5IO Journal of Agricultural Research voi. v, no. u 



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 



