Sodium Hexachlor-rhodite, Na₃RhCl₆

Sodium Hexachlor-rhodite, Na₃RhCl₆.18H₂O, is prepared by heating finely divided rhodium and sodium chloride to redness in a current of chlorine. Claus recommends heating the rhodium in chlorine, cooling, adding the alkali chloride, and again heating in chlorine. There is then less danger of particles of rhodium remaining unattacked.

On extracting the product with water and evaporating, the salt crystallises out.

A more convenient method of preparation consists in warming sodium rhodium nitrite, 3NaNO₂.Rh(NO₂)₃, with concentrated hydrochloric acid. The salt crystallises in garnet-red octahedra, which effloresce on exposure to air. They are soluble in water, but not in alcohol. The amount of water of crystallisation has been a matter of dispute. Berzelius found 18H₂O, a result agreeing with that of Leidie obtained many years later.