82 
THE NATURE AND 
[■SECT. II. 
Body. 
Specific gravity 
of the gas, air 
being unity. 
Specific gravity of 
liquid, water 
being unity. 
Temperature. 
Force in 
atmospheres. 
Mechanical power 
of equal weights 
of the gases. 
Carbonic acid gas 
1-527 
32° 
36 
Sulphuric acid gas 
2-777 
1-42 
45 
■ 2 
426 
Sulphuretted hydrogen gas 
1-192 
0-9 
50 
17 
630 
Euchlorine gas 
2-365 
Nitrous oxide 
1-527 
45 
50 
Cyanogen 
1-818 
0-9 
45 
3-6 
395 
Ammonia 
0-5962 
0-76 
50 
6-5 
1057 
Muriatic acid gas 
1-285 
50 
40- 
Chlorine 
2.496 
1-33 
50 
4- 
440 
Steam of water 
0-48 
1-000 
212 
1- 
1711 
These are the principal researches that have been made on the force of vapours 
at different temperatures, when in contact with liquids; but, in order to render 
the subject more complete, we must consider the force when not in contact with 
the liquids which generate them, and also their density and volume. 
Of the Elastic Force of Vapour separated from the Liquids from 
which they were generated. 
118. It has been remarked, that the elastic force of steam or vapour produced 
by increase of temperature ceases to follow the same law where it is not in 
contact with the liquid from which it was formed. (Art. 87.) The density of the 
steam no longer increases, the force being solely that which prevents it expanding, 
and is measured from the quantity it would expand if unconfined. The expansion 
by the same increase of temperature having been found to be the same in all 
gases and vapours, and the density as the compressing force, as far at least as 
60 atmospheres, it becomes an easy task to compute this species of force within 
that range of compression. 
This will also be further useful in determining the volume occupied by steam 
of a given density and temperature as far as about 60 atmospheres: higher we 
need not attempt to go for useful purposes; and if we did, our rules would fail, for 
there is not even a probable chance of the law, of the density being as the force, 
extending to very high degrees of compression. 
119. The quantity a gas or vapour expands under a constant pressure, is 
found by the following rule. 
Rule. To each of the temperatures before and after expansion, add 459. Then 
divide the greater sum by the less, and the quotient multiplied by the volume at 
the lower temperature will give the volume at the higher temperature. 
Or let t be the temperature with the volume v, and t' any other temperature, 
then