302 EXPERIMENTS AND OBSERVATIONS 



ment, too, are such as to preclude any such supposition ; and 

 this more peculiarly so, than in the experiment of obtaining 

 water from the muriate of ammonia by heat; for in the present 

 case, the acid gas is alone employed, while in the other there 

 is an additional equal volume of ammoniacal gas, which may 

 be supposed to afford a double quantity of hygrometric vapour.. 

 In the latter, both the gases are condensed into a solid pro- 

 duct, and any hygrometric vapour may be supposed to be li- 

 berated ; but in the present experiment, there remains the hy- 

 drogen gas, capable of containing hygrometric vapour, while 

 the muriatic acid gas contains none ; and the quantity of it 

 thus transmitted over the .humid surface, and expelled from 

 the apparatus, must have carried off more vapour than the 

 other, introduced at a lower temperature, could have convey- 

 ed. These circumstances, independent of the quantity of wa-. 

 ter deposited, precluded the supposition of any deposition from; 

 the condensation of hygrometric vapour. And there is no 

 other external source whence it can be derived. In this re- 

 spect nothing can be more satisfactory than the experiment 

 with the zinc in the apparatus described. The muriatic acid 

 gas rises from dry mercury in contact with muriate of lime, 

 passes through a narrow bent tube, thirty inches in length, 

 without exhibiting the slightest film of moisture, is received 

 into the retort perfectly dry ; and when the action of the metal 

 on it is excited by heat, humidity immediately becomes appa- 

 rent in the curvature of the retort, and this even while the 

 gas is warm., and of course capable of containing more water 

 dissolved, than it could do in its former state ; and the quanti- 

 ty increases as the experiment proceeds. No arrangement can 

 he supposed better adapted to prove, that any deposition of wa- 

 ter must be by separation from its existence in the gas in a 

 combined state. 



But 



