70 COHESION. 



from the spirit lamp is now being consumed, 

 not in making the ether any warmer, but in 

 converting it into vapour, and if I desired to 

 catch this vapour and condense it (as I could 

 without much difficulty), I should have to do 

 the same as if I wished to convert steam into 

 water and water into ice: in either case it would 

 be necessary to increase the attraction of the 

 particles, by cold or otherwise. So largely is 

 the bulk occupied by the particles increased by 

 giving them this diminished attraction, that if 

 I were to take a portion of water a cubic inch 

 in bulk (A, Jig. 23) I should produce a volume of 

 steam of that size B [1700 cubic inches ; nearly 

 a cubic foot], so greatly is the attraction of co- 

 hesion diminished by heat; and yet it still 

 remains water. You can easily imagine the 

 consequences which are due to this change in 

 volume by heat the mighty powers of steam 

 and the tremendous explosions which are some- 

 times produced by this force of water. I want 

 you now to see another experiment which will 

 perhaps give you a better illustration of the bulk 

 occupied by a body when in the state of vapour. 

 Here is a substance which we call iodine, and I 

 am about to submit this solid body to the same 



