MANGANESE AND CHROMIUM
| SYMBOL | ATOMIC | WEIGHT DENSITY | MELTING POINT | FORMULAS OF ACIDS | |
| Manganese | Mn | 55.0 | 8.01 | 1900° | H2MnO4 and HMnO4 |
| Chromium | Cr | 52.1 | 7.3 | 3000° | H2CrO4 and H2Cr2O7 |
General. Manganese and chromium, while belonging to different families, have so many features in common in their chemical conduct that they may be studied together with advantage. They differ from most of the elements so far studied in that they can act either as acid-forming or base-forming elements. As base-forming elements each of the metals forms two series of salts. In the one series, designated by the suffix "ous," the metal is divalent; in the other series, designated by the suffix "ic," the metal is trivalent. Only the manganous and the chromic salts, however, are of importance. The acids in which these elements play the part of a non-metal are unstable, but their salts are usually stable, and some of them are important compounds.