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. 



SEALING-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 les& 

 liable. 



BLACK 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 Tarnishes 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 thr 

 following possesses these qualities in a great degree : 



India-rubber drachm. 



Asphaltum 4 oz. 



Mineral naphtha 10 



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 

 asphaltura in mineral naphtha. The frequency with which 

 I have seen this solution thoroughly accomplished convince* 



