48 PREPARATION AND MOUNTING 
cover and partly on the slide, hiding the junction of the two. 
The medium used in these cases I term A VARNISH, and 
hereinafter mention one or two. Of course, the tenacity is 
not required to be so perfect as in the cements. 
Sratinc-Wax VARNISH is prepared by coarsely powdering 
sealing-wax, and adding spirits of wine; it is then digested 
at a gentle heat to the required thickness. This is very 
frequently used to finish the slides, as before mentioned, 
and can easily be made of any colour by employing different - 
kinds of sealing-wax; but is very liable to chip and 
leave the glass. The best qualities, however, will be less 
hable. 
Buack VarnisH—Is readily prepared by adding a small 
quantity of lampblack to gold-size and mixing intimately. 
Dr. Carpenter recommends this as a good finishing varnish, 
drying quickly and being free from that brittleness which 
renders some of the others almost worthless; but it should 
not be used in the first process when mounting objects in 
fluid. 
Amongst these different cements and varnishes I worked 
a long time without coming to any decision as to their 
comparative qualities, though making innumerable experi- 
ments. The harder kinds were continually cracking, and 
the softer possessed but little adhesive power. To find 
hardness and adhesiveness united was my object, and the 
following possesses these qualities in a great degree :— 
India-tabber : A<sscucee 3 drachm. 
Asphaltam ...22 0.500. 4 oz. 
Mineral naphtha ...... 10 <5 
Dissolve the india-rubber in the naphtha, then add the 
asphaltum—if necessary, heat must be employed. 
Some scientific friends have complained that they have 
been unable to dissolve either the india-rubber or the 
asphaltum in mineral naphtha. The frequency with which 
I have seen this solution thoroughly accompiished convinces 
