CHAPTER VII. 



THE CHEMICAL COMPOSITION OF PURE WATER. 



Had the question, " What is water ? " been asked a 

 century ago, the wisest chemist of the day could have re- 

 turned no answer, save that which might have been given 

 thousands of years earlier. He would have replied, in 

 short, that water, like air, is one of the elementary prin- 

 ciples of Nature. And, yet, there had not been altogether 

 wanting observations which suggested that water might, 

 after all, not be a simple substance. Thus, the sagacity of 

 Sir Isaac Newton led him to infer from his optical studies, 

 that water might consist of ingredients which were unlike 

 each other, and that one or more of these might be inflam- 

 mable. Such crude conjectures, however, could not be veri- 

 fied until considerable advance had been made in chemical 

 science ; and it was reserved for the chemists of the last 

 quarter of the eighteenth century, soon after they had 

 determined the composition of atmospheric air, to demon- 

 strate the true chemical constitution of water. Cavendish 

 and Watt in this country, and Lavoisier in France, not to 

 mention other chemists, have been put forward as compe- 

 titors for this honour, but the weight of evidence appears 

 strongly in favour of the claims of Cavendish. With- 



