420 Berzelius on a new Mineral Body, [Dec. 



it completely. The polish of the turquoise is not so good as 

 that of the calaite, and exhibits plates, rays, or filaments, 

 depending upon the bony structure. Rosnel affirms with justice 

 that all the turquoises of France have their surface covered with 

 radii, or filaments. And though Reaumur affirms that the more 

 sensible the plates are, the worse are the turquoises, this circum- 

 stance does not fail to be a certain character for distinguishing 

 the tooth turquoises of France from the true mineral, or the 

 calaite of Persia. 



Article III. 



Researches on a new Mineral Body found in the Sulphur extracted 

 from Pyrites at Fahlun. By J. Berzelius. 



(Continued from p. 265.) 



3. Seleniate of Ammonia. — We obtain the neutral salt by dis- 

 solving selenic acid in concentrated caustic ammonia, leaving a 

 small excess of acid. We leave the liquid in a temperate place; 

 the seleniate is gradually deposited in crystals, partly feather- 

 shaped, and partly in four-sided prisms, or oblique four-sided 

 prisms. The crystals deliquesce in the air. 



The biseleniate is formed when the neutral salt is dissolved in 

 water, and the solution allowed to evaporate spontaneously. A 

 portion of the ammonia exhales with the water, and the bisele- 

 niate is deposited in acicular crystals which are not altered by 

 exposure to the air. 



The quadriseleniate is produced by the evaporation of a solu- 

 tion of the biseleniate by means of heat, or by the addition of 

 selenic acid to the biseleniate. It does not crystallize, and, when 

 evaporated to dryness, soon recovers its liquidity by absorbing 

 moisture from the atmosphere. 



If we heat the seleniate of ammonia in a retort, water and 

 ammonia are at first disengaged ; then the ammonia decomposes 

 the selenic acid, producing azote and water which distils over. 

 This is usually followed by a little quadriseleniate, which is 

 likewise sometimes deposited in a dry state on the upper part of 

 the retort. At the bottom we find a button of melted selenium. 

 The decomposition takes place with a strong effervescence, but 

 without detonation, at least with the small quantities on which 

 1 operated. 



4. Seleniate of Barytes. — The neutral salt is insoluble in 

 water, pulverulent, and does not alter the colour of moist litmus 

 paper. At the temperature of melting glass it does not melt, 

 and it does not appear to contain combined water. It is soluble 

 both in selenic acid and in the- strong acids. We obtain this 



