22 THE AMERICAN MONTHLY [January, 



MICROSCOPICAL APPARATUS. 



An Excellent Mounting Medium. — Dissolve gum damarin 

 benzol to the consistency of a thin syrup. Get rid of the larger 

 particles of dirt by straining through an old silk handkerchief, 

 and add to the colate about one-third of its volume of liquor 

 potassae. Shake until mixed, cork well, and set aside in a warm 

 place for several weeks. On examination the mixture will be 

 found to have separated into two layers, the lower of which (a 

 resin soap) will contain all the impurities, the upper consisting 

 of pure neutral damar in benzol. Draw this off and to each 

 ounce add about 8 or ro drops of poppy oil. This latter prevents 

 the brittleness which the dry damar naturally possesses. The 

 mounting medium thus prepared is too thin for immediate use, 

 but tliis is easily remedied by leaving the bottle open or loosely 

 corked in a warm phice for a day or two. If left open, cover the 

 top of the vessel with a bit of lint cotton or a linen rag to keep 

 out dust. — National Druggist^ December /, i8g2. 



A Nearly Colorless Damar. — Dissolve the damar in benzol 

 and make sufficiently tliin to filter i^eadily through paper in a closed 

 filter. Filtration may be avoided, if you have plenty of time, by 

 adding zinc oxide, shaking well, and allowing to stand until the 

 oxide settles to the bottom, carrying all foreign matters with it. 

 The oxide should be wet with benzol before adding it, to insure 

 its thorough incorporation. Filter or decant, as the case may 

 be, and to the filtrate add alcohol in small quantities until the 

 addition no longer causes a precipitate. Filter oft' and wash the 

 precipitate with absolute alcohol two or three times, and then 

 dry. The result will be a white, finely divided powder, which, 

 when thoroughly dry, is dissolved in crystallizable benzol, giving 

 a colorless or nearly colorless solution. This solution evaporated 

 leaves a colorless but excessively brittle la3'er of resin. The 

 brittleness may be corrected by the addition of poppy oil. Thus 

 prepared the medium is practically colorless and has a high re- 

 fractive index. The residual alcoholic mixture rapidly clears 

 itself on standing, and on evaporation leaves a tenacious but 

 slowly drying gum that makes an excellent cement basis — 

 National Druggist^ December /, i8gz. 



Use of Compressed Carbonic Acid Gas for the Freezing 

 Microtome. — A method which has been in use in the Sears 

 Pathological I^aboratory of Harvard Medical School for over two 

 years is described by Dr. Frank B. Mallory in the Boston Aled- 

 Ical and Surgical Journal. This gas, carbon dioxide, is prefer- 

 able to ether or to rhigoline for freezing. The *•' liquid carbonate " 

 of commerce is obtained from the American Carbonate Co., 434 

 E. 19th street. New York, in cylinders of 10 or of 20 pounds each, 

 but some slight modifications are needed to adapt their cylinders 



