PROCEEDINGS OF SOCIETIES. 155 



similar in appearance, and, lie believed, perfectly trustworthy. It had 

 been produced by mingling with Canada balsam different pigments ; 

 and if it were urged that the addition of litharge to gold size made it 

 less trustworthy, it should be borne in mind gold size was an oily 

 preparation, while Canada balsam was not. 



Canada balsam, by long experience, had been found to be the 

 simplest, purest, most manageable and best working of all the media 

 in which to mount objects ; and if, at the same time, it could be made 

 to work with a brush, it then could be utilized as a cement. 



Canada balsam was known to be soluble in various substances, 

 such as ether, chloroform, and turpentine, none of which, from various 

 reasons, he should recommend ; but there was another solvent, which 

 he had used for some time, viz. benzole. Since employing it as a 

 solvent, he had found that Dr. Bastian had spoken very highly of it in 

 the pages of the ' Monthly Microscopical Journal.' When thinned 

 by the admixture of benzole, it dried rapidly ; it also readily mingled 

 with insoluble substances ; in fact, formed paints. 



Bearing in mind that lead was used in the manufacture of paints, 

 and that white-lead was the basis of some cements for repairing 

 china and glass, he thought, if he blended white-lead with balsam 

 he should obtain a trustworthy cement. Taking, then, Canada balsam 

 and white-lead as the basis of his experiments, he had produced the 

 results he had handed round. So tenacious was it that he had found 

 the greatest difficulty in removing a covering glass fixed by this 

 medium, and the specimen of two pieces of glass united by its means 

 showed its tenacity. There was one additional advantage in this 

 cement, it would take any colour, viz. such pigments as were used by 

 the colourman in making paints. 



His mode of operation, in making the white cement, was to rub 

 down, on a piece of glass, used as a slab, white-lead with Canada balsam, 

 thinned with benzole, until it would run freely with a brush. For a 

 thicker cement he added more lead. To obtain the colour seen on 

 some of the slides he had rubbed down, in a similar way, the powdered 

 pigments obtainable at any colourman's. If some objected to colour, 

 or the addition of an insoluble substance, then balsam thinned with 

 benzole could be used alone. In many of the slides exhibited he 

 had put the white cement over old mountings and then added the 

 coloured rings. He found the cement and varnish dried quickly and 

 acquired a high polish. Other balsams or resins might be found 

 which might do as well, but he preferred Canada balsam, because it 

 was very durable and worked easily ; the white-lead gave it body, 

 firmness, and drying properties. 



Some might think the subject trivial, but when one heard on all 

 hands of spoilt slides, through the use of untrustworthy cements, any- 

 thing likely to turn out a secure cement was worth consideration. 



Mr. C. P. Smith mentioned, in illustration of the untrustworthi- 

 ness of gold size thickened with litharge, that Jenner had spent 

 almost a lifetime in preparing diatoms and desmids, using gold size 

 thickened with litharge as a cement. At his death the whole col- 

 lection was found to be worthless. 



