459 
of carbon and hydrogen, 
made by Mr. Dalton, of a vapour in oil gas of greater spe- 
cific gravity than olefiant gas, requiring much more oxygen 
for its combustion, but yet condensible by chlorine. Mr. 
Dalton appears to consider all that was condensible by 
chlorine as a new and constant compound of carbon and 
hydrogen ; but Dr. Henry, who had observed that the pro- 
portion of oxygen required for its combustion varied from 
4,5 to 5 volumes, and the quantity of carbonic acid produced, 
from 2,5 to 3 volumes, was inclined to consider it as a mix- 
ture of the vapour of a highly volatile oil with the olefiant 
and other combustible gases ; and he further mentions, 
that naphtha in contact with hydrogen gas will send up such 
a vapour ; and that he has been informed, that when oil gas 
was condensed in Gordon’s lamp, it deposited a portion of 
highly volatile oil. 
A writer in the Annals of Philosophy, N. S. III. 37, has 
deduced from Dr. Henry’s experiments, that the substance, 
the existence of which was pointed out by Mr. Dalton, was 
not a new gas sui generis, “ but a modification of olefiant • 
gas, constituted of the same elements as that fluid, and in 
the same proportions, with this only difference, that the 
compound atoms are triple instead of double:” and Dr. 
Thomson has adopted this opinion in his Principles of Che- 
mistry. This, I believe, is the first time that two gaseous 
compounds have been supposed to exist, differing from each 
each other in nothing but density ; and though the propor- 
‘tion of 3 to 2 is not confirmed, yet the more important part 
of the statement is, by the existence of the compound de- 
scribed at page 452, which though composed of carbon and 
MDCCCXXV. 3 O 
