In the illustration given above, A and B are two bottles, both of which can be closed tightly with corks. A hole is made in the cork in the bottle, A, a little smaller than the glass tube which connects A and B. It is filed out with a rat-tail file until it is large enough to admit the tube very tightly. The tube may be bent easily, by being heated over a common fish-tail gas burner or over the top of the chimney of a kerosene lamp, so as to form two right angles, one end extending close to the bottom of the bottle B as shown. Having fitted up the apparatus, about two ounces of hyposulphite of soda are placed in the bottle A, while the bottle B is about three-fourths filled with water--distilled or melted ice water is to be preferred; some sulphuric acid--about two ounces--is now diluted with about twice its bulk of water, by first putting the water into a dish and pouring in the acid in a steady stream, stirring meanwhile. It is well to set the dish in a sink, to avoid any damage which might occur through the breaking of the dish by the heat produced; when cool, the solution is ready for use and may be kept in a bottle. The cork which serves to adapt the bent tube to the bottle A is now just removed for an instant, the other end remaining in the water in bottle B, and about two or three ounces of the dilute acid are poured in upon the hyposulphite, after which the cork is immediately replaced. Sulphurous acid is now evolved by the action of the acid on the hypo, and as the gas is generated it is led as a series of bubbles through the water in the bottle B as shown. The air space above the water in bottle B soon becomes filled by displacement with sulphurous acid gas, which is a little over twice as heavy as air; so in order to expedite the complete saturation of the water, it is convenient to remove the bottle A with its tube from bottle B, and after having closed the latter by its cork or stopper, to agitate it thoroughly by turning the bottle upside down. As the sulphurous acid gas accumulated in the air space over the water is absorbed by the water, a partial vacuum is created, and when the stopper is eased an inrush of air may be noted. When, after passing fresh gas through the liquid for some minutes, no further inrush of air is noted on easing the stopper as before described after agitating the bottle, it may be concluded that the water is thoroughly saturated with sulphurous acid and is strong enough for immediate use. More gas can be generated by adding more dilute sulphuric acid to the hypo until the latter is decomposed; then it should be thrown aside, and a fresh charge put in the bottle. On preparing the solution it is well to set the bottles on the outside ledge of the window, or in some other open situation where no inconvenience will result from the escape of the excess of sulphurous gas as it bubbles through the water.