Gas-Burners, and on the Illuminating Power of the Gases. 9G 
other gases, such as carbonic oxide, light carburetted hydrogen, and hydro- 
gen, which are most of them lighter than olefiant, and which give out very 
little light during their combustion. And he showed, at the same time, that 
the proportion of olefiant gas might be estimated, on the one hand, by the 
quantity of oxygen required to consume the coal or oil gas by detonation, and, 
on the other hand, by the diminution caused in the volume of the gas by the 
action of chlorine in the dark. 
Three methods of estimating the relative light of oil and coal gas, have 
been deduced from these researches. 
In the first place, as the specific gravity must always increase with the quan- 
tity of olefiant gas present in them, and as that gas was thought to be their sole 
illuminating ingredient, it was inferred that the illuminating power and the spe- 
cific gravity follow a certain ratio to each other. What that ratio is, must be de- 
termined by careful comparison of the specific gravities with the results of actual 
measurement of the light. The only attempt yet made to do this, has been by 
Mr Leslie, who supposes that the ratio is a simple arithmetical one ; that the 
illuminating power, in fact, is as the specific gravity of the gas. But his re- 
sults, as will soon be proved, are far from being correct, even according to the 
indications of his own photometer. And, after all, it is quite possible that no 
relation whatever exists between the two qualities, because the specific gravity 
is liable to be increased by the presence of various gases, which lessen instead 
of augmenting the illuminating power. 
Secondly , Dr Fyfe of this city has supposed, that the olefiant is not only 
the chief illuminating ingredient in oil and coal gas, but likewise expresses, by 
its quantity, the exact relation of their illuminating power. He therefore 
conceives the illuminating power may be estimated by the absorption caused by 
chlorine in the dark. He has even compared results drawn in this way with 
those procured by actual measurement of the light, and says he has found 
them to correspond very closely. 
It has been lately proved, however, by Mr Dalton, Dr Henry and others, 
that, besides olefiant, another analogous gas must be present in oil-gas, and 
probably in coal-gas also, which is superior to olefiant both in specific gravity 
and in the quantity of carbon it contains, and therefore most certainly supe- 
rior also in illuminating power. We may add, that this opinion is effectually 
substantiated, by our having procured an oil-gas, which, while it contained 
but a small proportion of carbonic acid, not exceeding 3 per cent., was never- 
theless of higher specific gravity than olefiant, or even atmospherical air itself. 
Now, this new gas, like the olefiant, is condensed by chlorine in the dark ; and, 
consequently, the condensation by chlorine cannot be always proportioned 
to the illuminating power, unless the two illuminating ingredients are al- 
ways in the same proportion to one another, or unless there is but one illumi- 
nating ingredient, not the olefiant, but a per-carbureited hydrogen gas. Nei- 
ther of these positions has been proved. 
But, farther, the extraneous ingredients of oil and coal gas, if we may use 
the expression, are, in all likelihood, not only negatively, but even positively 
injurious ; that is, the illuminating ingredients would give more light without 
Them. Nay, it is even probable, that the loss sustained differs with the rela- 
