8 
Walter Stiles 
Table XV 
Osmotic Pressures of Aqueous Solutions of Sucrose. 
(Data from Morse) 
Concentration Osmotic pressure at various temperatures 
in weight- 
normalities 
o° C. 
io° C. 
20° C. 
3 °° C. 
0*1 
2-462 
2-498 
2-590 
2-474 
0-2 
4723 
4-893 
5-064 
5-044 
o -3 
7-085 
7-335 
7-605 
7-647 
o- 4 
9-443 
9-790 
10-137 
10-295 
o -5 
11-895 
12-297 
12-748 
12-978 
o-6 
14-381 
I 4-855 
15-388 
I 5 " 7 I 3 
o -7 
16-886 
I 7-503 
18-128 
18-499 
o-8 
19-476 
20-161 
20-905 
21-375 
o-g 
22-118 
22-884 
23-717 
24-226 
1*0 
24-826 
25-693 
26-638 
27-223 
Osmotic Pressure of Electrolytes 
So far this discussion has been confined to sugars and the remarks 
already made may be regarded as applying generally to crystalloidal 
non-electrolytes. There are, however, two other groups of substances 
of the greatest importance which require some special treatment; 
these are electrolytes and colloids. 
In the case of electrolytes the osmotic pressure is found to be 
considerably higher than the theoretical pressure calculated from 
the gas law. This is correlated with the dissociation of the molecule 
into its constituent ions. If each particle, either ion or molecule, is 
regarded as exercising the same osmotic pressure then agreement 
with the general law is found to exist in the case of dilute solutions 
of electrolytes as well as dilute solutions of non-electrolytes. 
The formula 
PV = nRT 
must therefore be modified in the case of electrolytes to 
PV = n (ap + i - a) R . T, 
where a is the degree of dissociation of the electrolyte and )8 the 
number of ions into which the molecule dissociates. 
Electrolytes have not so far received the attention that has been 
devoted to sucrose with regard to exact measurement of the osmotic 
pressure. The investigation of electrolytes is fortunately being under¬ 
taken by Morse and some results have already been obtained with 
lithium chloride. The values obtained by de Vries for a number of 
electrolytes and non-electrolytes will be referred to in a later chapter. 
