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SECT. XI.----PLANTS USEFUL IN DYEING.

nutes, and is then washed in clean water. In this manner are triedcrimson, scarlet, flesh-colour, violet, ponceau, peach-blossom colour,different shades of blue, and other colours bordering upon these.

For the proof with soap : Two drachms of this substance are boiledjn a pint of water, and the small piece of dyed stuff that is to be triedis put into it, and likewise suffered to boil for the space of five mi-nutes. With this all sorts of yell«w, green, madder-red, cinnamon,and similar colours, are tried.

In the same manner is made the proof with tartar; only this shouldbe previously pounded very small, in order that it may be more easilydissolved. With this all colours bordering upon the fawn are tried.

From the above we discover that the art of applying and fixing co-lours in dyeing depends on the chemical affinity between the cloth andthe dyeing principle: and accordingly as tbis is more or less strong,so is the facility with which the substance is coloured., and on this thedeepness of the dye depends: for frequently one kind of cloth will befound to receive no colour at alj, whilst another will receive from the sameComposition a deep tinge. Cotton, for instance, receives scarcely anytinge from the same bath that will dye woollen a deep scarlet. Woolis that which appears to have the strongest affinity to colouring mat-ter ; next to it is silk ; then linen; and cotton the weakest, and is there-fore the most difficult of all to dye perfectly. Thus, if a piece oflinen cloth be dipped into a solution of madder, it will come out justtinged with the colour; but if a piece of the same be previously dip-ped into a solution of alum or copperas, and dried previously to be-ing dipped in the madder, the alum will become so far impregnatedwith the colouring principle, that the cloth will receive a perfect dye,and be so fixed that it cannot be separated by any common means.Thus it will be observed, that the art of dyeing permanent colours de-pends on this intermediate principle, which is termed a mordant. Thesemordants are very numerous ; and on a knowledge of them appears to restthe principal secret of dyeing. The following, mode is, however, a veryconvenient one for making experiments on fixing the colouring prin-ciples of any vegetable extract: To have several pieces of cloth, wool-len, cotton, silk, and linen, dipped in the different mordants, and bykeeping a small vessel filled with the colouring solution on a tire in astate a little below boiling, by cutting small pieces of each, and hn-iaersing them in the colour, and examining and comparing with eaeb.