WITH THE MICROSCOPE. 49 



any oil-shop, and forms a most useful cement, both for making very 

 thin cells, and also for fixing on the thin glass covers. If a little solu- 

 tion of India-rubber in mineral naphtha be added to it, there is no 

 danger of the cement cracking when dry. For this hint I have to 

 thank my friend, Mr. Brooke. I have many preparations which 

 have been cemented with Brunswick black which have been kept 

 for upwards of ten years. It is always desirable, however, to paint 

 on a new layer from time to time, perhaps once in twelve months. 



Common Brunswick black is made by melting one pound of 

 asphaltum, and then adding half a pound of linseed oil, and a quart 

 of oil of turpentine. The best Brunswick black is prepared by boiling 

 together a quarter of a pound of foreign asphaltum, and four and a 

 quarter ounces of linseed oil, which has been previously boiled with 

 half an ounce of litharge until quite stringy ; the mass is then mixed 

 with half a pint of oil of turpentine, or as much as may be required to 

 make it of a proper consistence. It is often improved by being 

 thickened with lamp black. It must be remembered that this cement 

 is soluble in oil of turpentine. 



Dr. Eulenstein, of Stuttgart, finds that equal parts of Brunswick 

 black and gold size with a very little Canada balsam form a very 

 lasting cement. 



92. Marine Glue. This substance was, I believe, first used for 

 microscopical purposes by Dr. Goadby, of Philadelphia. It is pre- 

 pared by dissolving, separately, equal parts of shell-lac and India- 

 rubber, in coal or mineral naphtha, and afterwards mixing the solu- 

 tions thoroughly with the application of heat. It may be rendered 

 thinner by the addition of more naphtha. Marine glue is readily dis- 

 solved by naphtha, ether, or solution of potash. It is preserved well 

 in a tin box. I shall describe the manner of using marine glue and 

 the different cements I have alluded to in 116, 123. 



93. Cement for attaching Gutta Pcrclm or India-rubber to the 

 Glass Slides. A cement for attaching cells of gutta percha or India- 

 rubber to the glass slide may be made as follows : According to 

 Harting, gutta percha is to be cut into very small pieces and stirred, 

 at a gentle heat, with fifteen parts of oil of turpentine ; the gritty, in- 

 soluble matter, which the gutta percha always contains, is to be 

 separated by straining through linen cloth, and then one part of shell- 

 lac is to be added to the solution, kept at a gentle heat, and occa- 

 sionally stirred. The mixture is to be kept hot until a drop, when 

 allowed to fall upon a cool surface, becomes tolerably hard. When 

 required for use, the mixture is to be heated, and a small quantity 

 placed upon the slide upon which the cell is to be fixed ; the slide 

 itself is then to be heated. 



