Ice and its Natural History 249 



expansion changes sign, and between 7*o and o*i, at which 

 the ice has practically all melted, the coefficient of expansion 

 is negative. Therefore the coefficient of thermal expansion 

 of this ice changes sign three times when it is warmed 

 from a temperature below the cryohydric point of solution 

 of chloride of sodium to that at which liquefaction is 

 complete. 



Curves C and Ca refer to ice of which 9167 grams or 

 10,000 c.c. at oC. contain 1-5105 gram NaCl. Above the 

 Z-like portion the curve shows a maximum volume of 

 9992*834 c.c. at 2*3. At temperatures higher than this 

 the coefficient of apparent expansion is negative. 



In the same figure curves A and Aa represent the volumes 

 of a block of ice weighing 91*67 grams and containing 

 1*5105 gram NaCl diffused through it. The line A.a repre- 

 sents its volume V at temperature /, the salt being inert ; 

 at o the volume is looc.c. The curve A, after the Z-like 

 portion, shows a maximum volume at 2O*5, above which 

 its apparent volume diminishes, as the temperature rises, and 

 at - i*o the ice is practically all melted. 



When 1*5105 gram NaCl is diffused in a block of ice 

 weighing 88 grams, then the volume of the ice, the salt being 

 inert, is 96 c.c. at o; and when the salt is active, the maxi- 

 mum volume is at the cryohydric temperature, so that from 

 2i72, the apparent volume U diminishes as the tempera- 

 ture rises. Therefore for blocks of ice which contain, per 

 100 parts by weight of ice, less than 29-97, and more than 

 1-7164 parts of NaCl, the coefficient of apparent expansion 

 is negative at all temperatures above 21 -72. 



In Fig. 2 we have curves D and Da, and E and Ert. The 

 same constant quantity of chloride of sodium, 1*5105 gram, 

 is diffused, in the case of D, in i cubic metre, and, in that of 

 E, in 10 cubic metres of ice. When melted these blocks 

 of ice would furnish waters containing chlorine in the pro- 

 portion of i gram to i ton of water in D and to 10 .tons of 

 water in E. The critical temperature at which the coefficient 

 of expansion changes sign is o*2275 in D and 0^0725 

 in E. 



