Ice and its Natural History 



251 



of ice which can be melted under the inducing influence of 

 1-5105 gram of chloride of sodium at the critical tempera- 

 ture T, at which the apparent coefficient of cubic expansion of 

 the ice is equal to o. 



A block of 100 c.c. of ice, which contains 1-5105 gram of 

 NaCl diffused through it, furnishes on being melted 91-67 c.c. 

 of water, which contain 0-9167 gram of chlorine, dissolved in 

 it as chloride of sodium. This water contains chlorine in the 

 proportion I gram to 100 grams of water, and represents a 

 concentration about one-half that of average sea-water. When 

 the volume of ice, F , is I cubic metre, the water produced by 

 its melting contains chlorine in the proportion of one part to 

 one million parts of water by weight. 



TABLE III. 



Waters which contain dissolved matter equivalent to no 

 more than I gram of chlorine in 10,000 grams of water are 

 in the category of ordinary fresh waters, and we see that the 

 critical temperature of ice which furnishes such water lies as 

 low as - 2'3. When the dissolved matter is equivalent only 

 to I gram of chlorine in 100,000 grams of water, the critical 

 temperature is o"725. The other waters are in the cate- 

 gory of distilled waters, and it is doubtful if, by any chemical 

 means whatever, vye could determine as little dissolved matter 

 as i gram chlorine in i ton of water ; yet the critical tem- 

 perature of such ice lies nearly a quarter of a degree below 

 the melting temperature of pure ice. The critical temperature 

 of expansion of ice affords a means of detecting impurity 

 equivalent to quantities of chlorine as small as i gram in 

 10 tons, and even I gram in IOO tons of water. 



