Thorium n. (Chem.) A metallic element found in certain rare minerals, as thorite, pyrochlore, monazite, etc., and isolated as an infusible gray metallic powder which burns in the air and forms thoria; formerly called also thorinum. Symbol Th. Atomic weight 232.0.
... So far only radium, thorium, and uranium are generally known. We know that the radioactive elements are constantly breaking down, and one often hears uranium, for instance, called the 'parent' of radium. Radium also gives off an emanation, and among its products ... — The Poisoned Pen • Arthur B. Reeve
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