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



leder are similar to those of rubianic acid. It is therefore very 

 probable that the two acids are identical. But the description 

 given by Rochleder of his acid is not sufficiently minute to 

 enable me to come to a decision as to their identity, and the 

 composition ascribed to it by him (C 54'48, H 5*16, 40*36 per 

 cent.) differs so much from that of rubianic acid as almost to 

 lead one to beheve that they are not the same. Until therefore 

 the properties and composition of ruberythric acid have been 

 more accurately studied, it will be impossible to arrive at any 

 positive conclusion on this point, and for the present the two 

 acids must be considered as distinct*. Rochleder has ventured 

 to express his conviction that rubian is nothing but impure 

 ruberythric acidf. The experiments which I have here described 

 must lead to the conclusion that such an opinion cannot for an 

 instant be entertained. If rubianic acid and ruberythric acid are 

 identical, then Rochleder has only committed the common error 

 of mistaking a product for an educt. 



Rubidehydran, — As obtained by the method above described, 

 this body is not perfectly pure. It may be purified by redis- 

 solving it in water, evaporating the solution to a syrup, and then 

 adding a quantity of alcohol, which precipitates a reddish-yellow 

 glutinous substance mixed with sulphates of lime, magnesia, and 

 soda. The alcoholic liquid having been allowed to clear, is de- 

 canted and evaporated to dryness, when it leaves a dark yellow 

 or reddish-yellow, brittle, transparent residue like gum or var- 

 nish, which cannot be distinguished from rubian in appearance. 

 It still gives, when burnt, a quantity of ash, consisting of sul- 

 phates of lime and magnesia, but I did not attempt to purify it 

 any further, for fear of inducing a change in its composition. 

 Rubidehydran resembles rubian exactly in most of its properties. 

 It is not in the least deliquescent. If it shows any tendency to 

 deliquesce on exposure to the air, this must be attributed to its 

 containing some impurity. It has a strongly bitter taste. The 

 watery solution is yellow, and when boiled, with the addition of 

 sulphuric or muriatic acid, deposits yellow flocks, and after cool- 

 ing appears almost colourless. Like rubian, it is also decom- 

 posed on boiling the watery solution with the addition of caustic 

 potash or soda, the solution becoming purple and depositing 

 yellow flocks on supersaturating the alkali with acid. It is not 

 precipitated from its aqueous solution by any earthy or metallic 



♦ The easiest way of arriving at a conclusion would be by determining 

 the amount of alizarine which ruberythric acid by its decomposition is 

 capable of yielding. If Rochleder's formula C^^ H^o O^ be accepted, it 

 should give 67*04 per cent, of alizarine. Variations of several per cent, in 

 the amount of aUzarine obtained would still allow a positive decision to be 

 arrived at. 



t Ann. der Chem, und Pharm. vol. Ixxxii. p. 215. 



