44. THE MICROSCOPE 



American Cement (Dr. Hunt). — Take some zinc white, as sold 

 for painters' use, drain off the oil, and mix with Canada balsam, 

 dissolved very thin with chloroform. If it does not flow freely 

 from the brush, add a little turpentine. The mixture should be 

 about the thickness of cream and kept in a bottle with a glass 

 cap. Ring the slide with the cement, and paint on it with artists' 

 oil colours, thinned if necessary with turpentine, and when dry 

 varnish with very dilute balsam, to give it a gloss. 



Liquid Cement. — Compound tragacanth powder and powdered 

 gum acacia from any chemist, and if these are well mixed in 

 equal parts and moistened according to requirements at the time 

 with dilute acetic acid, or, if the colour be not of any importance, 

 with ordinary vinegar, a strong and lasting cement will be 

 obtained. 



"White Hard Varnish consists of gum sandarac dissolved in 

 spirits of wine, and mixed with turpentine varnish. 



Zinc White is composed of benzole, 8 parts ; gum dammar, 8 

 parts ; oxide of zinc, i part. Mix the gum dammar and the 

 benzole, filter through cotton wadding, after which mix in the 

 oxide of zinc in a mortar, and again filter through the wadding. 



Gelatine Cement.— For sections mounted in glycerine, undoubt- 

 edly the best method is Dr. Marsh's,* who suggests gelatine 

 solution as a cement for first fixing the slide. The reason for this 

 is that gelatine readily mixes with the glycerine in its immediate 

 neighbourhood. He prepares the solution by placing a small 

 quantity of gelatine in a narrow glass beaker, covering it with 

 water, and allowing the gelatine to take up as much of the water 

 as it will. Any superfluous water is poured off, mixture heated, 

 and three or four drops of creosote are added to each ounce of 

 the fluid. Keep in a small bottle, and each time that the mixture 

 is needed it is " rendered fluid by immersing the bottle containing 

 it in a cup of warm water." The slide must be perfectly freed 

 from glycerine by the aid of a camel-hair pencil and a damp 

 cloth. A ring of the gelatine fluid is painted round the edge of 

 the cover-glass. As soon as this is set, paint it over " with a solu- 

 tion of bichromate of potash, made by dissolving lo grs. of that 



* Dr. S. Marsh's " Section-Cutting, etc.," 2nd edition. 



