108 METHODS OF MICROSCOPICAL RESEARCH. 



oneself, the ordinary white oxide of zinc in drying 

 oil. The tube of zinc white is to be emptied into a 

 large bottle, and as much as possible of the oil to be 

 removed, by shaking up the white zinc in a con- 

 siderable quantity of benzol, and when the zinc has 

 settled to the bottom of the bottle, pouring it off. 

 A saturated solution of gum dammar in benzol is 

 to be made in another bottle, which should be 

 placed in a water bath, kept hot, until the gum 

 dammar is dissolved. "When this is accomplished 

 the solution of gum dammar is to be poured upon 

 the white zinc, the bottle thoroughly shaken up, 

 and the mixture strained through fine muslin. Now 

 add about half a drachm of best gold size to each 

 ounce of the solution. If too thin, allow the benzol 

 to evaporate until the cement becomes of a con- 

 sistency to flow smoothly and readily from the 

 brush if too thick, add benzol. This cement 

 should be kept for use in a capped bottle with a 

 wide mouth, and thoroughly stirred (not merely 

 shaken) up each time it is used. White zinc cement 

 properly made according to this formula, is tho- 

 roughly reliable and safe. It never cracks, will 

 stand ordinary wear and tear well, but not, of 

 course, rough usage. The author's experience is, 

 that no other white zinc cement than this is of any 

 value or permanency. Preparations intended for 

 use with oil immersion objectives must not be 

 finished with this cement, as the essential oils used 

 for immersion purposes at once attack and soon 

 destroy it. 



Cement for finishing preparations to be 

 examined with immersion objectives. 



Place five or six pieces of gum mastic, about the 



