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Much the best practical source of helium is thorianite, a mineral imported from Ceylon for the manufacture of thoria.

In other words, it is easier to accelerate the motion of the corpuscles in ceria, thoria and the other ingredients of the mantle, than it is those of carbon.

The specific gravity of pure thoria is 10.2207 to 10.2198.

Metallic thorium is brittle and almost infusible; the powder takes a metallic luster under pressure, is permanent in the air at temperatures up to 120°, takes fire below a red heat either in air or oxygen, and burns with a dazzling luster, leaving a residue of perfectly white thoria.

It is then weighed as thoria, ThO2.