238 Ice and its Natural History 



into the crystalline state. The mother-liquor was drawn off, 

 as perfectly as possible, before removing the beaker, in which 

 the freezing had been effected, from the bath. The crystals 

 were transferred quickly to a funnel, and drained by means 

 of the jet pump. The chlorine and sulphuric acid were then 

 determined in each fraction, and the ratio Cl : SO 3 calculated 

 (Cl = 100). As an example, the following values of this ratio 

 were obtained for water from the Firth of Forth : In the 

 original water ir83, in the mother-liquor 1 1*67, and in the 

 crystals i r62. In water from the Firth of Clyde the ratios 

 were: in the original water 1 1'58, in the mother-liquor ii'57, 

 and in the crystals 1 1 '67. These ratios agree with each other 

 as closely as the analytical possibilities permit. 



Inasmuch as the chlorides and sulphates together make 

 up more than 99 per cent, of the solid contents of sea-water, 

 the constancy of these ratios makes it so probable as to be 

 certain that the ice of sea-water is salt only in virtue of 

 adhering sea-water of slightly increased concentration. 



It follows, therefore, that the evidence furnished by the 

 quantitative freezing of a composite saline solution confirms 

 the conclusion arrived at on the basis of the identity of the 

 temperature at which a saline solution freezes, with that at 

 which ice melts in it ; namely, that the crystalline body 

 formed by freezing a non-saturated saline solution is pure ice. 



It was not until after this had been established, in 1887, 

 that it became legitimate to say : " The freezing-point of 

 water is lowered by the presence of salt dissolved in it," 

 instead of saying : " The freezing-point of a saline solution is 

 so much lower than that of pure water." The former of these 

 statements expresses the fundamental principle of cryometric 

 chemistry. 



Distinction between tJte Melting- Point of a Substance and 

 tJie Temperature at wliich it melts under given conditions. An 

 important consequence of this research was that the melting 

 temperature of a body is not necessarily identical with the 

 temperature at which it melts under particular circumstances. 



I define the freezing-point of a substance to be : The 

 temperature at which it, as a liquid, passes into itself as 



