fcURrFCATION OF ALUM. S07 



in which case it dissolves, but reappears entirely by evapo- 

 ration. 



From the experiments that have been described it appears, Component 



i i i i • i i x • P art °f tn $ 



that the schist analysed contains schi;t. 



Silex .....71 



Alumine. • • • 15 



Oxide of iron 5 



Magnesia • 2 



Lime (at most) . • • • 0'5 



Potash 2*5 



Water... 3 



99 

 Loss • • • • 1 



100 



tt is possible, that the potash found in this schist comes The potash 

 from the feldspar, which I suspect to be in it. It would be Jjj^be j£ 

 interesting to ascertain, whether the alkali be inherent in 

 the rock, by the analyses of a more homogeneous fragment. 



XIX. 



Method of rendering common Alum as good for Dyeing as 

 Roman Alum; by Mr. Seguin, Corresponding Member of 

 the Institute*, 



JL O the means that have been suggested for improving Method of 



common alum, by freeing it from the iron it contains, Mr. purifying 



. alum. 



Seguin has added a new one, founded on the different so- 

 lubility of pure alum and alum contaminated with iron. 

 He dissolves sixteen parts of common alum in twenty-four 

 parts of water ; crystallizes ; and thus obtains fourteen parts 

 of alum equal to the Roman, and two nearly equal to that 

 of Liege. 



This process might be employed in the manufacture of May be adopt- 



the alum, so as to obtain at first an alum worth one third more ed i n thc nu * 



. . . mtfjctur... 



than in its impure state. 



* Sonmni's Bibliotheque Physico-^conomique, August 1807, p 132. 

 X 2 SCIENTIFIC 



