[ 264, ;,] 
LVIII. On melting Caoutchouc, or India-Rubber, and pre- 
serving Iron and Steel from Rust. By Artnur Arxry, Esq. 
Secretary to the Society for the Encouragement of Arts, 
Manufactures and Commerce*, 
19, John-street, Adelphi, Dec. 24, 1821. 
DEAR StR,—- You well know the many attempts that have 
been made to preserve iron and steel from rust, and the small 
success with which they have been in general attended. Greasy 
and oily, or resinous, substances have formed the basis of the 
different preparations proposed and employed for this purpose: 
but in the former, when raneidity comes on, an acid is produced 
which corrodes the iron; and the latter, when dry, are apt to 
crack, and thus afford an inlet to moisture, which, as soon as it 
has insinuated itself, begins to act on the iron, and to throw off 
the varnish in scales, on account of the enlargement of bulk 
which the particles of irou undergo when converted into oxide, 
Some time ago the thought occurred to me, that melted 
caoutchouc would be found to possess peculiar advantages in 
preserving the surface of iron from being acted on by the atmo- 
sphere; arising from its little susceptibility of chemical change 
when exposed to the air; from its treacly consistence under all 
ordinary temperatures; from its strong adhesion to the surface 
of iron or steel; and at the same time from the facility with 
which it is removed by a soft rag and a piece of stale bread. 
I accordingly made the trial, by procuring smail plates of iron 
and of steel, and smearing one half of their surface lightly over 
with the caoutchouc, and exposing them on a table in a labora- 
tory during the last five or six weeks. The result has been, that 
the portions of the plates covered by the caoutchouc have been 
preserved unchanged, while the unprotected. portions have been 
almost entirely corruded. The finger or a soft brush are the 
most convenient implements for applying the caoutchouc ; and, 
as soon as the article has been covered, it ought to be set up on 
end, in order that the excess may drain from it, which will take 
place in a day or two. 
The temperature for melting caoutchouc is nearly equal to 
that required for the fusion of lead; but if this is attempted to 
be performed in 2 pipkin, or any other open vessel, a copious 
emission of vapour will take place, the mass will become more 
or less charred, and is very likely to take fire. J therefore re- 
quested my friend Mr. P. Taylor, of Bury court, St. Mary Axe, 
to melt some for me in a close vessel; and this plan succeeded 
perfectly. The vessel employed on this occasion, was a kind of 
* From the Technical Repository, No. I. 
coppet 
