DYE

DYE

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It does not fenfibly alter the natural tint, as itgives a deep and durable crimfon. It evenreftores tire crimfon to cloth dyed fcarlet by thecompound tin mordant.

■ The aftonifhing efleet of all the folutions oftin in heightening the colour of cochineal, ap-pears to have been iirft difeovered and put inpraftice by one Kufter, a German, who fettledat Bow, near London , about the year i543, pwhence fcarlet was called the Bow dye in thiscountry. It has been generally fuppofed thatthe change of the natural crimfon of this drugto fcarlet was owing Amply to the effect of thenitro-muriat of tin, which is the common fo-lution ufed by the dyers, but Dr. Bancroft hasfully proved (as indeed is acknowledged byBerthollet in his fecond edition) that this is amiftake, and that the nitrat or muriat or nitro-muriat of tin ufed alone only heightens thecolour of cochineal, but does not materiallychange its natural crimfon •, but that it is theaddition of tartar to the tin folution which con-verts the crimfon to that fiery bright fcarletfor which this dye is fo preeminently valuable.Now as fcarlet is a colour compofed of crimfonand yellow, and as tartar changes the cochinealcrimfon to yellow, it may be inferred that theAmple effect of the tartrite of tin (which fait isformed by double decompofition when the nitro-muriat of tin and tartar are mixed) is that ofadding a yellow. This pofition Dr. Bancroftfound by experiment to be accurate; for whencloth was dyed with cochineal, and the tartriteof tin fingly made by diffolving this metal inthe tartareous acid, the dye was a full fcarlet.An equal effedf was produced by fubftitutinglemon juice or elfe the pure citric acid to thetartareous. Berthollet alfo found that on dyeingthree famples of cloth, the firft with nitro-muriat of tin, tartar and cochineal in the pro-portions commonly ufed; the fecond with thefame ingredients but with a double proportionof tartar; and the third omitting the tartar,that the firff fample was of a fuil fcarlet, thefecond a fcarlet more inclining to yellow, andthe third a crimfon.

The folution of tin ufually employed by thedyers is prepared in the following way. Dilutenitric acid of the kind called ftngle aquafortis isthe acid ufed, and may be made by proper ma-nagement to take up about one-eighth of itsweight of tin. A fmall quantity of tin (pre-vioufly granulated by being poured when meltedinto cold water, kept brilkly agitated with abundle of rods) is put into a glafs veffel, to

which is added the aquafortis mixed with fromTT to i of its weight of common fait or falammoniac, and ftill further diluted with water.A ftrong action begins almoft immediately,without artificial heat, and it is the bufinefs ofthe preparer to'keep this action as moderate aspoflible, by fetting the veffel in a cool place andadding only fmall quantities of tin at a time, inproportion as the lalt added quantity is diffolved.By this method the acid becomes fully faturatedwith oxyd of tin, whereas if the heat generatedin the procefs is not checked, or if the acid istoo ftrong, the greater part of the tin willremain undiflblved in the form of a whiteoxyd. Even when well made, the folution (orfpirit as the dyers call it) is apt to coagulate bymere keeping and to depofit the oxyd of tin,which it cannot again be made to take up. Theufe of the muriat of foda or ammonia is toprevent the fpontaneous feparation of the tin.The muriatic acid fingly is a much better folventfor tin, taking up a large quantity and retainingit for any length of time, but the fimple muriatof tin, and indeed of many other metals, isfound to have a very corrofive effedt on thefibres of wool, and even (in a lefs degree) onthofe of linen and cotton.

To preferve the muriatic acid in the folution,and at the fame time to combine it with fomeother acid which has not fuch a corrofive effecton cloth, Dr. Bancroft recommends the murio-fulphuric folution of tin, as equal in efficacy tothe nitro-muriatic and much cheaper. For thispurpofe 14 ounces of granulated tin are to beadded to a mixture of two pounds of fulphuricacid of ordinary ftrength, with three pounds ofmuriatic acid. No particular precautions arerequired in making the folution, which will beequally permanent with or without artificialheat.

As the ftate of oxygenation of all metallic fo-lutions, and particularly of thofe of tin, very ma-terially affedts all their chemical properties, afew obfervatioos on this fu Eject may be men-tioned after deferibing the procefs of fcarletdyeing.

Woollen cloth is generally dyed fcarlet intwo operations, though a Angle one will fuffice,but in general is lefs convenient. To dye ahundred pounds of wool, 8 or 10 pounds oftartar are firft put into the boiler with a fuf-ficient quantity of foft water, and 6 or 8 ouncesof cochineal. Immediately afterwards 10 or12 pounds of the nitro-muriat of tin are added,and when the mixture is ready to boil, the cloth

* Bancroft.