396 ORGANIC CHEMISTRY. 



loids are generally preferred in medicine, in view of 

 their ready solubility. In large doses they are all 

 poisonous. The tincture of nut-galls is employed as 

 an antidote, because of the property of the tannic acid 

 which it contains, to form with most of the alkaloids 

 insoluble precipitates. 



991. OCCURRENCE. Morphine is con- 



Wfiat is the . r 



source of the tamed in opium, qmmne is extracted from 

 alkaloids ? Peruvian bark, and strychnine, from the nux 

 vomica. The latter is also the poison of the celebrated 

 upas. Theine and nicotine are other alkaloids, the 

 former of which is found in tea and coffee, and the latter 

 in tobacco. Theine may be obtained, as a sublimate 

 of silky crystals, by moderately heating tea in an iron 

 pot covered with a paper cone. 



992. PREPARATION. Most of the alka- 



How are the 



alkaloids ex- loids may be extracted from the material 

 which contains them by means of acidu- 

 lated water. A salt of the alkaloid is thus obtained in 

 solution. From this salt the alkaloid may be precipi- 

 tated, like oxide of iron or any other base, by. am- 

 monia. Nicotine is a most energetic poison, falling 

 scarcely below prussic acid in its destructive properties. 



COLORING MATTERS. 



What is said 993. INDIGO. The vegetable dye-stuffs 

 of indigo? are extremely numerous. Indigo, madder, 

 and logwood are among the more important. Indigo 

 is deposited from the colorless juice of certain plants 

 by simple exposure to the air. It may be sublimed in 



