486 BARIUM. 



sorbs that gas with avidity, and becomes peroxide of barium, the 

 compound for the preparation of which anhydrous barytes is 

 chiefly required. This earth slakes and falls to powder, when 

 water is thrown upon it, combining with one equivalent of water 

 with the evolution of much heat. 



Hydrate of barytes is a valuable reagent. Of the different 

 processes for this substance, one of the most convenient is that 

 from the native sulphate. This is a soft mineral and easily re- 

 duced to an impalpable powder, which is intimately mixed with 

 I -3rd of its weight of coal-dust, or coal pounded and sifted ; the 

 mixture is introduced into a cornish crucible, and exposed in a 

 furnace to a bright red heat for an hour. The sulphate is con- 

 verted by this treatment into sulphuret of barium ; the last salt 

 is dissolved out of the black residuary mass, by boiling water, 

 and the solution, which generally has a yellowish tint but is 

 sometimes colourless, is filtered while still hot. The solution, 

 if strong, may crystallize on cooling, in thin plates. As it also 

 absorbs oxygen from the air, and returns to the state of sul- 

 phate of barytes, it must not be exposed long in open vessels. 

 To a boiling solution of sulphuret of barium in a flask, black 

 oxide of copper from the nitrate is added, in successive small 

 portions, till a drop of the liquid ceases to blacken a so- 

 lution of lead, and precipitates it entirely white; the liquid 

 then contains only hydrate of barytes in solution. It may im- 

 mediately be filtered, with little access of air, as it absorbs car- 

 bonic acid. The decomposition in this process, for which we 

 are indebted to Dr. Mohr of Coblentz, is rather complicated. 

 Six eq. of sulphuret of barium and 8 of oxide of copper produc- 

 ing 5 of barytes, 1 of hyposulphite of barytes, and 4 of subsul- 

 phuret of copper: 



6 BaS and 8CuO=5BaO and BaO, S 2 O 2 and 4 Cu 2 S. 



Peroxide of manganese may be substituted in this process for 

 oxide of copper, but generally gives a solution of barytes co- 

 loured by some impurity. The reaction is then similar* : 



6Ba S and 4Mn O 2 =5BaO and BaO, S 2 O 2 and 4MnS. 

 If the solution of sulphuret of barium has been concentrated, 

 the greater part of the hydrate of barytes separates on cooling, 

 in voluminous and transparent crystals. It is soluble in 3 



* Liebig's Annalen, v. 27, p. 21. 



