Dr. Schunck on Ruhian and its Products of Decomposition. 213 



air-tight. The other half was mixed with the same quantity of 

 caustic soda and left exposed to the air. After twenty-one days 

 both liquids were examined in the same manner. The soda was 

 supersaturated with acetic acid, the liquid was again rendered 

 alkaline with ammonia, and then chloride of barium was added, 

 which gave in each case a red precipitate. This precipitate was 

 treated as usual with sulphuric acid and carbonate of lead, and 

 the filtered liquid was evaporated to dryness. From that part 

 of the solution which had been enclosed in the bottle I obtained 

 in this manner a quantity of a substance resembling rubian, 

 which was probably rubidehydran, but not a trace of rubianic 

 acid; whereas, by adding baryta water to the liquid filtered 

 from the precipitate with chloride of barium, leaving the mix- 

 ture to stand exposed to the air for some time, filtering and 

 treating the substance left on the filter with sulphuric acid as 

 usual, I obtained a small quantity of the acid. On the other 

 hand, the precipitate with chloride of barium from the second 

 half of the solution, which had been left in an open vessel, 

 yielded at once 0'60 grm. of rubianic acid as well as a quantity 

 of rubidehydran, but the liquid filtered from this precipitate, on 

 being mixed with baryta water and treated as before, gave no 

 more acid. Hence it follows that the presence of oxygen is as 

 essential as that of alkalies to the formation of this acid. 



As regards the manner in which the formation of rubianic 

 acid takes place, we may suppose it to be effected in two ways. 

 Assuming 1 equivalent of rubian to absorb 10 equivalents of 

 oxygen, it may then yield 1 equivalent of rubianic acid, 4 equi- 

 valents of carbonic acid, and 5 of water, as the following equa- 

 tion will show : — 



C66 H34 030 _,_ 100 = C^2 H29 0^7 + 400^ + 5H0. 



But since acetic acid is found among the products of decom- 

 position, it is possible that this acid takes the place of carbonic 

 acid, and the equation will then appear as follows : — 



cm H34 030 + 20 = C^2 H29 Q^^ + C^ H^ 0^ + 2H0. 



It is a very remarkable circumstance, that a body like rubianic 

 acid, which belongs to a class of a highly complex nature, and 

 having in general a high atomic weight, should owe its forma- 

 tion to a process of oxidation. It is probably the first known 

 instance in which the formation of a body of this class by means 

 of oxidation has actually been observed. 



Some years since Rochleder described a body obtained from 

 madder to which he gave the name of ruherythric acid*. This 

 body, like rubianic acid, is decomposed by strong acids into ali- 

 zarine and sugar, and the other properties mentioned by Roch- 

 * Berichte der Wiener Academic, April 1851. 



