177 On a new System of Defence: 
Stons as are safely deducible from the foregoing investigatiort. 
These may be briefly recapitulated as follows: 
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 ear- 
bonic acid; and that if olefiant gas be considered as constituted 
of one atom of charcoal united with one atom of hydrogen, car- 
buretted hydrogen must consist of one atom of charcoal iu com- 
bination 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 en- 
tirely 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, on all which it is inefficient, provided light be per- 
fectly 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 variable 
proportions of hydrogen and carbonic oxide; and that they owe, 
moreover, much of their illuminating power to an elastie fluid, 
which resembles olefiant gas im the property of being speedily 
condensed by chlorine. 
5, That the portion of oil gas and coal gas, which chlorine 
tius 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 af- 
fords one additional volume of carbonic acid. It is probably, 
therefore, either a nrixture of olefiant gas with a heavier and 
more combustible gas or vapour, or a uew gas sui generis, con- 
sisting of hydrogen and charcoal in proportions that remain to- 
be determined. 
Manchester, Jan. 1821. 
NXXIX. On Mr. Carnor’s new System of Defence of Places 
~ by what he calls Vertical Firing. 
Sour years past, Mr. Carnot, a celebrated French mathemati- 
cian and military engineer, published a work on a new mode of 
defence of forts against an enemy besieging the place when he 
‘has got possession of the ditch, where the guns of the fort can- 
not 
