398 ORGANIC CHEMISTRY. 



shall, as it were, hold them together. Such a substance, 

 with strong affinity for the coloring matter of the dye, 

 and also for the fibre of the cloth, is called a mor- 

 dant. The fabric to be dyed being first impregnated 

 with the mordant, is then introduced into the dyer's 

 vat to receive its permanent color. 

 What is said 997. MORDANTS. Alumina and oxide of 

 of mordants? j ron are fa e p r i nc ip a i mordants employed. 



They may be " fixed " in the cloth by immersion in the 

 acetates of these oxides. A subsequent exposure for 

 several days to the air is essential, in order that the 

 acetic acid may in part be expelled. A portion of it, 

 however, remains, so that the oxides are, strictly speak- 

 ing, in the condition of basic acetates. After this ex- 

 posure, and subsequent washing in hot water, the fabric 

 may be immersed in the dye. An ounce of madder 

 heated with a pint of water will be sufficient for an 

 experiment. The fabric is to be boiled for an hour or 

 more with the unstrained decoction. 



998. PREPARATION OF THE MORDANT. 



How is the alu- . 



minous mor- The solution of acetate of alumina is 



most conveniently prepared from alum, by 

 the substitution of acetic for its sulphuric 

 acid. This is accomplished by the addition of acetate 

 of lead. Sulphate of lead is at the same time precipi- 

 tated, and may be filtered off from the acetate which is 

 formed. Three pounds of alum and two of sugar of 

 lead, to three gallons of water, are the proportions to 

 be employed. This mordant produces a red color. 



How are vari- 999. VARIOUS COLORS BY THE SAME 



ous colors pro- DYE g y fa Q use o f different mordants. 



ducedfrom one 



dye? various colors may be produced from the 



