376 On Ice of Irregular Fusibility. [ 1 858. 



distance between these temperatures would be less, but the 

 water particles would keep their respective places. 



When water freezes, it does not appear that this process is 

 continuous, for many of the characters of the ice seem to show 

 that it is intermittent; i. e. either a film of ice is formed, and 

 then the process stops until the heat evolved by solidification 

 has been conducted away upwards, and the next stratum of 

 water has been sufficiently cooled to freeze in turn; or else the 

 freezing being, so to speak, continuous, still is not continued 

 at the same constant rate, but, as it were, by intermittent 

 pulsations. Now it may well be, when a layer next the pre- 

 viously-formed ice, and containing an undue proportion of salts, 

 has been cooled down to its required temperature for freezing 

 (which would be below 32) , that on freezing, the congelation 

 will pervade at once a certain thickness of the water, excluding 

 the salts from the larger portion of ice formed, but including 

 them as a weak solution within its interstices. The next in- 

 crement of cold conducted from the ice above would freeze up 

 these salts in the ice containing them, at the same time that a 

 layer of pure ice was formed beneath it. Thus a layer of ice 

 fusible at a lower temperature than the ice either above or 

 below it might be produced ; and by a repetition of the process 

 many such layers might be formed. 



It does not follow necessarily that the layers would be per- 

 fectly exact in their disposition. Very slight circumstances 

 tending to disturb the regularity of the water-molecules would 

 be sufficient, probably, to disturb the layers more or less. Ice 

 contains no air, and the exclusion of a minute bubble of air 

 from the water in the act of freezing might disturb the direction 

 and progress of the congelation, and cause accumulation of the 

 extra saline liquid in one spot rather than another. So might 

 the tendency to the formation of little currents, either arising 

 from the separation of the saline water from the forming ice, or 

 from the elevation of temperature in different degrees at those 

 places where the congelation was going on at different rates. 



The effect would not depend upon the quantity of salts con- 

 tained in the freezing water, though its degree would. The 

 proportion of salts necessary to be added to pure water to lower 

 its freezing-point 1 Fahr. may be very sensible to chemical 

 tests, but the proportion required to make the difference T J^th 



