eces
and heated in a current of air, when it gives up its chlorine, partly
in the uncombined condition and partly in the form of hydrochloric
acid, and leaves a residue of magnesia, which can again be utilized
for the decomposition of more ammonium chloride (W. Weldon, _Journ. of
Soc. of Chem. Industry_, 1884, p. 387). Greater success attended the
efforts of Ludwig Mond, of the firm of Brunner, Mond & Co. In this
process the ammonium chloride is volatilized in large iron retorts
lined with Doulton tiles, and then led into large upright wrought-iron
cylinders lined with fire-bricks. These cylinders are filled with
pills, made of a mixture of magnesia, potassium chloride and fireclay,
the object of the potassium chloride being to prevent any formation of
hydrochloric acid, which might occur if the magnesia was not perfectly
dry. At 300 deg. C. the ammonium chloride is decomposed by the magnesia,
with the formation of magnesium chloride and ammonia. The mixture is
now heated to 600 deg. C. in a current of hot dry gas, containing no free
oxygen (the gas from the carbonating plant being used), and then a
current of air at the same temperature is passed in. Decomposition
takes place and the issuing gas contains 18-20% of chlorine. This
percentage drops gradually, and when it is reduced to about 3% the
temperature of the apparatus is lowered, by the admission of air, to
about 350 deg. C., and the air stream containing the small percentage of
chlorine is led off to a second cylinder of pills, which have just
been treated with ammonium chloride vapour and are ready for the hot
air current. With four cylinders the process is continuous (L. Mond,
_British Assoc. Reports_, 1896, p. 734).

More recently, owing to the production of caustic soda by electrolytic
methods, much chlorine has consequently been produced in the same
manner (see ALKALI MANUFACTURE).

Chlorine is a gas of a greenish-yellow colour, and possesses a
characteristic unpleasant and suffocating smell. It can be liquefied at
-34 deg. C. under atmospheric pressure, and at -102 deg. C. it solidifies
and crystallizes. Its specific heat at constant pressure is 0.1155, and at
constant volume 0.08731 (A. Strecker, _Wied. Ann._, 1877 [2], 13, p.
20); and its refractive index 1.000772, whilst in the liquid condition
the refractive index is 1.367. The density is 2.4885 (air = 1)
(Treadwell and Christie, _Zeit. anorg. Che