CEMENTING. 247 



The solution of mastic should be nearly saturated. 



2. Oxide of Zinc, Dammar, and Drying Oil. Bub up 

 well-ground oxide of zinc, 2oz., with drying oil, to the 

 consistence of thick paint. Then add an equal quantity 

 of gum dammar, previously dissolved in benzoline, and 

 of the thickness of syrup. Strain through close-meshed 

 muslin. Keep in well-corked bottle, and, if necessary, 

 thin with benzoline. 



3. Kitton's Cement is made of white lead and red 

 lead in powder and litharge powder in equal parts. 

 Grind together with a little turpentine, until tho- 

 roughly incorporated, and then mix with gold size. 

 The mixture should be thin enough to use with a 

 brush; in- using one coat should be allowed to dry 

 before applying another ; no more cement should be 

 mixed with the gold size than is required for imme- 

 diate use, as it sets quickly, and becomes unworkable. 



Certain precautions are necessary to be observed in 

 using varnishing fluid or glycerine preparations : 



1. Use no more glycerine or fluid than is just neces- 

 sary to fill up the space beneath the cover. 



2. If the medium should escape beyond the cover- 

 glass, soak it up with a piece of blotting-paper, and ba 

 careful not to press the cover, or the cement will run 

 into the cell. 



Of preservative mounting media, the most useful 

 are balsam, glycerine, and glycerine jelly. 



Canada balsam should be exposed to heat until it 

 becomes quite brittle when allowed to cool, then it 

 should be dissolved in benzole till as thin as glycerine, 

 and should always be used cold. 



Glycerine. Specimens which have been hardened 

 in chromic acid or bichromates may be mounted in 

 pure glycerine alone, but if they have been hardened 

 in spirit, glycerine and carbolic acid, in the propor- 

 tion of glycerine fifteen parts to carbolic acid one 

 part, is better, as it is less refractive, and prevents tho 

 sections becoming granular. For carmine stained 

 preparations it is well to add a trace of acetic acid 

 to the glycerine (2m., loz.). Glycerine jelly is a good 

 medium, as it offers the advantages of glycerine with- 



