the metal of 99% purity by electrolysing
calcium iodide at a low red heat, using a nickel cathode and a graphite
anode; he also showed that a more convenient process consisted in heating
the iodide with an excess of sodium, forming an amalgam of the product, and
removing the sodium by means of absolute alcohol (which has but little
action on calcium), and the mercury by distillation.

The electrolytic isolation of calcium has been carefully investigated, and
this is the method followed for the commercial production of the metal. In
1902 W. Borchers and L. Stockem (_Zeit. fuer Electrochemie_, 1902, p. 8757)
obtained the metal of 90% purity by electrolysing calcium chloride at a
temperature of about 780 deg., using an iron cathode, the anode being the
graphite vessel in which the electrolysis was carried out. In the same
year, O. Ruff and W. Plato (_Ber._ 1902, 35, p. 3612) employed a mixture of
calcium chloride (100 parts) and fluorspar (16.5 parts), which was fused in
a porcelain crucible and electrolysed with a carbon anode and an iron
cathode. Neither of these processes admitted of commercial application, but
by a modification of Ruff and Plato's process, W. Ruthenau and C. Suter
have made the metal commercially available. These chemists electrolyse
either pure calcium chloride, or a mixture of this salt with fluorspar, in
a graphite vessel which serves as the anode. The cathode consists of an
iron rod which can be gradually raised. On electrolysis a layer of metallic
calcium is formed at the lower end of this rod on the surface of the
electrolyte; the rod is gradually raised, the thickness of the layer
increases, and ultimately a rod of metallic calcium, forming, as it were, a
continuation of the iron cathode, is obtained. This is the form in which
calcium is put on the market.

An idea as to the advance made by this method is recorded in the variation
in the price of calcium. At the beginning of 1904 it was quoted at 5s. per
gram, L250 per kilogram or L110 per pound; about a year later the price was
reduced to 21s. per kilogram, or 12s. per kilogram in quantities of 100
kilograms. These quotations apply to Germany; in the United Kingdom the
price (1905) varied from 27s. to 30s. per kilogram (12s. to 13s. per lb.).

_Properties._--A freshly prepared surface of the metal closely resembles
zinc in appearance, but on exposure to the air it rapidly tarnishes,
becoming yellowish and ultimately grey or white in colour owi