REAGENTS AND PROCESSES 531 



Barium Chloride. ( i ) This is sometimes used to distinguish calcium oxalate from 

 calcium sulphate. When barium chloride is run under the cover-glass, calcium 

 oxalate, if present, is left unchanged, while a fine granular layer of barium sulphate 

 comes to incrust any crystals of calcium sulphate. (2) To determine the presence 

 of tartaric acid, barium chloride and antimonic oxide in hydrochloric acid are run 

 under the cover-glass, producing, with tartaric acid, rhombic crystals of antimon- 

 ium-barium tartrate, whose obtuse angles measure 128. 



Beale's Carmine Solution. Mix 0.6 Gm. with 3.75 Gm. ammonia water (10 

 per cent.) ; heat on a water-bath for several minutes; then add 60 Gm. of glycerine, 

 60 Gm. of water and 15 Gm. of alcohol, and filter. 



Benzol. Used in detecting caffeine, thus: Sections are heated on the slide in 

 a drop of distilled water until bubbles arise, then the water is allowed to evaporate, 

 and the residue is dissolved with a drop of benzol. The benzol is then allowed to 

 evaporate and the caffeine is deposited on the edge of the drop in the form of color- 

 less needle-crystals. 



Bismarck Brown. This is preeminently a nuclear stain. The powder is solu- 

 ble with difficulty in water. It is a good plan to treat with boiling water and after 

 a day or two to filter. Or a saturated solution may be made in 70 per cent, alcohol. 

 Although Bismarck brown stains rapidly, it does not overstain. It may be used 

 for staining in toto or for staining sections on the slide. 



Bohmer's haematoxylin solution is prepared by mixing the two following solu- 

 tions and filtering after allowing the mixture to stand for several days: (a) One 

 part of a 3.5 per cent, alcoholic (95 per cent.) solution of haematoxylin and (b) 

 three parts of a 0.4 per cent, aqueous solution of potassium alum. 



Boric Acid. Used as a mounting medium for sections containing mucilagi- 

 nous membranes. The sections are cut from dry material and placed in a 10 per 

 cent, solution of neutral lead acetate to harden the mucilaginous layers. Then 

 the sections are stained in a solution of methyl-blue, washed in water, and mounted 

 under a cover-glass in a 2 per cent, solution of boracic acid. The cover-glass should 

 be sealed down with a mixture of paraffin and vaseline, which is applied with a 

 brush while melted. 



Borax-carmine. A 4 per cent, solution of borax is made and to it is added 

 3 per cent, of carmine; an equal bulk of 70 per cent, alcohol is then added to this. 

 The mixture is left standing for a day or so and then filtered. Sections should lie 

 in the stain for about twenty-four hours, and should then be transferred without 

 previous washing to acidulated alcohol, made by adding 4 drops of hydrochloric 

 acid to 100 mils of alcohol. Here they should remain until they become bright 

 and transparent. This is a useful stain for aleurone grains, for differentiating cell- 

 contents from cell-walls when the sections are subsequently stained with methyl 

 green, and much used also in the differentiation of the cell-contents of filamentous 

 algae. 



Bordeaux Red. Used in conjunction with haematoxylin in staining nuclear 

 figures, particularly where Heidenhain's platinic chloride fixative has been used. 

 The sections are placed in a weak aqueous solution of the Bordeaux until they are 

 intensely stained; they are then rinsed and placed in a 2 to 5 per cent, solution of 

 iron oxide-ammonium sulphate for three hours. If the sections are mounted on a 

 slide, they should be placed upright in this solution, so that any precipitate may not 

 gather on the slide. Then the sections are carefully washed in an abundance of 

 water, and placed for twenty-four hours in a solution of haematoxylin prepared as 

 follows: I Gm. of haematoxylin is dissolved in 10 Gm. of alcohol and 90 Gm. of water. 

 This is allowed to stand for about four weeks, and then an equal bulk of distilled 

 water is added. The stain is then ready for use. When the sections are taken from 

 the haematoxylin, they will be found overstained; they are, therefore, rinsed and 



