Ammonium , the metal which is supposed to exist in ammoniacal salts; its existence being extremely probable in theory, and extremely difficult to prove in practice. Under conditions of temperature and pressure which do not obtain in our planet, there is little doubt that ammonium would be easily obtainable in the metallic state, and further might be incapable of resolution into NH3+H. The existence of the ammonium compounds furnishes a strong argument in favour of the assumption that all metals are really complex in structure. Just as at lower temperatures and higher pressures we can conceive of ammonium as an irresolvable metal, so at higher temperatures and reduced pressures we can conceive of ordinary metals assuming the hypothetical condition now presented by the ammonium radicle. Alchemists in believing that all metals could be transmuted into gold were perhaps not, in the essence of the thing, such idle dreamers as they are commonly supposed.