CRUDE DRUGS. 665 



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 and finally to a blue color. Ferric chlor- 

 ide 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 (Bar- 

 badoes) aloes. The aloin obtained from Curasao or Barbadoes 

 aloes gives with nitric acid a cherry-red color 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 (isobarbaloin), 

 which is not found in the aloins of Socotrine and Cape Aloes. 

 Alcoholic solutions of barbaloin and isobarbaloin lose their bitter- 

 ness on standing, the aloin being replaced in part at least by a 

 suerar aloinose, which forms yellow crystals that are colored red 

 and then green with concentrated hydrochloric acid and orcin. 

 Aloin is considered by some to be an emodin-glucoside which on 

 oxidation splits ofif emodin, the latter on further oxidation form- 

 ing rhein. (See also Fig. 275, C.) 



Adulterants. Aloes formerly contained various mechanical 

 impurities, and this was the reason for the introduction of a puri- 

 fied aloes into the U. S. Pharmacopoeia. As heat impairs the 

 quality of aloes and as the requirements forbid adulteration the 

 untreated aloes should be employed. The aloin is sometimes 

 removed, as in the Curacao aloes, when it has the appearance of 

 Cape aloes and is sometimes sold for it. Recently aloes has been 

 coming into market packed in thin layers separated by paper. 



Allied Plants. Natal Aloes is a hepatic variety of Aloes 

 which was at one time exported from Natal, the botanical origin 

 being unknown. It occurs in grayish-brown or greenish- 

 black, dull, opaque masses, often covered with a brownish pow- 

 der. The odor somewhat resembles that of Cape Aloes. The 

 powder is grayish-green or pale yellowish-brown and microcrys- 

 talline, giving a permanent crimson color with nitric acid and a 

 deep blue with sulphuric acid and vapor of nitric acid. The latter 

 test serves to distinguish this aloes from all the other varieties. 

 The drug contains aloin (nataloin), but not emodin. Both Natal 

 Aloes and nataloin are physiologically inactive. 



