a. Chem. Of the nature of cobalt; applied to the di-compounds of the metal, as Cobaltous oxide Co O.
1863–72. Watts, Dict. Chem., I. 1048. Protoxide of cobalt or cobaltous oxide … is a light greenish-grey or olive-green . powder. Ibid., 1049. Hydrated cobaltous oxide, or Cobaltous hydrate … is produced when a cobaltous salt is decomposed by potash out of contact of air.
