222 Dr. Sclmnck on Rubian audits Products of Decomposition. 



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, provided 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 sulphuric 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 employ car- 

 bonate of lead, and not carbonate of baryta, for the neutralization 

 of the sulphuric 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 un- 

 dergo decomposition. In evaporating the solution of rubian, 

 care must be taken not to employ too great a heat when the 

 evaporation approaches to a conclusion. The ordinary heat of 

 a sand-bath is sufficient to decompose rubian in great part, 

 especially if a large quantity of the substance be present. It is 

 therefore advisable, when the solution is nearly evaporated, to 

 complete the evaporation either in a water-bath or in a mode- 

 rately 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, according 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 de- 

 scribed, 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 Rubian. — 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 beautiful 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 aether, which pre- 

 cipitates 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. Acetate of 

 alumina, alum, protacetate and pcracetate of iron, acetate of zinc, 

 neutral and basic acetate of copper, acetate of lead, nitrate of 



* On the Nature and Preparation of the Active Principles of Plants, 

 Ann. de Client, et de Phys. 3 me ser. t. xxiv.p. 58. [Chem. Gaz. vol.vi.p.442.] 



