SCIENTIFIC AND APPLIED PHARMACOGNOSY 



and finally to a blue color. Ferric chloride gives a brownish-green 

 color to an alcoholic solution of aloin. The amount of aloin varies 

 from 4 to 10 per cent in Socotrine (Zanzibar) aloes, is about 6 per 

 cent in Cape (Uganda) aloes and is stated to range from 10 to 30 

 per cent in Curasao (Barbadoes) aloes. The aloin obtained from 

 Curagao or Barbadoes aloes gives with nitric acid a cherry-red color 



A 6 



O 



FIG. 36. Crystals from exudations and extracts; A, crystals found in the residue 

 after treatment of catechu with water; B, long prisms of catechin (d) found 

 on treatment of gambir with a solution of hydrated chloral, the crystals soon 

 dissolving, and prismatic plates (e) usually seen in glycerin mounts of gam- 

 bir; C, crystals from aloes, including aloin (o), broad prisms (6) from Bar- 

 badoes aloes, and plates (c) from Cape aloes; D, crystals of benzoic acid 

 obtained by subliming benzoin on a slide or in a watch crystal. 



or with Klunge's reagent a deep-red color. These color reactions are 

 due to the presence of about 0.5 per cent of an isomeric body (iso- 

 barbaloin), which is not found in the aloins of Socotrine and Cape 

 aloes. Alcoholic solutions of barbaloin and isobarbaloin lose their 



