CHEMICAL AND PHYSICAL NOTES. 85 
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 concentrated and saturated solutions when 
exposed to great cold has received comparatively little attention. 
Consequently the chemist and physicist of the Expedition has a 
comparatively 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 snow 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 
salt and ordinary moist snow, the salt forms little local freezing 
mixtures where it comes into actual contact with a snow-crystal, and 
the cold produced freezes the moisture adhering to contiguous snow- 
crystals, with the result that an altogether impracticable and 
heterogeneous mass of lumps of ice and masses of salt is formed. 
In the Antarctic regions cold powdery snow will be common enough, 
and exact experiments on the temperature and concentration of the 
freezing mixtures which it makes with different salts, and especially 
with definite mixtures of salts, will be easy, and cannot fail to be 
interesting. 
The salts must be pure, dry, and in fine powder. When mixtures 
are used they should be in simple molecular proportions, as for 
instance, NaCl 4+- NH,Cl, NaCl + 2NH,Cl, 3NaCl + 2NH,Cl, and so 
on. The weighed quantities of the two salts must be thoroughly 
mixed in a mortar before they are brought together with the snow. 
The experimenter must feel assured that there is no risk of his 
freezing mixture consisting of an indefinite association of local 
freezing mixtures, of, for instance, snow and NaCl and of snow and 
NH,Cl, but that it is certainly a homogeneous mixture, every 
element of which consists of three bodies. 
The dry snow has necessarily a low temperature. The salt, or 
mixture of salts, when finely pulverised and intimately mixed, should 
be cooled in a stoppered bottle to a temperature below 0° C. When 
the cold dry salt is mixed with the cold dry snow, and the tempera- 
