208 Dr. Schunck on Rubian and its Products of Decomposition, 



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 

 is entirely removed from its solution by hydrate of alumina, to 

 which it communicates a light red colour, and also by hydrated 

 peroxide of iron, though not so easily as by alumina. Rubianic 

 acid dissolves easily in a boiling solution of perchloride of iron, 

 forming a dark greenish-brown liquid, which contains proto- 

 chloride of iron. The solution deposits nothing on standing, 

 and on evaporation only a small quantity of black powder sepa- 

 rates, which is probably a compound of alizarine and oxide of 

 iron. Acetate of copper gives in watery and alcoholic solutions 

 of the acid a brownish-red precipitate, which is soluble in boil- 

 ing acetic acid. Neutral acetate of lead turns the watery solu- 

 tion of the acid red, but produces no precipitate ; basic acetate 

 of lead, however, gives a copious red flocculent precipitate, just 

 as in a solution of rubian. An alcoholic solution of the acid 

 gives with an alcoholic solution of acetate of lead a light red pre- 

 cipitate, which after filtration of the alcoholic liquid dissolves in 

 pure water. On adding nitrate of silver to an aqueous solution 

 of the acid and boiling no change takes place, but on the addi- 

 tion of a few drops of ammonia a dark reddish-brown precipitate 

 slowly subsides as a fine powder, which is soluble in an excess of 

 ammonia, forming a red solution, which does not change, and 

 shows no signs of any reduction taking place when it is boiled. 

 On adding chloride of gold to a watery solution of the acid no 

 change takes place even on boiling, but on the addition of a 

 little caustic alkali metalUc gold is deposited, partly as a brown 

 powder, partly in shining scales. If rubianic acid be mixed 

 with water to which a quantity of erythrozym has been added, 

 the yellow crystals of the acid gradually disappear, and are 

 converted into alizarine. The liquid is found to contain sugar. 



It is impossible to dye with rubianic acid. Mordants acquire 

 in boiling solutions of the acid no more colour than in solutions 

 of rubian or rubianine. 



On submitting the acid to analysis the following results were 

 obtained : — 



I. 0*4605 grm., formed by the action of bicarbonate of baryta 

 on rubian, dried in the water-bath and burnt with chromate of 

 lead, gave 0*9445 carbonic acid and 0*2250 water. 



