Till-: VALENCY AND SI'KCIFIC HEAT OF THE METALS 607 



varbonate a precipitate of barium carbonate, BaCO 3 . Both these salts 

 are able to give barium oxide, or baryta, BaO, and the hydroxide, 

 Ba(HO).,, which differs from lime by its great solubility in water, 5 '"' 

 and by the ease with which it forms a crystallo-hydrate, BaH 2 O 2 ,8H 2 O, 

 from its solutions. Owing to its solubility, baryta is frequently 

 employed in the manufactures and in chemical practice as an alkali 

 which has the very important property that it may be always entirely 

 removed from solution by the addition of sulphuric acid, which 

 entirely separates the baryta as the insoluble sulphate, BaS0 4 . It 

 may also be removed so long as it remains in an alkaline state (for 

 example, the excess which may remain when it is taken for saturating 

 acids) by means of carbonic anhydride, which also entirely precipitates 

 barium oxide as a sparingly soluble, colourless, and powdery carbonate. 

 Both these reactions show that baryta has such properties as would 

 render its use in practice most widely extended were its compounds 

 as widely distributed as those of sodium and calcium, and if its soluble 

 compounds were not poisonous. Barium nitrate is directly decomposed 

 by the action of heat, barium oxide being left behind. The same takes 

 place with barium carbonate, especially that precipitated from solutions 

 and when mixed with charcoal or ignited in an atmosphere of steam. 



Barium oxide combines with water with the development of a large 

 amount of heat, and the resultant hydroxide is so stable in its retention 

 of the water that it will not part with it under the action of heat 

 alone, although it entirely dissociates when strongly ignited in a current 

 of hydrogen or other gas, and especially of air. With oxygen the 



or strontium chlorides. They are obtained by the action of nitric acid on the carbonates 

 or oxides. They may also be obtained by the action of nitric acid on solutions of the 

 chlorides, all the more as they are comparatively little soluble, especially in water con- 

 taining nitric acid 100 parts of water at 15 dissolve 6'5 parts strontium nitrate and 

 N'2 parts of barium nitrate, whilst more than 800 parts of calcium nitrate are soluble 

 at the same temperature. Strontium nitrate communicates a crimson coloration to the 

 flame of burning substances, and is therefore frequently used for Bengal fire, fireworks, 

 and signal lights, for which purpose the salts of lithium are still better fitted. Calcium 

 nitrate is exceedingly hygroscopic. The barium nitrate, on the contrary, does not show 

 this property in the least degree, and in this respect it resembles potassium nitrate, and 

 is therefore used instead of the latter for the preparation of a gunpowder which is called 

 ' saxifragin powder ' (76 parts of barium nitrate, 2 parts of nitre, and 22 parts of charcoal). 

 55 The dissociation of the crystallo-hydrate of baryta is given in Chapter I. Note 65. 

 100 parts of water dissolve 



20 40 60 80 



BaO 1-5 8'5 7-4 18'8 90'8 



SrO 0-8 0-7 1-4 8 9 



Supersaturated solutions are easily formed. 



The anhydrous oxide BaO fuses in the oxyhydrogen flame. When ignited in the 

 vapour of potassium, the latter takes up the oxygen ; whilst in chlorine the oxygen is 

 separated and barium chloride formed. 



