Ice and its Natural History 



243 



of 999,000 parts of ice and 1000 parts of liquid water containing I part of 

 chlorine. The remainder of the ice will melt at a temperature gradually 

 rising from -o 0< i too'-oC. 



" The consideration of this example furnishes an easy explanation of 

 the anomalous behaviour of ice formed from anything but the very purest 

 distilled water, in the neighbourhood of its melting-point. This subject 

 has been studied with great care and thoroughness by Pettersson. The 

 apparent expansion of all but the very purest ice, when cooled below 

 o C., is ascribed by him in part to solid saline contents of the ice, which 

 exercise a disturbing and unexplained influence on its physical properties. 

 Viewed in the light of the fact that the presence of even the smallest 

 quantity of saline matter in solution prevents the formation of ice atoC, 

 and promotes its liquefaction at temperatures below o C., we see that 

 this apparent expansion of the ice on cooling is probably due to the fact 

 that we are dealing, not with homogeneous solid ice, but with a mixture 

 of ice and saline solutions. As the temperature falls this solution deposits 

 more and more ice, and its volume increases. But the increase of volume 

 is due to the formation of ice out of water, and not to the expansion of a 

 crystalline solid already formed. 



TABLE IX. Water containing 7 parts Cl in 1,000,000. 



"In Table IX are given the volumes occupied by the ice (with 

 enclosed brine) formed by freezing 100,000 c.c. (at o C.) of a water con- 

 taining chloride of sodium equivalent to 7 grams chlorine in i ,000,000 c.c. 

 (at o C). 



" The volume (z' 2 ) of the ice and brine formed on freezing this water 

 is compared with (P) that observed by Pettersson in freezing a sample of 

 the distilled water in ordinary use in the laboratory. It will be seen that 

 the volumes observed agree very closely with those calculated for a water 

 containing 7 parts of chlorine in a million, on the assumption that the 

 saline matter is contained entirely in adhering liquid brine." 



1 6-2 



