Applied to compounds containing a greater proportion of tantalum than those called tantalic, as tantalous oxide, tantalum dioxide, TaO2.
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tantalic1842
tantalous1868
1868 H. WattsDict. Chem. V. 665 Dioxide of Tantalum, or Tantalous Oxide..is a dark-grey mass, which scratches glass, and acquires metallic lustre by burnishing.