximately the per cent. of gliatliii i:itroge!i. The time of estraction \\.it11 alcohol can hc 1eFse:ietl by the use of a shaking machine antl tlieii clarifying the solution by centrifugal action. Excessive shaking is to be avoided, otherwise cloudy filtrates are obtaiiietl \vliicli cniiiiot be polarized. Sonie flours, particularly soft n-hcat floiirs~frequeiitl! cloudy filtrates. If the alcoholic solutioii? are kept too lo!i< 5.7), and that from 55 to 65 per cent. should be i n thc form of gliadin. l t is believed that the method as here propose(! of tlcterniining the gliadin content of flour by means of the po1ar;scope will be found IJothrapid antl accurate, and particularly applicable where large numbers of determinations are to be made. C N I V E R S I T S OF M I S X E S O T A . MINNEAPOLIS,M I N N .
T H E HYDROLYSIS OF M4LTOSE A N D OF DEXTRIN BY DILUTE ACIDS A N D T H E DETERflINATION OF STARCH. BY
W I L L I A M A . NOSES, G I L B E K T C R A W F O H D , C H A R L E S H. J U M P L R , E D G A R A N D ROBERT13 .&RSOLD.I
Received December
10,
L
FLORS,
I903
The method of determining starch in common use consists in converting the starch into a mixture of maltose and dextrin by 1 The work here described formed the basis for theses which were presented for the degree of Bachelor of Science at the Rose Polytechnic Institute by Mr. Crawford in 1 9 1 , by Messrs. Jumper and Flory in 1902. and by Mr. Arnold in 1903.
HYDROLYSIS O F MALTOSE AND DEXTRIN.
267
means of diastase, followed, after filtration, by hydrolysis of this mixture to glucose by means of a dilute acid. The time required for the hydrolysis of maltose has been determined empirically by finding the length of the time necessary to give a product which shows a maximum reduction of Fehling's so1ution.l So far as we are aware no one has ever determined the rate of hydrolysis for maltose and dextrin under the conditions which obtain in the determination of starch. It appeared to us that a determination of this rate would give valuable information with regard to the length of time required for the hydrolysis. Sigmond2 has determined the rate of hydrolysis for maltose at temperatures of 63.7" to 83.76", but these determinations have little value for the purpose in question. In our early experiments Mr. Crawford followed the hydrolysis of maltose by means of the decrease in rotation occasioned by the change from maltose to glucose. Using a IO per cent. solution of maltose, to which IO per cent. by volume of hydrochloric acid (sp. gr. 1 . 1 2 5 ) was added, and heating on a water-bath for varying times, the following results were obtained : Time. Minutes.
Maltose.
Rotation. Degrees.
Per cent.
5 I5 30 45
21.07 16.j 11.8 9.3 9.0
60
8.5
...
8.53
0
0
m
(calc.)
Glucose.
Per cent.
100.0
C.
.....
0
65.2 26.1 6.I
0.0372 0.0427 0.0404 0.031j
34.8 73.9 93.9 96.0
4.0
...
..... .... --
100.0
Average, 0.0380
Time for 50 per cent. hydrolysis (calculated), 7.9 minutes. "
' I
90
' I
( 6
' I
99 99.5''
( (
I' I '
I'
' I
26.2 52.6
'' < I
' 6
" 60.5 " I' " In the table the rotation for complete hydrolysis is
'I
21.07X 5 2 . 7 - -8..53O, 130.2
assuming 130.2' as the rotation for maltose containing I molecule of water of crystallization and 52.7" as the rotation for 1
2
M e i s s l : j . p r a R i . Chcm., [2], 25, Zischr. phys. Chem., a7,385.
124
(rsz).
268
W. A . N O Y E S A N D OTHERS.
glucose for sodium light. usual formula
The constant C is calculated by the
in which A represents the change in rotation for complete hydrolysis of the maltose to glucose and x represents the change in rotation which has taken place at a given time.' The time for 50 per cent. hydrolysis is calculated by the formula
in which A = 100 and K is the per cent. assumed as hydrolyzed. I n most of the work, more dilute solutions were used and the determinations were made with Fehling's solution. A large number of experiments were carried through, which, in the end, are treated as preliminary, becausc they were superseded by others, in which the methods employed were more satisfactory. i1;hile probably three-fourths of our time wa$ spent upon experiments of this nature, and many of these experiments gave results similar to those recorded below, we shall make no attempt to describe them, nor shall we separate, in the further description, ihe work of individuals. E f f e c t 01Heating Gliicosc with I l y d i o c h l o r i c Acid.-To a solution of pure glucose containing approximately 0.5 per cent., IO per cent. of hydrochloric acid (sp. gr. 1 . 1 2 5 ) ~by volume was added; different portions were heated on a water-bath for varying times, with care that the volume was unchanged, then neutralized and the glucose was determined by Fehling's solution. The results given were obtained by three different observers at considerable intervals of time. Solution of glucose not heated.. ...... 0. I 903 ..... " '. ' I heated one hour.. . " ' ' two hours. . 0.1906 ', '< 'I three .. 0.1918 ,' " four . . .....
