46 THE MICROSCOPE AND HOW TO USE IT. 



Certain precautions are necessary to be observed in using 

 varnishing fluid or glycerine preparations : — i. — Use no more 

 glycerine or fluid than is just necessary to fill up the space 

 beneath the cover. 2. — If the medium should escape beyond the 

 cover-glass, soak it up with a piece of blotting-paper, and be 

 careful not to press the cover, or the cement will run into the cell. 



Many students find the white zinc has run under the covers in 

 course of time. The only remedy I believe is to wash off and 

 clean with benzole ; then slightly warm the slide and lift off the 

 cover-glass. I believe it results from not using a varnish previous 

 to the white zinc. A friend of mine recommends two coats of 

 " painters' knotting " before laying on the coloured rings, and has 

 seldom a slide spoiled. 



Smith's New Cement. — This is especially adapted for slides 

 mounted in the stannous chloride mounting medium. It is made 

 by diluting a somewhat thick shellac cement with benzole, and 

 adding sufficient litharge to give a consistency about the same as 

 the white zinc cement. It dries very quickly, forms very hard 

 rings, and it becomes dark-brown on exposure. A thin coat 

 should first be applied, and when this is well dried add as many 

 more as required. 



Strong Cements for attaching Brass Cells to Glass Slides.— 



(1) Carbonate of lead, | oz. ; red oxide of lead, | oz. ; litharge, 

 1 1 oz. Grind thoroughly together in a mortar. Stir some of this 

 into enough gold-size to make it work stiffly. If too much 

 adheres to the work, turn it off on turn-table when a little set. 



(2) Best quality gum-arabic. Dissolve in cider-vinegar; add a 

 little sugar. 



Mucilage for Slide Labels. — Dissolve 2 oz. dextrine in i oz. 

 acetic acid, diluted with 5 oz. water; when dissolved, add i oz. 

 alcohol. This is the same as that used for postage-stamps. 



Literary. — The Shell-collector's Handbook for the Field, by 

 J. W. Williams, M.A., D.Sc, Editor of The Naturalisfs Monthly, 

 giving directions as to the collecting and preserving of British 

 Land and Fresh-Water Shells, and describing the habitat of each. 

 This volume will be iniblished immediately by Messrs. Roper and 

 Drowley of Ludgate Hill, and will give full details of every genus, 

 species, and variety known to the Conchological Society up to 

 date of publication. 



