of boiling point 117 deg. C., and is to be regarded as the acid chloride
corresponding to chromic acid, CrO2(OH)2. It dissolves iodine and
absorbs chlorine, and is decomposed by water with formation of chromic
and hydrochloric acids; it takes fire in contact with sulphur,
ammonia, alcohol, &c., and explodes in contact with phosphorus; it
also acts as a powerful oxidizing agent. Heated in a closed tube at
180 deg. C. it loses chlorine and leaves a black residue of trichromyl
chloride, Cr3O6Cl2, which deliquesces on exposure to air. Analogous
bromine and iodine compounds are unknown, since bromides and iodides
on heating with potassium bichromate and concentrated sulphuric acid
give free bromine or free iodine.

The oxyfluoride, CrO2F2, is obtained in a similar manner to the
oxychloride by using fluorspar in place of common salt. It may be
condensed to a dark red liquid which is decomposed by moist air into
chromic acid and chromic fluoride.

The semi-acid chloride, CrO2.Cl.OH, chlorochromic acid, is only known
in the form of its salts, the chlorochromates.

Potassium chlorochromate, CrO2.Cl.OK, is produced when potassium
bichromate is heated with concentrated hydrochloric acid and a little
water, or from chromium oxychloride and saturated potassium chloride
solution, when it separates as a red crystalline salt. By suspending
it in ether and passing ammonia, potassium amidochromate, CrO2.NH2.OK,
is obtained; on evaporating the ether solution, after it has stood for
24 hours, red prisms of the amidochromate separate; it is slowly
decomposed by boiling water, and also by nitrous acid, with liberation
of nitrogen.

Chromic sulphide, Cr2S3, results on heating chromium and sulphur or on
strongly heating the trioxide in a current of sulphuretted hydrogen;
it forms a dark green crystalline powder, and on ignition gives the
sesquioxide.

Chromic sulphate, Cr2(SO4)3, is prepared by mixing the hydroxide with
concentrated sulphuric acid and allowing the mixture to stand, a green
solution is first formed which gradually changes to blue, and deposits
violet-blue crystals, which are purified by dissolving in water and
then precipitating with alcohol. It is soluble in cold water, giving a
violet solution, which turns green on boiling. If the violet solution
is allowed to evaporate slowly at ordinary temperatures the sulphate
crystallizes out as Cr2(SO4)3.15H2