36 Chemical and Physical Notes 



has been called the cryohydrate of the particular salt. If 

 warmed it will melt again at a constant temperature until all 

 the salt has been dissolved, when the temperature will begin 

 to rise. The case is quite analogous to the boiling mixtures 1 

 of constant temperature produced by blowing steam through 

 salt, the temperature remains quite constant at that of the 

 boiling saturated solution until nearly all the salt is dissolved, 

 after which the temperature falls in proportion as the solution 

 is diluted by the condensation of steam. 



The temperature at which the cryohydrate forms has 

 been called the cryohydric temperature. At this temperature 

 crystals of ice and of the salt remain side by side without 

 melting each other, and they behave with the same indiffe- 

 rence to each other at lower temperatures. At temperatures 

 above the cryohydric point they cannot be brought together 

 without melting, when they produce the cryohydric tempera- 

 ture. The cryohydric temperatures of different salts differ. 

 From the observations of Weyprecht, Nordenskjold, and 

 others, we learn that even at a temperature of 40 C. 

 there is liquid brine in the surface layers of the sea-ice ; so 

 that the cryohydric point of some of the salts in sea-water 

 must be lower than this temperature. The temperature of 

 this mixture of ice and brine must be the freezing temperature 

 of the brine and the melting temperature of ice in tfte brine. 



It has been said that above the cryohydric temperature 

 crystals of the salt and of ice cannot be brought together 

 without liquefaction. When air is saturated with moisture 

 at temperatures below o C. the moisture is deposited as 

 rime, which is ice. If the surface on which it is deposited 

 is a soluble salt, and if the temperature is above the cryo- 

 hydric temperature of the salt, liquefaction will take place 

 at the point of deposit. Hence it follows that every salt is 

 deliquescent at temperatures between o C. and its cryohydric 

 temperature. 



Numerical data regarding the freezing-points of saline 



1 'On Steam and Brines,' by J. Y. Buchanan, F.R.S. Trans. A\ S. . 

 (1899), vol. xxxix. p. 529. (Below, p. 151.) 



