Contents xvii 



PAGE 



Quotations from the paper 'Ice and Brines' in illustration 

 of this . 242 



These quotations from my paper of 1887 are given at 

 length, because, though published so many years ago, it 

 appears to have been but little read. I know of no treatise 

 on natural ice in which the dependence of the melting tempera- 

 ture of ice on the nature of the medium in which it melts is 

 even mentioned, still less taken into account. For these 

 reasons, I have made the development of this important sub- 

 ject the principal feature of this Lecture 244 



After stating the constants involved, the cryoscopic prin- 

 ciple established in the paper on 'Ice and Brines' is applied 

 to the discussion of the apparent variations of volume of a 

 block of ice, the volume of which at o C. is 1000 cubic centi- 

 metres. It contains 1-5105 gram Nad, diffused through it, 

 and it is provisionally assumed to be in the inert state, in 

 which it is deprived of the power to induce the melting of 

 ice at temperatures between o C. and its cryohydric point 

 ( 2 1 "72 C). If the temperature of the block containing the 

 inert NaCl be reduced to 23 C., its volume will be reduced 

 to 996-320 c.c., and as the temperature is below the cryohydric 

 temperature, the salt is by nature inert. At such temperatures 

 ice and common salt are indifferent to each other. Returning 

 to the initial state, let the temperature of the block be reduced 

 to 2iC., the ice remaining inert. The volume of the ice 

 will then be 996 64 c.c. Let the NaCl now recover its activity, 

 it will melt 5 '628 c.c. ice producing 5-160 c.c. water under a con- 

 traction of 0-469 c.c. so that the apparent volume of the ice at 

 -21 C. is 996-171 c.c. By the aid of Table I and the other 

 constants, we can calculate the composition of a block of ice 

 of any weight or volume which contains 1*5105 gram NaCl. 

 The results of such a calculation are given in Table II for a 

 block of ice having the volume 1000 c.c. at o C. The results 

 are given graphically in Curve B, Fig. i. This curve has the 

 remarkable feature of two acute angles, giving the appearance 

 of the letter Z at the cryohydric temperature. Above this 

 temperature the ice expands with heat, but at a gradually 

 diminishing rate, until at 7'o C. the increase of volume 

 due to simple expansion of the ice is exactly balanced by the 

 contraction due to induced melting. At this temperature the 

 coefficient of apparent expansion changes sign and becomes 

 negative. Therefore, the coefficient of apparent thermal ex- 

 pansion of this ice changes sign three times when it is warmed 

 from a temperature below the cryohydric point of solution of 



