322 
Journal of Agricultural Research 
Vol. XIV, No. 8 
a way that one of its constituents was omitted from each test and the 
hydrogen-ion concentration measured immediately after the addition 
of the acid or alkali. It was stated in a previous paper that possibly 
the mannitol exerts a buffer effect. However, later investigations do 
not support this statement. The concentration of hydrogen ions in 
pure water to which varying amounts of acid and alkali were added, 
as well as the concentration in the synthetic culture medium plus acid 
and alkali, is shown in figure i. It appears from the graphs that the di¬ 
basic potassium phosphate is the chief buffer substance and that the 
mannitol has little effect on the concentration of hydrogen ions. 
