92 On the aériform Compounds 
that a similar decline in the value of the products takes place, 
but not to the same extent, owing, probably, to the greater uni- 
formity of temperature which is attainable in large operations *. 
On the practical conclusions, which it was the object of the 
Jast mentioned Essay to establish, I forbear to dwell, because they 
are unconnected with my present purpose, which is limited to 
the chemical constitution of these compound gases, and to the 
methods of separating them accurately from each other. The 
view of their nature and composition, which was taken in the 
first Essay, was opposed by those able philosophers M. Berthol- 
let, and Dr, Murray, of Edinburgh, who both contended for 
greater latitude as to the proportions in which hydrogen and 
charcoal are capable of uniting, and considered these proportions 
indeed as subject to no limitation, ‘The facts, however, which 
have since been multiplied in this, as well as in other depart- 
ments of chemistry, tending to prove that bodies capable of 
energetic combination unite in a few definite proportions only, 
leave little doubt that the same law holds good with respect to 
the compounds of hydrogen and charcoal. Not that it is meant 
that the known compounds of those elements are the only possi- 
ble ones; for others will probably be discovered, which will still 
be found conformable to the general law, that when one body 
combines with another in different proportions, the greater pro- 
portions are multiples of the less by un entire number. 
A different view of the subject has lately been taken by the 
ingenious author of the Bakerian Lecture, published in the Phi- 
losophical Transactions for 1820. In that paper, Mr. Brande 
has endeavoured to prove, that the gas called light carburetted 
hydrogen, or simply carburetted hydrogen, or hydro-carburet, is 
not entitled to be considered as a distinct species; that the only 
aériform compound of charcoal and hydrogen, which is with cer- 
tainty known to exist, is the gas called olefiant, or bi-carburetted 
hydrogen; and that the gases evolved by heat from coal and oil, 
are in fact nothing more than mixtures of olefiant’ and simple 
hydrogen gases in various proportions. 
In assuming, in the first Essay, the existence of light carbu- 
retted hydrogen as a definite compound, characterized by its re- 
quiring, for the complete combustion of each volume, two volumes 
of oxygen, and giving one volume of carbonic acid, I relied on 
the sole authority of Mr. Dalton; for the gas of marshes, though 
before known to be inflammable, had not been subjected to ac- 
eurate examination by any other chemist. Mr. Cruickshank, 
indeed, speaks of it as ‘¢ pure hydro-carbonate ¢ ;” but since he 
classes it in that respect with the gas obtained by the destructive 
* Manchester Society's Memoirs, New Series, vol. iii. 
+ Nicholson's Journal, 4to. vol. v. p. 6. 
distillation 
= SO Rema ss ee 
