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 
isan 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 frem 
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 
be 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. 3 
‘cas But 
