"338 Dr. Henry's Experiments on the Gas from Coal. [Nov. 



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 pub- 

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

 rapidly increasing in this, and, I believe, in other countries, and 

 promises to attain an extent and importance sufficient to justify 

 any labour that may tend, however remotely, to its improved 

 application. 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 

 determine 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 

 considered as impurities, are chiefly evolved ; and whether they 

 are essential or accidental products ; whether the method of 

 removing 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 

 necessary supplies of gas to Mr. Lee, at whose extensive manu- 

 factory the principal facts were ascertained that formed the basis 

 of the first accurate calculations respecting the economy of gas 

 from coal.* 



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



The gas which I first submitted to experiment was obtained 

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

 hood as affording aeriform products, which, both by their quantity 

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

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

 are never suffered, during the whole of the winter season, to fall 

 below the temperature of ignition. The gas was collected in a 

 bladder furnished with a stop-cock, which was fixed into an 

 opening in the pipe between the retort and the tar-pit. It was 

 taken at this place, in order to avoid contact with water, and 



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

 economical Purposes" .Phil. Trans. 1S08, p. 124. 



t About a shilling per cwt. of 1 121b. or ISJd. delivered in Manchester. 



