ANALYSIS OF ALUM ORES. 359 



The clear liquor was then evaporated to dryness In a pla- Solution eva- 

 tina crucible, and the residuum heated red hot. The am. £°^tiJ^,ej\ot 

 moniacal salts being expelled, there remained a salt of the 

 weight of 21 cent. [3-243 grs.], which was sulphate of 

 magnesia. This quantity of 21 cent, gives at least 77 milli. 

 [1*189 gr.] of earth, supposing the crystallized sulphate to 

 contain 19 per cent of base; for that which has been heat- 

 ed red hot must have lost some of its acid, and it is neces- 

 sary to add a little to the solution, to make it crystallize. 



On reducing the products above-mentioned to hundredth 



parts, we shall have 







Fragments of quartz 



- 2-58 



Componem 



Red oxide of iron 



48-45 



parUi 



Brown oxide of manganese - 



1-80 





Lime - - - - - 



0-52 





Magnesia - - - - 



. 1-98 





55-33 

 The remainder is carbonic acid, water, and loss. 

 From this result it appears, that Bergman did not ex- Magnesia mi»- 

 -.1, ffi- ^ ^1, X f ^i, .u • • taken for lim». 



amine with sufficient care the nature of the earthy princi- 

 ples contained in the iron spars he analysed ; and it is very 

 probable, that he examined other ores, in which magnesia 

 was contained in still larger proportion, and mistaken by 

 him for lime *. 



XI. 



Chemical Examination of the Alum Ore of Tolfa, and the 

 Earthy Aluminous Schist of Freyenwalde. By Mr. 

 Klaproth f . 



x\lUM, a substance so Indispensable in dyeing and se- Alum an artifi- 

 veral other arts, is a triple salt, composed of sulphuric ^ronf ore".*^ '*'** 

 acid, alumine, and potash, with an excess of acid. It is 



• In the last number of our Journal, p. 314, an analysis of two 

 varieties of iron spar was given, which corroborates the fact of 

 magnesia having been mistaken for lime. 



t Journal des Mines, No. 117, p. 179. First published in the 



Berlin Chemical Journal, vol. VL 



obtained 



