ALOES 91 



72.4 per cent of fresh and 62.8 per cent of old Barbadoes aloes is 

 soluble in chloroform. It contains about 9 per cent of moisture. 



3. Cape Aloes. Of a reddish-brown or of an olive-black color, 

 usually covered with a yellowish powder, transparent in thin pieces; 

 fracture smooth and glassy; odor characteristic; powder greenish- 

 yellow, becoming light brown and giving a greenish color with nitric 

 acid. 



About 60 per cent of Cape Aloes is soluble in cold water. It is 

 almost completely soluble in alcohol or boiling water; and the latter 

 solution gives a precipitate of 60 per cent of " resin of aloes." From 

 81 to 86.8 per cent is soluble in chloroform, and from 1.5 to 6.5 per 

 cent in ether. It contains about 9 per cent of moisture, and yields 

 but a small percentage of ash. 



Uganda (or crown) Aloes is a hepatic variety of Cape Aloes pre- 

 pared by allowing the juice to stand and undergo a partial fermenta- 

 tion, after which the clear liquid is decanted and evaporated by 

 exposure to the sun. It occurs in reddish-brown masses, producing 

 a powder, which is colored yellow to brown with nitric acid. 



Microscopic Examination. Powdered aloes may be examined 

 under the microscope and is best mounted in one of the fixed 

 oils. Socotrine aloes consists of yellowish- or reddish-brown, irregular 

 and more or less angular fragments. In Curasao aloes the fragments 

 are irregularly angular, blackish-brown or reddish-brown and more 

 or less opaque. The fragments in Cape aloes are bright yellow and 

 distinctly angular. 



Constituents. A crystalline, bitter principle, aloin, the per- 

 centage (4.5 to 30 per cent) and composition of which varies in the 

 different varieties, and which is supposed to occur in largest amount 

 in old aloes; emodin (see Rhubarb) ; a pale yellow, volatile oil, which 

 is apparently not identical in the different varieties, giving them 

 their characteristic odors; 13 to 63 per cent of resinous material, 

 which consists chiefly of a resinotannol ester of cinnamic acid (Curasao 

 and Barbadoes aloes) or of a resinotannol ester of paracumaric acid 

 (Cape aloes) ; and 1 to 4 per cent of ash. 



Aloin is a neutral, bitter principle, which on distillation with zinc 

 dust yields anthracene. It forms minute, lemon-yellow to yellowish- 

 brown acicular crystals, which are sparingly soluble in water but 

 more so in alcohol, the solutions becoming brown on standing (Fig. 

 36, C). Alkaline solutions of aloin have a deep red color and exhibit 

 a greenish-red fluorescence. Upon the addition of aloin to sulphuric 

 acid a yellowish-red solution is formed, which, upon the addition of a 

 small quantity of potassium dichromate is changed to olive-green 



