DISCUSSION OF EVIDENCE. 149 



These examples suffice to show the general nature of the relation 

 between water of crystallization and the temperature at which the 

 salt crystallizes. This relation could have been foreseen as a necessary 

 consequence of the theory of hydrates in aqueous solution, and the 

 instability, with temperature, of those hydrates. 



HYDRATE THEORY IN AQUEOUS SOLUTIONS BECOMES THE SOLVATE THEORY IN 



SOLUTIONS IN GENERAL. 



The earliest work on the problem of the nature of solution was 

 limited to water as the solvent. It was found that salts in general 

 have the power to combine with more or less of the water in which they 

 are dissolved have a greater or less hydrating power. This power 

 is, however, possessed to a very different degree by the different com- 

 pounds. As we have seen, the degree of hydration of a salt can be 

 approximately determined by the amount of water with which it 

 crystallizes at ordinary temperatures. 



It having been made probable that hydration exists in aqueous 

 solution, the question arose, do dissolved substances have the power 

 to combine with other solvents in which they are dissolved? 



To test this Jones and Getman 1 studied, by the boiling-point method, 

 solutions of lithium chloride and nitrate, and calcium nitrate in ethyl 

 alcohol. They used also a number of other salts. It was found that 

 the molecular rise in the boiling-point was not only greater than the 

 theoretical rise at nearly all of the concentrations studied, but the 

 molecular rise increases rapidly with the concentration of the solution. 

 The molecular rise of the boiling-point of ethyl alcohol, produced by 

 lithium chloride, increases from 1.28 at 0.07 normal to 2.43 at 2.07 

 normal. In calculating the theoretical molecular rise the dissociation 

 is, of course, taken into account. The dissociation decreases with the 

 concentration, which would tend to decrease the molecular rise in the 

 boiling-point. Notwithstanding this influence, we have seen that the 

 molecular rise in the boiling-point of solutions of certain salts in ethyl 

 alcohol increases as the concentration of the solution increases. 



The differences between the theoretical and the experimental results 

 are in some cases quite large. Jones and Getman 2 interpreted these 

 results in ethyl alcohol in a manner analogous to that which they had 

 adopted in the case of aqueous solutions. The abnormally large rise 

 in the boiling-point of ethyl alcohol, produced by certain salts, and 

 the increase in the molecular rise of the boiling-point with increase 

 in the concentration of the solution, are due to combination between 

 the dissolved substance and part of the solvent to the formation of 

 ethyl alcoholates in solution. The part of the alcohol that is combined 

 with the dissolved substance is thus removed from the field of action 

 as far as solvent is concerned. There being less alcohol present acting 



. Chem. Journ., 32, 338 (1904). 2 Ibid., 339 (1904). 



