78 THE MICROSCOPE. ier 
COPAL CEMENT. 
W. Z. DAVIS. 
T THE last meeting of the American Society of Microscopists 
Dr. F. L. James made some remarks in regard to a clear copal 
varnish made by himself. The substance of Dr. James’ remarks was 
recently published in the Microscopical Bulletin. He disclaims entire 
originality in his formula. 
As I have for some time, before I knew of the process of Dr. 
James or any other person, used a copal cement and varnish made 
by myself, I give to the readers of Tue Microscope the result of 
my numerons experiments, although I have never been at the pains 
to reduce it to an exact formula. 
Take best clear copal gum coarsely pulverized, and mix with a 
sufficient quantity of benzol to cover it, and let stand for twenty- 
four hours. The benzol will not dissolve the gum, but is a valua- 
ble aid in making a perfectly clear varnish. Take of chloroform 
twice as much as the benzol and dissolve in it enough gum camphor 
to saturate the chloroform, and then add a small quantity of pale 
linseed, nut, or poppy oil. The quantity of oil will vary, as a quick 
or slow-drying cement is desired. If no oil, or a very small propor- 
tion, is added, the cement will dry very quickly. A larger quantity 
- of oil makes a slow-drying preparation of much greater toughness. 
Next add this mixture to the copal and benzol, shaking at intervals 
for several days, until as large a quantity as possible of the gum has 
been dissolved. Pour off, filter, and evaporate to any desired 
consistency. 
This makes a perfectly transparent and colorless cement, useful 
both as a finishing varnish and for cell building. It adheres exceed- 
ingly well to glass, especially if the glass is warm when the first 
coat is applied. I have block-tin cells so firmly fixed to the glass 
by it that it seems scarcely possible to push or jar the cell from its 
place without breaking the glass. Cells built up entirely with the 
cement are as colorless as the glass itself, and when thoroughly seas- 
oned, as all cells should be, are handsome, durable and of as wide a 
range of usefulness as any material known, not excepting gold size. 
I formerly used ordinary copal varnish, diluted with equal parts 
of benzol and chloroform, and after standing some time in bottle, 
with animal charcoal (in small lumps) filtered through paper. This 
varnish has a little color when used cold, and when a cell made of it 
is slightly heated on the slide it becomes of an amber color. 
