534 POWDERED DRUGS 



Chrom-acetic Acid. Prepared by mixing 70 mils of i per cent, chromic acid 

 with 5 mils of glacial acetic acid and 90 mils of water. Particularly good for fixing 

 algae. The algae should remain in the fixative for twelve hours, then they should be 

 thoroughly washed out in running water or in water which is frequently changed, 

 and thereafter they may be preserved indefinitely in 10 per cent, glycerine, to 

 which a bit of camphor has been added. If it is at any time desired to stain and 

 imbed the algae which have been fixed and preserved as above, the 10 per cent, 

 glycerine in which the algae are preserved may be evaporated in the drying oven 

 until quite concentrated, and the algae may be washed out in strong alcohol; they 

 may then be doubled-stained in the following manner: To the strong alcohol (95 

 per cent.) in which the algas are lying are added a few drops of a concentrated solu- 

 tion of magdala red in 95 per cent, alcohol; the algae are quickly rinsed in alcohol 

 and transferred to a rather dilute solution of aniline blue in 80 per cent, alcohol, 

 where they remain for a few minutes, and are immersed for a few seconds only in 

 a 25 per cent, hydrochloric acid-alcohol solution. The algae are next rinsed in pure 

 alcohol, and transferred to a 10 per cent, solution of Venetian turpentine. The 

 turpentine is concentrated by the evaporation of the alcohol which was used as the 

 solvent (see Turpentine) in the drying oven. Permanent mounts should be made 

 in the concentrated turpentine. 



Chromic Acid. Solutions of i per cent, and 0.5 per cent, have been much used 

 for fixing plant tissues. The material to be fixed should lie in the chromic acid for 

 a day or more, according to the size of the pieces of material to be fixed. The 

 material should then be thoroughly washed out in water and dehydrated by slow 

 degrees in ascending grades of alcohol. A concentrated aqueous solution of chro- 

 mic acid may be used as a macerating fluid to cause the separation of tissues into 

 their separate cells. To this end rather thin bits of the tissue to be macerated 

 should be placed in the chromic acid for about half a minute, and then carefully 

 washed in water. This operation may be carried on with sections under the cover- 

 glass. Silicious skeletons of diatoms, incrustations on the epidermis of equisetum, 

 etc., may be prepared by allowing the material to lie in concentrated sulphuric acid 

 until it becomes black, and then, after transferring to a 20 per cent, solution of 

 chromic acid for some minutes, washing thoroughly in water. In the case of 

 equisetum and the like the tissues should be scraped away from the inside down to 

 the epidermis before treatment with the acids. Chromic acid is useful in the rec- 

 ognition of tannins, since sections containing tannins, when treated with a i per 

 cent, solution of chromic acid, yield a brownish precipitate. 



Clearing Media. See Carbolic Acid, Cedar Oil, Chloral Hydrate, Canada 

 Balsam, Clove Oil, Glycerine, Javelle Water (or Eau de Javelle), Origanum Oil, 

 Turpentine, Xylol. 



Clove Oil. This is an excellent clearing medium, but it has the power of ex- 

 tracting certain stains, and so can not be used in all cases; it is, however, for this 

 very reason of great advantage in the safranin-gentian violet-orange method of 

 staining. See under this head. 



Congo-red. This stain is particularly useful in studying the growth of mem- 

 branes. Old membranes are, as a rule, left unstained by it, while the newly formed 

 membranes are colored red. In a o.oi per cent, solution that is, i part of the stain 

 to 10,000 of water algae may continue to live and grow, and they are, therefore, 

 well adapted to the study of the growth of membranes with the employment of this 

 stain. 



Copper Acetate. Used in the determination of tannins. Small bits of the plant 

 to be tested are placed in a saturated solution of copper acetate, where they remain 

 for 8 or 10 days; the sections are then placed on a slide in a drop of a 0.5 per cent, 

 solution of ferrous sulphate; after a few minutes the sections are washed in water, 



