262 On ihe Gaseous Combinations of 
2. It has no smell, and no sensible taste, provided it be 
previously washed in clean water. 
3. It always contained a mixture of carbonic acid. The 
least quantity of this gas present was 5 per cent.; the 
greatest, 74 per cent. é 
4. It always contained a mixture of common air. It is’ 
remarkable, that the proportion present was in every casé 
the same, and amounted to 12°5 per cent., or 2°5 per cent. 
of oxygen and 10 per cent. of azote. Mr. Dalton says, 
that the gas which be examined contained 20 per cent. of 
azote. This was never the case with the gas from Restal- 
rig; but the common air and carbonic acid gas together 
sometimes amounted to 20 per cent., and always to ‘near 
that quantity. ' 
5. After depriving it of its carbonic acid, T found its 
specific gravity 0°611, that of air being 1°000. But as it 
contained a mixture of 12:5 per cent. of air, it would have 
been obviously lighter, if this portion had been removed, 
By calculation I find that the specific gravity of the pure 
gas would have been 0°5554*. 
My method of taking the specific gravity of gases being — 
extremely simple, yet precise, | think it worth while to de- 
scribe it inthis place. Jt is founded on the well-known 
fact, that when two gases are mixed, their bulk does not 
alter. I Have a large flask fitted with a stop-cock. I weigh 
this flask very accurately, then exhaust it, and weigh it 
again. Let the loss of weight be a. I then fill the flask 
with the gas whose specific gravity I want, and weigh it 
again. If the weight of the flask be the same as at first, 
it is obvious that the yas has exactly the specific gravity of 
common air. If it be heavier than at first, the gas 1s heavier 
than common air; if lighter, the gas is lighter than com- 
mon air. Suppose the flask lighter than at first, I add 
weights till the flask is exactly poised. Let the weight 
added be l. We have the weight of common air to that 
of the gas as atoa—b. And to find the specific gravity, 
we have this proportion, a: @—b:: 1 :a” = specific gra- 
i ey) by y 
vity wanted, or © = — . Ifthe flask is heavier than at 
first, weights are added to the other scale, ull it is exactly 
poised; Jet these weights, as before, be 4; we have in this 
a+b : ' FS G 
case © = ——. In this process no correction is necessary 
* Let x= the specific gravity of the pure gas, A = the quantity of air 
in the mixture, a = the specific gravity of air, B = quantity of pure gas 
(A+ B) c—Aa 
present, c = specific gravity of the mixture, we have x = 
for 
