1819.] -  Muriatic Acid Gas. 35 
obvious result in the experiment that no quantity that can be 
assumed would be adequate to account for the quantity actually 
obtained. The circumstances of the experiment too are such as 
to preclude any such supposition; and this more peculiarly so 
than in the experiment of obtaining water from the munate of 
ammonia by heat ; for in the present case the acid gas is alone 
employed, while m 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 product, and any hygrometrie vapour 
may be supposed to be liberated ; but in the present experiment, 
there remains the hydrogen gas capable of containing hygrome- 
tric 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 
conveyed. These circumstances, independent of the quantity of 
water 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 respect, 
nothing can be more satisfactory than the experiment with the 
zinc m the apparatus described. The muriatic acid gas rises 
from dry mercury in contact with muriate of lime, passes through 
a narrow bent tube,. 30 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 apparent 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 quantity creases as the experiment proceeds. 
No arrangement can be supposed better adapted to prove that 
any deposition of water must be by separation from its existence 
in the gas in a combined state. 
But though I consider this conclusion as established, there is 
a considerable difficulty attending the theory of the experiment. 
The result of water being cbtained is actually different from what 
is to be looked for on the doctrine of muriatic acid gas contain~ 
ing combined water; and even when the fact is established, the 
theory of it is not easily assigned. . On that doctrine, it must be 
held that in the action of metals on muriatic acid gas, the metal 
attracts oxygen from the water, the corresponding hydrogen is 
evolved, and the oxide formed combines with the real acid. No 
water, therefore, ought to be deposited ; for none is abstracted 
from the acid but what is spent in the oxidation of the metal. 
This will be apparent by attending to the proportions in a single 
example from the scale of chemical equivalents: 100 gr. of ion 
combine with 29 of oxygen, and im thig state of oxidation unite 
with 99 of real muriatic acid. This quantity of acid exists in 
131-8 of muriatic acid gas combined with 32°8 of water; and this 
c2 
