Chemistry . 223. 
ric acid. When a thin slice of hydrophane, of an elliptic form, 
was placed in a tube containing sulphuret ol* carbon, and view- 
ed diagonally, it exhibited the appearance of a molten mirror, 
encircled by an opaque rim or annulus. 
17. Dr Henry on Coal and Oil Gas . — In a very able paper 
44 On the Aeriform Compounds ol* Charcoal and Hydrogen,” 
by Dr Henry of Manchester, which will appear in the Phil. 
Trans, for 1821, the following results are given : 
1. That carburetted hydrogen-gas must still be considered as 
a distinct species, requiring for the perfect combustion of each 
volume two volumes of oxygen, and affording one volume of 
carbonic acid ; and that if olefiant-gas be considered as consti- 
tuted of one atom of charcoal, united with one atom of hydro- 
gen, carburetted hydrogen must consist of one atom of char- 
coal in combination with two atoms of hydrogen. 
2. That there is a marked distinction between the action of 
chlorine on olefiant gas, (which, in certain proportions, is entirely 
independent of the presence of light, and is attended with the 
speedy condensation of the two gases into chloric ether,) and its 
relation to hydrogen, carburetted hydrogen, and carbonic oxide 
gases, in all which it is inefficient, provided light be perfectly 
excluded from the mixture. 
3. That since chlorine, under these circumstances, condenses 
olefiant-gas, without acting on the other three gases, it may be 
employed in the correct separation of the former from one or 
more of the three latter. 
4. That the gases evolved by heat from coal and from oil, 
though extremely uncertain as to the proportions of their ingre- 
dients, consist essentially of carburetted hydrogen, with vari- 
able proportions of hydrogen and carbonic oxide ; and that they 
owe, moreover, much of their illuminating power to an elastic 
fluid which resembles olefiant-gas in the property of being 
speedily condensed by chlorine. 
5. That the portion of oil-gas and coal-gas which chlorine 
thus converts into a liquid form, does not precisely agree with 
olefiant-gas in its other properties ; but requires for the com- 
bustion of each volume nearly two volumes of oxygen more 
than are sufficient for saturating one volume of olefiant-gas, and 
affords one additional volume of carbonic-acid. It is probable, 
