Note 203 — RESEARCH III. (continued 2)

There are many analogous decompositions. Dr. Priestley noticed (and I have often made the observation) that green oxide of iron, or the precipitate from pale green sulphate of iron by caustic alkali, became red at the surface, when covered by a thick stratum of water. In my experiments on the green muriate and sulphate of iron, I observed that part of some dark oxide of iron which was at the bottom of a trough of water 9 inches deep, became red at the surface nearly in the same time as another portion of the same precipitation that was exposed to the atmosphere. This oxygenation must depend upon the decomposition of atmospheric air constantly dissolved by the water.