156 



PREPAKATION OF ADHESION-PLATES. 



Should a projecting corner remain anywhere, as in fig. 109, n 

 move it with the flat pliers, by carefully breaking off little pieces < 

 glass, one after another, each not larger than about a millimetre. Tl 

 edges of the discs are then smoothed and rounded off upon a grim 

 stone, one person turning it, and another holding the edge of the di, 1 

 upon it, taking care to change often the points in contact with tl 

 stone, lest angles or curves should be produced. The whole breadt 

 of the stone should be used successively for grinding, or grooves w: 

 be produced in it, which render the stone useless. 



The plates are polished by being ground upon each other with emei 

 powder. One plate is fixed upon a small wooden board by drivii 

 three or four wire-pins into the wood, so placed that the plate res 



FIG. 109 ( real size). 



FIG. 110 (% real size). 



securely between them. The other plate is provided with a ban 

 consisting of a piece of stout sealing-wax, 2'5 or 3 cm long, whicl 

 fixed to it by heating the plate cautiously over the lamp, and press: : 

 the sealing-wax upon the heated plate. Sealing-wax will not adh ' 

 to metal or glass unless the latter substances are heated to the melt ; 

 point of the sealing-wax. A small portion of emery is placed u] ' 

 the fixed plate with a few drops of water. The moveable plate is n 

 moved upon the fixed plate with moderate friction, being turuet t 



