THE VALENCY AND SPECIFIC HEAT OF THE METALS 615 



ftwiurn chloride, BaCl 2 , is obtained in solution, and the sulphur is dis- 

 engaged as gaseous sulphuretted hydrogen, BaS-f 2HCl=BaCl 2 -r-H 2 S. 

 In this manner barium sulphate is converted into barium chloride, 53 

 and the latter by double decomposition with strong nitric acid or 

 nitre gives the less soluble barium nitrate, Ba(NO 3 ) 2 , 64 or with sodium 



dride, so that barium carbonate is formed. An equivalent mixture of sodium sulphate 

 with barium or strontium sulphates when ignited with charcoal gives a mixture of 

 sodium sulphide and barium or strontium sulphide, and if this mixture be dissolved in 

 water and the solution evaporated, barium or strontium hydroxide crystallises out 

 on cooling, and sodium hydrosulphide, NaHS, is obtained in solution. The hydroxides 

 BaH. 2 O 2 and SrH 2 2 are prepared on a large scale, being applied to many reactions ; for 

 example, strontium hydroxide is prepared for sugar works for extracting crystallisablel 

 sugar from molasses. 



We may remark that Boussingault, by igniting barium sulphate in hydrochloric acid 

 gas, obtained a complete decomposition, with the formation of barium chloride. Attention 

 should also be turned to the fact that Grouven, by heating a mixture of charcoal and 

 strontium sulphate witk magnesium and potassium sulphates, showed the easy decom- 

 posability depending on the formation of double salts, such as SrS,K 2 S, which are easily 

 soluble in water, and give a precipitate af strontium carbonate with -carbonic anhydride. 

 In such examples as these we see that the force which binds double salts may play a part 

 in directing the course of reactions, and the number of double salts of silica on the earth's 

 surface shows that nature takes advantage of these forces in her chemical processes. It 

 is worthy of remark that Buchner (1893), by mixing a 40 per cent, solution of barium 

 acetate with a 60 per cent, solution of sulphate of alumina, obtained a thick glutmous 

 mass, which only gave a precipitate of BaS0 4 after being diluted with water. 



85 Barium sulphate is sometimes converted into barium chloride in the following 

 manner: finely-ground barium sulphate is heated with coal and manganese chloride 

 (the residue from the manufacture of chlorine). The mass becomes semi-liquid, 

 and when it evolves carbonic oxide the heating is stopped. The following double decom- 

 positions proceed during this operation : first the carbon takes up the oxygen from the 

 barium sulphate, and gives sulphide, BaS, which enters into double decomposition with 

 the chloride of manganese, MnCl 2 , forming manganese sulphide, MnS, which is insoluble 

 in water, and soluble barium chloride. This solution is easily obtained pure because 

 many foreign impurities, such as iron, remain in the insoluble portion with the man- 

 ganese. The solution of barium chloride is chiefly used for the preparation of barium 

 sulphate, which is precipitated by sulphuric acid, by which means barium sulphate is 

 re-formed as a powder. This salt is characterised by the fact that it is unacted on by 

 the majority of chemical reagents, is insoluble in water, and is not dissolved by acids. 

 Owing to this, artificial barium sulphate forms a permanent white paint which is used 

 instead of (and mixed with) white lead, and has been termed ' blanc fixe ' or ' permanent 

 white. 



The solution of one part of calcium chloride at 20 requires T86 part of water, the 

 solution of one part of strontium chloride requires 1*88 part of water at the same tem- 

 perature, and the solution of barium chloride 2'88 parts of water. The solubility of the 

 bromides and-iodides varies in the same proportion. The chlorides of barium and stron- 

 tium crystallise out from solution with great ease in combination with water ; they form 

 BaCl 2 ,2H 2 and SrCl 2 ,6H 2 O. The latter (which separates out at 40) resembles the 

 salts of Ca and Mg in composition, and Hitard (1892) obtained SrCl 2 ,2H ? O from solutions 

 at 90-180'. We may also observe that the crystallo-hydrates BaBr 2 ,H 2 O and BaI 2 ,7H 2 O 

 are known. 



* The nitrates Sr(N0 3 ) 2 (in the cold its solutions give a crystallo-hydrate containing 

 4H 2 O) and Ba(NO 3 ) 2 are so very sparingly soluble in water that they separate in consider- 

 able quantities when a solution of sodium nitrate is added to a strong solution of either 



