MOUNTING AND PRESERVING OBJECTS. 61 



A solution of Canada balsam in ether or turpentine, evapo- 

 rated to such a consistence that it can be laid on with a camel' s- 

 hair pencil, may be used like the last described, as a substitute 

 for marine glue. 



Lampblack and white hard varnish, when laid on imme- 

 diately, is a good cement. Sealing-wax and white lead have 

 also been recommended. 



For the thin glass covers, a mixture of the gum mastich 

 cement, above described, with asphaltum dissolved in turpen- 

 tine, will be found very suitable. Dr. G-oadby recommends for 

 the same purpose, a mixture of equal parts of gold size and 

 asphaltum dissolved in camphene. This should be applied in 

 layers, which should be isolated from each other by coating with 

 a solution of gum arabic or of marine glue dissolved in white- 

 wood naphtha. The object of this isolation is to prevent the 

 cement from penetrating between the glasses. Some very 

 valuable preparations have been ruined from this cause. 



MOUNTING IN BALSAM. 



Before objects are mounted in Canada balsam they should 

 be perfectly clear and free from moisture. They are commonly 

 soaked in turpentine, especially opaque objects, as it renders 

 them more transparent. Grease may be removed by sulphuric 

 ether. 



Very thin and transparent objects become indistinct in bal- 

 sam ; they should be made dark. Vegetable matters may be 

 charred between two plates of glass over a lamp. Other 

 structures which cannot be charred, may be dyed by soaking 

 in a decoction of fustic or logwood, or a weak tincture of 

 iodine. 



The balsam should be warmed on the slide to expel the air. 



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