STRONTIUM CHLORIDE 197and furthermore, to show that strontium sulphate may be at-
tacked without the use of a furnace, we shall employ quite a differ-
ent method.
The method consists in first converting the sulphate into the
carbonate by boiling it with a concentrated solution of sodium
carbonate, and then dissolving the carbonate in hydrochloric
acid, thereby yielding a solution of the chloride. The conversion
of solid strontium sulphate into solid strontium carbonate fur-
nishes an interesting illustration of the solubility product principle,
for the solubility of these two salts in pure water is as follows:
SrSO 4
SrCO 3Solubility in grams
per 100 cc.0 Oil
0.0011Solubility in mols
per liter0.0006
0.00007Strontium sulphate would dissolve in the solution of sodium
carbonate in the same manner as it would in pure water until
it had saturated the solution, and its solubility product, which is
equal to 0.0006 X 0.0006, was reached, but for the fact that long
before this could occur the solution would be supersaturated with
respect to strontium carbonate, the solubility product of which is
only equal to 0.00007 X 0.00007. Thus strontium carbonate is
precipitated continuously as strontium sulphate dissolves; and
since the solution cannot become saturated with the latter as long
as a large excess of carbonate ions is present, the solid salt finally
remaining will consist entirely of strontium carbonate, pro-
vided a sufficient amount of sodium carbonate were employed.
The reaction which takes place is, however, reversible, SrSC>4 +
Na 2 CO 3 ^ SrCO 3 + Na 2 SO4, and, if strontium carbonate were
boiled with a solution of sodium sulphate, the solid would change
into sulphate until carbonate ions had accumulated in the solution
to such an extent as to make the concentration ratio [CO3~~] :
[SC>4~~] = 1:74. When this ratio prevails, both solids are in equi-
librium with the solution and no change takes place in either
direction.
Materials: celestite, SrSO 4 , 61 grams = 0.33 F.W.
anhydrous Na 2 CO 3 , 73 grams.
chlorine water.
6ATHC1, lllcc.