MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
391 
and then treated in the same manner as the red flocks obtained by means of bicar- 
bonate of baryta, affords in each caserubianic acid and rubidehydran, while the liquid 
contains rubihydran. If a small quantity of any acid be added to a watery solution 
of rubian, and if the acid be then neutralized with carbonate of baryta, the small 
quantity of bicarbonate of baryta formed is sufficient to induce a decomposition of 
the rubian, for the filtered solution on exposure to the air very soon begins to deposit 
red flocks, which consist of rubianic acid and rubidehydran in combination with 
baryta. It is for this reason that I have recommended the employment of carbonate 
of lead instead of carbonate of baryta for the purpose of neutralizing the sulphuric 
acid used in purifying rubian=^. Even oxide of lead is a sufficiently strong base to 
cause rubian to undergo this process of decomposition, when oxygen is present at the 
same time. If rubian be precipitated from its watery solution by means of basic 
acetate of lead, and the lead compound be left exposed to the air for a short time, it 
will be found no longer to contain unchanged rubian. If the compound be decom- 
posed with sulphuric acid in the cold, and the excess of acid be neutralized with 
carbonate of lead, the filtered solution deposits during evaporation crystals of rubianic 
acid, and leaves at last a brown deliquescent mass, which unless it be strongly dried 
is with difficulty removed from the vessel containing it-f-. In short, whenever rubian 
is brought into contact at the same time with oxygen and an alkaline or other strong 
base, it undergoes decomposition. Hence it follows, that in preparing the so-called 
xanthine according to the methods proposed by Kuhlmann, Berzelius, Runge and 
Higgtn, as well as the ruberythric acid of Rochleder, the use either of alkaline 
earths or basic acetate of lead being prescribed by all these chemists, products of the 
decomposition of rubian must in every case be formed. 
For the purpose of preparing the three bodies which result from this process of 
decomposition, it is not necessary to employ pure rubian. If madder be extracted 
with boiling water, and sugar of lead be added to the extract, a purple precipitate is 
produced, and ammonia being added to the filtered liquid, the whole of the rubian is 
precipitated together with some chlorogenine in combination with oxide of lead. 
The precipitate is decomposed with sulphuric acid in the cold, and the excess of the 
acid is removed by means of carbonate of lead. To the filtered solution a quantity 
of baryta-water is to be added, and the baryta is then converted into bicarbonate of 
baryta by a stream of carbonic acid gas. The solution is then left exposed to the 
air for some time and then slowly evaporated. The red flocks which are deposited 
are collected on a filter as they form, and after being treated in the same way as the 
flocks from pure rubian, yield rubianic acid and rubidehydran. The liquid filtered 
* See Philosophical Transactions for 1851, p. 440. 
t In purifying ruhian by precipitation with basic acetate of lead, as described in the first part of this paper, 
care must be taken to wash the precipitate with alcohol and not with water. If the former be employed, 
decomposition is almost entirely prevented, whereas in using water the rubian in the precipitate undergoes 
complete decomposition during the short time necessary for edulcoration. 
MDCCCLV. 3 G 
