Note 11 — Chapter III · OXYGEN AND THE CHIEF ASPECTS OF ITS SALINE COMBINATIONS

All acids rich in oxygen, and especially those whose elements form lower oxides, evolve oxygen either directly at the ordinary temperature (for instance, ferric acid), or on heating (nitric, manganic, chromic, chloric, and others), or if basic lower oxides are formed from them, by heating with sulphuric acid. Thus the salts of chromic acid (for example, potassium dichromate, K2Cr2O7) give oxygen with sulphuric acid; first potassium sulphate, K2SO4, is formed, and then the chromic acid set free gives a sulphuric acid salt of the lower oxide, Cr2O3.