This is a new officinal of the U. S. Pharmacopoeia, introduced as a substitute for ammonia alum, which it resembles in composition; the sesquioxide of iron being substituted for alumina. Hence it has been called ammonio-ferric alum. It is prepared by dissolving a due proportion of sulphate of ammonia in boiling-hot solution of tersulphate of iron, with insufficient water to hold, when the solution cools, the salt formed by their combination. It consists of 1 eq. of tersulphate of sesquioxide of iron, 1 of sulphate of ammonia, and probably 24 eqs. of water (Fe2O3, 3 So3 + Nh4o1so3 + 24 HO).

It may be given in the same complaints in which alum is employed, and has been especially recommended internally in leucorrhoea, diarrhoea, chronic dysentery, and other complaints requiring the joint use of astringent, tonic, and chalybeate remedies. The dose is from three to fifteen grains twice or three times daily.