¥819.] Muriatic Acid Gas. 37 
difficulty under consideration by the opposite assumption. And it 
is to be remarked, that should even such a portion of water exist 
in the gas, it cannot be supposed that the acid should carry 
this with it mto its saline combinations, and retain it so that it 
should not be expelied by heat. It cannot be supposed to exist, 
therefore, in muriate of ammonia thus heated, and, of course, 
cannot account for the water obtained by the action of the 
metals on this salt. 
When it is proved that no extrinsic water exists in muriatic 
acid gas, there remain apparently only two modes on which the 
production of water can be explained, either that the metal may 
require less oxygen than is supposed in combining with the acid, 
so that a portion of water will remain undecomposed to be 
deposited ; or that the oxide attracts more real acid, so as to 
liberate a larger proportion of water. The first of these suppo- 
sitions is improbable, from the consideration of the law which 
regulates the combination of metallic oxides with acids; that 
the quantity of acid is proportional to the quantity of oxygen, so 
that if an oxide were formed in these cases at a lower degree of 
oxidation, it would only combine with a proportionally smaller 
quantity of acid, and the quantity of water detached from the 
combination would be the same. 
No improbability is attached to the second supposition ; and 
it has even some support from the consideration that many 
metallic saline compounds form with an excess of acid, and that 
it is difficult, with regard to a number of them, to procure them 
neutral. Metallic muriates, with excess of acid, seem in patti- 
cular to be established with facility. And although an excess of 
metal be present in the action exerted on muriatic acid gas, this 
may not prevent the formation of-a super-muriate, more espe- 
cially as the excess is in the metallic form, and exerts no direct 
action, therefore, on the real-acid. 
To ascertain if a super-muriate were formed in these cases, 
the product obtained from the action of the muriatic acid on the 
metal was raised to a heat as high as could be applied without 
volatilization, so that no loosely adhering acid might remain, and 
the air in the retort was repeatedly drawn out by a caoutchouc 
- bottle. The solution from the residue both of iron and zinc was 
very sensibly acid. Some fallacy, however, attends this, from 
the circumstance that the liquid state is necessary to admit of 
the indications of acidity; and in adding water to produce this, 
a change occurs in the state of combination in a number of the 
metallic muriates ; a supermuriate being formed which remains 
in solution, and a submuriate being precipitated, so that the 
agidity of the entire compound cannot justly be inferred from 
that of the solution. I found accordingly, that on adding water 
to the product from the action of the acid gas on zinc this 
change occurs ; a little of a white precipitate being thrown down, 
while the liquor remained acid. But the fallacy can be obviated, 
