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.
1. Aug. Husemann in Chur, in the Archive of Pharmacy, 1875, recommends the addition of a small quantity of citric acid as a preservative for natural ferruginous mineral waters, having got very satisfactory results by experimenting, and the same may be applied to artificial combinations.
His proportion is based upon careful experiments, and he recommends the addition of 5 to 6 milligrammes (equal to 1/10 of a grain) of citric acid per bottle, containing three-fourths of a liter, about 750 grammes or one pint and a half of the ferruginous mineral water. The water was unchanged and clear after 16 months, and was in every respect in good condition. A reduction in the amount of citric acid under 5 milligrammes caused a small reduction of soluble iron, an increase up to 8 milligrammes and more caused, after a storage from 6 to 8 months, a faint smell of sulphuretted hydrogen. As citric acid is a harmless adulterant in ferruginous mineral water, there is nothing to say against its employment as a preservative. The quantity to be added to 10 gallons of water would be 267 to 321 milligrammes (about 5 to 6 grains) cryst. citric acid. The effect of citric acid is, that it absorbs oxygen present in mineral waters, and thus prevents the oxidation and separation of iron.
2. The addition of small quantities of pyrophosphate of soda as a preservative is also resorted to by some manufacturers, but it is, like citric acid, also an adulterant, however harmless, as both substances are no components of natural mineral waters. It does not prevent oxidation, but the precipitation of the oxides by the aid of the alkalies in solution. When no lime or magnesia is present, it keeps the artificial water clear at all times; however, when those alkaline earths are components, it will only keep clear as long as a high gas pressure in the bottle is retained.
3. Dr. Hager says: "Some well-prepared mineral waters, with iron as a constituent, separate at a low temperature a white flaky precipitate. This precipitate, which again disappears at a higher temperature, has been observed when the water contained organic substances or phosphoric acid, or when silicic acid or phosphates were constituents. From these observations the conclusions follow to employ but distilled and filtered water, and water free of phosphates, in the manufacture of ferruginous mineral waters, also to omit phosphates, and silicic acid (silicate of soda) in their combination".
There is a plain way to avoid the troubles experienced with ferruginous mineral waters, viz., to leave the ferruginous salts out altogether from the artificial combination. This may be done where an artificial mineral water is intended for table use, as a thirst-quenching refreshment, where its medicinal value is not so much to be considered. Especially when a mineral water is used for commingling with delicate wine the ferruginous salts are better left out, as it is well established that iron, even a slight presence, renders water uufit for such use, because it will render them dark and objectionable to sight and taste.
However, where the good effects of iron are intended, and a "ferruginous" water is desired for its medicinal properties, it should be imitated as closely as possible, properly prepared by excluding all the atmospheric air from the apparatus and water, carefully charged with carbonic acid gas, and when intended for storage or shipment, one of the "preservatives" may be resorted to.