CEMENTING. 221 



results. No more should be dissolved than can be 

 used up, as after solution the light spoils it, and gives 

 it colour. Vegetable tissues, foraminifera, the palates 

 of moluscs (the latter, after boiling in liquid potash, 

 and washing in water to remove all traces of alkali), 

 may be immersed in carbolic acid. If it be wished to 

 mount them foi-thwith, then place the specimen, after 

 washing in a glass slip, and drop one or two drops of 

 acid upon it. Should it appear to be thick or cloudy, 

 warm the slide over a spirit lamp ; set it aside to get cool, 

 and drain away the acid, or remove it with blotting- 

 paper. If not perfectly clear add another drop or two 

 of fresh carbolic acid and again warm it ; place a cover- 

 glass over it, remove as much of the acid as possible, 

 and then let a drop of fluid Canada balsam run under 

 the cover to take the place of the acid. Gently 

 warming the slide will facilitate this operation. A 

 number of specimens may be put into a test tube with 

 the carbolic acid solution and boiled for a few minutes, 

 corked up tightly, and put aside for mounting at leisure, 

 either in balsam or dammar. When the balsam becomes 

 too thick, it can be rendered fluid by adding either 

 benzoline or chloroform. 



Dammar varnish for cementing the cover-glass is 

 prepared as follows : 



Take of gum dammar, 1 oz. ; spirits of turpentine, 

 1 oz. ; dissolve by gentle heat : then take gum mastic, 

 1 oz. ; chloroform, 2 oz. ; dissolve without heat, and, 

 having filtered out all impurities, mix the two solutions 

 together by shaking. 



Method of Cementing. After many years' experience, 

 I have arrived at the conclusion that for cementing 

 down the cover-glass, there is nothing better than either 

 gold size or gum dammar varnish. The latter, for 

 some preparations, will be improved by the addition 

 of a small proportion of india-rubber dissolved in 

 naphtha. Whichever is used, it should be applied 

 with care and some skill. The brush should be held 

 nearly in the upright position, and the turn-table spun 

 round rapidly, so that the gold size may form a warm 

 ring round the outside of the cover-glass. After the 



