278 SILVERING. 



long, stroke it every way, that there be no crease 

 or wrinkles in it; then drop a little mercury upon it, 

 and with a piece of cotton, w^ool, or hair's foot, 

 spread it all over the foil, so that every part may 

 be touched with the mercur}-. Then, keeping the 

 marble slab nearly level with the horizon, pour the 

 mercury 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 silvered 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 sil- 

 vered, and have the paper also quite clean ; other- 

 wise, when you have drawn the paper from under 

 it, dull white streaks will appear, 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 mercuiy, 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 possi- 

 ble ; let it remain two days before you venture to 

 take it up» But before you take the weights offj 

 gently brush the edges of the glass, that no mer- 

 cury may adhere to them ; then take it up, and 

 turn it directly over, wuth 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. 



