MADDER.

237

from that substance a certain amount of colouring principle. Recent Zealandmadder-root, provided it be unbroken, can be washed with cold water withoutthe slightest loss of colouring matter. The experiment was made upon2 kilos, of fresh root, carefully cleaned from adhering earth with a sponge.When an aqueous infusion of madder is slowly evaporated in an open vesselexposed to the air there is formed on the surface of the liquid a pellicle, whichsoon sinks to the bottom, and is succeeded by the appearance of another,which goes on until the whole is evaporated to dryness. The extract): thusformed is only in part soluble in water. From the experiments made byRobiquet and Colin while preparing pure alizarin from Alsace madder, itfollows that in this madder at least a portion of the alizarin is present in astate soluble in water.* The quality of the water may seriously affedt the resultsof such experiments. Experiments instituted some years ago with fresh Zealandmadder and Zealand racine in sufficient quantity (5 kilos, of each) showthat cold water does not appear to extradf any of the tindtorial matters. Withground madder it is different. On drying the substances previously experi-mented with very carefully, powdering and dyeing with them against standardsamples of madder of known tindtorial value, no inferiority was found in theroots. On submitting them to analysis, the quantity of alizarin found didnot differ from that extradted from roots treated as usual. The above-mentioned chemists mixed 1 part of madder with 3 parts of water, filteredand pressed the substance upon a piece of cloth, and obtained a red-brownliquid, which in about ten minutes was converted into a jelly. This wasfound to be a mixture of pedtic acid and gelatin, which had becomeinsoluble. As far back as 1823, Kuhlmann observed that madder contains ayellow colouring matter, very soluble in water, which he named Xanthin.He obtained this xanthin by exhausting madder with boiling alcohol,evaporating the solution to dryness, and taking up the dry residue with water,which dissolves the xanthin, and leaves any alizarin that may have beenextradted undissolved. The fluid is first filtered, then acetate of lead isadded, whereby a brownish matter is precipitated. This is removed byfiltration, and to the filtrate baryta-water is added, whereby a precipitate isformed, containing xanthin combined with oxide of lead. This precipitateis thoroughly washed, and, after having been suspended in pure water, isdecomposed with very dilute sulphuric acid. The sulphates of lead andbaryta having been removed, the liquid is evaporated to dryness, the dryresidue taken up with alcohol, and again evaporated. The xanthin is thenleft as a viscid, bright orange-coloured substance readily soluble in water. Ithas a sweetish bitter taste, and is soluble in alcohol, but insoluble in ether.Alkalies turn it red. Neither the neutral nor the basic acetate of lead givesa precipitate with this substance. It dyes mordanted cotton a bright orange.It is decomposed by strong sulphuric acid, yielding chlorrubin, so that thissubstance is a mixture of at least two substances as well as glucose. Zealand,Alsace, and Avignon madder contain far more xanthin than the madderfrom the Levant and Barbary.

Runge obtained a yellow soluble substance by exhausting Zealand madderwith sixteen times its weight of water, and precipitating the solution with

* " Annales de Chimie et de Phys.,” t. xxxiv., p. 225 ; and " Bulletin de la Soc. Indust, de

Mulhouse," t. i., p. 10S. 1828.