5 io 
Journal of Agricultural Research 
Vol. V, No. 12 
experiments were all carried out at 30° C. This temperature was chosen 
in order to study the respiration of the sweet potatoes under conditions 
similar to those to which the freshly dug roots are subjected during the 
curing process, which consists essentially in keeping them at a tem¬ 
perature in the neighborhood of 30° C. for about 10 days. 
EXPERIMENTAL METHODS 
The methods employed in the experiments require but little descrip¬ 
tion. The sweet potatoes were placed in a large receptacle in an 
ordinary water-jacketed incubator, which was kept at a temperature 
of 30° C. A current of air having the same temperature and freed 
from carbon dioxid was drawn through the receptacle at the rate of 
40 to 50 liters per hour. The carbon dioxid of respiration was collected 
in approximately one-half normal potassium-hydroxid solution, whose 
titre for pure potassium hydroxid had been determined. The absorp¬ 
tion was effected by means of Reisette flasks. At the end of every 24- 
hour period the carbon dioxid in the Reisette flask was precipitated by 
means of an excess of barium chlorid, and the residual potassium hydroxid 
was determined by titration with normal or half-normal hydrochloric 
acid. 
About 2 to 3 kgm. of sweet potatoes were used in each experiment. 
At the beginning of the experiment the sugar content was determined 
in a collateral sample of 3 to 4 kgm. from the same lot. At the end of 
each experiment all the sweet potatoes which had been used for that 
experiment were ground and sampled for determinations of sugar and 
moisture. 'The figures giving the sugar determinations are averages of 
five samples from each lot. The directly reducing sugar was calculated 
as glucose. The soluble carbohydrates yielding reducing sugar after 
inversion were calculated as cane sugar, which is the most abundant 
disaccharid present in the sweet potato. Jersey Big Stem sweet potatoes 
were used in all the experiments. 
EXPERIMENTAL DATA 
The results of all the experiments are collected in Table I. The 
percentages of total sugar (as glucose), cane sugar, and reducing sugar 
(as glucose) in the collateral sample' taken at the beginning of each 
experiment, and in the experimental sweet potatoes at the end of the 
experiment, are given at the head of the table. These figures were in 
each case calculated for sweet potatoes of the water content of the 
collateral sample—i. e., the assumed original water content of the 
experimental sweet potatoes. The carbon-dioxid output is given in 
milligrams per kilogram per hour for each day. In the calculation the 
loss of weight of the sweet potatoes during the experiment was taken 
into consideration and was distributed uniformly over the period. At 
