440 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
probably formed by the application of too great a heat in the process of drying the 
madder. There are two ways in which this substance may be removed. The first 
consists in adding to the solution sugar of lead, which precipitates it in dark reddish- 
brown flocks. These being separated by filtration, the rubian is precipitated by means 
of basic acetate of lead, and the light red compound or lake, after being washed with 
alcohol to remove all excess of lead salt, is decomposed either with sulphuretted 
hydrogen, or better still with sulphuric acid, the excess of the latter being removed 
by carbonate of lead. The other method, which is more expeditious, consists in add- 
ing sulphuric acid to the cold solution, after the greatest part of the alcohol has been 
evaporated. The sulphuric acid completely decomposes the foreign substance, pro- 
vided a sufficient quantity is employed, and converts it into a substance which renders 
the solution milky, and then falls in the shape of brown resin-like drops. The sul- 
phuric acid being neutralized with carbonate of lead, the filtered solution, which is 
yellow and now contains pure rubian, is evaporated to dryness. It is necessary to em- 
ploy carbonate of lead, and not carbonate of baryta, for the neutralization of the sul- 
phuric acid in both cases ; for if carbonate of baryta be used, the bicarbonate of baryta 
which is usually formed, even if present only in small quantity, causes part of the 
rubian to undergo decomposition. In evaporating the solution of rubian, care must 
be taken not to employ too great a heat when the evaporation approaches to a con- 
clusion. The ordinary heat of a sand-bath is sufl^icient to decompose rubian in great 
part, especially if a large quantity of the substance be present. It is therefore ad- 
visable, when the solution is nearly evaporated, to complete the evaporation either in 
a water-bath or in a moderately warm place. The free access of atmospheric air 
need not be feared, as rubian is not thereby decomposed, unless some other substance 
be present at the same time. The quantity of rubian which I have obtained, accord- 
ing to this method of preparation, amounts to about 1000 grs. from 1 cwt. of madder. 
It may be mentioned that the method of preparing rubian, as above described, by 
means of animal charcoal and alcohol, is not new in principle. Lebourdais* has 
proposed the same method for the preparation of several vegetable substances, such 
as colocynthine, strychnine, quinine, &c. 
Properties of Ruhian . — When prepared according to the method just described, 
rubian is obtained as a hard, dry, brittle, shining, perfectly uncrystalline substance, 
similar in appearance to gum or dried varnish. It is not in the least deliquescent, as 
xanthine is described to be. In thin layers it is perfectly transparent and of a beau- 
tiful dark yellow colour. In large masses it appears dark brown. It is very soluble 
in water and alcohol, more so in the former than the latter, but insoluble in ether, 
which precipitates it from its alcoholic solution in brown drops. Its solutions have 
an intensely bitter taste. When it is pure, its solution in water gives no precipitates 
with the mineral or organic acids, nor with salts of the alkalies or alkaline earths. 
♦ On the Nature and Preparation of the Active Principles of Plants, Annal. de Chim. et de Phys. 3“' ser. 
t. xxiv. p. 58. 
