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.
The plan at present extensively in use in Europe is the so-called "continuous direct-action process," or continuous plan. The principle of this is as follows:
The carbonic acid gas is made in a leaden vessel, the carbonate being placed in, generally being mixed with water: the acid, which is contained in a continuous vessel, being poured on by a simple arrangement in just sufficient quantities to generate the gas, no more being used than is absolutely required for the purpose, the waste product, when exhausted, being easily drawn off and a fresh charge inserted.
The gas passes from the leaden vessel called the "generator" into what is called the "gasometer," in which it is allowed to expand, after passing through water. The soda-water machine proper is a gas and water pump and condenser (or globe) mounted on a strong iron frame, the one action of the person turning the fly-wheel, pumping the gas and water at the same time, and forcing them into the globe, inside of which is an agitator, driven at a very rapid rate, which thoroughly breaks up the water into a spray, and in this condition it takes up a large quantity of gas, according to the pressure the machine is being worked at. The water is then drawn off, the pump constantly refilling the globe as it is taken away, thus obtaining the largest quantity of produce in the shortest time possible.