Note 41 — Chapter XIX · PHOSPHORUS AND THE OTHER ELEMENTS OF THE FIFTH GROUP

As antimonious oxide answers to the type SbX3, it is evident that compounds may exist in which antimony will replace three atoms of hydrogen; such compounds have been to some extent obtained, but they are easily converted by water into substances corresponding with the ordinary formulæ of the compounds of antimony. Thus tartar emetic, C4H4(SbO)KO6, loses water when heated, and forms C4H2SbKO6—that is, tartaric acid, C2H6O6, in which one atom of hydrogen is replaced by potassium and three by antimony. But this substance is reconverted into tartar emetic by the action of water.

A similar compound is seen in that intermediate oxide of antimony which is formed when antimonious oxide is heated in air: its composition is SbO₂ or Sb₂O₄. This oxide may be regarded as orthantimonic acid, SbO(HO)₃, in which three atoms of hydrogen are replaced by antimony in that state in which it occurs in oxide of antimony—i.e. SbO(SbO₃) = Sb₂O₄. Oxide of antimony is also formed when antimonic acid is ignited; it then loses water and oxygen, and gives this intermediate oxide as a white infusible powder, of sp. gr. 6·7. It is somewhat soluble in water, and gives a solution which turns litmus paper red.