14 ,6 Dr. Henry on the aeriform compounds 
and undecomposed carburetted hydrogen, the proportions of 
the two last increasing as, within certain limits, we reduce the 
relative quantity of chlorine. These changes were ascertained, 
both by Dr. Davy and the late Dr. Murray,* to depend on 
the presence of moisture, which is unavoidably introduced in 
the common mode of operating; for when the gases, first per- 
fectly dried, were mixed in an exhausted glass vessel, and ex- 
posed even to the direct rays of the sun, no mutual action was 
found to ensue. In the theory of these changes there is, it must 
be confessed, a little uncertainty. Does the chlorine, it may 
be asked, act simultaneously on the hydrogen of water, and 
on that of the combustible gas; or does it decompose water 
only ? The former view of the subject appears to me most 
probable, because, if the chlorine acted on water only, free 
hydrogen would be evolved from that portion of the hydro- 
carburet which abandons its charcoal to the oxygen of the 
water; which is not consistent with experience. When it is 
required to form carbonic acid, four volumes of chlorine must 
be used for the decomposition of each volume of carburetted 
hydrogen. In this case, two atoms of chlorine unite with 
the two atoms of hydrogen existing in the combustible gas, 
and the two other atoms of chlorine with the two atoms of 
hydrogen from the water. But to convert carburetted hy- 
drogen into carbonic oxide, three atoms of chlorine are suffi- 
cient, two of which are employed, as in the first case, and the 
third is expended in saturating the hydrogen of one atom of 
water, which supplies to the charcoal an atom of oxygen for 
the formation of carbonic oxide. Calculating in the same 
* Nicholson’s Journal, xxviii. 143, and 201. 
