94 C. F. ROUSSELET ON SOME MICRO-CEMENTS FOR FLUID CELLS. 



A cement that has been specially recommended to me is a 

 mixture of two third parts of gum damar dissolved in benzole, 

 and one third coach builder's gold size. This has undoubtedly 

 very good qualities ; it flows readily from the brush, is very adhesive 

 to glass, and makes a perfect joint between the cover-glass and 

 slide. The water or solution of formalin in the cell has no effect 

 upon it. On the other hand I have been warned against the use 

 of gum damar, because when its solvent is all evaporated it can 

 be scraped off as a white powder ; but the admixture of gold size 

 modifies this property considerably. Gold size alone has long 

 been known as a good cement, and I have been recommended by 

 a maker to use the variety known in the trade as " Extra Stout," 

 which is not so liable to run in, and which never becomes abso- 

 lutely hard and dry, and when scraped comes off in strings. Pure 

 gold size, however, does not adhere so strongly to glass as when 

 mixed with gum damar. The solvents of gum damar and gold 

 size are benzole and turpentine, and it has been suggested to 

 me by Dr. Measures that the evaporation of the last trace of 

 these solvents might be prevented by covering the gold size with 

 a ring of another cement, having a purely alcoholic or naphtha 

 solvent. 



Such a cement is Ward's brown cement. In some respects 

 this cement resembles Miller's caoutchouc cement, but it contains 

 no caoutchouc and is more finely grained and better in quality ; 

 it dries with a fine gloss, never cracks, and is not attacked by 

 benzole or turpentine ; its composition is not known, and its best 

 solvent is a mixture of wood naphtha and methylated spirit. 



Taking all these considerations into account, I have of late 

 sealed my fluid cells, which are hollows ground out in the glass 

 slip, containing mounted Rotifers, as follows : — First I close the 

 cell with the gum damar and gold size cement, which fixes the 

 cover-glass firmly to the slide ; when this is dry I put on a ring of 

 the pure gold size, and when that is dry a third ring of Ward's 

 brown cement, taking care that each succeeding coat slightly 

 overlaps the previous ring. 



In this way I hope and trust that my slides may remain per- 

 manent, but it will take years of experience before a definite 

 judgment can be pronounced. 



A few days after reading the above paper, Mr. F. Hughes was 



