i$6 Dr. Henry on the aeriform compounds 
oxide is in greater proportion than in the best kinds of gas 
from coal, and the carburetted hydrogen is most abundant 
in the latter gas. This, however, is more than compensated, 
so far as their illuminating power is concerned, by the greater 
richness of the aeriform products of oil in that denser species 
of gas, which is separable by chlorine. The proportion of 
hydrogen, both in oil gas and coal gas, appears to increase 
as they are formed at a higher temperature, and is always 
greatest in the latter portions of the gas from coal. But no 
instance has ever occurred to me of a gas obtained from 
oil or from coal, which, after the action of chlorine upon it 
with the exclusion of light, presented a residuum at all ap- 
proaching to simple hydrogen gas ; nor do I believe that 
such a gas can be generated under any circumstances of 
temperature, by which the decomposition of coal or of oil 
is capable of being effected. 
Inferences respecting the composition of that part of the gas from 
coal and oil, which is condensed by contact with chlorine. 
When a given volume of a mixture of olefiant and carbu- 
retted hydrogen gases is fired with oxygen, and an equal 
volume of the same mixture is first deprived of olefiant gas 
by the action of chlorine, and then fired with oxygen, it must 
necessarily happen that the excess of oxygen spent in the 
first combustion, above that consumed in the second, will be 
three times the volume of the olefiant gas, and that the ex- 
cess of carbonic acid formed in the first experiment above 
that generated in the second, will be double the volume of 
the olefiant gas. A remarkable anomaly however, was, 
during the last summer, observed by Mr. Dalton . 
