Physical Properties of Cerium

Cerium is a metal which resembles steel in appearance and takes a high polish. Its density is 6.92 at 25°. It is malleable and highly ductile, may be readily cut with a knife, and can be machined fairly well, although there is a tendency to buckle. Its ultimate strength is 9 kilos, per square mm. The metal is paramagnetic, its magnetic susceptibility at 18° being 15×10^-6 c.g.s. units per gram. Cerium is a fairly good conductor of heat, but a poor conductor of electricity, its resistance being 71.6 micro-ohms per cm. cube at the ordinary temperature. The following values have been obtained for the specific heat: -

	temp. range	spec. ht.	atomic ht.
Mendeleeff	?	0.05	7.01
Hillebrand	0°-100°	0.0448	6.28
Hirsch	20°-100°	0.05112	7.17

Hirsch's value was obtained by using the differential steam calorimeter and operating with 70 grams of cerium. The atomic heat of cerium thus appears to be unusually high. Cerium melts at 635° (Hirsch), 623° (Muthmann and Weiss).

Cerium takes fire in air at 160°, burning with even greater brilliancy than magnesium and evolving much heat. A shower of sparks is produced by striking the metal with a flint. When a lump of cerium is kept warm in a closed bottle, a black powder slowly forms on the surface, and when the bottle is opened the powder inflames spontaneously. Cerium burns brilliantly in chlorine at 210°-215°, and in bromine at 215°-220°; it also combines directly with hydrogen, nitrogen, iodine, sulphur, selenium, tellurium, arsenic, antimony, etc. It reduces carbon monoxide and carbon dioxide with the separation of carbon.

Cerium preserves its lustre in dry, but tarnishes in moist air. It is very slightly attacked by cold water, but in boiling water a slow evolution of hydrogen occurs. At the ordinary temperature ethyl and amyl alcohols, chloroform, carbon tetrachloride, and concentrated solutions of sulphuric acid, sodium and ammonium hydroxides have no action on cerium; dilute hydrogen peroxide, ammonium and potassium chloride slowly attack it, and the action of hydrochloric or nitric acid, both dilute and concentrated, and dilute sulphuric acid is moderately vigorous. At boiling temperatures the mineral acids, dilute or concentrated, attack the metal rapidly, except concentrated sulphuric acid.

According to Hirsch, cerium is best purified by heating it with boiling mercury in a long iron pipe. The cerium amalgamates with the mercury, and the impurities may be skimmed off from the molten amalgam. The amalgam is placed in a magnesia vessel, the whole placed inside a larger quartz vessel, and the amalgam heated very strongly in vacuo to drive off the mercury.