The cooler the water is kept, the more gas it absorbs ; and it is also advisable to have thorough ventilation. The boiler should be covered with some non-conducting material, and the pumps kept perfectly cool. A steam engine attached to each of the mixing machines is hardly a gain. When the make is sufficiently large for the adoption of steam, several machines are generally used ; to provide for cases of stoppage for repairs, the pumps may be required to work by manual labour. To avoid accidents, care should be taken to allow only those whose duty it is to see to the various parts of the machinery to have access to it.
Bottles.—Many varieties of bottles to hold aerated waters have been intro duced during the last few years. The ordinary corked bottle is too well known to need description, and is, moreover, rapidly falling into disuse. The use of corks in stoppering, to which there are many objections, has been almost superseded by the introduction of bottles of various kinds which are self stoppering. Of these, one of the best known is that devised by Codd, and shown in Figs. 298 and 299. In this bottle, a glass ball, or marble, forms a joint against an indiarubber seating fixed in the month. The ball, being larger than the orifice of the bottle, is introduced in the process of making, and the narrow groove to hold the rubber ring is formed in finishing the mouth. A contraction in the neck prevents the ball from falling into the bottle, and it is securely held in pouring out by an indentation in the neck. In opening, a firm but gentle pressure forces the ball from its seating, when it I immediately falls into the shoulder of the bottle. The advantages possessed by this bottle over the ordinary kind are numerous. The glass stopper is practically everlasting. No string or wire is needed. Skilled labour is not required, tyers, wirers, and fitters being at the same time dispensed with and the chances of breakage consequently diminished.
Besides being conducive to cleanliness, it is claimed for this stopper that since it is not allowed to fall into the liquid, the full amount of gas is retained in the battle. If the stopper were allowed to fall back into the bottle, a con siderable percentage of the gas would he immediately discharged and wasted. This action may be seen by dropping a stone into an ordinary soda water bottle, when first opened ; the gas at once collects in bubbles, which rush to the surface and are wasted. Codd's bottle, the merits of which are now widely recognized, is largely used by manu facturers of aerated waters.
Another bottle, on a similar principle, is that known as Lamont's, and shown in Fig. 300. The stopper is made either of ebonite or of glass, and is provided with an indiarubber ring fastened round it ; this ring, when the bottle is full, is pressed tightly against a small rim in the neck. This bottle is opened in the same manner as Codd's, by pressing down the stopper.
If the aerated water is used for supplying iced fruit drinks from counter fountains, portable cylinders, such as that shown in Fig. 301, are used; these are made of steel and copper, and ought to be glass-lined whenever the water is to remain in them for any length of time. In England, aerated waters are usually sent out in bottles ; in France, siphons are more commonly used ; in America, cylinders form the principal receptacles, and are largely supplied to chemists, confectioners. and fruiterers, many of these having large amounts invested in marble counter-tountains from which the drinks are dispensed.
Corks.—The corks should be carefully chosen, those only befog selected which are capable of resisting a high pressure. Old wine corks may be used, but they must be well cleansed in a solution that will thoroughly purify them. They may be slightly moistened before using, in order that they may be readily compressed in the machine ; large hard corks can be brought to almost any degree of softness by steamiog. The use of corks has been to a large extent superseded by the self-stoppering bottles already described.
It will be well to make here a few general remarks upon the most im portant points in the manufacture. Above everything else, it is indispensable that the maker of aerated beverages should have a constant supply of the purest and freshest water. On the purity of the water depends in a great measure the quality of the produce; and on its abundance and freshness depend the cleanliness and temperature of the work-room and the regular working of the entire process.
The most scrupulous cleanliness is also indispensable, and this fact cannot be too strongly insisted upon. No conceivable precaution which would help to ensure this condition should he omitted, since not only does the success of the business depend Upon it, but the health of the hands employed also, and the cleanliness, or otherwise, of a factory is the flrsl /Writ to which a sanitary inspector visiting it wonld direct his attention. When, as is often the case, the factory is situate in the heart of a large town, the manufacture is sometimes earned on in cellars, by the help of artificial light. In such a case, it is essential that the rooms be thoroughly ventilated in order that the carbonic acid gas, of which a large quantity is inevitably wasted, may he carried away as soon as it is evolved, and the air thereby be kept pure and fresh. Refrigerators disposed around the apparatus arc used with advantage, in order to preserve the required low temperature ; in het weather, indeed, it is impossible to acquire it in any other way. Although the expansion of the gas occasioned by a rise in temperature may not appear considerable, it becomes readily perceptible in practice, when liquids are sometimes saturated at a pressure of 10 or 14 atmosphen s.