cobaltous

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Relating to or containing cobalt, especially with valence 2.

from The Century Dictionary.

• Pertaining to or of the nature of cobalt; consisting of or derived from cobalt: specifically applied to compounds in which the cobalt atom appears to be combined as a dyad element.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Chem.) Pertaining to, derived from, or containing, cobalt; -- said esp. of cobalt compounds in which the metal has its lower valence.
• adjective 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective chemistry Containing cobalt in oxidation state 2.