10 VIEWS OP THE MICROSCOPIC WORLD. 



Cells may be composed of various materials: for dry objects a small ring of paper, 

 card-board, gutta-percha, or vulcanized India-rubber may be fixed upon the slide 

 by cement ; the object is then placed within it and covered by thin glass, which is 

 cemented to the slide at the edges. 



If the cell is to contain fluid, some substance must be employed which is not af- 

 fected by moisture. Cells of this kind are formed by gold size, a solution of asphaltum 

 dissolved in alcohol, and marine glue. In making a cell with marine glue, the glass 

 slide must be warmed upon a metallic plate heated by a spirit-lamp. When hot 

 enough a small piece of glue is allowed to melt upon the slide, and is moved round 

 and round in the position in which we wish to make the wall of the cell. When the 

 glue is allowed to cool, any excess may be removed from the slide by the aid of a 

 sharp knife, and the glass still further cleaned by using a solution of potash. The 

 surface of the glass to which a cement is to be applied should be roughened by 

 grinding, as the cement adheres better than when the glass is polished. Glass is 

 cemented together with marine glue, which is regarded as one of the best cements 

 that can be employed. In addition to the modes already mentioned, cells may be 

 formed from tinfoil and pieces of perforated thin glass. In making large cells of 

 thin glass, the edges are united together by means of marine glue. 



Cement. The chief cements employed in microscopical work are gold size, sealing- 

 wax varnish, a solution of shell-lac, a solution of asphaltum, marine glue, Canada 

 balsam, gum, and French cement. 



Gold size, for microscopical purposes, is made by boiling 25 parts of linseed oil 

 with one part of red-lead, and a third part of as much umber, for three hours. The 

 clear fluid is to be poured off and mixed with equal parts of white-lead and yellow 

 ochre, which have been previously well pounded together. This mixture is to be 

 added to the fluid in small successive portions and thoroughly incorporated with it; 

 the whole is then again to be well boiled, and the clear fluid poured off for use. 



SeaNng-wax varnish is made by dissolving the best sealing-wax in moderately 

 strong alcohol. 



The shell-lac solution, which is very useful in cementing down the thin glass 

 covers, is made by dissolving shell-lac in alcohol. 



The solution of asphaltum is prepared by boiling together a quarter of a pound of 

 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 to be 

 mixed with half a pint of oil of turpentine, or as much as is required to make it of 

 a proper consistence. It is improved by being thickened with lamp-black. This 

 cement is soluble in oil of turpentine. 



Marine glue is made by dissolving separately equal parts of shell-lac and India- 

 rubber in coal or mineral naphtha, and afterwards mixing the solution thoroughly 

 by the aid of heat. It may be rendered thinner by the addition of more naphtha. 

 Marine glue is readily dissolved in naphtha, ether, or a solution of potash. 



Canada balsam is a pure turpentine, which becomes soft on the application of a 

 gentle heat. It is chiefly employed for mounting hard dense structures ; and in 

 consequence of its great power of penetrating textures, and highly refractive prop- 

 erties, the structure of many substances which cannot be distinguished in the 

 ordinary mode of examination is clearly seen when immersed in this medium. 

 Liquid g,,i is made by placing common gum-arabic in cold water, and then keep- 

 ing the bottle containing it in a warm place until the solution has become thick. 

 This preparation is found very useful in fixing the thin glass covers, when objects 



