198 PRACTICAL MICROSCOPY. 



The balsam is then to be rendered fluid again, and the 

 polished section made gradually hot, when it is let down 

 gently, taking care to avoid air bubbles, pressed down 

 firmly and then put aside to set thoroughly. After several 

 days, the rough side may be ground down on the leaden 

 lap with emery, and finished off on the brass lap with the 

 finest emery. The slide is now finished off by cleaning 

 with spirits of wine and a camel's-hair brush, then dropping 

 some fluid balsam upon the centre of the section and 

 covering in the usual way with thin glass. If the glass of 

 the 3 X I -inch slide be disfigured with scratches it may be 

 covered with an ornamental cover-paper, sold by Wheeler 

 and other dealers in microscopic specialities. The fore- 

 going method will produce good results for almost any 

 kind of work ; but of course there are simpler methods 

 which may suit the student, requiring however much more 

 labour. One of our friends grinds down roughly upon a 

 grindstone or emery wheel, and finishes upon an Arkansas 

 oil-stone. It is rather tedious work, but produces good 

 results. 



Mr. J. H. Jennings gives the following simple instruc- 

 tions : 



I. Preparing sections of hard rocks : In the first place a 

 thin chip must be procured by the use of a hammer. This 

 chip should be about I inch square, and not more than 

 \ inch thick ; chips of sedimentary rocks may be thicker. 

 Rub the chip down by hand with emery and water on an 

 iron plate, until one side is perfectly flat. To remove 

 scratches, next rub the chip on a glass plate with fine 

 emery, and polish on a Water-of-Ayr stone ; when quite 

 smooth, wash it well and let it dry. Meantime place 

 some old balsam on a glass slip, and warm it over a lamp 

 until all the more volatile parts of the balsam evaporate, so 

 that on cooling it becomes hard and tough. Do not let the 



