32 
Another portion of the residue was extracted in the same way 
and the filtrate treated with basic lead acetate to precipitate the 
starch. This was then filtered through a dry asbestos mat, and an 
aliquot portion, after removal of the lead, inverted with hydrochloric 
acid in the usual way. 
The portion soluble in water and not precipitated by basic lead 
acetate is designated in the table as dextrin, and the portion soluble 
in water but precipitated by basic lead acetate is designated as 
soluble starch. 
It must be remembered that these figures are but rough indica- 
tions of the actual quantity of these substances present, for it is 
hardly possible that a complete separation of the various constit- 
uents can be made in this way. However, the samples were all 
handled in the same manner and the figures are, therefore, entirely 
comparable. 
A glance at the table shows that very great changes occur during 
the precooking. Three to four times as much material was extracted 
by the alcohol from the cooked as from the uncooked potatoes. 
During precooking, large quantities of starch are changed to re- 
ducing sugar, probably maltose, and other intermediate products. 
Dextrose, cane sugar, probably maltose, and substances closely 
related to dextrin are found in the alcoholic extract, while the 
residue contains starch, dextrin, and intermediate products. 
The increase in sugars in the alcoholic extract, after inversion 
with diastase, would seem to indicate the presence of polysaccha- 
rides. However, a blue color is not given by iodine, but a slightly 
reddish color instead. This increase probably is due to inversion 
of maltose. 
There is no difference in the reducing power after the acid 
inversion and after the action of diastase in the extract of the raw 
sample, but in the extract of the cooked sample the difference 
amounts to 3 to 4.5 per cent. 
The amount of reducing sugars in the raw sample is unusually 
low, less than 1 per cent. Ordinarily, the reducing sugars amount 
to about 2 per cent in the fresh, raw, sweet potato. 
During precooking, the percentage of reducing sugars increases 
very greatly, amounting to as much as 8.9 per cent in some cases. 
The figures indicate very little change in the cane sugar. The 
difference in results before inversion and after inversion is a little 
greater in the cooked than in the uncooked sample. This is prob- 
ably due, however, to the influence of intermediate sugars rather 
than to increase in cane sugar. 
The change in sugar content during cooking is greater after 
storage than when the cooking is done immediately after digging. 
Some transformation evidently occurs during storage which, upon 
cooking, results in a marked change of starch into sugar. 
Grore (SO) has shown that the sweet potato contains a considerable 
amount of diastase and that, with a very slow cooking of it in water, 
very nearly all the carbohydrates are changed to a soluble form. He 
has applied this fact in the manufacture of sweet-potato sirup. 
When the potato is cooked rapidly, the action of this diastase is 
apparently much less complete. The amount of change that occurs 
with rapid cooking differs with the variety of sweet potato used and 
