200 | Experiments on Muriatic Acid Gas, + 
and the ay of- it thus transmitted over the humid surface, 
and expelled from the apparatus, must have earried off more va- 
pour than the other, introduced at a lower temperature, could 
have conveyed. ‘These circumstances, independent of the quan- 
tity of water deposited, precluded the supposition of any deposi- _ 
tion 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 in the apparatus described. ‘The muriatie acid gas 
rises from dry mercury in contact. with muriate of lime, passes 
through a narrow bent tube, thirty inches in length, without 
exhibiting t he slightest film of moisture, is received into the re- 
tort perfectly dry; and when the action of the metal on it is ex- 
cited by heat, humidity immediately becomes apparent in the 
curvature of the retort, and this even while the gas is warm, and 
of course gapable of containing more water dissolved, than it 
could do in its former state; and the quantity increases as the 
experiment proceeds. No arrangement can be supposed better 
adapted to prove, that: any deposition of water must be by sepa- 
ration 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 theary of the experiment. 
The result of water being obtained 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 fromthe water, the corresponding hydrogen is 
evolved, and the oxide formed combines with the real acid. No 
water, therefore, ought to he 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 sine 
gle example, from the scale of chemical equivalents: 100 grains 
of iron combine with 29 of oxygen, and in this 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 portion of water contains 29 of oxygen with 3:8 of hy- 
drogen. There is present, therefore, exactly the quantity of 
oxygen which the metal req inires to combine with the acid: and 
no water remains above this, Or it may be illustrated under 
another point of view. Muriatic acid gas is composed. of oxy- 
muriatic gas and hydrogen. — A metal acting on it must attract . 
the oxymuriatic acid, —that i is, the muriatic acid and oxygen,— 
and liberate the hydrogen. No water, therefore, aught to ap- 
pear, more, on this theory, than on the other ; but the real pro- 
ducts in both must be a dry muriate, or chloride, and hydrogen 
gas, 
