220 



SELECTION AND USE 



WATER BATH. A water bath is indispensable in those cases 

 where a certain very moderate degree of heat is not to be ex- 

 ceeded. Few persons fully appreciate the difficulty of regu- 

 lating or even estimating the temperature of an object held over 

 a naked flame, and mischief is often done before the operator 

 is aware of it. A serviceable water bath is easily extemporized 

 out of an old fruit can and a small beaker glass. This serves 

 for exposing material and preparations to a temperature lower 

 than that of boiling water. Where slides are to be so heated, 

 the simplest contrivance is a flat tin box, with all the joints 

 (cover and all, of course,) tightly soldered. A small tube, 

 closed with a cork, serves to admit the water. 



SPEING CLIPS. One of the first of the needs which impress 

 themselves upon the mind of the beginner, is the necessity foi 

 something to retain the thin cover in its place, until the ce- 

 ment, which is intended to hold it permanently, dries. An end- 

 less variety of spring clips have been invented for this purpose, 

 but we have never seen anything that we liked better than the 

 simple article shown in Fig. 73, and which we have used for 



Fig. 73. 



over fifteen years. It consists simply of a piece of brass wire 

 bent as in the engraving. The slide being held in the left 

 hand, the clip, held by the upper wire, is brought so that the 

 projecting part of the ring is placed under the edge of the 

 slide. The upper part is then lifted up so as to open the clip, 

 which is then slid on to the slide until the vertical point is in 

 the right position. When a broader surface than the point of 

 the wire is needed, a piece of cork may be stuck on it, and if 



