37(i The Art of Dyeing. 



cotton in the cow-dung bath. If it is dissolved in water, 

 and mixed with solutions of alumina, iron, copper, or tin 

 mordants, brown precipitates are formed, which are nothing 

 but combinations of bosopric acid and bosoprine, with alu- 

 mina, iron, copper, and tin. The same compounds are 

 formed when calico, printed with these mordants, is boiled 

 with it. The bosopric acid and bosoprine take the place of 

 the acids which were united with the mordants on the 

 calico. Hence, when calico printed with acetate of alumina 

 mordant is boiled in the mixture described, of bosopric acid 

 and bosoprine, the acetic acid separates from the alumina, 

 and both the constituents of cow-dung combine in its place, 

 and form bosoprate of alumina, united with bosoprine, 

 which are both insoluble in water; and, therefore, remain 

 in combination with the calico, which now acquires a 

 brown colour. The other mordants act in the same man- 

 ner. Acetate of iron, for example, printed upon calico, 

 will be converted into bosoprate oi iron. 



When cow-dung itself is employed instead of the two 

 constituents, the same combinations are formed upon the 

 calico, while the remaining elements of the cow-dung have 

 no action upon the mordants. Hence, the effect of passing 

 the mordanted calico through a hot cow-dung bath is 

 nothing else than actual dyeing ; so that in applying the 

 subsequent dyes, the combinations of the cow-dung colours 

 must be again destroyed, in order that the new colours 

 may be substituted. 



All colouring matters do not produce this decomposition 

 in the same degree ; madder effects it most completely ; 

 therefore, goods dyed with madder-colours are always 

 cleansed with cow-dung ; cochineal, on the contrary, pos- 

 sesses the least effect ; a specimen dyed with alum mor- 

 dant, No. 1, and cochineal-red, shews that the colouring 

 matter of the cochineal cannot separate the colour of the 

 cow-dung from the alumina, but that it has combined with 

 both, and consists of a mixture of brown and red. 



With iron mordant this occurs in an equally remarkable 

 manner. The cotton is mordanted by simply dipping it in 

 a solution of iron alum, and washing it immediately after 

 in water. If one of the specimens is boiled with cow-dung, 



