Strontium Borates

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.