144 Mr. Faraday on the mutual action of 
heat much colourless naphthaline sublimed, and a black acid 
substance was left, which at a high temperature gave sul- 
phurous acid and charcoal. When heated in the air it took 
fire and burnt like naphthaline. Being rubbed in a mortar 
with water, a very large portion of it proved to be insoluble ; 
this was naphthaline ; and on filtration the solution contained 
the peculiar acid found to exist in the heavier substance , con- 
taminated with very little sulphuric acid. More minute 
examination proved that this lighter substance in its fluid state 
was a solution of a small quantity of the dry peculiar acid in 
naphthaline ; and that the heavier substance was an union of 
the peculiar acid in large quantity with water, free sulphuric 
acid, and naphthaline. 
It was easy by diminishing the proportion of naphthaline 
to make the whole of it soluble, so that when water was 
added to the first result of the experiment, nothing separated; 
and the solution was found to contain sulphuric acid with 
the peculiar acid. But reversing the proportions, no excess 
of naphthaline was competent, at least in several hours, to 
cause the entire disappearance of the sulphuric acid. When 
the experiment was carefully made with pure naphthaline, 
and either at common, or slightly elevated temperatures, no 
sulphurous acid appeared to be formed, and the action seemed 
to consist in a simple union of the concentrated acid and the 
hydro-carbon. 
Hence it appears, that when concentrated sulphuric acid 
and naphthaline are brought into contact at common, or mo- 
derately elevated temperatures, a peculiar compound of sul- 
phuric acid with the elements of the naphthaline is produced, 
which possesses acid properties ; and as this exists in large 
