ASTRINGENTS.

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serves for the production of that shade of colour. The grey obtained by theuse of Sicilian sumac is somewhat reddish, and this the more so the higherthe temperature of the decodtion while applied; it is therefore necessary notto increase the heat above 50°, and to steep the goods only for about half-an-hour. The shade of grey produced by galls is more ashy, while thatproduced by bablah holds an intermediate position between the two.

The French sumac is less liable to yield foxy greys and blacks by beingexposed to a too high temperature. Nutgalls are rarely employed for dyeingprinted goods, on account of the property of galls of injuring the ironmordants, that is to say, dissolving them, and spoiling the pattern by makingit spotted; a small quantity of galls added to logwood for black dyeing turnsthe shade bluish-black. Bablah yields greys as pure as galls, while the colouris brighter than that yielded by sumac, and it moreover soils the whiteportions of the patterns less. Valonia holds the middle place between gallsand bablah as regards the colours it produces, but it is most advantageouslyemployed along with logwood ; when it is desired to dye calico, silk, or wooluniformly black, astringent matters are very generally mixed with logwood.For cotton, for instance, the operation is begun with a steeping of the tissuefor 12 hours in a bath of myrobalans, sumac, or galls, the goods being placedtherein while hot, and left until the liquid is quite cold ; the pieces are nextpassed through lime-water (weak milk of lime), then put in a bath of sulphateof copper, after that in a boiling logwood decodtion, and next again ina solution containing sulphates of iron and copper mixed. Sometimes theoperation is performed by first mordanting the goods with a salt of iron, anddyeing in a bath made up of decodtions of galls, logwood, and sumac mixed.Woollen goods, broadcloth chiefly, are dyed black by first dyeing them indigo-blue (vat blue), and after that the tissue is placed in a boiling bath made upof myrobalans and logwood (so called Sedan black), or in a boiling bathof sumac, logwood, and fustic (so called Elbeuf black); afterwards, there isadded to these baths, while the goods are yet steeped therein, either sulphateof iron alone, or a mixture of sulphate of iron and sulphate of copper, or, inplace of these, bichromate of potash. Silk is dyed black by being alternatelysteeped in astringent baths and a solution of pyrolignite of iron.

Decodtions of galls, sumac, and valonia are ingredients in some kinds ofsteam-grey and application-grey for cotton, along with acetate or pyroligniteof iron; the same astringent decodlions, mixed with logwood extradl and redliquor, or an iron mordant accompanied by an oxidising material, i.e., a copper-salt and sal-ammoniac, are applied for the production upon cotton and wool ofso-called wood, wainscot, and other complex colours. The astringent decoc-tions are also used, along with logwood extradt, for the production upon silk ofsome steam-blacks, nitro-sulphate of iron being used as a mordant.

Our ordinary black writing-ink is a ready-made colour which, by its mode.ofpreparation, is capable of fixing itself on paper. The best ink is made by addingto a decodtion of Aleppo, or Chinese galls, a solution of proto-sulphate of iron, inwhich case the precipitation of the tanno-gallate of iron is rendered so slowas to make it appear as if the ink were a solution, which, however, it is not;and the addition of some gum and sugar is required to keep the precipitatesuspended. One of the great drawbacks of ink thus prepared is its becomingreadily mouldy and viscous. The former defedt is best remedied by the