CARBON AND HYDROGEN. 



425 



known as the ammoniacal liquor, and the elastic fluids which 

 form coal gas. To purify the gas, it is cooled by transmitting 

 it through iron tubes or shallow boxes, in which it deposits some 

 condensible matter; and it is afterwards exposed to milk of 

 lime, to absorb sulphuretted hydrogen, which it invariably 

 contains, and frequently afterwards to solution of sulphate of 

 iron, which arrests a little hydrosulphuret of ammonia and a 

 trace of hydrocyanic acid. The hydrate of lime is sometimes 

 applied in the state of a damp powder, and not diffused through 

 water. 



Dr. Henry obtained the following results from an examination 

 of the gas from the best cannel coal, at different periods of the 

 distillation : 



COAL GAS IN 100 VOLUMES. 



Besides the constituents mentioned, coal gas when first made, 

 contains small quantities of 



Ammonia, Hydrocyanic acid, 



Sulphuretted hydrogen, Sulphuret of carbon, 

 Carbonic acid, Naphtha vapour.* 



All of these bodies are separated from it in the process of 

 purification, except the two last, namely, naphtha vapour, which 

 is the chief cause of the odour of coal gas, and sulphuret of 

 carbon, which affords a little sulphurous acid when the gas is 

 burned. The heterogenous nature of the gaseous mixture is well 

 shown upon introducing a quantity of dry iodine into a bottle 

 of it, when several liquid and solid compounds of iodine are 

 formed with the different hydrocarburets present. Iodine, on 

 the other hand, is not affected in the slightest degree by fire- 



* Dr. Henry's papers on coal gas are contained in the Phil. Trans, for 1808, 

 1820, and 1824 ; his instructions for the analysis of mixed gases, in his Elements 

 of Experimental Chemistry (182 ( J), vol. 2, p. ;~>17. 



