VALUE OF CERTAIN NUTRITIVE ELEMENTS 
A comparison of the above tabulated results shows that the con- 
centration of soluble salts is low in the solution in which calcium is 
deficient and comparatively high in the nitrogen-deficient solution. 
The lowering of the freezing-point caused by the respective solutions 
indicates a concentration in each case comparable to that expressed 
by the total soluble salts, but with less variation. The conductivity 
measurements, however, express variations in concentration notably 
similar to those expressed by the soluble salts (table 4 and fig. i), 
I 
I 
C3 
/.5 
/.O 
,05 
IDI7 
LEGEND 
CONDUCTIVITY 
SOLUBLE SALTS 
rffCEZ/NG PT. 
NORtl 
01 Ca 0.1 K 01 
CULTURE SOLUTIONS 
p 0.1 
NO./ 
Figure i. Curves showing the amount of salts in solution, electrical conduc- 
tivity, and depression of the freezing-point in the normal and modified nutrient 
solutions. 
which fact demonstrates that, at the dilute concentrations used in 
this work, the conductivity method supplies a very rapid and accurate 
method of determining the approximate concentration of a culture 
solution, since at these dilutions hydrolysis and other factors do not 
appear seriously to affect the conductivity. 
General Culture Methods 
During the years 191 5 and 191 6 glazed earthenware jars of two- 
gallon capacity were used for the containers. During the year 191 7 
