68 



COHESION. 



well stoppered so far as the alcohol is concerned; 

 the air can pass through, but the alcohol cannot. 

 And if I were to take an oil vessel this plan 

 would do equally well, for in former times they 

 used to send us oil from Italy in flasks stop- 

 pered only with cotton wool (at the present 

 time the cotton is put in after the oil has arrived 

 here, but formerly it used to be sent so stop- 

 pered). Now if it were not for the particles of 



Fig. 22. 



Fig. 23. 



liquid cohering together, this alcohol would 

 run out, and if I had time I could have shown 

 you a vessel with the top, bottom and sides alto- 

 gether formed like a sieve, and yet it would 

 hold water owing to this cohesion. 



You have now seen that the solid water can 

 become fluid by the addition of heat, owing to 

 this lessening the attractive force between its 



