<g»gS COMPARISON OP DIFFERENT KI?fDS OF ALUM. 



General eflFects With weld nnd cochineal, which arc colouring matters the 

 © He iron. j^-,ost sensible to the action of sulphate of iron, the purified 

 alums gave us colours more brilliant, fresh, and in a slight 

 degree lighter; while those with our commau alums were all 

 duller, and evidently of a deeper hue. This slight increase 

 of the inten:;ily of the colour arises solely from the small 

 quantity of sulphate of iron found in our common alums. 

 To satisfy ourselves of this, we added to our purified Liege 

 alum scarcely appreciable quantities of sulphate of iron, 

 and gradually more and more; till, by thus restoring all it 

 had lost in its purification, we caused it to assume the differ- 

 ent states of Roman alum, that of Bauvicr, Curaudau, and 

 Javelle, and lastly its original state of Liege alum. 



AiiT. Iir. Comparison of the alums of Rome, Houvier, Liege ^ 

 JavellCf and Curaudau, in their ordinari/ state, xcith ihe same 

 alums, to xchic/i ue had added increasing proportions of sul* 

 ^ phate of iron. 



Comparison of We Were convinced to demonstration, that the slight dif- 

 the alums with |-gj,^j^^^g produced by these several alums in dycini); were 

 owing to the different and scarcely calculable quantities of 

 sulphate of iron they Contained: but to remove completely 

 every doubt, that might still be entertained in this respect, 

 we confirmed by synthesis all the facts, that we had collected 

 from analysis. 



The substances to bo died, woollen, linen, and cotton, were 

 prepared with solutions of the alums purified, of the same 

 alums Avith the addition oi rhuf rV^ aV> tV> o? ^'^^ i ^^ ^^^^' 

 phate of iron, and of sulphate of iron alone. 



The silks were alumed in the same proportions with the 

 five different alums, and with pure alum to which from ^-^q-o 

 to Too- of sulphate of iron was added. 



additions of 

 iron. 



