GUAIACUM 461 



The commercial drug is never completely soluble in alcohol. The 

 residue, which in the case of tear resin is about 1-5 per cent., and in 

 good samples of the lump averages about 7-5 per cent. (Evans, 1898 ; 

 not over 10 per cent., B.P., 1914), may in exceptional cases amount 

 to as much as 25 per cent. It consists chiefly of fragments of vegetable 

 debris, gummy matter, &c. 



Guaiacum resin is easily identified by its remarkable reaction with 

 oxidising agents. This is best seen by dissolving a little of the resin 

 in alcohol and adding a drop of dilute solution of ferric chloride ; 

 the liquid instantly assumes a deep blue colour which is destroyed by 

 reducing agents, but restored by oxidising agents. 



The student should observe 



(a) The varying colour that the resin exhibits when viewed by 



transmitted light, 



(b) The greenish powder with which it is often more or less 



covered, 



(c) Its characteristic, though not powerful, odour and taste. 



Constituents. Guaiacum resin consists chiefly of resin-acids and 

 has approximately the following composition : 



a-Guaiaconic acid 1 70-00 per cent. 

 /3-Guaiaconic acidj 



Guaiaretic acid . . 11-25 



Guaiac-#-resin ... . 15-00 



Guaiacic acid, guaiac-yellow, vanillin, sa- 



ponin, &c. . 2'25 



a-Guaiaconic acid is a colourless amorphous substance, probably a 

 mixture, one constituent of which is changed by oxidising agents to 

 deep blue guaiac-blue ; sulphurous acid reduces this to a colourless 

 substance, which may again be oxidised. 



/3-Guaiaconic acid is colourless and crystalline. Guaiaretic acid 

 is light brown, amorphous, and insoluble in ether. Guaiac-/3-resin 

 is brown and amorphous, and appears to be chiefly a decomposition 

 product of the guaiaconic acids ; it contains the substance that 

 yields guaiac-blue by oxidation. 



U ses< The action of guaiacum is that of a local stimulant or, in 

 large doses, irritant. It has been employed locally in the form of the 

 lozenge, and has also been given in chronic gout and rheumatism. 



Adulterants, &c. Guaiacum resin is normally so cheap that it offers 

 little inducement for adulteration. Colophony which has been mixed 

 with it may readily be detected by shaking the freshly powdered resin 

 with petroleum spirit and shaking the filtrate, which should be colour- 

 less, with O'l per cent, solution of cupric acetate ; if colophony is 

 present the petroleum spirit will assume a vivid green colour. The 



