MADDER.
267
Thejpetroleum oil is next again applied to the same purpose; three or fourtreatments as described are sufficient to exhaust all the alizarin ; the re-maining greenish-black mass can be utilised for the preparation of a peculiarcolouring matter (xanthazarin*), which possesses some curious properties.The pulverised greenish-black matter is gradually and cautiously introducedinto a mixture of nitric acid with 10 parts of water heated to ioo°, care beingtaken to avoid too strong adion, and the quantity of the material beingadjusted to three-fourths of the weight of the nitric acid employed. Abrownish-yellow matter hardly soluble in water is obtatned. This xanthazarinis sparingly soluble in boiling water, very soluble in alcohol and ether,yielding a deep yellowish-brown coloured solution ; with aqueous solutions ofthe caustic and carbonated alkalies it yields a very rich and brilliant orangesolution. It dyes woollen and silken fibres very readily even withoutmordants, producing a deep golden-yellow colour. Cotton mordanted withalumina and dyed with this material assumes an orange-yellow colour.Reducing agents, viz., nascent hydrogen, sulphuretted hydrogen, hyposulphites,the protochlorides of tin and iron, deoxidise xanthazarin, and convert it into ared colouring material, which yields upon mordanted silken, woollen, and cottonfabrics colours approaching those produced by impure purpurin. Wool, pre-viously dyed with xanthazarin a golden-yellow colour, assumes, when placed ina boiling solution of tin-salt, a carmine-red colour. The colouring materialobtained by the reduction of xanthazarin is almost insoluble in water, and theshades it produces on textile fabrics are faster than those of the unreducedsubstance, which, however, stand ordinary washing.
M. Camille Koechlin was the first to suggest that alizarin might be dire&lyobtained from madder by sublimation. The volatility of alizarin is, however,not very great, and its sublimation point is too near that of its decompositionby heat to make it practicable to sublime it from either madder, garancin, orfleur de garance, while if it were possible to overcome this difficulty an enor-mous quantity of empyreumatic matters would accompany the sublimedproduct, rendering its further purification troublesome and expensive. M. C.Kcechlin and afterwards M. E. Kopp have endeavoured to obtain alizarin frommadder or garancin by the aid of superheated steam. The apparatus employedby Kopp for this purpose, represented in the annexed woodcut, consists of—a, a steam boiler, b , steam pipe leading to b, a furnace for superheating thesteam which enters by d ; it leaves by e , a tube fitted with a stopcock, h.p, spherically shaped chamber, divided internally into two compartments bymeans of a perforated diaphragm, shown by a dotted line, and placed there toadmit of a thorough admixture of the superheated with the ordinary steam,which latter is admitted by opening the stopcock g more or less. *, thermo-meter. c c, copper cylinder for containing dry garancin placed between two
* Whilst madder root has been the object of a vast amount of research, the leaves, stem,seed, and that woody matter which intervenes between the root and the parts just namedhas been very little investigated. Many intelligent madder growers, both in Zealand andFrance, hold that the colouring principles are developed in the parts above ground, and re-turned to the root there to undergo further elaboration. Experiments have been undertakento determine this question. Though these were never completed, it appears that the stemsand seeds contain a substance closely related to xanthazarin. The first indications of alizarinin the plant are found about 1 inch below the soil. The woody part of the stem containsneither alizarin nor purpurin.