40 ESSAYS BIOGRAPHICAL AND CHEMICAL 



transferred from one body to another without leaving it 

 uncertain whether water is not at the same time trans- 

 ferred, it will be very difficult to determine by experiment 

 which of these opinions is the truest; but as the com- 

 monly received principle of phlogiston explains all 

 phenomena, at least as well as Mr. Lavoisier's, I have 

 adhered to that.' We shall meet with this same difficulty 

 again, when we consider Davy's experiments, which led 

 to true views concerning the nature of chlorine. 



Cavendish's aim in these experiments, stated in modern 

 language, was to find out what becomes of the oxygen, 

 when substances burn in air ; whether the production of 

 carbon dioxide is a constant accompaniment of com- 

 bustion. He mentions five ways in which air may be 

 deprived of oxygen, namely, by the calcination of rnetals ; 

 by burning in it sulphur or phosphorus; by mixing it 

 with nitric oxide; by exploding it with hydrogen; and 

 lastly by submitting it to the action of electric sparks. 

 In the second series of his experiments on air, he ex- 

 amines in detail the action of a continued rain of sparks 

 on air ; and this led to the discovery of the composition 

 of nitric acid ; for the ' caustic lees ' on evaporation to 

 dryness ' left a small quantity of salt, which was evidently 

 nitre, as appeared by the manner in which paper im- 

 pregnated with a solution of it burned.' But he doubted 

 whether ' there are not, in reality, many different sub- 

 stances confounded by us under the name of phlogisticated 

 air.' He ' therefore made an experiment to determine 

 whether the whole of a given portion of the phlogisticated 

 air of the atmosphere could be reduced to nitrous acid, 

 or whether there was not a part of a different nature 

 from the rest, which would refuse to undergo that change.' 

 On experiment, he found that ' if there is any part of the 

 phlogisticated air of our atmosphere which differs from 

 the rest, and cannot be reduced to nitrous acid, we may 



