120 Experiments on I he Gas from Coal. 



ascertained to exist in the quality of the gas from diflferent kinds 

 of coal ; that from Wigan cannel holding the highest rank in 

 illuminating power, and that from the stone coal of South Wales 

 the lowest. 



Since the period when the second of these papers was published, 

 the use of artificial gases, as a source of light, has been rapidlv 

 increasing in this, and, I believe, in other countries, and pro- 

 mises to attain an extent and importance sufficient to justify any 

 labour that may tend, however remotely, to its improved appli- 

 cation. It has frequently happened, of late years, that I have 

 been requested by the proprietors of large manufactories lighted 

 by gas in this neighbourhood, to give an opinion on practical 

 points, respecting some of which 1 felt myself incompetent to 

 decide, from the want of the necessary data. It is to supply 

 these data, that I have once more returned to the investigation 

 of the subject. The objects which I have had it in view to de- 

 termine by the following course of experiments, are, whether, on 

 the large scale of manufacture, there is a decline in the value of 

 the aeriform products of coal, from the beginning to the end of 

 the distillation, similar to that which takes place on a small scale; 

 — at what stages of the process those gases, which may be con- 

 sidered as impurities, are chiefly evolved ; and whether they are 

 essential or accidental products ; — whether the meciiod of re- 

 moving the sulphuretted hydrogen and carbonic acid gases by 

 quicklime, which I suggested in the second memoir, is adequate 

 to the complete purification of coal gas ; — whether this purifica- 

 tion is attended with any loss of that portion of the gas which, 

 on account of its superior illuminating power, it is desirable not 

 to remove; — and, if such a loss should be found to ensue, whether 

 it may not be avoided by some modification of the purifying pro- 

 cess. In determining these points, I was indebted for the neces- 

 sary supplies of gas to Mr. Lee, at whose extensive manufactory 

 the principal facts were ascertained, that formed the basis of the 

 first accurate calculations respecting the oeconomy of gas from 

 coal.* 



On the Quality of the Gas, at different Stages of the Distilla- 

 tion. 

 The gas which I first submitted to experiment was obtained 

 from Wigan cannel coal, a substance preferred in this neighbour- 

 hood as affording ac^riform products, which, both by their quan- 

 tity and quality, more than compensate its higher price f. The 

 retorts are charged while red hot with this substance, and indeed 



* See Mr. Murdoch's " Account of the Application of the Gas from Coal 

 to oecononiical Purposes," Piiil. Tiar.s. 18()S, page 124. 



t About a shilling per cwt. of 1121b. or \'6\d. delivered in Manchester. 



are 



