150 The Microscope. 



this as it may, it seems to me that a revival of this subject with 

 a view of doing the best we can with our present improved 

 methods, and increased knowledge, would result in having a 

 great deal more uniform objective fittings than we now have. 



REFERENCE TABLES FOR MICROSCOPICAL WORK. 



III. 



CEMENTS AND VARNISHES. 

 COMPILED BY PROFESSOR A. B. AUBERT. 



Alphalt VARNISH : asphalt, 450 grms. ; linseed oil, 225 grms. ; 

 turpentine, 1,000 c. c. ; or dissolve asphalt in benzol and to the 

 solution add gold size. In the first method, dissolve by the aid 

 of heat ; dilute when ncessary, with turpentine. Not very reli- 

 able as a cement. 



Bell's cement : probably a solution of shellac, but the exact 

 composition is not known. This in the opinion of many is an 

 excellent cement. 



Gold size : linseed oil, 25 ounces ; red lead, 1 ounce ; pow- 

 dered white lead and yellow ochre, of each a sufficient quantity. 

 Boil the oil and red lead together carefully for 3 hours ; pour off 

 the clear liquid, and boil with a mixture of equal parts of the 

 white lead and yellow ochre added in small successive portions. 

 Let it stand, and pour off the clear liquid for use. 



Gram-Rutzon's cement: hard Canada balsam, 50 grms. ; shel- 

 lac, 50 grms. ; absolute alcohol, 50 grms. ; anhydrous ether, 100 

 grms. The ingredients are mixed, and when the gums are dis- 

 solved, filter if necessary, and evaporate, away from the flame^ 

 over a water bath until of syrupy thickness. 



Gutta-percha cement (Harting) : gutta-percha cut in pieces, 

 1 part; turpentine, 15 parts; shellac, 1 part. Heat the gutta- 

 percha and turpentine together, filter, add the shellac pulverized, 

 and heat until a drop hardens on a cold glass plate. Used to 

 attach cells ; the slide must be warm when using the cement. 



Brown cement : pure gum rubber, 20 grains ; carbon disulph- 

 ide, a sufficient quantity ; shellac, 2 ounces ; alcohol, 8 ounces. 

 Dissolve the rubber in the smallest possible amount of the car- 

 bon disulphide ; add this slowly to alcohol, avoiding clots ; add 

 powdered shellac and place the bottle in boiling water until the 

 shellac is dissolved and no more smell of carbon disulphide is 

 given off. 



