Characters. - Thin, transparent scales of a deep garnet colour, Slightly sweetish and astringent in taste.

Solubility. - It is soluble in water and sparingly soluble in spirit.

Reactions. - The aqueous solution, when acidulated with hydrochloric acid, gives the reactions of a ferric salt only. When the salt is boiled with solution of soda, peroxide of iron separates, but no ammonia is evolved (not the ammonia-citrate), and the filtered solution when slightly acidulated by acetic acid gives, as it cools, a crystalline deposit (potassium).

Dose. - 5 to 10 grains. The double salts of iron with potassium, ammonium, quinine, etc, are usually called the scale preparations of iron from their appearance. These are less astringent than, and do not confine the bowels so much as, either the proto-sulphate or the per-salts. Another advantage is that they may be given along with alkaline carbonates without being precipitated. They are employed in cases where the other preparations cause headache, or derange the digestion, on account of the stomach being irritable.