80 THE AMERICAN MONTHLY [Mar 



things, you may not be able to do this nicely the first time. 

 I have done thousands of slides in this way. 



It must be borne in mind that slides on which balsam 

 and benzole is used never get hard all through. This is 

 an advantage, as should a slide fall, the object is not lia- 

 ble to fly off as in the case of old balsam mouijts, for the 

 balsam gets brittle by age. 



Caoutchouc Cement, for Making and Sealing Cells. 



To Turn Cells. — Centre the glass slide on the turn- 

 table, and with a sable-hair brush charged with sufficient 

 cement, mark off the foundation of the cell in width and 

 size required, the turn-table being somewhat rapidly re- 

 volved. Dip more cement and apply directly, before the 

 first layer can set, and so on, always touching the top of 

 the stream only, until the cell be raised to the height 

 desired. Then lay the slide aside in a level position to 

 dry. Slight cells dry in a few hours, deep cells, say 1-8 

 of an inch in two or three days. Keep the bottle tightly 

 corked. 



The brush may be cleansed with some alcohol. Before 

 uncorking the bottle for use, always give it a sharp shake, 

 and turn it over so as to mix the apparently thickened 

 surface of the cement with the bottom contents. In the 

 case of the cement becoming absolutely thickened by ex- 

 posure or neglect, a small quantity of spirits of wine (not 

 methylated) will fairly restore it ; but a diluting fluid is 

 sold in a very cheap form, a few drops only of which ad- 

 ded will improve the working quality of it to the last 

 drop in the bottle. It is always better to turn a few do- 

 zen cells at the time in the various sizes for circles usu- 

 ally preferred, and to lay them out to dry, exposed to 

 the air until required for mounting purposes. 



To Mount Ob.tcets in Gtlycerine, Oil, Canada Balsam 

 OR Other Fluids. — Take a cell perfectly dry, apply or 

 turn a sufficient layer of this cement round the top of the 



