4 BULLETIN 1041, U. S. DEPARTMENT OF AGEICULTUEE. 
It will he seen from Table 1 that the ^weet potato has a low mois- 
ture content : it is high in total carbohydrates and low in fat. fiber, 
protein. The protein content is slightly lower than that of the 
Irish potato: but about half of the total nitrogen calculated as pro- 
tein in the Irish potato is really in the form of amids. whereas in 
the sweet potato, as shown by Keitt (11) , no amids are present. 
The low crude-fiber content indicates high digestibility, and the 
fuel value is also seen to be high. 
From the standpoint of the canner the acidity of the sweet potato 
is : considerable importance, since it affects the transformations 
which take place within the can both during and after processing 
and likewise has an important bearing upon sterilization. Published 
data upon this subject, however, are meager. Bigelow and Cath- 
cart i % > approached the subject from the standpoint of the hydrogen- 
ion concentration and give the results of six determinations upon 
canned sweet potatoes from different sources packed in No. 2| and 
No. 3 cans and processed at different temperatures for variable lengths 
of time. Their determinations place the P h value for sweet potatoes 
at between 5.27 and 5.56. with an average of 5.39. According to 
the findings of these authors the hydrogen-ion concentration of the 
oed sweet potatoes is a little lower than string beans and green 
peppers and slightly higher than spinach. Lima beans, peas, and 
corn show a considerably less hydrogen-ion concentration, and pump- 
kins and carrots somewhat more. 
In the present investigations the titratable acidity was determined 
upoi ned material of each of the varieties and strains under 
study. The material examined was in the form of pie stock, which 
was I dry int No. 2 tin cans and processed for 45 minutes at 116° 
C. Samples of 10 grams each were shaken up in 100 c. c. of distilled 
water, boiled one minute to expel carbon dioxid, and titrated with 
N 1 >: H. using phenolphthalein as an indicator. From 3.2 to 
7.3 . •. of the standard alkali were required to neutralize the acidity 
10-gram samples. These figures represent the extremes, the 
average of the 43 varieties and strains being 4.5 c. c. which shows 
that the sweet potato is quite low in acidity. The average titratable 
acidity was slightly higher in samples packed in 1920 than those 
. but this fact is not considered significant, as in some 
varieties the acidity was higher in 1919 than in 1920. The differences 
in acidity among the varieties were small, and in these tests they 
con! relate:! with keeping qualities, discoloration, or any 
other significant quality. They therefore seem to be too small to be 
of importance. 
The most important constituents of sweet potatoes are the carbo- 
hydrates, and since the nature and relative proportions of these 
fundamentally affect the physical character and quality of the 
