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DYEING AND CALICO PRINTING.

Since the researches of Persoz, Gautier de Claubry, Runge, and others, theexistence of another red pigment, purpurin, has been admitted. It differsfrom alizarin by the purple colour of its alkaline solution, whilst alizarinyields violet-blue solutions. Kopp subsequently succeeded in producing, on amanufadturing scale, a preparation containing no alizarin, and exhibiting allthe charadters of purpurin. One kilo, of this produdt represents about60 kilos, of Alsace madder. It was carefully investigated by Schiffert andSchiitzenberger. They considered the existence of the following colouringmatters as decided:—(i), alizarin; (2), purpurin; (3), pseudopurpurin—these three are either red or orange, and yield red shades with aluminousmordants ; (4), an orange matter which likewise yields, with aluminous mor-dants, a red shade ; (5), a yellow matter, xanthopurpurin (not to be confoundedwith Kuhlmann’s xanthin), yielding, with aluminous mordants, yellow shades.

The existence of the three last colours mentioned by Schiitzenberger isconsidered by Schunck more than doubtful. They are either mixtures or areidentical with substances previously known. The yellow colour has exadtlythe same percentage composition as rubiacih. The latter is distinguishedfrom all the other madder colours by dissolving in per-salts of iron with apurple or brownish-red colour; this simple test would have decided theidentity or distinbtion of the two bodies. The practice of giving little morethan analyses of new substances without any account of their characteristicreactions is highly objectionable.

Alizarin, or lizaric acid, is the most important and the most valuablecolouring matter contained in madder. It is the only one which yields fastdyes capable of resisting the operation of cleansing. By a series of experi-ments made by Schiitzenberger with variously-mordanted cloths, submittedafterwards to dye-becks containing madder and its commercial preparations,it has been fully proved that in these dyed shades—Turkey-red included—alizarin alone is present. Hence it is inferred that alizarin pre-exists in themadder-root, and is not a product of any subsequent decomposition.

Alizarin is readily obtained in crystals, both by sublimation and by theevaporation of its solutions. It is procured as hydrate by the slow evapora-tion of its ethereal solution. In this state alizarin has the appearance ofmicaceous plates of a golden-yellow lustre, not unlike mosaic gold. At 100° C.it loses 3 equivalents of water. The anhydrous crystals exhibit brilliantprismatic needles of a red tint, verging upon yellow. These crystals are bestobtained by sublimation at 240 0 C., or by deposition from strong boilingalcohol not containing more than 14 per cent of water. This process only yieldsgood crystals with alizarin that has once, at least, been purified by sublima-tion. It can also be obtained by crystallisation from water, in a sealed tube,at 250° or 280° C., or, better still, by the use of a mixture of 9 parts of waterand 1 part of alcohol.

Alizarin fuses at 215° C., and sublimes between 215 0 and 240°, but if keptfor a long time at 100° C. it slowly evaporates, more readily if placed in acurrent of water or of steam. If it is desired to sublime alizarin withoutdecomposition, it should be heated in small quantities only. The best methodof subliming alizarin, from impure alizarin, alcoholic madder extract, extractof garancin, or any other substance containing alizarin, is to place the sub-stance to be operated upon at the bottom of a small porcelain capsule capable