her chromous
salts and consequently can be used for their preparation. Chromic
salts are of a blue or violet colour, and apparently the chloride and
bromide exist in a green and violet form.

Chromic chloride, CrCl3, is obtained in the anhydrous form by igniting
a mixture of the sesquioxide and carbon in a current of dry chlorine;
it forms violet laminae almost insoluble in water, but dissolves
rapidly in presence of a trace of chromous chloride; this action has
been regarded as a catalytic action, it being assumed that the
insoluble chromic chloride is first reduced by the chromous chloride
to the chromous condition and the original chromous chloride converted
into soluble chromic chloride, the newly formed chromous chloride then
reacting with the insoluble chromic chloride. Solutions of chromic
chloride in presence of excess of acid are green in colour. According
to A. Werner, four hydrated chromium chlorides exist, namely the green
and violet salts, CrCl3.6H2O, a hydrate, CrCl3.10H2O and one
CrCl3.4H2O. The violet form gives a purple solution, and all its
chlorine is precipitated by silver nitrate, the aqueous solution
containing four ions, probably Cr(OH2)6 and three chlorine ions. The
green salt appears to dissociate in aqueous solution into two ions,
namely CrCl2(OH2)4 and one chlorine ion, since practically only
one-third of the chlorine is precipitated by silver nitrate solution
at 0 deg. C. Two of the six water molecules are easily removed in a
desiccator, and the salt formed, CrCl3.4H2O, resembles the original
salt in properties, only one-third of the chlorine being precipitated
by silver nitrate. In accordance with his theory of the constitution
of salts Werner formulates the hexahydrate as CrCl2.(OH2)4.Cl.2H2O.

Chromic bromide, CrBr3, is prepared in the anhydrous form by the same
method as the chloride, and resembles it in its properties. The iodide
is unknown.

The fluoride, CrF3, results on passing hydrofluoric acid over the
heated chloride, and sublimes in needles. The hydrated fluoride,
CrF3.9H2O, obtained by adding ammonium fluoride to cold chromic
sulphate solution, is sparingly soluble in water, and is decomposed by
heat.

Oxyhalogen derivatives of chromium are known, the oxychloride,
CrO2Cl2, resulting on heating potassium bichromate and common salt
with concentrated sulphuric acid. It distils over as a dark red liquid