from
The Collaborative International Dictionary of English v.0.48
Cobaltous \Co*balt"ous\, a. (Chem.)
Pertaining to, derived from, or containing, cobalt; -- said
esp. of cobalt compounds in which the metal has its lower
valence.
[1913 Webster]
{Cobaltous chloride}, a crystalline compound, {CoCl2}, of a
pale rose color when hydrous, blue when dehydrated. Its
solution is used for a sympathetic ink, the writing being
nearly colorless when dried in the air, owing to absorbed
moisture, and becoming bright blue when warmed.
[1913 Webster]