112 



CONRTIBDTTONS TO THE KNOWLEDGE 



contains a very much greater per centage of hydrogen than 

 that produced in the charcoal retort. Although we are not 

 yet sufiiciently acquainted with the action of watery vapour 

 upon organic substances at high temperature, to state posi- 

 tively the cause of this excess of hydrogen, yet there can be 

 little doubt that it is derived from the action of steam upon 

 the hydrocarbons of the tar ; for as watery vapour in acting 

 upon carbon transfers its oxygen to that element, forming 

 carbonic oxide and an equal volume of hydrogen, so also 

 when steam acts upon a compound of carbon and hydrogen, 

 it produces carbonic oxide, but in doing so sets at liberty 

 not only its own hydrogen but that of the carbohydrogen 

 also ; and thus the volumes of hydrogen and carbonic oxide 

 remain no longer equal, but the volume of the former becomes 

 double, treble, or even fourfold that of the latter. Thus the 

 non-luminous gases contain a very large proportion of hydro- 

 gen, which, as we have already proved, is very much prefer- 

 able to carbonic oxide and light carburetted hydrogen, on 

 account of the relatively small extent to which a given volume 

 vitiates the atmosphere and heats the apartments in which it 

 is consumed. 



It has been supposed that the gases generated by the new 

 process have, to some extent, the nature of naphthalized 

 gases, and that, therefore, when allowed to stand for some 

 time in the holder, and especially when exposed to a freezing 

 temperature, their illuminating power would be much dete- 

 riorated. It was of importance carefully to ascertain the 

 value of this objection, and I therefore allowed a specimen 

 of the Boghead hydrocarbon gas to stand over water in a 

 holder for forty-eight hours, but at the expiration of that 

 time, its illuminating power had not suflfered the least dete- 

 rioration. I then exposed various specimens of gas to the 

 temperature of melting ice for several hours ; the usual mode 

 of doing this, by allowing the gas to stream through a ser- 

 pentine pipe surrounded by ice, is nearly valueless, since the 



