Nature of Solution. 371 



these temperatures (volume at 20° = 100,000) are compared 

 with the volume of water at the same temperature, that of 

 water being taken as follows: — 



At 20° = 100,000, 

 „ 40° = 100,593, 

 „ 98° = 103,979. 



Thus it is seen that, comparing the expansion between 20° 

 and 40°, or 20° with that between 40° and 98° or 58 degrees, 

 that of water is about as 1 : 6, while in all the salt-solutions it 

 is less than 1:1; and in the case of KOI the volume at 98° 

 is very considerably less than that of water, contraction having 

 taken place between 40° and 98°. This has also been observed 

 by Kremers, as I have shown in a previous paper*, and the 

 table of molecular volumes at 20° and 40°*that I have already 

 published f also fully bears this out ; so that it is clear that, 

 in a strong solution, the effect of rise of temperature is to 

 cause an expansion which, as the temperature rises, becomes 

 more and more similar to that of water alone, and after that 

 actually is considerably less than it; so that at a high tempe- 

 rature the volume may be even less than that of water. 



Thus the experiments on the vapour-pressures of salt- 

 solutions of constant strength, and on the coefficient of ex- 

 pansion of such solutions, show most plainly that, by rise of 

 temperature, the attraction of salt for salt is so greatly dimi- 

 nished that it is equivalent to an increase in" attraction of salt 

 for water. That this is not the case with constantly saturated 

 solutions is due to the attractions of salt for water and of salt 

 for salt being in such solutions in equilibrium. Thus the effect 

 of heat is, as usual, to diminish the attraction of salt for water, 



P 



as is shown by the diminution of the value . 



P 



It is by a comparison of the values of for various 



salts at the same temperature that I hope to be able to arrive 

 at the comparative value of the attraction of water for salt, the 

 second factor in solution, while the ratios of the fraction F J 

 give the comparative values of the attraction of salt for salt. 



* Phil. Mag. February 1883. t Ibid. August 1883. 



X " Saturation of Salt-Solutions," Phil. Mag. June (Supplement) 1884. 



