igoS.] KELLER— NOTES ON CHILEAN COPPER MINERALS. 



81 



in a current of dry air and collecting the moisture in calcium chloride, 

 while the latter was estimated iodometrically in I. and II., and indi- 

 rectly in III., by heating a weighed portion, first in air and then in 

 hydrogen, and allowing for the water and the reduction of the 

 oxides of copper and iron. As a matter of course this method is 

 less reliable, but the result nevertheless agrees quite well with the 

 iodometric determinations. 



Chalcanthite and a Double Sulphate of Copper and 

 Magnesium. 



Among the specimens that claimed my special attention there 

 was one^ consisting of irregular and rounded masses, and which was 

 labeled " sulphate of copper and aluminium." While the shape of 

 the little lumps was about the same, three distinct kinds of material 

 could readily be picked from the specimen, even without the help 

 of a magnifying glass. 



One of these substances had a deep blue color and was recog- 

 nized without difficulty as chalcanthite. The blue masses were evi- 

 dently crystals which were strongly corroded and slightly effloresced 

 on the surface. A quantitative analysis confirmed the composition 

 CUSO4 -f 5H0O, with very small amounts of iron and magnesium 

 sulphates, and a slight admixture of silicious matter. It gave : 



Found. (Calculated. 



Per Cent. Per Cent. 



Sulphur trioxide 32 



Cupric oxide 31 



Ferrous oxide 



Magnesium oxide 



Water 35 



21 32.1 



52 31-8 



30 



35 



79 36.1 



19 lOO.O 



More interesting were the bluish-white masses which formed the 

 larger portion of the specimen. They were earthy and friable, but 

 presented shapes and surfaces exactly similar to those of the chal- 

 canthite, suggesting a pseudomorph after the latter. In composi- 

 tion, however, the material was found to differ from chalcanthite in 



* From Copaquire, Province of Tarapaca. 



