Illustration: FIG. 1. SODA-WATER APPARATUS.
In fig. 1 there is an illustration of the machinery used. It consists of a small vessel holding sulphuric acid, attached to another vessel containing chalk and water kept constantly stirred by a small windlass passing through a hole in the top, and working air-tight. When some of the sulphuric acid is allowed to run into the vessel holding the chalk an effervescence takes place, and a rapid extrication of carbonic acid; this is conducted by a tube to a gas-holder as a store. A tube leads from this gas-holder into a sort of air-pump, and a man, by turning a windlass, not only works this and thereby forces a certain quantity of gas into another vessel of copper (plated with silver inside), but turns this vessel itself rapidly round. In this vessel the solution of carbonate of soda is placed, and is agitated under pressure with the carbonic acid thus forced into it, and which it rapidly absorbs. From this vessel it is drawn off into bottles, which are adroitly corked before much of the carbonic acid can escape, and then wired down, a fresh supply of solution of soda and carbonic acid being constantly introduced. Potash-water and Carrara water are made in the same way, using potash in the former, and chalk in the latter, instead of soda.
Illustration: FIG. 2. (‡ SODA-WATER BOTTLE.)
The form of a soda-water bottle is shown in fig. 2; it is made of very thick glass, that it may resist the outward pressure of the carbonic acid, and so formed that it cannot stand on its bottom, and when laid on its side the bubble of air shall rise up to the middle of the bottle and not to the cork, or else it would escape through the cork before long, however nicely it may be fitted.
Illustration: FIG. 3. (‡ DISPENSING BOTTLE.)
Fig. 3 is a convenient vessel for holding about a quart of soda-water or any other effervescing drink, all of which is not at once required. A tube passes from the top to nearly the bottom of the vessel, and when this is filled with aerated water, the expansive power of the carbonic acid forces the water up this tube and out of the spout when the handle is depressed and the tap opened, and when sufficient is obtained, the tap can be immediately closed.