Mineralogy. 357 



salt was dissolved in caustic ammonia ; the solution formed was of a violet- 

 blue colour. After some time it yielded a green precipitate, the colour of 

 the solution being at the same time changed into a peach-blossom red. 

 The precipitate gave a pure blue solution with caustic ammonia ; and, ex- 

 posed to air, it deposited a verdigris-green salt. This salt was repeated- 

 ly dissolved in caustic ammonia to obtain a pure salt of nickel, which was 

 completely precipitated, so as to leave the liquid perfectly colourless when 

 the blue ammoniacal solution was exposed to the air. L. The ammonia- 

 cal solutions of cobalt were evaporated to dryness, and yielded pure oxide 

 of cobalt. 



The results of two analyses, conducted in this manner, were 



Arsenic, 78.449 77-530 



Cobalt, 9.860 9.876 



100-609 99.206 



The chemical composition of this mineral appears to be quite peculiar, 

 and it is likely to belong to a new species. A good description of the species 

 itself is therefore now a desideratum, as would be also the analysis of a well- 

 defined crystalline variety, from which it might appear which of the nu- 

 merous ingredients are essential, and which of them must be considered 

 as accidental. 



f 27. Selenium discovered in Cupriferous Minerals. — Mr Charles Kersten 

 of Gottingen observed the peculiar disagreeable odour characteristic of 

 selenium, when exposing the capillary red copper ore from Rheinbreit- 

 bach to the action of the blowpipe. The red ring, which forms another 

 character of it, likewise appeared when the mineral was heated in a glass 

 tube. He afterwards subjected the capillary crystals to a chemical exami- 

 nation in the humid way, and succeeded in separating the selenium from 

 the other ingredients. Two specimens of an earthy substance, from the 

 same locality, chiefly consisting of oxide of copper, showed likewise traces 

 of selenium, which was not the case in similar varieties from the Bannat. 



28. Silicate of Cerium. — Dr Wollaston examined this substance in June 

 1825. A perfect crystal of it, in the form of a regular hexagonal prism, is 

 contained in the cabinet of Sir Alexander Crichton, which is to be sold by 

 auction in the ensuing months of April and May. Cleavage parallel to the 

 axis of the prism. Colour pale yellowish-brown. Translucent. Occurs 

 along with magnesian carbonate of lime and emerald. Locality Santa 

 Fe de Bogota, in Peru. Fragments of this substance, associated with the 

 Peruvian emeralds, are preserved also in the British Museum. It is not 

 mentioned whether this be a species of its own, or whether it be the same 



