114 



HEAT OR CALORIC. 



9. Influence of pressure on the escape of gaseous substances from 



combination. 



" When one of the ingredients of a Solid, or Liquid, is prone to 

 assume the aeriform state, its extrication will be more or less easily 

 effected, in proportion, as the Pressure of the Atmosphere is increas- 

 ed, or diminished." 



" If a tall cylindrical jar, containing a car- 

 bonate undergoing the action of an acid, be 

 placed under a receiver, and the air with- 

 drawn by an air pump, the effervescence will 

 be augmented. But if, on the other hand, 

 the same mixture be placed in a receiver, in 

 which the pressure is increased, by condensa- 

 tion, the effervescence will be diminished. In 

 the one case, the effort of the carbonic acid to 

 assume the gaseous state, is repressed ; in the 

 other, it is facilitated. Hence the necessity 

 of condensation, in the process for manufac- 

 turing mineral water. Beyond an absorption 

 of its own bulk of the gas, the affinity of the 

 water is inadequate to subdue the tendency of 

 the acid to the aeriform state ; but when, by 



exterior mechanical pressure, a great number 

 of volumes of the gas are condensed into the space ordinarily occu- 

 pied by one, the water combines with as large a volume of the con- 

 densed gas, as if there had been no condensation." 



If a gas, under the ordinary pressure of the atmosphere, will com- 

 bine with water in the proportion of equal volumes, the pressure be- 

 ing doubled, the water will combine with two volumes of the gas, and 

 if this last pressure be doubled, the volume of gas combined will be 

 again doubled ; that is, it will be quadrupled, compared with the 

 first quantity combined under the ordinary atmospheric pressure, and 

 so on. When thus charged, if suddenly relieved from all the extra 

 pressure, by simply opening the vessel, as in drawing soda water, 

 the fluid is violently agitated, because the gas that was forcibly com- 

 bined, then resumes its elastic form. 



