138 On Ice and Brines 



removed as ice before a cryohydrate would form, and if it 

 contained nothing but sulphate of soda in the proportion 

 corresponding to the sulphuric acid found in it, over 90 per 

 cent, of the water would have to go as ice, before the cryo- 

 hydrate would be formed. 



In my experiments about 15 per cent, of the weight of the 

 water was frozen out as ice, causing a lowering of freezing- 

 point by o'3 C. In nature it is probable that the ice forming 

 at the actual freezing surface does so at an almost uniform 

 temperature, the local concentration produced by the forma- 

 tion of a crystal of ice being immediately eliminated by the 

 mass of water below. In the interstices of the crystals there 

 will be retained a weight of slightly concentrated sea-water 

 at least as great as that of the ice crystals. These retain the 

 brine in a meshwork of cells, and, as the thickness of the ice 

 covering increases, and the freezing surface becomes more 

 remote, the ice and the brine become more and more exposed 

 to the atmospheric rigours of the Arctic winter. The brine 

 will continue to deposit ice until its concentration is such 

 that, for example, the cryohydrate of NaCl is ready to sepa- 

 rate out. It probably will separate out until it comes in 

 conflict with, for instance, the chloride of calcium or the 

 chloride of magnesium, which will retain some of the water, 

 without solidifying, even at the lowest temperatures. At the 

 winter-quarters of the " Vega " brine was observed oozing out 

 of sea-water ice and liquid at a temperature of - 30 C. It 

 was very rich in calcium and especially magnesium chlorides. 

 In fact, it is probably quite impossible by any cold occurring in 

 nature to solidify sea-water. 



(b) Melting of pure ice in sea-water and other saline solu- 

 tions. A large number of experiments were made with 

 solutions of concentration comparable with that of sea-water, 

 and in one or two cases the experiments were extended to 

 low temperatures and strong solutions. As a rule, from 50 

 to 100 grammes of solution, cooled to o C., were mixed with 

 an equal weight of pounded ice, also at o C. The thermo- 

 meter used for all these determinations was one of Geissler's 

 normal ones, divided into tenths of a degree Centigrade ; and 



