POROSITY OF LIQUIDS. 31 



produced which combine to form a single large bubble, 

 free from air if the stopper closes airtight, or contain- 

 iug air if, as frequently happens, the stopper does not 

 close perfectly. In any case, however, the space now 

 occupied by the two liquids when mixed is smaller than 

 that filled by them before they were mixed. The two 

 substances have, as it were, penetrated each other, 

 which could not happen had there been no interstices. 

 The same phenomenon may be observed in mixing 

 many other liquids. 



The separation of the water and alcohol in this experiment, 

 before they are mixed, may be shown by colouring the water with 

 a solution of aniline- red (magenta). About 50 CC (40 grammes) 

 of alcohol are poured over one gramme of the magenta, which in 

 the solid state is of a golden-greenish colour. The solution is 

 allowed to stand for a few hours, and is occasionally well shaken. 

 One cubic centimetre of it is sufficient to give a red colour to two 

 litres of water. 



Put a few grains of iodine l into a small flask of the 

 size represented in fig. 21, close the flask with a good 

 cork, and heat it gently ; the iodine gives off beautiful 

 violet vapours, which fill the bottle. This experiment 

 proves that air is highly porous, for the diffusion of the 

 iodine vapours is not prevented although the flask is 

 filled with air. The porosity of gases may also be 

 deduced from their high compressibility (art. 3). It is 

 impossible to conceive that the ultimate matter of 

 which these bodies consist can alter its volume, and it 

 follows that if a body be compressed, it is not the 

 material particles themselves which become smaller, 

 but the pores between them. Not only gases, but 



1 Iodine is very poisonous j it forms bluish-black lustrous scales, and pro- 

 duces brown stains upon the skin, paper, and most organic substances. 



