The Microscope. 23 



meet with in the books devoted to the use of the microscope, 

 and it is for m;iny purposes one of the best, if properly made, 

 and one of the worst if not properly made. It cannot be pre- 

 pared at home, but must be always bought. Its composition is 

 asphalt, linseed oil (as a dr3'er), a little India rubber to reduce 

 its proneness to crack, and turpentine. It dries readily, with 

 a gloss}' black surface that is exceedingly attractive, and is 

 in man}' ways the best cement for general use in making cells, 

 although for finishing the slide it has one tendency which makes 

 it obnoxious. By the addition of turpentine, if it gets too thick, 

 it can be made to flow reaililj' from the brush, and, man}- micro- 

 scopists to the contrary' notwithstanding, it does not readily 

 crack, nor easily separate from the glass. It is a trustworthy 

 cement, but that fatal tendency of running under the cover is 

 an objection that must be remembered. According to my experi- 

 ence, Brunswick black will run under rather easier than any other 

 cement, except, perhaps, zinc white, to be considered hereafter. 



For making cells of moderate depth it is excellent, and if the 

 worker will give the cell a thin coat just before he is ready to 

 appl}" the cover glass, and after he has the object ready for that 

 application, he can gently force the cover into the fresh layer so 

 that when it is dry additional coats may be applied without risk. 

 But to place the cover on the cell that is entirely dry and then 

 to add the cement as a finish, is to invite disaster in the form of 

 the running under of the black liquid, and the disfiguring of the 

 mount if not its destruction. It is pleasant to w^ork with, as it 

 dries rapidly and presents so beautiful a surface, but it must be 

 used with its perverse character always in mind. In making 

 cells with it the brash may be well filled, if the cement is in 

 good condition and not too thick, and the ring made at one 

 sweep, but when fastening down the cover it is better to use a 

 brush but slightly charged with the cement, and to add several 

 coats in succession. In this way it may be mastered, and the 

 result will be pleasing. If well made it will not crack nor allow 

 the cell to leak ; yet here, as with other cements, it is well for 

 the microscopist to look over his cabinet ©f slides at least once 

 a 3^ear, and to give a fresh coat to those that seem to be in need 

 of it. Good slides may thus be kept in good condition, while 

 weak ones may be treated and saved from total extinction. 



Objections have been made against the method of applying a 



