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.
For the manufacturing of carbonated beverages in general, and for the production of ferruginous and sulphur waters especially, it is important to remove all the atmospheric air from the carbonic acid gas. The mixed solution of sulphate of iron and soda mentioned, to absorb sulphuretted hydrogen gases, will also absorb the atmospheric air, and be sufficient for ordinary manufacturing; but where those mineral waters are largely manufactured, and particular care for the removal of atmospheric air has to be taken, Hager recommends an extra cylinder or washer through which the gas is to pass, with a washing liquid consisting of 5 parts by weight of sulphate of iron (green vitriol) and 1 part bicarbonate of soda in 100 parts of water; or, what is still better, a solution of 5 parts by weight of sulphate of iron and 2 parts of ordinary cooking salt in 100 parts of water. On the continuous apparatus of the English plan this washing cylinder, practically, should be placed between the gasometer and pump.