The third cylinder, before having the gas let into it from the generator, is connected with the first cylinder by a pipe which passes underneath and is not shown in the figure.
By this means, as much of the compressed gas contained in the first cylinder as the water iu the last cylinder will absorb is drawn over, and the pressure in the first considerably reduced, thus making it easier to refill with water, since the resistance is considerably diminished. In recharging the first cylinder, when the middle one is empty, it is connected with the latter, and the extra pressure reduced as in the previous case. When the third is empty, its surplus gas is withdrawn in refilling the middle one, the process being, therefore, continuous. The pipe shown at the bottom of the figure and connected with the three cylinders is attached to a pump at the right-hand side, and is used for filling them with water.
Fig. 296 shows another apparatus belonging to the compression system, recently introduced. The gas is generated by the action of heat upon bicarbonate of soda, which is placed over a fire in a closed vessel. One half of the gas contained in the salt is driven off by heat, leaving a. residue which by dissolving and crystallizing becomes the ordinary washing soda. The gas when generated is deprived of moisture and filtered before passing into a long, narrow cylinder, furnished with a pressure gauge at one end. This cylinder has a row of nipples upon its upper surface against which the bottles previously filled with the liquid to be aerated are placed. The gas is then passed into them, and they are agitated by means of the handle shown at the side. At the right hand side of the machine is placed a screen inside which the workman stands while conducting the process, in order to protect himself from danger in case of a bottle bursting.
Another apparatus, devised and constructed by Mondellot, of Paris, is shown in Fig. 297. Its chief peculiarity is that it generates just sufficient gas at each revolution of tho handle to aerate a definite quantity of water.
Arrangement of a Factory.—For the benefit of those who are about to engage in this manufacture a description is here given of the best and most convenient arrangement of the plant. The details must, of course, be varied in many cases to meet special requirements and circumstances.
Any well-lighted, ventilated and drained building of two floors, basement, and cellars may be • utilized as a soda water factory. The cistern, which should be of elate, cast iron, or galvanized iron, and be supplied from the well or main, but not by lead pipes, should be placed at the top of the building. This cistern should be furnished with outlet pipes to convey water through a filter
to the several machines and apparatus requiring it ; and also with other outlets for sluicing the factory and other washing purposes. On the same floor there should be a crane for lifting in the various materials. A lift should run from the top floor to the cellars, and there should be, upon all floors, light and noiseless trollies, running on three or more wheels ; these are useful for shifting orates about, as necessity arises. The first floor should be used for storing the acid and the car bonate; and the other portions of it may be partitioned off for Lt laboratory, and syrup-making rooms, and other purposes. The machinery, viz. the gas generator, purifier, and gas holder, mixing and bottling machine, washing apparatus, and the motive power should be all situate on the ground•floor. By this arrangement, the generating apparatus is supplied with vitriol and carbonate, and the filling machines with dosing material, directly from above. This floor should be asphalted and well draiued, so that it may be easily flushed whenever necessary. The cellars, which should be kept perfectly cool, may be utilized as stores for the finished product. Any place likely to give off effluvia, such as stables or closets, must be kept as far away as possible. When the production is over 2000 bottles a day, it is well to employ horse or steam power ; in small factories, the horse which takes out the goods may be utilized by means of a simple horse-wheel. If steam be used, and steam is generally most convenient, the boiler should be of sufficient size to provide for jacket pans, for boiling water or syrups, or for steam coils in the water tubs and washing troughs. Syrups should be kept in stone jars, and all solutions in slate tanks, for sweetness and cleanliness. It should be borne in mind that whiting is very liable to absorb foul gases. Aerated water exerts a corrosive action upon lead; all pipes therefore which contain it must be of tin, or thickly tinned, the joints being covered with pure tin. Indiarubber pipes are apt to become foul and to decay. Mixing cylinders should be examined once a year and retinned whenever necessary, in order to avoid contamination. All water pipes and taps should be tested occasionally. When desired, meters for measuring carbonic acid gas and water may be used. Pipes and globes should be emptied, and cocks shut, when not in use, to prevent metallic contamination, or danger from frost in winter.