1908] 071 Ice and its Natural History. 245 



It was found that when a non-saturated saline solution is gradually 

 frozen, certain crystals, which we call ice-crystals, separate out ; and, 

 during this process, the temperature of the mixture gradually falls, 

 while its concentration increases. When this mixture was warmed, 

 the crystals gradually melted, the temperature rose, and the concen- 

 tration of the solution diminished. When, in the process of cooling 

 and freezing, the temperature had fallen to a certain point, say t and 

 the salinity to s, it was found, Avhcii this process was reversed, and 

 the same temperature t was reached during the process of warming 

 and melting, that the solution had regained the same salinity s. 

 Therefore, the substnnce which forms the ice-crystals which separate 

 out at a temperature t during cooling, melts again at the same tem- 

 perature during warming ; and the concentration of the solution at 

 that temperature is the same whether the temperature is arrived at 

 by cooling or warming. 



When a solution of the same salt, having a higher concentration 

 than that which was used in the previous experiment, was cooled to 

 nearly 0° 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-crystais which had been 

 formed by the freezing of the solution itself, and at the same tem- 

 perature for the same concentration. 



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 determination 

 of the temperature at which snow or comminuted ice melts in saline 

 solutions was substituted for the determination 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 pre- 

 viously 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 other- 

 wise 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 CI : SO3 in 

 the samples of sea- water was, as was to be expected, almost constant, 



