806 EXPERIMENTS AND OBSERVATIONS 
acid gas, this may not prevent the formation of a super-muriate, 
more especially as the excess is in the metallic form, and ex- 
erts 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 with- 
out volatilization, so that no loosely adhering acid might re- 
main, 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, at- 
tends this, from the circumstance, that the liquid state is ne- 
cessary to admit of the indications of acidity, and in adding wa- 
ter to produce this, a change occurs in the state of combina- 
tion, in a number of the metallic muriates ; a super-muriate be- 
ing formed, which remains in solution, and a sub-muriate being 
precipitated, so that the acidity of the entire compound cannot 
justly be inferred from that of the solution. I found, accord- 
ingly, that on adding water to the product from the action of 
the acid gas on zinc, this change occurs ; a little of a white pre- 
cipitate being thrown down, while the liquor remained acid. 
But the fallacy can be obviated, by adding only as much water 
as produces fluidity, without subverting the combination. Por- 
tions, therefore, of the residue were exposed to a humid atmo- 
sphere, until by deliquescence, liquors were formed transpa- 
rent, without any precipitation ; and these were strongly acid, 
reddening litmus paper when it was perfectly dry and warm. 
I farther found, that the product of the solution of zinc in li- 
quid muriatic acid, when digested with an excess of metal, and 
evaporated to dryness, afforded by deliquescence a liquor sen- 
sibly acid. And in both cases, even when the solid product 
was retained liquid by heat, acidity was indicated by litmus pa- 
per. Lastly, What is still less liable to objection, the residue — 
in 
