By following the freezing-point curve of mixtures of strontium oxide with boric anhydride, Guertler established the existence of the pyroborate, 2SrO.B2O3, the metaborate, SrO.B2O3, the biborate, SrO.2B2O3, comparable with borax, and possibly the orthoborate, 3SrO.B2O3. The metaborate crystallines in long, doubly refracting needles, and the pyroborate forms a finely crystalline, marble-like mass. Certain products formerly supposed to be compounds, for example 2SrO.3B2O3 and 3SrO.2B2O3, are probably only eutectic mixtures.
Compounds of varying composition and containing water of crystallisation are obtained by precipitation or by the action of boric acid on strontium hydroxide. A strontium metaborate tetrahydrate, SrO.B2O3. 4H2O, has been obtained electrolytically. |