236 Ice and its Natural History 



centration than that which was used in the previous experi- 

 ment, was cooled to nearly o C, and was then mixed with 

 sufficient freshly fallen snow to form a sludge, and heat was 

 supplied, there arrived a moment in the course of the melting 

 when the temperature of the mixture had returned to t, the 

 concentration of the brine was then found to be represented 

 by the same salinity s, which had been found to correspond 

 to the temperature t in the previous operation. Therefore, 

 the snow melted in exactly the same way as did the ice- 

 crystals which had been formed by the freezing of the solution 

 itself, and at the same temperature for the same concentra- 

 tion. 



But it was only a question whether the salt was in the ice 

 or in the brine. There is no salt in snow; yet it behaved in 

 the saline solution in the same way as the crystals formed by 

 freezing that solution; therefore, the crystals formed by 

 freezing the saline solution must be equally free from 

 salt with the snow. 



It was thus proved that the crystals formed in freezing 

 a non-saturated saline solution are pure ice, and that the 

 salt from which they cannot be freed does belong to the 

 adhering brine. 



After the main principle had been established, the deter- 

 mination of the temperature at which snow or comminuted 

 ice melts in saline solutions was substituted for the determi- 

 nation of their freezing-points ; and in the case of many of 

 the common salts and acids, even at high concentrations, 

 yielded results which agreed with those previously determined 

 by others by the more laborious freezing method. 



The evidence on which Dr Pettersson arrived at the 

 conclusion that the ice, formed on freezing saline solutions, 

 contains salt otherwise than as mechanically enclosed brine, 

 was furnished by his analyses of sea- water and of melted sea- 

 ice, brought home from the Arctic regions. In these samples 

 he found that the ratio Cl : SO 3 in the samples of sea-water 

 was, as was to be expected, almost constant, while, in those 

 of the sea-ice, it varied within very wide limits; and he justly 

 observes that, if it is claimed that the ice of sea-water is salt 



