VOLATILE LIQUIDS. 



Or care and patience in the blowing may be 

 used instead. The vapour is highly inflammable. 

 The rush of fresh air and disturbance of the 

 surface of the ether caused by blowing on to 

 and into it give it abundant opportunities of 

 vaporising, and it rapidly does so. The prin- 

 ciple involved is that applied by a washer- 

 woman in hanging out her clothes on a windy 

 day. What she wants is to give the liquid 

 water in the wet clothes an opportunity of dis- 

 integrating into its constituent molecules, and 

 to give these an opportunity of exchanging 

 their vibratory movements in the liquid mass 

 for energetic movements of translation among 

 the similarly moving molecules of the surround- 

 ing atmosphere. (This is what she wants, but 

 she does not express it in this kind of language.) 

 The object is attained by getting the clothes 

 out in a brisk drying breeze. It is possible 

 for the vapour from a liquid to pass into the 

 surrounding space until that space is saturated 

 with it. Under given conditions of tempera- 

 ture and pressure a space can only receive a 

 definite number of molecules of a liquid. When 

 this saturation point has been reached, further 

 vaporisation can only take place by gradual 

 diffusion of the saturating vapour into spaces 

 further afield, so that by its thinning out room 

 is made for a further number of molecules to 

 come from the liquid and keep the space round 

 it saturated. It is a much more rapid process 



167 



