162 Dr. Thomson on Coal Gas. 



mined carbonic acid and hydrogen, then azotic gas, then deut- 

 oxide of azote, muriatic acid gas and ammoniacal gas. In 

 1774; he discovered sulphurous acid gas, and oxygen gas, which 

 was destined to make such an alteration in the chemical theo- 

 ries of the time. He discovered fluoric acid gas and carbonic 

 oxide, though he was not aware of its peculiar nature, and 

 indeed remained ignorant of it to the end of his life. 



It is curious that Dr. Priestley nowhere, so far as I know, 

 mentions carburetted hydrogen or heavy inflammable air, as 

 it was then called. It constitutes the Jire damp of coal mines; 

 its combustibility and its property of exploding with great vio- 

 lence in certain circumstances must have been known in coal 

 countries at a pretty early period. In the Philosophical 

 Transactions for 1667, there is an account of a blower of this 

 gas passing through and taking fire from the flame of a candle, 

 and burning briskly ; and in the same work there are many 

 histories of explosions in coal mines attended with the loss of 

 many lives. 



Though carburetted hydrogen occurs so commonly in coal 

 mines, and though it burns with a strong flame and gives out 

 a good deal of light, and although it had been ascertained that 

 when common coal was distilled at a red heat it gave out a 

 great deal of inflammable gas, it does not seem to have oc- 

 curred to any person to employ it as a substitute for candles, 

 till the idea struck Mr. Murdoch, an Ayrshire gentleman in 

 the employ of Watt and Boulton. In the year 1808 he pub- 

 lished a paper in the Philosophical Transactions, pointing out 

 the advantages that would result from employing coal-gas in- 

 stead of oil for illuminating the streets of towns and manu- 

 factories *. 



In this paper he gives an account of the apparatus which 

 he had fitted up for lighting the cotton manufactory of Messrs. 

 Phillips and Lee at Manchester, which was at that time the 

 greatest cotton mill in the kingdom. He shows that the ex- 

 pense was only about one-fourth of that of the candles or oil ne- 

 cessary to produce the same quantity of light that the gas did. 

 The coal used was the best Wigan cannel, a ton of which he 

 says yields 7160 cubic feet of gas, and produces about two- 

 thirds of a ton of coke. 



In this interesting paper Mr. Murdoch gives the history of 

 the discovery of gas making. In the year 1792, while at Red- 

 ruth in Cornwall, he made a set of experiments on the quan- 

 tity and qualities of the gases produced by distillation from 

 different mineral and vegetable substances. He was induced 

 by some observations which he had previously made on the 



* [Mr. Murdoch's paper was reprinted in Phil. Mag. S. 1. vol. xxxii., 

 p. 113,— Edit.] 



