Action of Iron Mordant upon Copper Mordant. 376 



upon the madder- red, as some oxide of tin precipitates 

 from the milky solution upon the calico fibre and injures 

 the lustre of the red. 



ACTION OF THE ALUM MORDANT UPON THE IRON MORDANT. 



The action of calico impregnated with acetate of alumina 

 is not less remarkable than that of the copper mordant. 

 Let the mordanted calico which has been hung up several 

 days and well washed, be placed in a solution of 10 lbs. 

 iron alum in 1200 lbs. water, and remain there for a 

 quarter of an hour, it acquires a dark rust yellow colour, 

 while a piece of unmordanted calico, treated in the same 

 way, becomes only slightly yellow. As the sulphuric acid 

 of the iron alum is in a state to dissolve the alumina of the 

 calico, it is rather remarkable that this does not occur in 

 the present instance. The alumina rather forms with the 

 oxide of iron, a double combination on the calico. This 

 more especially takes place when a solution of iron alum 

 several months old is employed, as by the precipitation of 

 much oxide of iron it has become acid. Since the iron 

 alum solutionis colourless, it is interesting when two pieces 

 of calico are placed in the solution, to observe the one 

 impregnated in the alumina becoming gradually dark rust 

 yellow, while the other (an unmordanted piece of calico) 

 remains quite white. 



Numerous experiments have already proved the affinity 

 existing between the earths and oxides, but it is impossible 

 to shew it more clearly by experiment than as in the present 

 instance by means of calico. 



This affinity of alumina for oxide of iron explains the 

 utility of previously boiling the cotton with alum, when 

 for the purpose of dyeing it with prussiate of potash it 

 is impregnated with iron salts. 



It is convenient for the dyer to employ alum mordants 

 mixed in different proportions with iron mordants. 



ACTION OF IRON MORDANT UPON COPPER MORDANT. 



A piece of cotton impregnated with iron mordant. No. 

 2, and well rinsed, alters by being placed in copper mordant, 

 No. 2, only a little while ; it loses the deep yellow lustre 

 of the rust colour and appears paler yellow. 

 ( To be continued. J 



