1816.] respecting the Nature of Oxymuriatic Acid. 435 
in contact with dry carbonic acid gas, the gas is not absorbed, or 
the absorption is scarcely perceptible. But allow aqueous vapour to 
enter, and the absorption is completed in a few minutes, though 
water does not constitute one of the constituents of carbonate of 
lime. Whoever has studied the experiments of Mrs. Fulhame is 
acquainted with other instances of the same kind. Water, there- 
fore, produces an alteration in most oxidized substances, whereby 
they enter more easily at low temperatures into combination with 
other oxides. We are not yet well acquainted with the nature of 
this action of water, and of all the theoretical explanations of it 
that have been proposed, there is not one worthy of adoption, 
It is known that in the distillation of green vitriol a smoking, 
liquid, crystallizable matter, the nature of which was long un- 
known, follows the sulphuric acid. Mr. Vogel, of Bareuth, found 
that this peculiar body formed, with lime, gypsum; with barytes, 
sulphate of barytes; with soda, Glauber’s salt; and with water, 
common sulpburic acid. Owing to the great difference of the 
physical properties of this body from those of common sulphuric 
acid, he did not draw the very natural conclusion that, as it forms 
common sulphuric acid with water, it must be an anhydrous sul- 
-phuric acid. He found, likewise, that when sulphur was heated 
with this body, it formed at least two combinations with it, neither 
of which was sulphurous acid. Mr. Vogel appears, therefore, to 
‘have discovered new oxides of sulphur, by reducing anhydrous 
sulphuric acid by means of sulphur, which are very highly deserving 
of the attention of chemists. 
From what has been said, it is evident that anhydrous acids (not 
saturated with a base) may be accurately distinguished by means of 
their physical characters from the same acids combined with water 
—a difference which may very well be compared to that between a 
combustible radical and its oxide, or perhaps any other of its com- 
pounds, 
The compounds formed by two or more acids are well entitled to 
the attention of chemists, especially as this class of bodies has not 
been long known, and therefore has not been much examined. I 
cannot here notice the compound acids into which muriatic acid 
and fluoric acid enter as ingredients, but must confine myself to the 
compound acids, which are acknowledged by both doctrines. 
If highly concentrated sulphuric acid be brought in a small 
vessel in contact with nitrous gas over mercury, the gas is not ab- 
sorbed by the acid, a proof that in this way no sulphate of nitrous 
gas is formed. If we introduce a little oxygen gas, nitrous acid is 
formed, which is absorbed by the sulphuric acid, and forms with it 
a small crystallized compound. If we continue to add oxygen gas 
in small quantities till no more nitrous acid is absorbed by the sul- 
phuric acid, the whole is converted into a magma full of plumose 
crystals. ‘I'he crystals may be separated from the liquid by throwing 
the whole into a funnel filled two-thirds with pounded glass, and 
covering the mouth of the funnel with a glass plate, to keep out the 
