326 Mr. Faraday on the mutual Action of Sulphuric Acid 
Or the angle PSM < PTX and .«. the pole S lies without the 
curve as in fig. 2. 
In this case the equilibrium is stable when the force is at- 
tractive, and unstable when repulsive. 
In the other case the curve may be convex or concave to 
the pole, or both. 
In the case in which the extremities of the string are joined, 
we have but one position of equilibrium, and 
2 
P= MN’ 
In this case the form of the curve will be the same as though 
it were inextensible. 
LE. On the mutual Action of Sulphuric Acid and Naphthaline, 
and on a new Acid produced. By M. Faravay, Esq. F.R.S. 
Corresponding Member of the Royal Academy of Sciences, 
Sc. de.* 
| a paper * On new compounds of carbon and hydrogen +,” 
lately honoured by the Royal Society with a place in the 
Philosophical Transactions, I had occasion briefly to notice, 
the peculiar action exerted on certain of those compounds by 
sulphuric acid. During my attempts to ascertain more mi- 
nutely the general nature of this action, I was led to suspect 
the occasional combination of the hydro-carbonaceous matter 
with the acid, and even its entrance into the constitution of the 
salts, which the acid afterwards formed with bases. Although 
this opinion proved incorrect, relative to the peculiar hydro- 
carbons forming the subject of that paper, yet it led to expe- 
riments upon analogous bodies, and amongst others, upon 
naphthaline, which terminated in the production of the new 
acid body and salts now to be described. 
* From the Philosophical Transactions for 1825, Part II. 
+ See Philosophical Magazine, vol. Ixvi. p. 180. 
Some 
