370 
Tin, 
Zinc was long ago recommended for the tinning of 
copper vessels, in preference both to the mixture of tin 
and lead, and to pure tin* : and zinc certainly has the 
advantage of being harder than tin, and of bearing a great- 
er degree of heat before it will be melted from the surface 
of the copper ; so that on both these accounts it would, 
when applied on the surface of copper, last longer than 
tin ; just as tin, for the same reasons, lasts longer than a 
mixture of tin and lead. But whether zinc makes any 
part of the compound metal for tinning copper, so as W 
prevent the necessity of repeated tinning, for which a pa- 
tent was granted some years ago, is what I cannot affirm* 
Whatever may be the excellence of that composition, or 
of any other composition, which may be invented with 
respect to its durability, and its not contracting rust ; still 
it ought not to be admitted into general use, till it has 
been proved, that it is not soluble in vegetable acids, or 
that its solutions are not noxious, f A method has of 
late years been introduced at Rouen , of applying a coat of 
zinc upon hammered iron sauce -pans. The vessels are 
first made very bright, so that not a black speck can be t 
seen ; they are then rubbed with a solution of sal ammo- 
niac, and afterwards dipped into an iron pot full of melted 
zinc, and being taken out, the zinc is found to cover the 
surface of the iron ; and if a thicker coat of zinc is want- 
ed, it may be obtained by dipping the vessel a second 
time. This kind of covering is so hard, that the vessels 
may be scoured with sand without its being rubbed off*4 
* Mem. de PAcad. des Scien. a Par. 1742. 
f This doubt with respect to zinc is said to have been removed. 
M. de la Planche, a physician at Paris, tried the experiment on 
himself: he took the salts of zinc, formed by the vegetable acids, 
in a much stronger dose than the aliments prepared in copper 
vessels, lined with zinc, could have contained, and he felt no dm- 
gerous effects from them. Fourcroy’s Chem. voL I. p* 442, 
| Journ. de Phy. Becera. 1778- 
