148 Mr. Faraday on the mutual action of sulphuric acid 
to rise, the red colour became deep brown, and then a sudden 
action commenced at the bottom of the tube, which spread 
over the whole, and the acid became black and opaque. 
Continuing the heat, naphthaline, sulphurous acid, and char- 
coal were evolved ; but even after some time the residuum 
examined by water and carbonate of baryta, was found to 
contain a portion of the peculiar acid undecomposed, unless 
the temperature had been raised to redness. 
These facts establish the peculiarity of this acid, and dis- 
tinguish it from all others. In its solid state it is generally 
a hydrate containing much combustible matter. It is readily 
soluble in water and alcohol, and its solutions forms neutral 
salts with bases, all of which are soluble in water, most of 
them in alcohol, and all combustible, leaving sulphates or 
sulphurets according to circumstances. It dissolves in naph- 
thaline, oil of turpentine, and olive oil, in greater or smaller 
quantities, according as it contains less or more water. As 
a hydrate, when it is almost insoluble in naphthaline, it 
resembles the heavier substance obtained as before described, 
by the action of sulphuric acid on naphthaline, and which is 
the solid hydrated acid, containing a little naphthaline, and 
some free sulphuric acid ; whilst the lighter substance is a 
solution of the dry acid in naphthaline ; the water present 
in the oil of vitriol originally used being sufficient to cause a 
separation of a part, but not of the whole. 
2. Salts formed by the peculiar acid with bases. 
These compounds may be formed, either by acting on the 
bases or their carbonates by the pure acid, obtained as already 
described ; or the impure acid in solution may be used. 
