ON COLORING. 53 



potash, dislodging at the same time the tartaric acid, which 

 seizes in turn oa the clay just abandoned by the sulphuric acid. 

 The tartaric acid, having a weaker affinity for the clay than the 

 sulphuric acid possesses, yields it more readily to the cloth. 

 Another purpose is also gained : the sulphuric acid remains 

 combined with the potash, and this corrosive substance is there- 

 by prevented from injuring the texture of the cloth. For cot- 

 ton and linen, which have a weaker affinity to clay than wool or 

 silk, another process becomes necessary. Lead or lime dis- 

 solved in acetic acid (vinegar) is poured into the solution of 

 alum. A solution of sugar of lead is frequently used. The 

 sulphuric acid quits the clay and seizes on the lead or lime, both 

 of which, united with this acid, form insoluble powders, which 

 fall to the bottom, and the acetic acid unites with the clay, for 

 which it possesses only a weak affinity, and readily yields it to 

 the cotton or linen immersed in it. 



Metallic salts may also be used as mordants. Those of iron 

 and tin are extensively used in dyeing. Iron is used as a mor- 

 dant in two states, in that of sulphate of iron, (copperas) or 

 acetate of iron, that is, iron dissolved in vinegar or in the acid 

 •obtained by distilling wood (pyrolygneous acid.) 



Tin is used as a mordant in three states — dissolved in nitro 

 muriatic acid, (a mixture of the acids obtained from saltpetre 

 and from common salt), in acetous acid, and in a mixture of sul- 

 phuric and muriatic acids. The nitro muriate of tin is the com- 

 iBon mordant employed by dyers. It is prepared in the follow- 

 ing manner. Melt block tin and pour it into water briskly agi- 

 tated with a bundle of small rods, 



Take of this granulated tin - two ounces. 



Nitric acid - one pound. 



Water - - half a pound. 



Common salt or sal ammoniac two ounces, 

 tnix ihem together in a glass vessel, and the tin will be slowly 

 dissolved* When nitro-rauriate of tin is to be used as a mor- 



* When common salt, which is composed of muriatic acid and soda, or sal ammoniac, 

 composed of the same acid and ammonia, is mixed with diluted nitric acid, a part of the nitric 

 acid seizes on the soda or ammonia and sets at liberty a part of the muriatic acid, which mix- 



