an excess of sodium phosphate to
chromic chloride solution.

Carbides of chromium are known; when the metal is heated in an
electric furnace with excess of carbon, crystalline, C2Cr3, is formed;
this scratches quartz and topaz, and the crystals are very resistant
to the action of acids; CCr4 has also been described (H. Moissan,
_Comptes rendus_, 1894, 119, p. 185).

Cyanogen compounds of chromium, analogous to those of iron, have been
prepared; thus potassium chromocyanide, K4Cr(CN)6.2H2O, is formed from
potassium cyanide and chromous acetate; on exposure to air it is
converted into the chromicyanide, K3Cr(CN)6, which can also be
prepared by adding chromic acetate solution to boiling potassium
cyanide solution. Chromic thiocyanate, Cr(SCN)3, an amorphous
deliquescent mass, is formed by dissolving the hydroxide in thiocyanic
acid and drying over sulphuric acid. The double thiocyanate,
Cr(SCN)3.3KCNS.4H2O, is also known.

Chromium salts readily combine with ammonia to form complex salts in
which the ammonia molecule is in direct combination with the chromium
atom. In many of these salts one finds that the elements of water are
frequently found in combination with the metal, and further, that the
ammonia molecule may be replaced by such other molecular groups as
-NO2, &c. Of the types studied the following may be mentioned: the
diammine chromium thiocyanates, M[Cr(NH3)2.(SCN)4], the
chloraquotetrammine chromic salts, R(sup1)2[Cr(NH3)4.H2O.Cl], the
aquopentammine or roseo-chromium salts, R(sup1)3[Cr(NH3)5.H2O], the
chlorpentammine or purpureo-chromium salts, R(sup1)2[Cr(NH3)5.Cl], the
nitrito pentammine or xanthochromium salts, R(sup1)2[NO2.(NH3)5.Cr], the
luteo or hexammine chromium salts, R(sup1)3[(NH3)6.Cr], and the
rhodochromium salts: where R(sup1) = a monovalent acid radical and M = a
monovalent basic radical. For the preparation and properties of these
salts and a discussion on their constitution the papers of S.F.
Joergensen and of A. Werner in the _Zeitschrift fuer anorganische
Chemie_ from 1892 onwards should be consulted.

P. Pfeiffer (_Berichte_, 1904, 37, p. 4255) has shown that chromium
salts of the type [Cr{C2H4(NH2)2}2X2]X exist in two stereo-isomeric
forms, namely, the cis- and trans- forms, the
dithiocyan-diethylene-diamine-chromium salts being the trans- salts.
Their configuration was determined by their relationship to their