The process of forcing gas into the water by mechanical pressure, in the manner described, requires great labour, for the pump has to be worked against a pressure exceeding fifty pounds on the square inch. With a view to remove that inconvenience, and to avoid the use of costly machinery, so that private individuals might manufacture soda-water, the author contrived a modification of Nooth's apparatus, for which he obtained a patent in 1831. By that means, the gas is generated in a closed vessel, and forces itself into the water by its own elasticity. Any amount of pressure can thus be obtained by chemical action alone. The accompanying woodcut represents a section of the apparatus in its improved form. The vessel, A, is made of very strong stone ware, inside which is the gas generator _b_. A few inches from the bottom of the generator is the partition, _a_, perforated with holes, and near the top there is inserted the small tube, _c_, which conveys the gas down to a perforated expansion of the tube, _d_, through the apertures of which the gas issues into the water contained in A. Another tube, _e_, reaches near the bottom, and is connected with a stop-cock for the purpose of drawing off the aerated liquid. In charging the apparatus, the interior, A, is nearly filled with water, or other liquid, through the opening, _f_, which is then closed by cork, which is kept in its place by a screw nut. A few ounces of carbonate of soda, mixed with water, are then poured into the generator through the opening at _g_. The mixture flows through the apertures in the partition, and occupies the lower part of the generator. A proportionate quantity (about three-fourths of the weight of the soda) of tartaric acid in crystals is then introduced through _g_, which lodge on the top of the partition without touching the soda. The opening being then closed by a screw-nut, the apparatus, which is mounted on pivots, with an appropriate stand, is swung backwards and forwards like a pendulum. The effect of this agitation is to force a portion of the water saturated with carbonate of soda through the apertures at _a_, where it comes in contact with the tartaric acid, and instantly generates carbonic acid gas. The gas, having no other escape than through the tube, _c_, is forced into the vessel A, and becomes mingled with the water by the same act of vibration that brings the soda and tartaric acid together. The continuance of the vibratory action for a short time generates sufficient gas to aerate the water or other liquid contained in the vessel, A. When the aeration is completed, the soda-water may be drawn off, as required, through the stop-cock. The apparatus is made of two sizes, to hold one and two gallons. [Illustration] The tartaric acid and soda in the generator do not mingle with the water, and the tartrate of soda, resulting from the combination, is emptied after the soda-water is drawn off, before renewing the charge.