532 POWDERED DRUGS 



placed in a 2.5 per cent, solution of ferric-ammonium sulphate, where they remain 

 until examination of the sections under the microscope shows them to have the 

 proper intensity of stain. The sections are then thoroughly rinsed in water and 

 passed through alcohol and xylol before mounting in balsam. 



Borodin's Method. To determine the nature of a precipitate Borodin treats 

 it with a saturated solution of the same substance as the precipitate is supposed to 

 be. Thus, if the precipitate is supposed to be asparagin, it is treated with a satu- 

 rated solution of asparagin. If the precipitate dissolves by this treatment, it is 

 then some other substance than asparagin. This method is not very reliable for 

 substances which are very readily soluble, such as potassium nitrate. Care must 

 be taken that the solution used for the test is entirely saturated. 



Brown Discoloration of Material in Alcohol. Some plants, such as Mono- 

 tropa, are apt to become quite brown in alcohol. This can be prevented by placing 

 the fresh material in alcohol which is acidulated by vapor of sulphuric acid in the 

 following manner: For each 100 mils of alcohol several mils of 80 per cent, 

 sulphuric acid are poured over J- of a Gm. of sodium sulphite, and the vapors 

 arising are conducted into the alcohol. This operation need require hardly more 

 than a minute. After twenty-four hours the material should be transferred from 

 the acid alcohol to neutral alcohol. Thereafter the material will not discolor, and 

 will take stains very well when used for histological purposes. 



Calcium Nitrate. (i) Used to differentiate more clearly the lamellae of starch- 

 grains. Potato starch, for instance, is placed in a rather strong aqueous solution 

 of methyl violet. After the grains have become deeply colored, they are treated 

 with a weak solution of calcium nitrate, when the methyl violet becomes precipi- 

 tated, particularly in the less dense lamellae of the starch-grains. (2) Calcium 

 oxalate.is precipitated in the form of crystals when sections containing oxalic acid 

 are treated with a solution of calcium nitrate. The calcium nitrate is thus a test 

 for the presence of oxalic acid. 



Canada balsam is used almost exclusively for mounting. Very thick balsam 

 is very disagreeable to handle and makes unsatisfactory mounts. Very thin bal- 

 sam, in drying out, allows bubbles to run under the cover. Xyol is cheaper than 

 balsam and, consequently, the balsam on the market is likely to be too thin for 

 immediate use. The stopper may be left out until the balsam acquires the proper 

 consistency. Material cleared in clove oil or cedar oil may be mounted directly 

 in xyol balsam. It is not necessary that the clearing agent should be also the sol- 

 vent of the balsam. 



Canarin. This is often used as a stain for tissues which have been cleared in 

 caustic potash. Canarin is not affected by this reagent. 



Carbolic Acid (Phenol). Used as a clearing agent. If leaves which have been 

 hardened and bleached in alcohol are placed in 3 parts of turpentine and i part of 

 carbolic acid, or in pure carbolic acid, the leaves will become so transparent that 

 their cellular structure may be made out from one surface to the other. Pollen- 

 grains may be made transparent in the same manner. 



Carmalum, Mayer's. Carminic acid I Gm., alum 10 Gm.; dissolve in 200 

 mils of hot distilled water; filter and add a few crystals of thymol, or o.i per cent, 

 of salicylic acid, or 0.5 per cent, of sodium salicylate. This stains material well in 

 bulk, with little danger of overstating. If this happens, it may be corrected by 

 washing with a o.i per cent, solution of hydrochloric acid. Material which has 

 been stained in bulk with carmalum may be sectioned, and the sections may then 

 be double-stained with some aniline stain, such as blue de Lyon. See borax-car- 

 mine for another carmine stain. Very fine double staining may be achieved by 

 placing sections first in an aqueous solution of iodine green and then for a some- 



