544 The Philippine Journal of Science 1920 
Table 2 . — Partial concentrations of each of the four salts required to 
produce from 0.1 to 0.7 of the total osmotic concentration of 1.60 
atmospheres for series I. 
Fractional 
parts of 
1.60 at- 
mospheres. 
KCl. 
KH 2 PO 4 . 
Ca(NOs) 2 . 
MgS04. 
M. 
M. 
M. 
M. 
0.1 
0. 0033 
0. 0033 
0.0023 
0. 0038 
0.2 
0.0067 
0. 0068 
0. 0047 
0. 0081 
0.3 
0. 0101 
0.0103 
0. 0072 
0. 0126 
0.4 
0. 0136 
0. 0138 
0. 0098 
0.0171 
0.5 
0.0170 
0. 0173 
0. 0124 
0. 0216 
0.6 
0.0205 
0. 0208 
0. 0160 
0. 0261 
0.7 
0. 0240 
0. 0243 
0. 0177 
0. 0309 
The method used in these calculations may be illustrated with 
potassium chloride, the calculations for the other salts being 
made in the same way. It was first necessary to obtain certain 
physico-chemical data regarding each of the four salts dealt 
with, and these data as used for potassium chloride are given 
in Table 3. The numbers in the first column represent the 
tenths (from 0.1 to 0.7) of the total concentration of 1.60 at- 
mospheres. Those in the second column represent the corre- 
sponding actual pressures in atmospheres. According to the 
van’t Hoff equation, tt = CRT, the osmotic value (tt) of any 
solution may be obtained from the concentration of the particles 
in solution (C), the gas constant (R ) , and the absolute tem- 
perature (T). 42 If the osmotic value is expressed in atmos- 
pheres, then R has the value 0.08207. The osmotic values here 
used are all calculated for a temperature of 25° C. (298° Abs.), 
so that T becomes 298, and the equation may be restated: 
tt = (298) (0.08207) C = 24.46 C. 
For substances which do not dissociate or polymerize or form 
hydrates in solution the concentration, C, corresponds to the 
volume-molecular concentration, M; and the osmotic pressure 
formula becomes : n = 24.46 M. But for salts, such as potas- 
sium chloride, which dissociate in solution into ions, C = iM; 
43 The osmotic pressure equation here used must be understood to be 
only approximately true for solutions such as are dealt with in the present 
work. It really applies only to very dilute solutions. For a good discus- 
sion of osmotic pressure equations see Washburn, E. W., Principles of Phys- 
ical Chemistry. New York (1915) 150-164. Also see Renner, O., Ueber 
die Berechnung des osmotischen Druckes, Biol. Centralbl. 32 (1912) 
486-504. 
