38 



explosion is so much diminished, that though the affinities of hydrogen 

 and oxygen are sufficient to determine at that temperature the forma- 

 tion of water, the affinities of nitrogen and oxygen are not sufficient to 

 determine the production o^ nitric acid^. 



These were the last and the only experiments which Cavendish ever 

 made on the combustion of hydrogen and oxygen ; he had completed 

 the investigation, and reverted no more to the subject. Few rough day- 

 books of experiments would tell their own tale with such certainty and 

 distinctness as these ; in few could the consecutive course of reasoning 

 be traced thus clearly from the experiments themselves : there cannot 

 remain a doubt on the mind of any one who reads them, that in January 

 1783 Cavendish had not only discovered the certain fact that oxygen 

 and hydrogen in definite proportions form water, but likewise the strong 

 probability that oxygen and nitrogen form nitric acid, two months be- 

 fore Priestley began to experiment, and Watt to speculate, on the no- 

 tice which Cavendish had given the former of the composition of 

 water, and four months before Lavoisier received from Blagden a 

 similar notice. 



These experiments were followed by an analysis of the gas distilled 

 from charcoal, which it is probable from some expressions in his paper 

 he may have been led to make by the circumstance of Priestley's ha- 

 ving used this gas in repeating his experiments without noticing the 

 production of nitric acidf. The quantity of oxygen which he found 

 consumed in its combustion corresponds precisely with Dr. Henry's 

 determination ; the quantity of carbonic acid appears to be less, pro- 

 bably from his manner of estimating it, by weighing the carbonate of 

 lime precipitated, instead of measuring the gas. At the same time, that 

 is to say in September 1783, it appears from these MSS. that by burn- 

 ing nitre with charcoal, and effecting a total decomposition of the nitric 

 acid, he confirmed analytically his synthetical discovery of its composi- 

 tion. 



In 1 784 he proceeded to investigate the diminution effected in air by 

 the electrical spark, and found, on examining the amount and product 

 of the condensation, not only a further confirmation of the composition 

 of nitric acid, but the means of discovering, by the same method of 



* Experiments on Air, Phil. Trans, vol. Ixxiv. part 1. p. 134. 



f " It is remarkable that neither of these gentlemen (Priestley and Lavoisier) 

 found any acid in the water produced by the combustion, which might pro- 

 ceed from the latter having burnt the two airs in a different manner from what 

 I did, and from the former having used a different kind of inflammable air, 

 namely, that from charcoal." Phil. Trans, vol. Ixxiv. part 1. p. 135. 



