48 HOW TO WORK 



the cases of instruments and apparatus sold by many of the micro- 

 scope-makers. 



CEMENTS. 



The chief cements employed in microscopical work, are Goid 

 size, Sealing-wax varnish, Solution of shell-lac, Solution of asphalt, 

 Marine glue, Canada balsam, Gum, and a French cement composed of 

 lime and India-rubber. These cements are used for attaching the 

 i;lass cell to the glass slide, for fixing the cover upon the preparation 

 after it has been properly placed in the cell, and for other purposes. 

 The liquid cements should be kept in wide-mouthed bottles, or in 

 capped bottles, fig. 88, pi. XVI. 



87. Gold Size is prepared by melting together gum animi, boiled 

 linseed oil, red lead, litharge, sulphate of zinc, and turpentine. Gold 

 size adapted for microscopical purposes may be also prepared as fol- 

 lows : 25 parts of linseed oil are to be boiled with one part of red 

 lead, and a third part 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. This is to 

 be added in small successive portions, and well mixed the whole is 

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

 In this country it may be obtained of any varnish maker. 



88. sealing-wax varnish is easily made by dissolving the best 

 sealing-wax of any colour, in tolerably strong alcohol. This cement 

 is, however, apt to dry rather brittle, and should not, therefore, be 

 used in cases where it is of the greatest importance to keep the cell 

 perfectly air-tight. It forms a good varnish for the last coat. Various 

 colours may be kept according to taste. 



89. Solution of Shcii-iac is recommended by Mr. Ralphs for 

 fixing down the thin glass cover. It is made by dissolving shell-lac 

 in spirits of wine. The shell-lac should be broken in small pieces, 

 placed in a bottle with the spirit, and frequently shaken, until a thick 

 solution is obtained. It dries rapidly, and, if put on in thin layers 

 successively, forms a good cement. It ^is not acted upon by weak 

 spirit. 



90. Bell's cement. The best cement for specimens immersed 

 in glycerine is sold by Messrs. Bell, chemists, Oxford-street. This, 

 I believe, was originally suggested by Mr. Tomes, but I do not know 

 its exact composition. It appears to contain shell-lac and gold size. 



III. i mnsTvick Black. Solution of asphalt in turpentine com- 

 monly known by the name of Brunswick black, may be obtained at 



