66 



KNOWLEDGE. 



[Mahch 1, 1896. 



The shell was filled with water and the hole securely stopped 

 lip with an iron ping weighing three pounds. When the 

 freezing process began the water expanded, and something 

 had to give way in order to provide accommodation for its 

 increased bulk. So great was the force exerted that the 

 plug burst from the shell with a loud report and was 

 projected to a distance of nearly one hundred and forty 

 yards, and the ice protruded from the plug-hole in the 

 shape of an icicle eight inches in length. Another shell was 

 filled in a similar way, and the plug was more securely 

 fastened, but when the water froze the shell burst, and 

 the ice spread out all over the cracks. The mechanical 

 force exerted in both these experiments was unmistakable. 

 But let us note the peculiar behaviour of the ice. In 

 the one case it spurts out from the plug-hole and remains 



form, some in the interspaces, and some outside. The 

 compressed water spread over the cracks, and through the 

 plug-hole in the shells, and there instantly turned into ice, 

 while other molecules of water inside, becoming solid, pushed 

 with irresistible force in all directions the crystals already 

 formed. Thus there was an expenditure of energy, and an 

 amount of work done by the water in giving up heat it had 

 derived from the sun, and in assuming a crystalline condition. 



In order to make this point more clear, we may briefly 

 mention another well-known experiment with water and ice. 



Take a pound of water, the temperature of which is 80° 

 on the Centigrade thermometer scale, and mix it with a 

 pound of water at 0°, or freezing point ; the mixture will 

 make two pounds of water, the temperature of which is 

 40^ Centigrade. 



Jostedal Glauier, Korwav. Illustrating the zigzag course of a Glacier, with the source of supply in the distance, 



and the terminal river in the foreground. 

 From a photoijmph by] [T'oifiifiiu- anil Soul!. 



there, joined with the ice inside the shell, a brittle icicle 

 eight inches long. If the ice had been of the consistency 

 of putty, this form of protrusion is what one would have 

 expected, but when it occurs in a brittle and crystalline 

 substance, it demands thought and consideration. 



On account of the very low temperature to which the 

 shells were subjected, the greater part of the contents would 

 be formed into ice. This is indeed a necessary condition 

 in order that sufficient pressure might be exerted to 

 prevent all the water from freezing. Inside the shells 

 there would be a crystalline mass, the minute interstices of 

 which would be filled with molecules of liquid water ready 

 to freeze the moment the pressure acting on them was 

 reduced. This moment arrived when the shells gave way. 

 The molecules of water began to assume a crystalline 



Now take another pound of water at 80° Centigrade, and 

 mix with it a pound of crushed ice — that is, ice crystals— at 

 0° Centigrade, the same temperature as the cold water in 

 the first mixture, and the result is that we have two pounds 

 of water at freezing point. 



In both cases the weight of matter at 0° Centigrade 

 introduced into the warm water was the same ; how then 

 is it that in the latter experiment the water is reduced 

 40° lower than in the former ? Before the ice-crystals 

 could assume a liquid condition they had to absorb a 

 certain amount of heat. That heat was drawn from the 

 warm water, and consequently reduced its temperature, 

 but it did not raise the temperature of the ice ; it simply 

 acted as energy in enabling the ice to become liquid, and 

 remained in that liquid in the form of latent heat, to be 



