Mar. 34. X993 
Determination of Starch Content 
999 
cent. A combustion determination 13 of carbon and hydrogen gave the 
following results: Carbon, 40.67 per cent, and hydrogen, 6.68 per cent, 
indicating a hexosan content of 91.53 14 per cent and a water content 
(uncombined) of 8.79 per cent. 
The foregoing determinations were made on the starch near the close 
of the experimental work, several months after the samples had been 
prepared. The material was quite hygroscopic, and the percentage of 
starch determined by modifications of the official malt-diastase method 
was higher at the time of preparing the starch than four and five months 
later. The percentage of starch ranged from 89.65 to 87.19, owing, it 
is believed, to the absorption of moisture from the air. The values 
accepted as representing the true starch content of this standard sample 
are 88.9 per cent for the earlier experiments and 87.5 per cent for the 
later work. Throughout this study, the factor 0.90 was used in cal¬ 
culating starch from dextrose. The factor 0.93 probably more nearly 
represents the actual yield (r, p. 95). Had this factor been used, the 
accepted values would have been 91.9 per cent for the earlier and 90.4 
per cent starch for the later work. The validity of the figures showing 
the value of the methods of analysis is not affected by the factor used. 
Working with dried apple by-products, with and without added 
starch, the new method was compared with the Cassal colorimetric method 
and the official malt-diastase method. The results obtained were not 
entirely satisfactory. While the official method yielded results that 
were too high, owing undoubtedly to the inclusion of some pectin, the 
alcohol precipitation method failed to fully account for all the starch 
present The results obtained on a sample of linseed meal containing 
known quantities of starch also were unsatisfactory in this first test with 
the method. 
CORRECTION OF REVISED METHOD 
It was thought that the failure to account for all starch known to be 
present might be due to: (a) Formation of mucilaginous lumps in the 
material, during gelatinizatton, which subsequently served to shield par¬ 
ticles of starch from the dissolving action of the malt extract; (b) failure 
to thoroughly break up the ropy coagulum formed in the 60 per cent 
alcohol, with consequent occlusion of some of the more concentrated 
portions of the solution; (c) adsorption of maltose and dextrine by the 
coagulated colloids. 
Accordingly, the method of analysis was reviewed to correct any 
errors in technic. The details and precautions to be observed are 
fully set forth in the final statement of the method of analysis advocated 
(p. 1002-1005). 
If adsorption of the starch conversion produets were primarily re¬ 
sponsible for the low results, it seemed reasonable to expect that this 
error could be obviated by double precipitation with the 60 per cent 
alcohol. 
TESTING FOR ADSORPTION BY DOUBLE PRECIPITATION 
After the first precipitation in 60 per cent alcohol, the 500 cc. of 
liquid was thoroughly mixed with the coagulum, by pouring the mixture 
1* The of nitrogen, carbon, and hydrogen were conducted by J. F. Hills, of the Nitrogen 
Section, Bureau of Chemistry. , . . 
m a small quantity of cell wall tissue (cellulose) in the sample counts as starch m a combustion deter¬ 
mination. 
