~ 
OGe : M. Grotthus on the / . [Fez 
But to be able to determine the specific gravity = 2 of a sub- 
stance supposed in the gaseous state, which is not capable of. 
existing alone in that state, we must, in the first place, endeavour 
to ascertain the specific gravity = A of a gaseous combination | 
of this substance with another gas, of which last the specific 
gravity = B is already known. Further, we must know the 
number of volumes of each which are requisite to form one 
volume of the compound gas, whose specific gravity is = A. 
Let a be the number of volumes of the body whose specific gra- 
vity = @ isrequired, and let 6 be the number of volumes of the 
gas whose specific gravity = B is already known: it is evident 
thata c= A — b B, and, of course, x Oi aad dd 5 
s nes 
Sect. 28.—An example or two will be sufficient to elucidate 
this rule. From the experiments of Davy and Gay-Lussac, it is 
known that hydrogen and oxygen gases do not alter their volume 
when they combine with sulphur, and are converted respectively 
into sulphuretted hydrogen and sulphurous acid gases. We 
may, therefore, assume it as very probable, and as conformable 
to.the law of gaseous combinations, that one volume of sulphur 
in the state of gas unites with one volume of hydrogen or oxygen 
gases ; and that the two volumes in both cases are condensed 
into one volume. Let us. apply our formula in this case where 
a=1,and6=1. The specific gravity of a volume of sulphur 
A—16 
in the state of gas willbe x = 7 =A-—B. According to 
Thomson, the specific gravity A of sulphuretted hydrogen gas 
= 1-177, and the specific gravity B of hydrogen gas = 0-073. 
Hence A — B = 1-177 — 0-078 = 1-104 = specific gravity 
of gaseous sulphur. 
Let us now derive the specific gravity of gaseous sulphur from 
that of sulphurous acid gas. The specific gravity of sulphurous 
acid gas is according to Thomson = 2-193, and that of oxygen 
gas = 1103. Hence gaseous sulphur = 2:193 — 1103 = 
1-090, a number which differs from the former by only =1,. §, 
therefore, assume the round number 1-100 as the specific gravity 
‘of gaseous sulphur. 
Sect. 29.—The specific gravity of carbonic acid is = 1:519. 
If from this we subtract 1-103 = specific gravity of oxygen gas, 
we get 0'416 = specific gravity of carbon in the state of gas. I 
take it for granted that it is known that when oxygen gas is con- 
verted into carbonic acid gas by the combustion of charcoal in 
it, the bulk is not altered. z 
We obtain almost the same number when we employ the 
specific gravity and the constituents of olefiant gas for the data 
of our calculation. This gas requires for complete combustion 
three times its volume of oxygen gas, and forms twice its volume 
of carbonic acid gas. Hence it follows that one volume of olefiant 
gas must be composed of two volumes of gaseous carbon and 
