IOOO 
Journal of Agricultural Research 
Vol. XXIII, No. 1 a 
back and forth from one container to another, and filtered through dry 
paper, care being taken to avoid the loss of any of the solution or mate¬ 
rial. 15 The filter was allowed to drain until there was no danger of loss 
of filtrate on removing the paper and its contents from the funnel. The 
total volume of filtrate that had drained through was ascertained. The 
aliquot represented by it 16 was designated F and the whole solution, 
Solution i. Using about 150 cc. of hot water, the filter paper and 
coagulum contained in it were returned to the 500 cc. volumetric flask, 
care b^ing taken to rinse back all material adhering to the containers 
previously used in the mixing operation. (This serves to redissolve the 
mucilage, and the solution also contains that portion of Solution 1 which 
did not drain through the filter.) The aqueous mixture in the 500 cc. 
flask was shaken hard and thoroughly and, after cooling, the colloids 
were reprecipitated with 316 cc. of 95 per cent alcohol, the precaution 
of adding the alcohol in small portions and mixing to keep the coagulated 
material broken up being taken. 
The total volume of liquid was completed to 500 cc. with water, 
mixed as before, by pouring it back and forth, and filtered through dry 
paper. This filtrate is called Solution 2. Aliquots of 200 cc. of Solution 
1 and Solution 2 were evaporated in separate beakers, over steam, and, 
after the usual add hydrolysis and purification, the dextrose in each ali¬ 
quot was determined. 
The additional determination of dextrose can not be avoided when 
double predpitation is employed. Hypothetically, the charge of starch 
rendered soluble by the diastase digestion, after die predpitation of col¬ 
loids by alcohol, may be considered as existing in two forms: Unadsorbed 
portion ( 5 ), freely in solution in the 60 per cent alcohol; and a portion (A) 
supposedly adsorbed by the coagulum. 
As S is entirely in solution, its quantity is readily obtainable from the 
quantity of dextrose found in the aliquot of Solution 1. The estimation 
of A, however, is not so simple. In the second alcohol extract (Solution 
CQQ—F 
2) there is presumably not only all of A 17 , but also of S. (The 
quantity represents the aliquot of Solution 1 that adhered to the 
filter and coagulum.) Thus the dextrose determined on the 200 cc. 
200 CQQ— F 
aliquot of Solution 2 is represented by (A + $ and the dex¬ 
trose determined on the 200 cc. aliquot of Solution 1 is represented by 
200 
^^• 5 . In the two equations indicated, F is known, and S and A are 
readily obtainable. The total dextrose representing the starch in the 
original charge should equal S+A. This value, of course, must be cor¬ 
rected for the dextrose determined in the malt blank. This correction 
properly is made by calculating back to the quantity of dextrose in the 
malt infusion added to the mash, and subtracting this directly from 
5 + A, The remainder, multiplied by 0.9, gives the starch content. 
16 A correction was obtained for dextrose due to the malt infusion and filter paper, by proceeding with 
the malt blank determination in exactly the same way. 
18 The aliquot may be accurately and conveniently determined by weighing the original 500 cc. of solu¬ 
tion (by deducting the weight of solid material from the total), and also the filtrate, on a balance sensitive 
to x gm. 
17 Theoretically this would not be strictly true, owing to the proportional distribution of solute maintained 
between solution and adsorbent. The quantity of starch conversion products so withheld from solution, 
however, would be negligible, because of the dilution. 
