202 On the. Co't^jmsilion and Analysis 



and that from moistened charcoal when purified is ,480*. It 

 became evident, therefore, that coal gas could not consist princi- 

 pally of the two hydrocarburets ; nor could the presence of car- 

 bonic oxide be suspected, its specific gravity being ,9834. Hence 

 it occurred to me, that the only mode of explaining these appa- 

 rent anomrJies, was to consider coal gas as a mixture of olefiant 

 and hydrogen gases ; and the following experiments were under- 

 taken with a view to determine this point. 



1. One hundred volumes of coal gas were detonated by the 

 electric spark over mercury, with 200 of oxygen ; the carbonic 

 acid was absorbed by liquid potassa, and 36 volumes of pure 

 oxygen remained in the tube. Whence it appears that 100 vo- 

 lumes of the coal gas under examination required for its perfect 

 combustion 164 parts of oxygen; consequently, as 100 parts of 

 olefiant gas require 300 of oxygen, and lOO of hydrogen 50, for 

 their respective combustion, it might be concluded from the 

 above experiments, supposing no foreign gases present, that the 

 100 of coal gas consisted of about 55 parts of hydrogen and 48 

 of olefiant gas ; a mixture, of which 100 cubical inches would 

 weigh nearly 15 grains, and which closely corresponds with the 

 specific gravity of the coal gas. 



2. One hundred measures of coal gas were introduced into a 

 small bent glas tube containing a little sulphur, and inverted in 

 mercury ; a red heat was applied until the inclosed gas under- 

 went no further dilatation ; and on examining its volume when 

 cold, it was found to occupy 140 measures. If we consider the 

 increase of bulk as resulting from the decomposition of olefiant 

 gas, this experiment gives the composition of coal gas 60 hydro- 

 gen and 40 olefiant by volume. 



3. One hundred measures of coal gas were introduced into a 

 mercurial gasometer, connected with a second gasometer by 

 means of a platinum tube, in the manner describell by Messrs. 

 Allen and Pepys in their Essay on the Combustion of Carbon*. 

 Some small quartz crystals previously heated red hot were intro- 

 duced into the platinum tube, which was heated bright red ; the 

 gas was then passed through it from one gasometer to the other, 

 for about a quarter of an hour. The apparatus having cooled, 

 the gas was founc^, to have sustained an increase of volume =40 

 parts; it burned with the pale flame of hydrogen; and when de- 

 tonated over mercury, required scarcely more than half its vo- 

 lume of oxygen, and afforded a very minute portion of carbonic 

 acid. The interior of the platinum tube was lined with charcoal, 

 the crystals were covered with it, and some had assumed a beau- 

 tiful brown tint. 



* Henry's Elements, p. 320. 



t Phil. Trans. 1807. Phil. Mag. Vol. XXIX. pp. 216, 315. 



4. The 



