This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Sulphate of iron should be kept in well-closed vessels. Large, pale bluish-green, monoclinic prisms, efflorescent and absorbing oxygen on exposure to air, without odor, having a saline, styptic taste, and an acid reaction. Soluble in 1.8 parts of water at 15° C. (59°F.), and in 0.3 part of boiling water, insoluble in alcohol. When quickly heated the crystals fuse. When slowly heated to 115° C. (239° F.), they fall to powder and lose 38.86 per cent of their weight (water of crystallization).
This salt is best dissolved for immediate use in some carbonated water drawn from the fountain. One part by weight in nine parts of carbonated water. Filter. Specific gravity 1.054 at 15° C, containing 10 per cent, of sulphate of iron crystal. Proportion 10 to 1. When it has absorbed oxygen from the air, it will give a turbid, yellowish solution, and is in this state unfit for our purpose. Small traces of oxidation may be remedied by shaking the solution with some iron filings and filtering. The solution is added to the mixture in fountain, after the at mo-spheric air has been removed.
Liquor of iron is not adapted for use in compounding mineral waters.