180 Life and Matter [chap. x. 



molecule being still classifiable as that of a 

 definite chemical compound. But there are 

 also some non-elementary bodies which, 

 although they are chemically complete and 

 satisfied, retain a considerable vestige of 

 power to link their molecules together so as 

 to make a complex and massive compound 

 molecule ; and these are able not only to 

 link similar molecules into a more or less 

 indefinite chain, but to unite and include 

 the saturated molecules of many other 

 substances also into the unwieldy aggregate. 

 Of the non-elementary bodies possessing 

 this property, water appears to be one of the 

 chief ; for there is evidence to show that 

 the ordinary H 2 molecule of water, 

 although it may be properly spoken of as a 

 saturated or satisfied compound, seldom 

 exists in the simple isolated shape depicted 

 by this formula, but rather that a great 

 number of such simple molecules attach 

 themselves to each other by what is called 

 their residual or outstanding affinity, and build 

 themselves up into a complex aggregate. 



