1908] ^ on Ice and its Natural Histonj. 247 



crystals II* 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 91) 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 foUoAvs, therefore, that the evidence furnished by the quantita- 

 tive 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 ])ody 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 the Meltiag-Foint of a Substance and the 

 Temiierature at which 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 a 

 solid ; and its melting-point to be the temperature at which 

 it, as a solid, passes into itself as a liquid. 



Under " substance " I understand a single substance, completely 

 defined as a chemical individual. K good example of what I mean 

 is afforded l^y the substance, of which eighteen parts, by weight, 

 consist of two parts of hydrogen and sixteen parts of oxygen, which 

 have combined with the liberation of a quantity of heat sufficient 

 to raise the temperature of the product by some 2000° C. In 

 chemistry this substance is expressed by the symbol H^O. In the 

 solid state it is called ice, in the liquid state water, and in the gaseous 

 state steam. 



If we have a quantity of this substance, partly in the sohd and 

 partly in the Uquid state, and in such conditions that, if ever so 

 little heat be removed from the mixture, the quantity of ice is 

 increased, and, if ever so little heat be added to the mixture, the 

 quantity of ice is diminished and that of the water correspondingly 

 increased, the temperature of the mixture is the freezing and melting 

 temperature of the substance H2O. 



When ice is melting in a mixture of ice and water, immersed in a 

 melting-bath, the temperature of the water must be a little higher 

 than that of the ice, else there would be no inducement for heat to 



