MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 395 
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 trans- 
parency. Acids now produce an immediate 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 ob- 
tained, 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 suri-ounded 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 solution depositing on cooling crystals of 
the acid. 
Baryta water gives in a watery solution of rubianic acid a beautiful crimson floc- 
culent precipitate, while the liquid becomes colourless. If carbonic acid be passetl 
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 seems to be again precipitated in combination with baryta. Lime 
water produces in a watery solution of the acid a light red precipitate, while the 
liquid becomes colourless. If carbonic acid be now passed through the liquid the 
precipitate dissolves, forming a yellow solution, which on exposure to the air becomes 
red, but gives no red film, and on evaporation deposits no flocks, but leaves at last a 
red mass, which dissolves again in boiling water. Acetate of alumina and peracetate 
of iron produce no change in a watery solution of the acid. Nevertheless the latter 
* 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 precipitated from its alcoholic solution by 
acetate of copper, but not by acetate of lead. 
