s but periodic. It is largely made as ferro-chrome, an alloy
containing about 60-70% of chromium, by reducing chromite in the
electric furnace or by aluminium.

Chromium and its salts may be detected by the fact that they give a deep
green bead when heated with borax, or that on fusion with sodium
carbonate and nitre, a yellow mass of an alkaline chromate is obtained,
which, on solution in water and acidification with acetic acid, gives a
bright yellow precipitate on the addition of soluble lead salts. Sodium
and potassium hydroxide solutions precipitate green chromium hydroxide
from solutions of chromic salts; the precipitate is soluble in excess of
the cold alkali, but is completely thrown down on boiling the solution.
Chromic acid and its salts, the chromates and bichromates, can be
detected by the violet coloration which they give on addition of
hydrogen peroxide to their dilute acid solution, or by the fact that on
distillation with concentrated sulphuric acid and an alkaline chloride,
the red vapours of chromium oxychloride are produced. The yellow colour
of normal chromates changes to red on the addition of an acid, but goes
back again to yellow on making the solution alkaline. Normal chromates
on the addition of silver nitrate give a red precipitate of silver
chromate, easily soluble in ammonia, and with barium chloride a yellow
precipitate of barium chromate, insoluble in acetic acid. Reducing
agents, such as sulphurous acid and sulphuretted hydrogen, convert the
chromates into chromic salts. Chromium in the form of its salts may be
estimated quantitatively by precipitation from boiling solutions with a
slight excess of ammonia, and boiling until the free ammonia is nearly
all expelled. The precipitate obtained is filtered, well washed with hot
water, dried and then ignited until the weight is constant. In the form
of a chromate, it may be determined by precipitation, in acetic acid
solution, with lead acetate; the lead chromate precipitate collected on
a tared filter paper, well washed, dried at 100 deg. C. and weighed; or
the chromate may be reduced by means of sulphur dioxide to the condition
of a chromic salt, the excess of sulphur dioxide expelled by boiling, and
the estimation carried out as above.

The atomic weight of chromium has been determined by S.G. Rawson, by the
conversion of pure ammonium bichromate into the trioxide (_Journal of
Chem. Soc._, 1899, 55, p. 213), the mean value obtained being 52.0