The dioxide (BaO_{2}) is used for the preparation of oxygen. On strong
ignition it gives up oxygen, and is converted into baryta (BaO), which,
at a lower temperature, takes up oxygen from the air, re-forming the
dioxide.
~Detection.~--Barium is detected by the green colour its salts,
especially the chloride, give to the flame. This, viewed through the
spectroscope, shows a complicated spectrum, of which two lines in the
green are most easily recognised and characteristic. The salts of barium
give no precipitate with sulphuretted hydrogen in either acid or
alkaline solution, but with sulphuric acid they at once give a
precipitate, which is insoluble in acetate of soda. In solutions
rendered faintly acid with acetic acid, they give a yellow precipitate
with bichromate of potash. These reactions are characteristic of barium.
Baryta is got into solution in the manner described under _Lime_; but in
the case of the sulphate the substance is fused with three or four times
its weight of "fusion mixture." The "melt" is extracted with water,
washed, and the residue dissolved in dilute hydrochloric acid.
~Separation.~--The separation is thus effected:--The solution in
hydrochloric acid is evaporated to dryness, re-dissolved in hot dilute
hydrochloric acid, and sulphuric acid is added to the solution till no
further precipitate is formed.
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