3o8 
JAMES GEERE DICKSON 
found practicable, on account of these difficulties, to take into account 
the effect of one constituent salt upon the dissociation of another in 
the culture solution, but the degree of dissociation in the various solu- 
tions was checked by measurements of electrical conductivity and also 
by freezing-point determinations. 
Samples of the culture solutions for the various measurements 
were obtained at the termination of the year's experiments. The 
solutions were thoroughly shaken and filtered through ashless paper 
without previous wetting of the filter or washing of the residue. The 
first 500 cc. was discarded and a quantity was then obtained from 
which samples were taken for all the measurements. 
The approximate total amount of soluble salts present in the solu- 
tions was determined by evaporating duplicate 10 cc. samples to dry- 
ness upon the water-bath. About 0.5 gram of zinc dust was added to 
each sample as a means of retaining as far as possible the nitric acid 
which might otherwise be lost on the water-bath and in subsequent 
drying. The residues were dried at 150° C, cooled in a desiccator, 
and weighed. The results, corrected for hydrogen evolved, are given 
in table 4, 
The depression of the freezing-point of the different solutions was 
measured by means of a special Beckman apparatus, care being taken 
to avoid supercooling below 0.2° C. Readings were obtained that 
checked within 0.002° C. upon five samples from each solution (table 4). 
Electrical conductivity measurements were made of all the solutions 
with a standard Kohlrausch apparatus. The average conductivity 
in reciprocal ohms is given in table 4. 
Table 4 
The Amounts of Salts in Solution, Electrical Conductivity, and Depression of the 
Freezing-Point of the Normal and Modified Nutrient Solutions. 
Solution, Deficient 
Element Given 
Total Soluble Salts in 
Grams per loo Cc. of 
Solution 
Conductivity X lo"^ 
Reciprocal Ohms 
Depression of Freezing- 
point in Degrees 
Centigrade. 
1916 
Sol. 
Tol 
Ave. 
1916 
Sol. 
1917 
Sol. 
Ave. 
1916 
Sol. 
1917 
Sol. 
Ave. 
Normal 
.110 
.105 
.107 
1-363 
1-507 
1-435 
-050 
.051 
.050 
Mg 0.1 
.105 
1-556 
.051 
Ca 0.1 
.085 
.070 
.077 
1. 144 
1-058 
I.IOI 
.050 
.050 
.050 
K 0.1 
.109 
.082 
.095 
1-343 
I-451 
1-397 
.050 
.051 
.050 
P 0.1 
.098 
.090 
.094 
1-383 
1-305 
1.344 
.050 
.051 
•050 
N 0.1 
.120 
.109 
.114 
1-455 
1.625 
1-540 
.050 
.061 
.055 
