DYE

f

DYE

383

)

(previoufly wetted) is put into the dyeing liquorand turned through it by a winch for an hourand a half, the liquor being kept boiling thewhole time. The cloth is then taken out andrinced, and is found to have acquired by thisfull operation a full flefli colour. The boileris emptied, and again filled with frefli water,and when nearly boiling, from five to fix poundsof powdered cochineal (according to the depthof colour wanted) are thrown in and wellftirred, after which about io pounds more ofthe folution of tin are added, and the cloth isthen put in and turned through the boilingliquor at firft brilkly, afterwards flowly, for halfan hour. It is then walhed and dried in theufual manner. The average proportion of co-chineal to dye a full fcarlet is an ounce to apound of the cloth, and hence from the highprice of this article the cochineal dye is one ofthe molt (if not the molt) expenfive of all theprocefles in the whole art of dyeing.

This dye may be given apparently with equaleffedt by a fingle procefs, that is, by mixingtogether the whole quantity of tartar, folutionof tin, and cochineal at once, and palling thecloth through the bath for a fufficient time; forthe affinity between the wool, and the mordant,and the colouring matter is fo ftrong, that thistriple union takes place at once, and with greatforce. Or the whole of the tin and tartar maybe ufed in the firft operation, and the whole ofthe cochineal in the fecond.

It may alfo be obferved that a great dif-ference is found in the refpective proportionsof thefe ingredients, ufed by different dyers.

When a very bright flame-coloured fcarletis wanted, a little yellow fuftic is added to thefirft bath, or elfe fome turmeric is added to thecochineal in the fecond. This gives both ayellow ground and mixes a portion of yellowwith the fcarlet. Thefe additions are difeoveredby cutting the cloth, for in this cafe the innerpart will be found dyed fimply yellow, the rea-fon of which is, that in the common procefsthe cochineal does not penetrate the inner partof the cloth, fo that where thefe yellows are notufed, this part remains white. If the fcarlethas too much of an orange tint, this is cor-rected by afterwards boiling the cloth in hardwater, or one that contains any earthy fait.

It is on account of the eafe with which al-moft any alkaline or earthy fait counteracts theyellow part of all thefe colours, that fcarletcloth is always changed more or lefs to a rofe orcrimfon by the procefs of fulling. Hence too

* Jour, dc I

the fcarlet is always given to wool after it ismanufactured, and not in the ftate of yarn.

After the full fcarlet has been given to thecloth, the liquor ftill retains part of the co-chineal with a large portion of the mordant, andthis is ufed for the lighter dyes, or with the ad-dition of fuftic, madder, and other ingredients,it is employed for a vaft variety of mixed or de-graded reds, orange, &c. Much technical lkiilfeems to he required to make the utmoft advan-tage of thefe refidues, which are ftill very va-luable.

It does not exaCtly appear in what ftate ofoxygenation the common dyer’s folution exifts,hut probably before the colour is completelybrought out, the metal is oxygenated in thehigheft degree. The nitric acid indeed whenufed alone, if weak and if the folution be madevery flowly, and without heat, is found byProuft to contain the fub-oxyd of tin, or thismetal in a very low ftate of oxygenation; forit is only in this ftate that it remains foluble,and when more highly oxygenated it totallyfeparates from the acid in the form of a whiteperfeCf oxyd.

But the muriat of tin on the other hand maycontain either the perfeCt oxyd or the fub-oxyd,the latter is the cafe when the folution is re-cently made, and has not been expofed to theair, from which it greedily attraCls oxygen, butin this cafe without feparating from its acidfolvent.

The muriat of tin, loaded with metal by be-ing boiled on more than it can take up, if cooledto the freezing point gives abundance of cryftals,which however again liquefy at a fummer heat,and hence mull be kept in a cool place. Mr.Hauflman q diflolved one ounce of this fait re-cently made in 8 pints of water, to which headded with conftant ftirring an infufion of zounces of cochineal in 8 pints of water. A verydeep violet coloured precipitate fubfided, (a mix-ture of the fub-oxyd of tin with the colouringmatter of the cochineal) which however by ex-pofure to air gradually turned to a fine car-mine : but kept clofe in a bottle no fuch changeof colour took place. If the folution of tin is ex-pofed to air before mixture with the cochineal,theprecipitate becomes carmine much more fpeedi-ly, as it already contains nearly oxygen fuffici-ent for this purpofe. The carmine-colouredoxyd turns fomewhat crimfon by the additionof ammonia, but returns to carmine when thisalkali is again evaporated.

If a carbonated alkali is added to the muri-

yf. tom. 48.