VALUE OF CERTAIN NUTRITIVE ELEMENTS 
from the stock solutions diluted with water condensed from a block- 
tin still. The average conductivity of the water at a carbon-dioxide 
equilibrium with the air was 0.9 X io~^ reciprocal ohms. The solu- 
tions were stored in fifty-liter pure flint glass containers, from which 
they were drawn when needed. 
Table i 
The Composition of Knop's Nutritive Solution and of the Modified Knop's Solution 
Used as the Normal Culture Solution. 
Salt 
Grams per Liter of Solution 
Concentration of Salts Used in Modified 
Solution 
Standard Knop's 
Modified Knop's 
Grams per Liter of 
Solution 
Percentage Compo- 
sition 
Ca(N03)2 
0.8 
0.8 
0.08 
0.0533 
KNO3 
0.2 
0.2 
0.02 
0.0133 
KH2PO4 
0.2 
0.2 
0.02 
0.0133 
MgS04 
0.2 
0.2 
0.02 
0.0133 
NaCl 
O.I 
O.OI 
0.0067 
Total salt ...... 
1.4 
1.5 
0.15 
O.IOOO 
Discussion of the Nutrient Solutions in Terms of Concentra- 
tion 
Throughout the following discussion concentration will be expressed 
in terms of percentage of dissolved salts, that is, of grams per 100 cc. 
of solution, and also in osmotic concentration. The osmotic con- 
centration was calculated upon the basis of electrolytic dissociation 
as given by Jones (1911, 1912) for all the salts employed except mono- 
potassium phosphate and monosodium phosphate, the data for which 
are not given in Jones' tables. The electrolytic dissociation of mono- 
potassium phosphate was taken from Tottingham's (19 14) table; 
that of monosodium phosphate was determined by the writer. All 
measurements were taken at 25° C, which approximates the average 
temperature of the culture solutions during the growing period. The 
procedure, as fully described by Tottingham (1914), is based upon 
the fact that osmotic pressure is a colligative or additive property, 
depending upon the total number of particles (ions, molecules, and 
molecular aggregates) in the solution irrespecitve of their kind. An 
approximation to the total osmotic concentration of any solution may 
be obtained by summing the values of the partial concentrations of 
the constituent salts (tables 2 and 3). 
