Experiments on the Gas from Coal. 169 



the residue with liquid potash, the last diminution showed the 

 quantity of carbonic acid. The gas left by potash was next ana- 

 lysed by combustion with a due proportion of pure hydrogen''', 

 which showed how much of the residue was oxygen, and how much 

 azotic gas. If more azote was found, than had l^een introduced as 

 an impurity of the oxygen gas, it was considered as having formed 

 a part of the combustible gas. A single experiment on any kind 

 of gas was never relied upon ; and to ensure accurate residts, the 

 same gas was fired with different proportions of oxygen. Deduct- 

 ing the pure oxygen found in the residue, from its quantity at the 

 outset, the volume of oxygen gas was learned, which had been 

 spent in saturating a given measure of combustible gas. 



In gases free from all admixture with carbonic oxide, it is easy to 

 know how much of the oxygen consumed has been spent in satu- 

 rating the charcoal; for as oxygen gas by conversion into carbonic 

 acid suffers no change of volume, the cjuantity which has com- 

 bined with the charcoal is exactly represented by the volume of 

 carbonic acid produced by the combustion. For example, as 100 

 meausures of olefiant gas afford by detonation 200 of carbonic 

 acid, 200 measures of oxygen must have united with the charcoal 

 of the olefiant gas. But beside these 200 measures, an additional 

 100 measures of oxygen are found to be consumed, and these 

 must have combined' with hydrogen, the other ingredient of the 

 gas, the volume of which in its full state of expansion would be 

 200 measures, as determined by the fact, that oxygen gas uni- 

 formly takes for saturation double its volume of hydrogen gas, 

 and no other proportion. 



Nature of the Gas from Coal. 



The opinion which I formerly advanced on this subject f, 

 thougli opposed by writers of so much authority as M. Berthol- 

 let and Dr. Murray, still appears to me to be much more pro- 

 bable, than that the varieties of gas fiom inflammable substances, 

 which may be almost infinitely diversified by modifications of 

 tem))erature, are, as those philosophers suppose, so many distinct 

 compounds of hydrogen and charcoal, or of hydrogen and char- 

 coal in combustion with oxygen. The reasons that induce me 

 to abide by mv original view of the subject are the following: 



1. We are acciuainted with two distinct and well characterized 

 compounds of hydrogen and charcoal, in one of which a given 

 weight of charcoal is united with a certain quantity of hydrogen, 

 ami in the other with double that quantity. I'lesidcs these two, 

 no other compound of those two elements has been hitherto 

 proved to exist. 



• The method of doing this is given in my I'^lenients of Chemistry, vol. i. 

 chap. V. sect. vi. + Nicholson's Journal, .Svo. xi. G8. 



2dlv. 



