112 PRINCIPLES OF CHEMISTRY 



CHAPTER II 



THE COMPOSITION OF WATER, HYDROGEN 



THE question now arises, Is not water itself a compound substance ? 

 Cannot it be formed by the mutual combination of some component 

 parts ? Cannot it be broken up into its component parts ? There can- 

 not be the least doubt that if it does split up, and if it is a compound, 

 then it is a definite one characterised by the stability of the union 

 between those component parts from which it is formed. From the 

 fact alone that water passes into all physical states as a homogeneous 

 whole, without in the least varying in its properties and without split- 

 ting up into its component parts (neither solutions nor many hydrates 

 can be distilled they are split up), we must already conclude, from this 

 fact alone, that if water is a compound then it is a stable and definite 

 chemical compound. Like many other great discoveries in the province 

 of chemistry, it is to the end of the last century that we are indebted 

 for the important discovery that water is not a simple substance, that 

 it is composed of two substances like a number of other compound sub- 

 stances. This was proved by two of the methods by which the com- 

 pound nature of bodies may be determined as self-evident ; by analysis 

 and by synthesis -that is, by a method of the decomposition of water 

 into, and of the formation of water from, its component parts. In 1781 

 Cavendish first obtained water by burning hydrogen in oxygen, both of 

 which gases were already known to him. He concluded from this that 

 water was composed of two substances. But he did not make more 

 accurate experiments, which would have shown the relative quantities 

 of the component parts in water, and which would have determined its 

 complex nature with certainty. Although his experiments were the 

 first, and although the conclusion he drew from them was true, yet such 

 novel ideas as the complex nature of water are not easily recognised so 

 long as there is no series of researches which entirely and indubitably 

 proves the truth of such a conclusion. The fundamental experiments 

 which proved the complexity of water by the method of synthesis, and 

 of its formation from other substances, were made in 1789 by Monge, 



