Dr. Schunck on Rubian and its Products of Decomposition. 207 



colour changes gradually from red to purple, and after prolonged 

 boiling to violet, similar to that of a solution of alizarine in 

 caustic alkali, the colour being generally so intense as to deprive 

 the solution of its transparency. Acids now produce an imme- 

 diate precipitate of dark yellow flocks, while the liquid becomes 

 almost colourless. If the action of caustic alkali has not been 

 continued long enough to produce a complete decomposition of 

 the acid, then after some time crystals of the latter appear in 

 the midst of the flocculent precipitate. The flocks consist of 

 alizarine, but less pure than when the decomposition is effected 

 by means of sulphuric or muriatic acid. On decomposing a 

 considerable quantity of the acid by means of caustic soda, and 

 treating the precipitated flocks in the same manner as those 

 formed by the decomposition of rubian with acids or alkalies, I 

 obtained, besides alizarine, a trace of verantine and a small 

 quantity of a substance resembling rubianine or rubiadine*. 

 The liquid filtered from the flocks contains sugar. Rubianic 

 acid dissolves in caustic ammonia with the same colour as in 

 caustic potash or soda, but with much greater difficulty than in 

 the latter. The solution does not change its colour, however 

 long it may be boiled, and on adding an excess of a stronger 

 acid, the rubianic acid crystallizes out unchanged. On'evapo- 

 rating the ammoniacal solution to dryness it loses part of its 

 ammonia, leaving some yellow crystals of acid surrounded by a 

 red uncrystalline coating like gum. The latter dissolves in cold 

 water, but on evaporation the solution again gives yellow crystals. 

 If to a boiling watery solution of the acid carbonate of ammonia 

 be added, the solution becomes red, and deposits on cooling 

 crystals of the ammonia salt, which have the same colour and 

 appearance as the potash salt. These crystals may be dried 

 without losing their ammonia, but, like the other alkaline salts, 

 are decomposed on redissolving them in boiling water, the solu- 

 tion depositing on cooling crystals of the acid. 



Baryta water gives in a watery solution of rubianic acid a 

 beautiful crimson flocculent precipitate, while the liquid becomes 

 colourless. If carbonic acid be passed through the liquid the 

 precipitate gradually dissolves, forming a clear yellow solu- 

 tion ; but if this solution be left exposed to the air, its surface 

 becomes covered with a red film, and on evaporation it deposits 

 a quantity of red flocks, until at length the whole of the acid 



* This substance is light yellow and crystalline. When heated it is 

 volatilized, giving a sublimate of yellow shining needles and scales. It is 

 insoluble in boiling water, but dissolves in boiling nitric acid, and crystal- 

 lizes out of the solution again on cooling in yellow needles. It is preci- 

 pitated from its alcoholic solution by acetate of copper, but not by acetate 

 of lead. 



