Prep. Made by dissolving ten grains of granulated sulphate of iron in one fluid ounce of boiling distilled water. It should be recently prepared.

Use. This is a solution of the protosulphate of iron; in contact with nitric acid and oil of vitriol it becomes of a dark purple colour.

It is employed under Acidum Nitricum, Acidum Phosphoricum, Acidum Sulphuricum, aetheris Nitrosi Spiritus, etc.