740 SUMMAEY OF CUERENT RESEARCHES RELATING TO 



is, to take the brusli along in one sweep. The cement falls from the 

 brush as one proceeds, and it is easy to see when enough has been 

 applied. While taking care to have sufficient cement to fill up the 

 angles, the aim should be to have as narrow a line as possible around 

 the edges of the preparation. The slide is now set aside for twelve 

 or twenty-four hours, when the layer of cement will have become 

 tough, and will be found to hold the cover effectively in its place. 

 The slide is now put into water, to wash off all trace of glycerine, and 

 is afterwards set on end to drain and dry. A ring of gold-size or 

 other cement may afterwards be applied in successive layers, and in 

 due time, when all is firmly set, a finishing layer of white cement or 

 of asphalt. 



Mounting Objects "Opaque" in Balsam.*— Mr. E. "Ward calls 

 attention to the fact that there are some few objects which, although 

 too opaque for transmitted light, are yet more beautiful, if mounted 

 in balsam, than when dry. This is most apparent in the various parts 

 of some diamond beetles, such as the genera of Entimus and Cyphus. 

 In the old days, when paper-covered slides were much in vogue, this 

 kind of preparation was readily made, it being only necessary to paint 

 the slide at the back with black varnish, which was protected by the 

 covering paper; but when it was seen how much better appearance 

 the slides presented if uncovered, but neatly ringed, it was found a 

 more difificiilt matter to get this same opacity for balsam mounts, as if 

 the opaque varnish was placed inside the cell it was frequently dis- 

 solved by the balsam, and if painted on the under side, it almost 

 always became unsightly through being rubbed, offending those who 

 care for the neatness of finish of their slides. 



Mr. Ward has succeeded in producing a black which can be used 

 with safety under the cell, and which he has given plenty of trial ; 

 the process being moderately easy, and the materials to the hands of 

 almost every worker. 



Having affixed to the glass slip, by means of the brown cement 

 originally introduced by the author, a metal cell of sufficient depth 

 (and it is absolutely necessary that it be quite as deep as the object to 

 be mounted, or the after process will be more difficult), allow this to 

 dry, and then paint the inside of the cell on the glass with a black 

 varnish made by adding lamp-black to brown cement. This black 

 varnish should only be made as required, and for a small quantity it 

 is only necessary to put a few drops of brown cement into a watch- 

 glass, and stir in with a camel-hair brush a small quantity of the 

 black ; this brush will also do for the painting of the cell. 



The varnish having been painted in, the cell will dry in an hour 

 or so, particularly if put in a moderately warm place ; and though the 

 surface will be very granular, this granulation will not interfere with 

 the after result. 



The elytron, or other object, may now be fastened down to the 

 cell-button with gum or brown cement, and when dry, the cell should 

 be filled with benzole, which will penetrate every crevice and nook. 



* Micr. News, iii. (1883) pp. 197-8. 



