MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION, 401 
4 equivalents of carbonic acid, and 5 of water, as the following' equation will show; — 
C56 H34 Ogo-}- 10 O=C 52 H29 O27 + 4CO2+5HO. 
But since acetic acid is found among the products of decomposition, it is possible 
that this acid takes the place of carbonic acid, and the equation will then appear as 
follows : — ■ 
Cjg H34 030 + 20= C52 H29O27 + C4 H3O3 + 2FIO. 
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 formation 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 ruberythric acid*. This body, like rubianic acid, is decomposed by 
strong acids into alizarine and sugar, and the other properties mentioned by Roch- 
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 5T6, O 40*36 per cent.) differs so much 
from that of rubianic acid as almost to lead one to believe 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-l-. Rochleder 
has ventured to express his conviction that rubian is nothing but impure ruberythric 
acid:|:. 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. 
Ruhidehydran . — As obtained by the method above described, this body is not perfectly 
pure. It may be purified by redissolving 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 decanted and evaporated to dryness, when it leaves 
a dark yellow or reddish-yellow, brittle, transparent residue like gum or varnish, 
which cannot be distinguished from rubian in appearance. It still gives, when burnt, 
a quantity of ash, consisting of sulphates of lime and magnesia, but I did not attempt 
* Berichte der Wiener Academic, April 1851. 
t The easiest way of arriving at a conclusion would be by determining the amount of alizarine which rub- 
erythric acid by its decomposition is capable of yielding. If Rochleder’s formula C72 O4Q be accepted, it 
should give 67'04 per cent, of alizarine. Variations of several per cent, in the amount of alizarine obtained 
would still allow a positive decision to be arrived at. 
t Ann. der Chem. und Pharm. B. Ixxxii. S. 215. 
3 H 2 
