144 MAGIE— THEORY OF SOLUTIONS. 



[April 19, 



posed of them in the soHd state, or, if this is not known, make up 

 a heat capacity for them by adding their atomic heats, as deter- 

 mined by Kopp, we find that the numbers obtained, with two excep- 

 tions, fall into two groups. For one of these groups, derived from 

 the constants for sodium chloride, hydrate, and nitrate, ammonium 

 chloride, and hydrochloric acid, the mean number obtained is 

 — 44.8, with a maximum deviation of less than five per cent. For 

 the other group, derived from the constants for potassium chloride, 

 hydrate, and nitrate, barium and strontium chloride, and barium 

 nitrate, the mean number obtained is — 65.7, with a maximum 

 deviation of less than five per cent. We may conclude from these 

 results that the effect of ions of different sorts in diminishing the 

 heat capacity of the water associated with them is in many cases 

 practically the same, but that other ions may exert on the water a 

 very different effect. The presence in one group of all the sodium 

 salts and in the other of all the potassium salts is especially signifi- 

 cant of this last conclusion. The differences between the effects 

 of the ions may be represented by supposing that the action of one 

 sort extends only so far as to affect the water molecules immedi- 

 ately contiguous to them, while that of the other sort extends further 

 into the water. 



It is unfortunately impossible to test the formula for heat capac- 

 ity in the region of extreme dilution, but the formula for the volume 

 has been applied to Kohlrausch and Hallwach's determinations of 

 the specific gravity of very dilute solutions in some cases and found 

 to hold with the constants determined from Thomsen's observations 

 at higher concentrations. In the region of high concentration the 

 formulas sometimes fail to reproduce the observations. This can 

 be ascribed, I believe, to the frequent interpenetration of the groups 

 of water molecules which are associated with each molecule or ion 

 of the solute ; or, what amounts to the same thing, to the frequent 

 action of two or more molecules or ions of solute on the same set 

 of water molecules. 



I would explain in the same way the apparent change in the 

 extent of hydration calculated by Jones and others from the abnor- 

 mal depression of the freezing points of concentrated solutions. 



