ON CUTTING GLASS. 265 



fixed into a block of wood in the same manner as a hone. 

 If the edges require to be polished, after having been ground, 

 they may be rubbed upon a flat piece of wood covered with 

 buff leather that has been impregnated with putty powder, 

 water being used in the same manner as with the emery. If 

 a large quantity of slides be required, the process of grinding 

 will be facihtated by employing a lapidary's wheel or mill, 

 charged with emery ; the polishing may also be done in the 

 same apparatus by using a wooden wheel charged with putty 

 powder. If the slides be intended to be covered with paper, 

 the grinding of the edges may be dispensed with, as the paper 

 wiU hide all inequalities of surface. 



ON CUTTING THIN GLASS FOR C0VEE8, ETC. 



The thin glass employed to cover microscopical preparations 

 is manufactured only by Messrs. Chance, of Birmingham, it 

 may be procured of various degrees of thickness, from the 

 one-twentieth to less than the one-hundredth of an inch; being 

 unannealed, it must, on account of its brittleness, be handled 

 with care. For cutting it, the board described at page 262 

 for the thick glass may be used, or a smaller one, consisting 

 of a piece of mahogany about eight inches long, three broad, 

 and a quarter of an inch thick, with a raised edge, as repre- 

 sented at c. The lines e f g, va. front of the raised edge, 

 should also be present, to indicate the length and breadth of 

 two slides of the size most commonly used, and to form a 

 guide for cutting the covers. As it matters little if the covers 

 be not cut exactly of the same size, one narrow ruler will 

 generally suffice for all purposes. 



The diamond to be employed must be the writing one, 

 having a sharp point, but the pressure exerted ought to be 

 slight, as the thin glass, from not being annealed, is apt to 

 break with the slightest touch ; should the operator, however, 

 not be provided with a writing-diamond, the glass may be cut 

 with a plough-diamond by laying it on a piece of plate-glass 

 that has been wetted, a plan first adopted by Mr. Warington. 

 This will fill up all inequalities and cause an adhesion between 

 them, and, with a little care, the diamond-point will cut it. 



