AND HOW TO USE IT. 41 



thinner, when a Httle more gum may be added. 



Marine Glue (Dr. Goadby). — Dissolve, separately, equal parts 

 of shellac and india-rubber in coal or mineral naphtha, and after- 

 wards mixing the solutions thoroughly with heat. Marine glue is 

 dissolved by naphtha, ether, or a solution of potash. 



Cement for attaching Gutta Percha or India-rubber to Glass 

 Slides(Hartin). — One part of gutta percha is to be cut into very 

 small pieces, and stirred at a gentle heat with 15 parts of oil of 

 turpentine. The gritty, insoluble matter, which is always con- 

 tained, is to be separated by straining through a linen cloth, and 

 then one part of shellac is to be added to the solution, kept at a 

 gentle heat, and occasionally 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. 



Dammar.— A good ringing cement is dammar dissolved in 

 chloroform, because if inclined to run under the cover it will 

 readily mix with the mounting materials. In drying, the dammar 

 shrinks, and thus renders it necessary to apply another coat in a 

 few hours' time. 



A good and inexpensive Cement for Glycerine Mounts, etc.— 

 Dissolve 10 grs. of gum-ammoniac in i oz. of acetic acid (No. 8) ; 

 then add to this solution 2 drachms of Cox's gelatine. It flows 

 easily from the brush, and is waterproof, though rendered more so 

 if subsequently brushed over with a solution of 10 grs. of bichro- 

 mate of potash in i oz. of water. This cement is especially 

 recommended on account of its power of adhesion to glass, even 

 should there be a little glycerine left behind on the cover. After 

 the gelatine ring is dry, any cement may be used. 



Ground Borax, mixed with plaster of Paris, makes a good 

 cement for large cells, etc. 



French Cement. — A quantity of india-rubber scraps are care- 

 fully melted over a clear fire in a covered iron pot, but they must 

 not be permitted to catch fire. When the mass is quite fluid, 

 lime in a perfectly fine powder, having been slacked by exposure 

 to the air, is to be added in small quantities at a time, 

 the mi.xture being well stirred. When moderately thick, it is 



