1002 
Journal of Agricultural Research voi. xxiii, no. « 
In Table II, A is greatest for the malt controls, in which the concentra¬ 
tion of solute was lowest and the quantity of coagulum was almost 
negligible. 20 Taking the other extreme (the mixture containing the 
largest quantity of added starch), the values for A are the smallest 
reported, while the concentration of solute was the second highest and 
the quantity of coagulum was relatively large. 
While the- indications are that there is little adsorption, if any, an 
attempt to explain from the data at hand the high relative values for A , 
particularly for the malt controls, must consist largely of theorizing. 
The quantities of cuprous oxid actually obtained (from an aliquot of 
Solution 2), on which the values for A are based, however, were small, 
ranging from 8.8 to 23.6 mgm. The application of any substantial cor¬ 
rection for the effect on the copper reduction of the reagents used in 
defecation 21 to these results would greatly reduce the values for A , and 
the effect would be emphasized in the case of the malt controls, for 
which the yield of cuprous oxid from Solution 2 was smallest. 
The results obtained by carefully following this method, using a single 
precipitation with 60 per cent alcohol, furnish sufficient evidence of its 
fundamental soundness, and the investigators recommend it for the 
determination of starch in materials which, like linseed meal and apple 
pomace, contain interfering polysaccharids. In using the method, 
however, the analyst must give painstaking attention to details, particu¬ 
larly to those operations dealing with the colloidal substances, such as 
the gelatinizing to a smooth paste, the thorough breaking up of coagula, 
and the subsequent mixing. It is also highly important to control 
carefully the conditions that prevail during die dissolving and con¬ 
version of the starch. Work conducted in the Bureau of Chemistry has 
shown that the starch is best brought into solution by starting the first 
digestion with* malt infusion at a temperature well below 55 0 C., then 
slowly raising it to 70°, holding it there for the specified time, and con¬ 
tinuing to increase the temperature to 8o°. While the saccharifying 
enzyms (the maltase) are believed to be destroyed by temperatures of 
70 p and higher, other starch liquefying enzyms present in the malt 
infusion are more active at the higher temperatures, and complete 
solution of the starch is attained. The second saccharifying digestion 
is conducted at 55 0 . 
Because of the difficulties mentioned, the method of analysis is dis¬ 
cussed in greater detail than would ordinarily be necessary. 
method recommended 
PREPARATION OF MAI/T EXTRACT 
Use clean, new barley malt of known efficacy and grind it only as 
needed. Grind the malt well, but not so fine that filtration will be 
greatly retarded. Prepare an infusion of the freshly ground malt, just 
before it is to be used. For every 80 cc. of the malt extract required 
digest 5 gm. of the ground malt with 100 cc. of distilled water, at room 
temperature, for 2 hours, or for 1 hour if the mixture can be stirred by 
*o The nature of the small quantity of coagulum from the malt controls differed from that , ob taine d from 
meal. This might have significance had there been sufficient adsorption to be of importance, 
a There is some cause for believing that the use of phosphotungstic acid slightly increases the reduction 
of copper in Fehling’s solution. 
