545 
in this equation 7 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: + = 24.46 iM. 
For un-ionized substances 7 is unity, and for ionized substances 
such as salts 7 has a value greater than unity. The equation may 
be written in the form: 
T 
iM 9446 
By substituting for 7 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. 
17, 6 
Trelease: Salt Requirements of Wheat Plants 
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 ox» 
motic concentration of 1.60 atmospheres, for series I. 
i = e Il. Ill. IV. 5 fe VI. 
‘action 2 “M. ole- 
Barts of | Partial os-| molectlar | Degree of | mumber,” | Coneentrar 
centration motic pres- concentra- Aorinations x05: van’t y an 
Optus) ee | eee er cot | C=iM. 
spheres). ‘ 
Atm. M. 
ED re BPH PAS, PE HR ND eet 20,0020 bO. 971 ¢1.971 0. 0089 
0.1 0.16 Cit. 9 a sae en Capa = Pe 0. 0065 
étbecs miakdaloabiveseunee 0. 0050 0. 956 1, 956 0. 0098 
0.2 0.32 OD0GT fico cancels es iaiaeen 0.0131 
ee tub as RG A eD 0.0100 0. 941 1.941] 0.0194 
0.3 0. 48 DONOR cictdeccuccs feces conwerad 0.0196 
0.4 0. 64 OCOIRG bese cece cee ae 0. 0262 
0.5 0. 80 P0010 toss. ort eco sued 0. 0327 
Anis weeks eae Conon. 0.0200 0. 922 1,922 0. 0884 
0.6 0.96 WAWOe boon. oc ceee EEO were 2 0. 0392 
0.7 1.12 OS0RIO. | 2c ee clea ade eee 0. 0458 
Tete dau sceeleeebbencbade 0. 0500 0. 889 1, 889 0. 0945 
* The values in italics have been obtained from Noyes and Falk. 
> From Noyes and Falk. . 
© This is the van’t Hoff coefficient. It is obtained from the relation i=1+(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 
