OBJECTS.] INTRODUCTORY. 59 



water cooled down to the same degree it would all 

 gradually change into the same kind of substance. 



In this condition water is solid. It occupies space, 

 offers resistance, has weight, and transmits motion as 

 the water did, but if you shake it out of the tumbler in a 

 cold place it retains its form without the least change. 

 If you press it, it proves to be exceedingly hard and 

 unyielding; and, if the pressure is increased, it be- 

 comes crushed and breaks like glass. It may thus be 

 crushed to powder, and the ice powder can be formed 

 into heaps as if it were sand. 



Just as any quantity of steam has exactly the same 

 weight as the waj:er which was converted into it by 

 heat ; so the ice has exactly the same weight as the 

 water which has been converted into it by taking away 

 heat. 



41. Ice has less Specific Gravity than the 

 Water from which it was formed. 



But though the ice in the tumbler has the same 

 weight as the water had, it has not the same volume. 

 The expansion which began at 39 goes on, and when 

 water passes into the solid state its volume is about 

 j^th greater than it was at 39. Taking water at this 

 temperature as i.o, ice has a specific gravity of 0*916. 



But although water in freezing expands only to this 

 small amount, it resembles steam in the tremendous 

 force with which it expands. If you fill a hollow 

 iron shell quite full of water, screw clown the open- 

 ing tight, and then put it in a cold place where the 

 water may freeze, the water as it freezes will burst 

 the iron walls of the shell. You know that when the 

 winter is severe, the pipes by which water is brought 



