GASES. C7 



lias since been effected by the application of cold alone, with- 

 out compression. 



The elastic force of the vapours arising from these gases in- 

 creases at a rapid rate with their temperature. Thus the vapour 

 from liquefied ammonia at 32 was found to exert a pressure 

 of 5 atmospheres, and when heated to 52% a pressure of 6j 

 atmospheres ; the vapour from liquid sulphuretted hydrogen 

 at 3 exerted a pressure of 14 atmospheres, and at 47 a pres- 

 sure of 17 atmospheres. Liquid muriatic acid at 32, 22, and 

 47 respectively, exerted a force of 20, 25, and 40 atmos- 

 pheres; carbonic acid at 12 and 32, a force of 20 and 36 at- 

 mospheres. Sir H. Davy threw out the idea that the prodi- 

 gious elastic force of these fluids might be used as a moving 

 power. But supposing the application practicable, it may be 

 doubted, from what we know of the constancy of the united sum 

 of the latent and sensible heat of high pressure steam, whether 

 any saving of heat would be effected by such an application 

 of the vapours of the liquefied gases. 



In certain gases, particularly hydrogen, nitrogen, oxygen, 

 nitric oxide, and carburetted hydrogen, compression alone seems 

 inadequate to produce liquefaction ; for these gases have pre- 

 served their elastic form under a pressure of at least 800 atmos- 

 pheres. There can be little doubt, however, that all other gases 

 at present known would yield to a less compressing force. Ex- 

 posure to extreme cold, with the application of great pressure at 

 the same time, is the most likely means of liquefying the more 

 refractory gases. 



All gases whatever are absorbed and condensed by water in a 

 greater or less degree, in which case they certainly assume the 

 liquid form. The quantity condensed is widely different in the 

 different gases ; and in the same gas the quantity condensed de- 

 pends upon the pressure to which the gas is subjected, and 

 the temperature of the absorbing water. In the case of carbonic 

 acid gas, Dr. Henry proved that the volume absorbed by water 

 is the same, whatever be the pressure to which the gas is sub- 

 ject. Hence, we double the weight or quantity of gas absorbed 

 by subjecting it, in contact with water, to the pressure of two 

 atmospheres ; and this practice is adopted in impregnating water 

 with carbonic acid, to make soda-water. The colder the water, 

 the greater also the quantity of gas absorbed. 



In the physical theory of gases, they are assumed to be ex- 



F 2 



