Tin. 
371 
Kitchen utensils, which are made of cast iron, are usually 
tinned to prevent the iron’s rusting ; and, as great im- 
provements have been lately made in rendering east iron 
malleable, it is not unlikely, but that tinned iron vessels 
may become of general use. 
The common method of tinning, consists in making 
the surface of the copper vessel quite bright, by scraping 
it, and by washing it with a solution of sal ammoniac ; it 
is then heated, and the tin, or metallic mixture designed 
for tinning, is melted, and poured into it, and being made 
quickly to flow over every part of the surface of the vessel, 
it incorporates with the copper, and, when cold, remains 
united with it. Rosin or pitch are sometimes used, to 
prevent the tin from being calcined, and the copper from 
being scaled, either of which circumstances would hinder 
the sticking of the tin. 
I had the curiosity to estimate the quantity of pure tin, 
which is used in tinning a definite surface of copper. The 
vessel was accurately weighed before and after it was tin- 
ned, its surface was equal to 254 square inches; its 
weight, before it was tinned, was 46 ounces, and its 
weight, after the operation, was barely 46 1-2 ounces ; so 
that half an ounce of tin was spread over 254 square inch- 
es, or somewhat less than a grain of tin upon each square 
inch. How innocent soever pure tin may be, yet the te- 
nuity of the coat of it, by which copper vessels are co- 
vered, in the ordinary way of tinning, cannot fail to ex- 
cite the serious apprehensions of those who consider it ; 
for in the experiment which I have mentioned, the tin was 
laid on with a thicker coat than in the common way ; 
instead of a grain, I suspect that not a quarter of a grain 
of tin is spread over a square inch in the common way of 
tinning. A discovery has been lately made at Paris of^a 
method of giving to copper or iron a coat of any required 
thickness, by tinning them ; the composition used for 
Vox. III. Zz 
