as ObjeSis of the Art of Dyings &c. 393 



previous to that operation. In this increafe 

 however, was included what it had acquired 

 in the operations of galling and aluming. 



The operation of galling, in this as well as 

 fome other proceffes of dying is ufed previous 

 to the application of the bafis to the material. 

 Galls contain an aftringent matter to which 

 chemifts have lately given the appellation of 

 the aftringent principle j and the Dijon Aeade- 

 micans have proved it to be of an acid 

 nature. It has not only the property of de- 

 compofing metallic, but alfo earthy foluti- 

 ons, and of combining, with ,the preci- 

 pitates which fall from them. Hence its 

 ufe previous to the aluming in the procefs of 

 dying. Steep cotton, which has not been 

 galled, in a folution of alum, the folution 

 remains clear, and the cotton, when dried, 

 fhall be covered with aluminous cryftals. Let 

 another parcel of cotton, which has been 

 galled, be immerfed in a fimilar folution, the 

 liquor (hall become turbid, and plain marks 

 of precipitation appeal-. 



This aftringent principle is of ftill farther 

 ufe in the art of dying, and we Ihall prefently 

 fee the manner in which it afts, when com- 

 bined in thofe vegetables which afford colouring 

 matter. 



Having thus given an account of the previous 

 operations in dying relative to the application 



of 



