10 Biographical Memoir of the late Dr Henry. 



tention, and he had at various times devoted much labour both 

 to their chemical analysis and to ascertain their respective fit- 

 ness for the purposes of illumination. The general conclusions, 

 which he had made known in several successive memoirs, 

 were, that these gaseous products are mixtures of defiant, car- 

 bonic oxide, carburetted hydrogen and hydrogen gases in va- 

 rying proportions, with other accidental impurities, as carbonic 

 acid and sulphuretted hydrogen. An opposite doctrine had 

 been proposed to the Royal Society by a distinguished chemist. 

 It was maintained that carburetted hydrogen does not consti- 

 tute a distinct gaseous species, that olefiant gas is the only 

 known compound of carbon and hydrogen ; and that the gases 

 obtained from oil and coal are nothing more than mixtures of 

 olefiant with simple hydrogen. 



In an elaborate paper published in the Transactions for 

 1821, Dr Henry succeeded, however, in establishing the sound- 

 ness of his original views. He contended that the concurring 

 results obtained by Dr Dalton, Sir H. Davy, Dr Thomson, and 

 himself, from the analysis of carburetted hydrogen collected 

 both from stagnant water and from the coal measures, at dis- 

 tant times and places, clearly demonstrate that gas to be a true 

 chemical compound, characterized by perfect uniformity of pro- 

 perties and composition. He proceeded to investigate the action 

 of chlorine both upon carburetted hydrogen and olefiant gases, 

 with a view to learn how far chlorine may be depended upon 

 as a means of effecting their separation. Carburetted hydro- 

 gen was found to be wholly unaltered by prolonged contact 

 with chlorine, when light was carefully excluded. Under the 

 same circumstances olefiant gas, on the contrary, was entirely 

 removed by chlorine. Hence he derived a simple and beautiful 

 mode of separating olefiant gas from the other gaseous com- 

 pounds of carbon with hydrogen or with oxygen, as well as 

 from pure hydrogen. After establishing the perfect accuracy 

 of this process, on artificial mixtures of the gases in known pro- 

 portions, he applied it to the mixtures of the same gases in 

 unknown proportions, which constitute oil and coal gases. The 

 best oil gas shewed forty per cent, of a gas condensible by 

 chlorine ; the best coal gas not more than thirteen per cent. 

 The residuary gases, left after the complete action of chlorine, 



