Lead Borates

Lead orthoborate is unknown, but the metaborate exists and several poly- or anhydro-borates.

Lead metaborate, Pb(BO₂)₂.H₂O, is formed as a white precipitate when cold concentrated solutions of lead nitrate and borax are mixed. It is almost insoluble in, but somewhat hydrolysed by, water, and dissolves readily in dilute acids.

The polyborate 2PbO.3B₂O₃.4H₂O is obtained by precipitating a solution of a lead salt with excess of boiling borax solution, and PbO.2B₂O₃.4H₂O by treating either of the former salts with a boiling solution of boric acid. Lastly, PbO.3B₂O₃ is obtained by fusing lead carbonate with boric acid, and extracting excess of the latter with cold water.