344 ODOEOGEAPHIA. 



(or are boiled with water), the combined extract evaporated down 

 to 9 parts, mixed whilst still hot, and digested for 24 hours with 1 

 part of litharge, filtered and evaporated to a syrup. The salicin 

 separates out and is purified by recrystallisation. An additional 

 quantity of salicin is obtained from the mother liquors after they 

 have again been treated with litharge and the entire product is 

 purified by repeated crystallisation. 



Erdmann's process is as follows : — 16 ounces of the bark are 

 macerated for twenty-four hours in 4 quarts of w^ater mixed with 

 2 ounces of lime, and the whole is then boiled for half-an-hour. 

 The process is repeated with the residue. The decoctions having 

 been mixed and allowed to clear by subsidence, the clear liquor is 

 decanted, concentrated to a quart, digested with 8 ounces of bone 

 black, filtered and evaporated to complete dryness. The residue, 

 after being pulverised, is exhausted at a gentle heat with alcohol 

 of 82 per cent. On the alcohol being gently distilled off from the 

 tincture, the salicin crystallises from the residue and is ao-ain 

 dissolved, purified by bone black and recrystallised. By this 

 process Erdmann obtained 300 grains of salicin from 16 ounces of 

 8al{x iKntandra bark. The red colour imparted to salicin by 

 strong sulphuric acid may serve for its detection in wallow barks. 



Salicin forms needles, plates or rhombic prisms which dissolve 

 in 30 parts of water at the ordinary temperature, and freely in hot 

 water and alcohol, but are insoluble in ether. It has a very bitter 

 taste, and forms a purple-red solution in sulphuric acid. Dilute 

 nitric acid oxidises it to Helecin,'^ which may be re-converted into 

 salicin by sodium amalgam and water. Helecin can be prepared 

 synthetically.! Salicin melts at 201^ C, and solidifies on cooling 

 to a crystalline mass ; when it is heated, however, for some time 

 to 230°-240^ it partially decomposes into saliretin and glucosane.l 

 Its aqueous solution rotates the plane of polarisation to the left.§ 



Populin or henzoylsalicin, a neutral substance discovered by 

 Braconnet in the bark, leaves and root bark of the "Aspen 

 Poplar" {Popidus tremida),]] and was also investigated by Piria^. 



* Piria, Journ. Chem. Soc, Ivi., p. 64. 



t Michael in Amer. Chem. Journ., i., p. 309. 



X Ber. Deustch. Chem. Ges., xiv., p. 304. 



§ Ann. Chem. Pharm., clxxvi.,;p. 116. 



II Ann. Chim. Phys., xliv., pp. 296, 311. 



^ Ann. Chem. Pharm., Ixxxi., p. 245 ; xcvi., p. 375. 



