Tetraboron pentoxide, B4O5, is prepared by treating the compound Mg3B2(OH)6 with strong ammonia for several days in an atmosphere of hydrogen, filtering, evaporating the filtrate to dryness in vacuo, and heating the residue. Thus prepared, it forms a pale brown solid, infusible at the softening point of Jena glass. When allowed to remain in vacuo in contact with water it dissolves, forming a golden-yellow solution that oxidises rapidly in the air; a small flocculent residue, apparently consisting of B4O3.2H2O, is also obtained. It is possible that the residue is produced by the following reaction: -
3B4O5 = B4O3 + 4B2O3. |