391 
Tin , . 
(as it is called)* an operation effected by means of an a- 
malgam. The tin leaf employed must be of the size of 
the glass, because, when pieces of that metal are united 
by means of mercury, they exhibit the appearance of 
lines. Tin is one of those metallic substances which be- 
come soonest oxydated by the means of mercury. If there 
remains a portion of that calx, of a blackish gray colour, 
on the leaf of tin, it produces a spot or stain in the mir- 
ror, and the part where it is cannot reflect objects pre- 
sented to it : great care, therefore, is taken in silvering 
glass to remove the calx of tin from the surface of the 
amalgam. 
The process is as follows The leaf of tin is laid on 
a very smooth stone table, and mercury being poured 
®ver the metal, it is extended over the surface of it by 
means of a rubber made of bits of cloth. At the same 
moment the surface of the leaf of tin becomes covered 
with blackish oxyd, which is removed with the rubber. 
More mercury is then poured over the tin, where it re- 
mains at a level to the thickness of more than a line, 
without running off. The glass is applied in a horizon- 
tal direction to the table at one of its extremities, and 
being pushed forwards it drives before it the oxyd of 
tin which is at the surface of the amalgam. A number 
of weights are then placed on the glass which floats on 
the amalgam, in order to press it down. Without this 
precaution the glass would exhibit the interstices of the 
crystals resulting from the amalgam. These crystals have 
the form of large square laminae irregularly disposed. 
To obtain leaves of tin, which are sometimes six or 
seven feet in length, with a proportionate breadth, they 
are not rolled but hammered. The prepared tin is first 
cast between two plates of polished iron, or between two 
smooth stones not of a porous nature, such as thunder 
stone. Twelve of these plates are placed over each other; 
