Chemical and Physical Notes 41 



the determined cryohydric temperature of nitrate of barium 

 agree with that found by de Coppet, namely o '/ C. The 

 thermometer was one of ordinary German manufacture divided 

 into whole degrees. The observations illustrate the fact that 

 the cryohydric temperature of a mixture of two salts is lower 

 than that of the salt which separately has the lower cryohydric 

 temperature of the two. The mixtures experimented on were 

 of equal molecular proportions, in fine powder, intimately 

 mixed with dry powdery snow. Perhaps the most remarkable 

 mixture in the table is that of the chloride and nitrate of 

 barium : the cryohydric temperature of the mixture is nearly 

 the sum of the separate cryohydric temperatures. In almost 

 every case where accurate observations have been made, it 

 has been found that the melting temperature of a mixture is 

 lower than that of the most fusible of its components. The 

 frequency of this observation has justified its enunciation as 

 a law, and the recognition and elaboration of this law have 

 done much for the advancement of physical chemistry. This 

 is not the place to enlarge further on it in its general aspect, 

 but in its particular application to the cryohydric and to the 

 freezing temperatures of solutions of salts and of mixtures of 

 salts, it is of great interest to the scientific members of an 

 Arctic or Antarctic expedition. In recent years workers in 

 physical chemistry have mainly limited themselves to the 

 study of very dilute solutions, and the behaviour of concen- 

 trated and saturated solutions when exposed to great cold 

 has received comparatively little attention. Consequently 

 the chemist and physicist of the Expedition has a com- 

 paratively unoccupied field before him, and he is free to 

 choose the simplest problems. 



In our country the opportunities for the exact study of 

 freezing mixtures are rare, because it seldom snows at all, 

 and when it does, the sftow is flaky and at or about its 

 melting-point. Crystalline powdery snow, which has never 

 experienced its melting temperature, is a rarity even on our 

 mountains. This is the only form in which ice should be 

 used for freezing or cryohydric mixtures, when these are to 

 be studied exactly. When a freezing mixture is made with 



