408 ALIZARIN. 



Anthraquinonedisulphuric acid, 



C 14 H 6 2 (S0 2 .OH) 2 . Dichlor- and dibromanthracene dis- 

 solve readily in fuming sulphuric acid with the aid of 

 gentle heat, forming dichlor-or dibromanthracenedisul- 

 phuric acids, C 14 IFC1 2 (S0 2 .OH) 2 , which when treated 

 with oxidizing agents, and also when heated with 

 concentrated sulphuric acid, are easily converted into 

 anthraquinonedisulphuric acid. The barium salt, 

 C 14 H 6 2 .(S0 3 ) 2 Ba, is difficultly soluble in water. 



Oxyanthraguinone, C 14 H 8 3 = C 14 H 7 (OH)0 2 . Is 

 formed by fusing potassium anthraquinonedisulphate 

 with potassium hydroxide, when the action is moder- 

 ated by the addition of indifferent bodies (sodium 

 chloride, chalk). Yellow laminae or needles, sublim- 

 able. Soluble in alkalies and baryta-water forming 

 reddish-brown solutions. 



Alizarin (Dioxyanthraquinone), C 14 H 8 4 = 

 C 14 H 6 (OH) 2 2 . Is contained in old madder, and is ob- 

 tained from rubianic acid (see Glucosides, p. 418), which 

 is contained in fresh madder, by boiling with acids or 

 alkalies. It can be artificially prepared by heating 

 dichloranthraquinone, mono- or dibromanthraquinone, 

 oxyanthraquinone and potassium anthraquinonedisul- 

 phate with potassium hydroxide at 250-270. The 

 mass is then dissolved in water, precipitated with hy- 

 drochloric acid, and the precipitate purified by recrys- 

 tallization from alcohol, or, better, by sublimation. 

 Long, orange-red needles. Carefully heated, sublim- 

 able without decomposition. Almost insoluble in cold 

 water, more easily in boiling water, in alcohol and 

 ether. 



Towards bases it conducts itself like a weak bi basic 

 acid ; soluble in alkalies, forming purple solutions. 

 The alcoholic solution gives blue precipitates, 

 C 14 H 6 (0 2 Ba)0 2 + H 2 and C 14 H 6 (0 2 Ca)0 2 + H 2 0, with 

 baryta- or lime-water ; the solution in alkalies gives a 

 beautiful red precipitate (madder lake) with a solution 

 of alum. 



