394 
fin 
I in . 
with nitric acid, which attacks and oxy dates the tin, I 
washed the mercury and strained it through a piece of 
linen. In this state it may be employed for gilding, but 
when it contains the smallest quantity of tin it stains the 
articles. 
What I have related in this memoir shows that red 
oxyd of iron, known under the name of colcothar, is not 
proper for polishing glass when it contains vitriol; that 
the tin employed for silvering mirrors contains lead and 
iron ; that when this tin is separated from the mercury by 
distillation this metal crystallizes with the greatest facili- 
ty and without any precaution ; and, in the last place, it 
is shown that a portion of tin is volatilized by the mercu- 
ry during the distillation of the amalgam, and that it can- 
not be separated but by the nitric acid. 
[22 Phil Mag . 113. 
To whiten Copper , Brass , or Iron Wire . 
Pins are whitened thus. Tin is reduced into a kind 
of powder, by first melting it, and pouring it out into an 
iron mortar, bruise it fine just at the moment as it is set, 
and while still hot — or take grain tin, and granulate it by 
pouring it through a birch broom into water. The tin 
thus granulated, is put into a boiler with the brass or cop- 
per wire to be whitened, and boiled with alum and crude 
tartar, or argol. I do not know the exact proportions, 
but in this manner the wire is penetrated by the tin. One 
part tartar, two parts by weight alum, and as much com- 
mon salt, will succeed. T. C. 
It is not necessary to employ this mixture of salts for 
the mere tinning of copper or brass. Either of these three 
salts singly with tin filings will answer the purpose, but 
cream of tartar gives a duller and more leaden looking 
tinning, and alum on the other hand gives a very fine sil 
