146 On Ice and Brines 



formed by freezing water which contains any salt at all is 

 perfectly explained on the hypothesis that in the act of 

 freezing the water rigidly excludes all saline matter from 

 participation in its solidification. 



The residual and unfreezable brine which remains in con- 

 siderable quantity liquid when sea-water is frozen, must also 

 remain in greater or less quantity when fresh water is frozen. 

 All natural waters, including rain-water, contain some foreign 

 and usually saline ingredients. If we take chloride of sodium 

 as the type of such ingredients, and suppose a water to 

 contain a quantity of this salt equivalent to one part by 

 weight of chlorine in a million parts of water, then we should 

 have a solution containing O'oooi per cent, of chlorine, and it 

 would begin to freeze and to deposit pure ice at a temperature 

 of -o-oooi C.; and it would continue to do so until, say, 

 999,000 parts of water had been deposited as ice. There 

 would then remain 1000 parts of residual water, which would 

 retain the salt, and would contain, therefore, OT per cent, of 

 chlorine, and would not freeze until the temperature had 

 fallen to o'iC. This water would then deposit ice at 

 temperatures becoming progressively lower, until, when 900 

 more parts of ice had been deposited, we should have 100 

 parts residual water, or brine as it might now be called, 

 containing i per cent, of chlorine, and remaining liquid at 

 temperatures above i'O C. When 90 more parts of ice 

 had been deposited, we should have 10 parts of concentrated 

 brine containing 10 per cent, chlorine and remaining liquid as 

 low as 13 C. In the case imagined, we assume the saline 

 contents to consist of NaCl only, and with further concentra- 

 tion the cryohydrate would no doubt separate out and the 

 mass become really solid. On reversing the operations, that 

 is, warming the ice just formed, we should, when the tempera- 

 ture has risen to about - I3C, have 999,990 parts ice and 

 10 brine containing 10 per cent, chlorine. Now, owing to the 

 remarkable fact that pure ice, in contact with a saline solution, 

 melts at a temperature which depends on the nature and the 

 amount of the salt in the solution, and is identical with the 

 temperature at which ice separates from a solution of the same 



