540 Intelligence and Miscellaneous Articles. 



p e 



yellow when the precipitation has ceased. The green colour is owing 

 to a mixture of the blue tint occasioned by the small quantity of tel- 

 lurium mixing with the yellow colour of the liquor. Sometimes the 

 remaining liquor is of a dull rose colour, and gives no precipitate in 

 several days ; this is owing to the telluret of iron which it contains. 



As long as the potash is in access, the sulphur and the selenium are 

 not precipitated, but the access of air converts them into acids j this 

 is a method of obtaining tellurium free from these substances. Mu- 

 riatic acid precipitates from the yellow solution the selenium and the 

 sulphuret of tellurium which it contains, in the state of sulphuret and 

 seleniuret of tellurium. 



The tellurium precipitated from the alkaline solution is a very fine 

 and dense powder : it must be purified by distillation ; but on account 

 of its slight volatility it cannot be sublimed from a retort in a common 

 furnace. In order to effect it, a long porcelain vessel, containing tel- 

 lurium, was put into a large porcelain tube in a furnace; it was heated 

 to redness, and a current of hydrogen gas passed over it. The tellu- 

 rium was converted into vapour, and it was constantly carried by the 

 hydrogen towards the cold parts of the tube, where it was condensed. 

 In order to make the tellurium flow after its condensation, the tube 

 must be slightly inclined. In a short time all the tellurium distils, 

 and there remains in the porcelain vessel a small button formed of 

 the tellurets of gold, copper, and iron • the product of the distillation 

 is pure tellurium. 



In general the process, which consists in fusion with potash and 

 charcoal, maybe employed to purify tellurium, especially if it contains 

 sulphur, selenium, or arsenic, all bodies which cannot be separated 

 from it by distillation. The arsenic goes off in vapour at a red heat, 

 and the two others, after the precipitation of the tellurium by the air, 

 remain dissolved in the liquor. The solution of potash contains the 

 metals which render the tellurium impure. If in this operation pow- 

 dered charcoal be employed instead of oil, the mixture may be strongly 

 heated at once, but the solution of telluret of potassium which is then 

 obtained contains telluret of calcium • and as the lime which is pro- 

 duced is precipitated with the metal, the precipitate must be first 

 washed with muriatic acid, and then with water. The quantity of 

 charcoal ought always to be sufficient to prevent the mass from fusing 

 during reduction, for then it would go over the edges of the crucible and 

 part of it would be lost. — Annalesde Chimie etde Physique, lviii. 132. 



ANALYSIS OF THE PLENAKITE. BY PROFESSOR BISCHOFF. 



This very rare mineral is found in the shallow part of an iron mine at 

 Ftamont (Vosges) • it is crystallized in rhomboids. Its physical cha- 

 racters are the same as those of the plenakite of Nordenskiold, and the 

 analysis of M. Bischoff confirms their similarity. It is as follows : 



Silica 17048 



Gtucina 14*280 



Lime and magnesia 0*030 



Matter unacted upon 2252 33*610 



It is considered as a bisilicate of glucina. — Ibid.* 



* See p. 239 of the present number. 



