17, 6 
Trelease: Salt Requirements of Wheat Plants 
545 
in this equation i is the van’t Hoff coefficient (or “mole-num- 
ber”), which may be defined as the quotient of the number of 
particles actually present in the solution, divided by the number 
that would be present in an equal volume-molecular concentra- 
tion of a substance that is unmodified in solution. Consequently, 
for salts the osmotic pressure formula becomes : n — 24.46 iM. 
For un-ionized substances i is unity, and for ionized substances 
such as salts i has a value greater than unity. The equation may 
be written in the form: 
iM 
7 r 
2446 ' 
By substituting for n in this equation each of the partial 
osmotic pressures from the second column of Table 3, the cor- 
responding values of iM were obtained, and these are given in the 
fourth column. They represent the osmotic concentrations which 
are necessary to give the corresponding partial osmotic pressures 
given in the second column. 
Table 3. — Data used in calculating the partial concentrations ( column III) 
of potassium chloride required to give from 0.1 to 0.7 of the total os- 
motic concentration of 1.60 atmospheres, for series I. 
I. 
Fractional 
parte of 
total con- 
centration 
(1. 60 atmo- 
spheres). 
II. 
Partial os- 
motic pres- 
sures. 
III. 
Volume- 
molecular 
concentra- 
tion of 
KC1. 
IV. 
Degree of 
ionization. 
v. 
"Mole- 
number." 
or van’t 
Hoff coef- 
ficient. i. 
VI. 
Concentra- 
tion calcu- 
lated from 
C—iM. 
Atm. 
M. 
a 0.0020 
b 0. 971 
cl. 971 
0. 0089 
0.1 
0. 16 
0. 0033 
0. 0066 
0. 0050 
0.956 
1. 956 
0. 0098 
0.2 
0.32 
0. 0067 
0.0131 
0. 0100 
0. 91*1 
1.941 
0. 0191* 
0.3 
0. 48 
0. 0101 
0. 0196 
0.4 
0. 64 
0. 0135 
0. 0262 
0.B 
0.80 
0. 0170 
0. 0327 
0. 0200 
0. 922 
1.922 
0. 0381* 
0.6 
0.96 
0. 0205 
0. 0392 
0.7 
1.12 
0. 0240 
0. 0458 
0. 0500 
0.S89 
1.889 
0. 091*5 
ft The values in italics have been obtained from Noyes and Falk. 
b From Noyes and Falk. ' 
c This is the van’t Hoff coefficient. It is obtained from the relation i = l+(n — 1) a. For 
non-electrolytes its value is 1. 
It was next necessary to calculate the volume-molecular con- 
centrations (M) of potassium chloride that correspond to these 
values of iM. To do this an indirect method is required. If 
