388 
Tin. 
that there be no creases or wrinkles in it, then drop a little 
mercury upon it, and with a piece of cotton, wool, or 
hair’s foot, spread it all over the foil, so that every part may 
be touched with the mercury. Then keeping the marble 
slab nearly level with the horizon, pour on the mercury 
all over the foil, cover it with a fine paper, and lay two 
Weights very near its lowest end or side, to keep the glass 
steady, while you draw the paper from between the silver- 
ed foil and the glass, which must be laid upon the paper. 
As you draw the paper, you must take care that no air 
bubbles be left, for they will always appear if left in at 
the first ; you must likewise be sure to make the glass as 
clean as possible on the side intended to be silverec^ and 
have the paper also quite clean, otherwise, when you have 
drawn the paper from under it, dull white streaks will ap- 
pear, which are very disagreeable. 
After the paper is drawn out, place as many weights 
upon the glass as you conveniently can, in order to press 
out the superfluous mercury, and make the foil adhere to 
the glass. When it has lain six or seven hours in this 
situation, raise the stone about two or three inches at its 
highest end, that as much of the mercury may run off as 
possible ; let it remain tw 7 o days before you venture to 
take it up ; but before yo\i take the weights off, gently 
brush the edges of the glass, that no mercury may adhere 
to them ; then take it up, and turn it directly over, with 
its face side downward, but raise it by degrees, that the 
mercury may not drip off too suddenly ; for if, when 
taken up, it is immediately set perpendicular, air will get 
in between the foil and the glass at the top, as the mercury 
descends to the bottom ; by which means, if you be not 
exceedingly careful, your labour will be lost. 
Another method, is to slide the glass over the foil, 
without the assistance of paper. 
