ALOIN. 455 



chinoline iodide, C 14 H 18 TI = C 9 H 7 .C 5 H n K[, which, when 

 heated with potassa, yields a beautiful, but not very 

 permanent blue dye, cyanide iodide (the cyanine of 

 commerce), C 28 H 35 ]& 2 L This crystallizes in beautiful 

 green plates, of a metallic lustre ; is insoluble in water 

 and ether, easily soluble in warm alcohol; fuses at 

 100. It combines directly, and without separation of 

 iodine, with two molecules of hydrochloric acid, form- 

 ing a colorless salt; when heated with silver oxide, 

 however, it gives up its iodine, and yields a bronze- 

 colored, amorphous base. 



Lepidine conducts itself like chinoline, and yields a 

 very similar dye, C 30 H 39 N 2 I. The cyanine of commerce 

 is either the derivative of chinoline or of lepidine, or 

 of a mixture of both. 



C. COLORING MATTERS, BITTER PRINCIPLES, ETC. 



These names are applied to a large number of pecu- 

 liar neutral or weakly acid substances, of which only 

 a few have been moderately well investigated. Least 

 known are the uncrystalline, although these often 

 possess interest from the fact that they are frequently 

 constituents of the so-called vegetable extracts. The 

 following, which are mostly crystalline, are among the 

 more remarkable substances of this kind, arranged in 

 alphabetical order. 



Aloin, C 17 H 18 7 . Is the purging, active principle 

 of aloes, the juice, dried in the sun, obtained from 

 various species of aloe, either by cutting the leaves, 

 and allowing it to exude spontaneously, or by pressing 

 the separated leaves. The best sort of aloes consists of 

 brown or dark greenish-brown transparent masses, of a 

 lustrous fracture, of a disagreeable odor and a disagree- 

 able, bitter taste. Aloin forms small, colorless crystals, 

 of a sweetish-bitter taste ; difficultly soluble in cold 

 water and alcohol ; becoming brown and resinous when 

 melted, and readily becoming amorphous under all 

 circumstances. When aloes is heated with nitric acid, 

 an orange-yellow powder, aloetic acid, C 7 H 2 (1S"0 2 ) 2 0, 



