1816.} On the Specific Gravity of Gaseous Bodies. 343 
Arricie II. 
Some Observations on the Relations between the Specific Gravity of 
Gaseous Bodies and the Weights of their Atoms. By Thomas 
Thomson, M.D. F.R.S. 
From the numerous papers upon the atomic theory which I have 
inserted in the successive volumes of the Annals of Philosophy, and 
from the paper by Berzelius on the theory of volumes, published in 
the same Journal, I take it’ for granted that my readers are ac- 
quainted with the outlines of both of these theories. Dr. Prout, in 
avery valuable paper published in the sixth volume of the Annals, 
has endeavoured to show that the specific gravity of any body may 
be obtained by multiplying the weight of its atom by half the spe- 
cific gravity of oxygen gas. This is the same thing as to say that 
the weight of an atom of every body is alwaysdouble its specific 
gravity in the state of gas. As the theory of volumes is exceed- 
ingly convenient in chemical experiments, I conceive that it will 
be interesting to practical chemists to see in one: view the very 
simple relations which exist between the specific gravities of 
gaseous bodies and the weights of their atoms. 
If we examine all the substances which can be exhibited in a 
gaseous state, and with the weight of the atoms of which we are 
acquainted with tolerable accuracy, we shall find that they may be 
divided into three sets. In the first set the specific gravity of the 
body, and the weight of its atom, are represented by the same 
number. In the second set, the weight of an atom is double that 
of the specific gravity, or of the weight of a volume. And in the 
third set the weight of an atom is equal to four times the specific 
gravity, or to four times the weight of a volume ot the respective 
bodies. 
In order to make this comparison, it is necessary to reduce the 
specific gravities to the same standard as the weights of the atoms. 
As we have chosen 1 to represent the weight of an atom of oxygen, 
we must employ the same number to represent the specific gravity 
of that body, and reduce the specific gravity of all the other gaseous 
bodies in that proportion. 
The following table exhibits what I consider as the specific 
gravity of the different gaseous bodies, according to the present 
state of our knowledge :— 
Weight of 109 
Specific Gravity. cubic inches 
in grains, 
Bilne a,0, 0:0, sninge; 4,8 ytbpsivig 0 M000). 4 «018,46 30°5 
Hydriodic acid gas....++-++. 47429  ..4++ 135°084 
Phosgene gas....eeseeeerss S ABD = Fay. asaceze 104°891 
@hilorine ;..»..s% x alabtivieriys cig DIOD cubslby opt fy 76°250 
Beal Orine «....\s.0.a;0'h oir ae's 66 BAAD) no's 0ce0.)) mae 
