628 
Journal of Agricultural Research 
Vol. XXI, No. 9 
ANALYSIS 
The halves were prepared for analysis by first being run through a 
pulping machine. The pulp was then thoroughly mixed, and duplicate 
samples were transferred to tared weighing bottles for dry-weight deter¬ 
minations. The pulp was covered with 95 per cent alcohol and then dried 
to constant weight in a vacuum oven at 6o° C. Another set of duplicate 
samples was taken from the pulp of each half for carbohydrate deter¬ 
minations. For this purpose 10-gm. portions of the pulp were placed in 
beakers containing about X gm. of calcium carbonate (CaC 0 3 ) and were 
then covered with 70 per cent alcohol and heated to boiling. The con¬ 
tents of each beaker were then transferred to a tared thimble and ex¬ 
tracted with 70 per cent alcohol in a Soxhlet’s extraction apparatus for 
about seven hours. The extract was made up to 500 cc. by the addition 
of water, and 100 cc. were transferred to a beaker and evaporated to 
about 25 cc. It was then transferred to a 100-cc. sugar flask and cleared 
in the usual way with lead acetate. The cane sugar was hydrolyzed 
according to the method of Davis and Daisli (4), and it and the reducing 
sugars and hydrolyzed starch were determined according to the method 
of Clark (2). 
After the sugars were extracted the solid material was dried to con¬ 
stant weight in a vacuum oven at 6o° C. The pulp was finely ground in 
a mortar, and a known amount was transferred to a 100-cc. volumetric 
flask and the starch hydrolyzed by boiling in a 5 per cent solution of 
hydrochloric acid (HC 1 ) for 2X hours with a reflux condenser. It was 
then neutralized by sodium hydroxide (NaOH), made up to volume, 
filtered, and the starch determined as reducing sugar. 
The Yellow Jersey variety of sweet potatoes grown on the Potomac 
Flats near Arlington, Va., was used for all these investigations. 
All the data were calculated to the original wet weight of the material 
used. The directly reducing sugar was calculated as glucose. 
It might be urged that the results both of the respiration experiments 
and of the carbohydrate determinations were vitiated by the presence 
of microorganisms other than Rhizopus tritici. It is not unlikely that 
bacteria were present on the surface and that they would contribute 
something to the total of the C 0 2 given off. Before the samples were put 
into the respiration chamber they were thoroughly washed but were not 
disinfected. The length of the respiration period was three days in all 
experiments except one, which continued another day longer. Cultures 
were made from the rotted potato at the close of the experiments, and a 
pure culture of R. tritici was obtained in every case. The writers 
do not believe that bacteria or fungi were present in sufficient amount to 
alter materially either the results of the respiration or the carbohydrate 
content. As a matter of fact, all respiration experiments of a sort where 
sterile conditions can not be employed are subject to alterations due to 
the presence of foreign organisms. 
