74 
recommend, but another solvent, viz., benzole, which he had used for 
some time. Since employing it as a solvent his views of its value had 
been confirmed by what Dr. Bastian had written in the Monthly 
Microscopical Fournal. Canada balsam, when thinned by the admix- 
ture of benzole, dried rapidly, and 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 that if he blended white lead with balsam he 
should obtain a trustworthy cement. Taking, then, Canada balsam 
and white lead he had experimented and produced the results he had 
handed round. He had found the greatest difficulty in re- 
moving a covering glass fastened by this medium, and the specimen of 
two pieces of glass united by it showed how tenacious it was. There 
was an additional advantage in this cement, it would take any colour, 
viz., such pigments as were used by the colourmen in making paints. 
His mode of operation in making the cement was to rub down with 
a spatula, on a piece of glass used asa slab, white lead with balsam 
thinned with benzole until it was thin enough to run freely with a 
brush. For a thicker cement more lead should be added. To obtain 
the coloured rings seen on some of the slides, the powdered pigment 
obtainable at the painter’s had been rubbed down in the same way. 
If colour, or the addition of an insoluble substance was objected to, 
then balsam, thinned with benzole, could be used alone. In the 
majority of the slides he had prepared, he had put the white over the 
old mountings, and then added the coloured rings. They dried very 
quickly, and acquired a high polish. Some other balsams or resins 
might be found which would do as well, but he preferred Canada 
balsam, because it was easy of working and of great durability, while 
the white lead gave it body, firmness, and drying properties. Some 
might think the subject trivial ; but when we heard on all hands of 
spoilt slides from using untrustworthy cements, any thing likely to give 
them a secure cement was worth consideration. 
Mr. P. C. SMITH mentioned, in illustration of the untrustworthi- 
ness of gold size, thickened with litharge, that Jenner had spent 
almost a life time in preparing diatoms and desmids, using litharge 
with gold size to make his cells. At his death the whole collection 
was worthless. 
In reply to a question from the Chairman (Mr. SEWELL), Dr. 
