Mr. F. Guthrie on Salt Solutions and Attached Water. 19 



cooled the sea-water to — 2° C. in a beaker, which I enveloped 

 thickly with flannel. I tried in vain to freeze the surface by 

 blowing over it dry air which had passed immediately before 

 through a long pewter worm immersed in a freezing-mixture* 

 But I succeeded in getting a sheet of ice when I hung a freezing- 

 mixture contained in a blackened tin pan within about \ inch 

 of the surface of the water, the whole being plentifully enveloped 

 in flannel. Perhaps here the actual conditions which obtain 

 when sea-water freezes were reproduced. I found that the 

 pressed ice contained only O4052 of solid residue at 100° C. 



§ 35. The question suggested itself to me whether, when 

 one part of a solution of a salt is cooled, there may not be 

 an accumulation of salt in the cooler part, although not ac- 

 companied by any solid separation. I accordingly cooled a 

 saturated solution of nitre to — 1° C. and decanted from the 

 separated nitre. I then warmed the solution in a tall beaker- 

 glass to 60° C. and placed the bottom of the beaker in melt- 

 ing ice. In an hour's time a thermometer at the bottom stood 

 at 10° C, at the top at 33°. A specimen from the bottom con- 

 tained 11*3 per cent, of nitre; one from the top contained 11*7 

 per cent, of nitre — showing that there was no sensible diffusion 

 of the salt one way or the other. 



General Considerations. 



§ 36. Maximum density of Water. — It was shown that brines 

 of various strength, when mixed with water, absorbed heat and 

 expanded. Let us look upon ice as the cryohydrate of water. 

 Water shrinks as it loses heat till it reaches 4° C. At this 

 point ice is formed, which, however, is dissolved in the water. 

 A solution is obtained having a temperature of solidification 

 below 4° C, namely at 0° C. At 0° C. the ice and the water 

 solidify together, producing the compound body or cryohydrate 

 called ice, which is thus a cryohydrate of water. The expansion 

 from 4° to 0°is due to the greater and greater amount of ice which 

 the water holds in solution, and which expansion is greater than 

 the contraction of the water due to the diminished temperature. 



§ 37. Variation of media. — There can be no doubt that the 

 discovery of an enormous number of new bodies of definite 

 composition will reward those who labour in this field. Taking 

 water as the medium for solution, there appears to be no doubt 

 that every soluble salt has a definite cryohydrate ; so that in this 

 direction alone the number of new bodies awaiting discovery 

 and description may be estimated at half the number of bodies 

 already known. If we vary the medium, employing, say, alcohols 

 or hydrocarbons as solvents, the number of new compounds will 

 be again indefinitely increased ; so that it is fairly within the 



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