264 MANIPULATION. 



placed in a bundle, they will be found to be all of one size, 

 which would not be the case were any other plan adopted. 

 The small strips cut off from plate-glass, which are not large 

 enough for slides, should not be thrown away, as they will 

 be found very usef J in making cells or boxes. It will be 

 noticed that slides of three inches by one have- only been 

 spoken of in the preceding description, of course any other 

 sizes may be cut by the same process, by having rulers of the 

 requisite breadth. 



Edging the Slides. — All glass that has been cut with the 

 diamond will present a rough edge, to obviate this, and at the 

 same time to improve the appearance of the slide, the edges 

 must be ground smooth, this is done by rubbing them on a 

 perfectly flat plate of metal, with fine emery and water. As 

 one of these plates will be found of great use for other pur- 

 poses than that just mentioned, it will be as well here to speak 

 of the best form to be adopted. Several metals will answer 

 the purpose, but the best is a mixture of lead and pewter ; 

 cast-iron and brass, especially the former, will answer very 

 well, but lead is rather too soft ; in order to get the surface 

 flat, it may be planed, or, if the plate be not very large, three 

 of the same size should be procured ; they may all be kept per- 

 fectly true by a process well known to most mechanics, this is 

 nothing more than grinding one alternately against the two 

 others, and these two against each other, whereby a perfectly 

 flat surface may be always kept. If cast-iron be employed, 

 three plates, about seven or eight inches in diameter, will 

 answer the purpose exceedingly weU. The process of grinding 

 the edges consists in holding the slide in a vertical position on 

 the plate, and rubbing it either round and round, or else 

 backwards and forwards, until perfectly flat; if the edges 

 require to be bevelled, the slide must then be inclined at an 

 angle of 45° with the plate, and be rubbed in the same 

 manner. The emery should be fine, and the slide dipped in 

 clean water occasionally, and then wiped to see how the grind- 

 ing proceeds. To receive the excess of emery and water, 

 which is sure to escape over the side of the plate, a cloth may 

 be placed around it, or, what is best, is to have the plate 



