616 PRINCIPLES OF CHEMISTRY 



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

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

 Ba(HO) 2 , which differs from lime by its great solubility in water, 55 

 and by the ease with which it forms a crystallo-hydrate, BaH 2 2 ,8H 2 0, 

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

 employed in manufactures and in practical chemistry 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 it as the insoluble barium sulphate, BaS0 4 . It may also be 

 removed whilst it remains in an alkaline state (for example, the 

 excess which may remain when it is used for saturating acids) by 

 means of carbonic anhydride, which also completely precipitates baryta 

 as a sparingly soluble, colourless, and powdery carbonate. Both these 

 reactions show that baryta has such properties as would very greatly 

 extend its use were its compounds as widely distributed as those of 

 sodium and calcium, and were its soluble compounds not poisonous. 

 Barium nitrate is directly decomposed by the action of heat, barium 

 oxide being left behind. The same takes place with barium car- 

 bonate, especially that form of it 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 very stable in its reten- 

 tion of the water, although it parts with it when strongly ignited. 55bi * 

 With oxygen the anhydrous oxide gives, as already mentioned in 



barium or strontium chloride. They are obtained by the action of nitric acid on the carbon- 

 ates or oxides. 1QO parts of water at 15 dissolve 6'5 parts of strontium nitrate and 8'2 

 parts of barium nitrate, whilst more than 300 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. 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. 3'5 7'4 18'8 90'8 



SrO 0'3 0-7 1'4 3 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, oxygen is sepa- 

 rated and barium chloride formed. 



55 t>u Brugellmann, by heating BaH 2 Oa in a graphite or clay crucible, obtained BaO 

 In needles, sp. gr. 5'32, and by heating in a platinum crucible in crystals belonging to 



