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 1PC1 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. 



Oxyanthrajuinone, 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 bibasic 

 acid ; soluble in alkalies, forming purple solutions. 

 The alcoholic solution g;ives blue precipitates, 

 C 14 H 6 (0 2 Ba)0 2 + IPO and C 14 H 6 (0 2 Ca)O 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. 



