54 ON COLORING. 



dant, it is dissolved in a large quantity of water, and the cloth is 

 dipped in the solution until sufficiently saturated. It is then 

 taken out, washed and dried. Tartar is usually dissolved in the 

 water along with the nilro muriate of tin. This changes the 

 compound into a solution of the tartrate of tin and nitro muriate 

 of potash. The tartrate of tin is again decomposed by the 

 cloth. The metal quits the acid and attaches itself to the fibres 

 of the cloth, and in tliis state possesses a strong affinity for col- 

 oring matters, and forUiS with them the most permanent and 

 brilliant dyes. 



Tan is also employed, along with other mordants. It is found 

 in nutgalls, oak and hemlock barks, sumach, and in a great variety 

 of other vegetables. It is that part of barks, &.c. which has a 

 strong affinity for glue, of which hides are chiefly composed, 

 unites with it and forms leather. It has a strong affinity also 

 for cloth and for several coloring matters. Silk is capable of 

 absorbing a very great proportion of tan, and thereby acquires a 

 great increase of weight. For this purpose alone it is sometimes 

 employed by silk manufacturers. Tan is often employed, also, 

 along with other mordants, in order to produce a compound mor- 

 dant. Oil is also used for the same parpose, in dyeing cotton 

 and linen. 



Besides these mordants there are several other substances fre- 

 quently used as auxiliaries, either to facilitate the combination of 

 the mordant with the cloth, or to alter the shade of color ; the 

 chief of these are tartar, sugar of lead, common salt, sal ammo- 

 niac, sulphate of copper, (blue vitriol) acetate of copper, Stc. 



Mordants not only render the dye permanent, but have also 

 considerable influence on the color produced. The same color- 

 ing matter produces very different dyes, according as the mor- 

 dant is changed. Cochineal, with salts of iron, produces black, 

 with the salts of tin, scarlet, and with alum, crimson. In dye- 

 ing, then, it is not only necessary to procure a mordant which 



ing with the leiiiainliij nitric acid, forms nitro muriatic aci.l, (aqua regia) which readily dig- 

 solves till, gold, &c. It is more economical, howevor, to add sulphuric acid enough to satu- 

 rate the hasR of the salt, wliich sets all the muriatic acid at liberty, and leaves the nitric 

 acid undimiuished. 



I 



