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.
In Germany, the mother country of natural and artificial mineral waters, they apply the following rules when iron or manganese salts are constituents of the artificial mineral waters. The cylinder is charged with water and all the other ingredients, except those salts, and impregnated with carbonic acid up to 5 atmospheres (80 pounds). The liquid is allowed to rest a few minutes, then the blow-off cock is opened (or the filling bung slightly turned), and the atmospheric air, which is compressed at the upper portion of the cylinder, allowed to escape - a few seconds will do. It is again charged up to 80 pounds and agitated, the liquid again allowed to rest, and then blown off a second time. This operation is repeated three or four times when artificial waters are made with iron or manganese salts. The carbonic acid gas has displaced the atmospheric air, which has been blown off. On the German apparatus is an air-tight chamber adjusted for salt solutions. It is described on page 220.
It is shaped and arranged like the acid chamber on American apparatus, movable, can be taken away if not required, and the opening closed with a cap. Into this mixer or salt-solution holder, the solutions of iron or manganese salts are introduced. A blow-off cock enables the operator also to let the atmospheric air escape. As it is adjusted with outlet cock and equalizing pipe, and able to stand the required pressure, it is a very practical contrivance in adding salt solutions to a charged cylinder, thus saving time, gas, and preventing access of air.
Other salt solutions, which are better added after the water has absorbed a certain amount of carbonic acid gas, may be, by its aid, also introduced to the fountain without opening again; indeed, all salt solutions may thus be introduced, an advantage when salts are used, which dissolve better in carbonated water than in any other.