by the condensation of gases as mechanical agents. 201 
force equivalent to that of an atmosphere compressed to ~ ; 
and by a farther addition of 2 6°, an elastic force equivalent to 
that of air condensed to of its primitive volume. These 
experiments were made in thick glass tubes hermetically 
sealed. The degree of pressure was estimated by the change 
of volume of air confined by mercury in a small graduated 
gage, and placed in a part of the tube exposed to the atmos- 
phere, and the temperatures were diminished from the degree 
at which the gage was introduced, i. e. the atmospheric tem- 
perature by freezing mixtures ; so that the temperature of 
the air within the gage could not be considerably altered ; 
and as the elastic fluid surrounding the gage must have had 
a higher temperature than the condensed fluid, the diminu- 
tion of the elastic force of the vapour from the fluids cannot 
be considered as overrated. 
From the immense differences between the increase of 
elastic force in gases under high and low pressures, by similar 
increments of temperature, there can be no doubt that the 
denser the vapour, or the more difficult of condensation the 
gas, the greater will be its power under changes of tempera- 
ture as a mechanical agent : thus carbonic acid will be 
much more powerful than muriatic acid. In the only ex- 
periment which has been tried upon it, its force was found 
to be nearly equal to that of air compressed to - 1 - at 1 2 0 F. , 
and of air compressed to at 32 degrees, making an in- 
crease equal to the weight of 13 atmospheres by an increase 
of 20 of temperature ; and this immense elastic force of 36 
atmospheres being exerted at the freezing point of water.* 
* Since this Paper was read, Mr. Faraday has ascertained that the vapour of 
ammonia at 32 0 exerts an elastic force equal to that of an atmosphere compressed 
MDCCCXXIII. D d ' 
