The Chemical Gazette 335, 1.10.1856
By MM. E. M. Plessy and P. Schützenberger.
Madder, and even madder-flowers, contain the colouring principle mixed with too much foreign matter, to allow a single treatment with water in a closed vessel to give very distinct results. Instead of operating on madder, the authors have therefore employed the concentrated methylic extract, which is the most conveniently prepared according to a process indicated by Gerber and Dollfus.
10 grms. of this extract, previously triturated, were put with 100 grms. of distilled water into a copper tube closed by a screw-stopper. The apparatus was placed in an oil-bath, and heated for fifteen minutes to 482° F. On cooling, the liquid was entirely filled with crystalline needles of a fine pale red. These crystals were easily separated by decantation from the undissolved excess of extract, which remained in a hard lump at the bottom of the tube. The weight of the crystals was only 1.63 grm.; and the residue, treated in the same way with 100 grms. or water, furnished a fresh quantity of crystals. In nine operations the colouring matter was exhausted, and the water no longer acquired colour. Nearly a fourth of the extract employed was obtained in crystals; the residue consisted of a brown resin, the alcoholic solution of which no longer acquired a violet colour with ammonia.
The colouring matter was in a state of great purity; it was crystallized a second time in water of 482° F., to get rd of he little resin which it might still retain. Its physical properties and analysis show it to be identical with the sublimed alizarine of Robiquet and Collin. Its dyeing power is also identical, and much greater than that of madder or madder-flowers; the authors value it at 80 times that of madder-flowers, and 40 times that of madder.
The solubility of alizarine in water at different temperatures is as follows: - At 212°F. 100 grms, of water dissolve 0.034 302°F ... ... 0.035 392°F ... ... 0-82 437°F ... ... 1.70 482°F. ... ... 3°16
- Comptes Rendus, July 21, 1856, p. 167.
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