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



The process of decomposition just described is always accom- 

 panied by an absorption of oxygen. In order to ascertain the 

 quantity of the latter which an alkaline solution of rubian was 

 capable of absorbing, I took 4*2280 grms. of rubian, which after 

 deducting the inorganic matter with which it was contaminated, 

 was equivalent to 4*1049 grms. of the pure substance, dissolved 

 it in hot water, poured the solution into a graduated tube, added 

 to it a solution of about 6 grms. hydrate of baryta, filled the rest 

 of the tube with mercury, and then inverted it over mercury. 

 Oxygen gas was then introduced, and the liquid was from time 

 to time agitated with the gas, in order to bring every portion, 

 and especially the red flocculent precipitate produced by the 

 baryta, and which sank to the bottom of the solution, into fre- 

 quent contact with it. After 143 days I found that 147 cubic 

 centimetres of gas had been absorbed. The contents of the 

 tube were then removed and filtered. There remained on the 

 filter a red baryta compound, which, on being treated as usual, 

 yielded rubianic acid and rubidehydran, as well as a small quan- 

 tity of alizarine. To the red liquid sulphuric acid was added ; 

 the excess of acid was removed with carbonate of lead, and sul- 

 phuretted hydrogen having been passed through the filtered 

 liquid, the latter, after being filtered again from the sulphuret 

 of lead, was submitted to distillation. The distillate was acid, 

 and after being neutralized with carbonate of soda and evapo- 

 rated, left a saline residue having all the characters of acetate of 

 soda. Acetic acid is therefore another product formed in this 

 process, but whether this acid is an essential product of decom- 

 position or not, still remains doubtful. The residue of the 

 distillation contained rubihydran, which was separated by pre- 

 cipitation with basic acetate of lead, as before described, and a 

 little sugar, which was obtained from the liquid filtered from the 

 lead precipitate. The sugar and the alizarine were probably 

 secondary products of decomposition formed from the rubianic 

 acid by the action of the alkali. 



Rubianic Acid. — This substance really merits the name of an 

 acid, for though its acid properties are not well marked, the fact 

 of its giving crystallized compounds with the alkalies is a suffi- 

 cient indication of the class in which it should be placed. It 

 crystallizes from its watery solution in silky needles of a pure 

 lemon-yellow colour, which when dry form a light, bulky inter- 

 woven mass. Sometimes it is slowly deposited from its watery 

 solution in grains and masses of an indistinctly crystalline form, 

 which have an orange tinge. This diifference in appearance is 

 due to some impurity, which may be removed by redissolving 

 the acid in boiling water and adding a little animal charcoal, 

 when the acid crystallizes rapidly from the filtered solution in 



