THE MICROSCOPE IN CHEMISTRY. 113 



prisms, or oblong plates. Ammonia, the alkalies, and their 

 carbonates produce tufts of crystals (Plate III, Fig. 72). 

 A drop of aqueous solution of a salt of narcotin, exposed 

 to vapor of ammonia, is covered with a crystalline film if 

 it only contains g^^th of its weight of alkaloid. 



Morphine. When pure crystallizes in short rectangular 

 prisms. Sulphuric acid dissolves them, and if bichromate 

 of potash be added, green oxide of chromium results. Con^ 

 centrated nitric acid turns it orange-red, and dissolves it_ 

 A strong solution treated with a strong solution of nitrate 

 of silver and gently heated, decomposes the latter and pro- 

 duces a shining crystalline precipitate of metallic silver. 

 In dilute solutions, alkalies precipitate a crystalline form 

 ( 'Plate III, Fig. 73). Xo precipitate with sulphocyanide 

 of potassium unless highly concentrated. 



Quinine. Amorphous precipitate with ammonia. Sul- 

 phoc} T anide of potassium gives irregular groups of acicu- 

 lar crystals, like those produced by strychnine, but longer 

 and more irregular (Plate III, Fig 74 . The solution 

 should be dilute, and twenty-four hours allowed for the 

 crystals to form. 



The iodo-disulphate, or Herapathite, gives crystals of a 

 pale olive-green color, which possess a more intense polar- 

 izing power than any other known substance. Dr. Hera- 

 path proposed this as a delicate test for quinine. A drop 

 of test-liquid made with 3 drachms of acetic acid, 1 

 drachm of rectified spirits, and 6 drops of dilute sulphuric 

 acid is placed on a slide and the alkaloid added. When 

 dissolved a little tincture of iodine is added, and after a 

 time the salt separates in little rosettes. By careful manip- 

 ulation crystals of this salt may be formed large enough 

 to replace Xicol's prisms or tourmaline plates in the polar- 

 izing apparatus. When the crystals of Herapathite cross 

 each other at a right-angle, complete blackness results. 

 Intermediate positions give a beautiful play of colors. 



Strychnine. Ammonia gives small prismatic crystals, 



8 



