This term being popularly applied to a variety of acidulous and alkaline beverages more or less impregnated with fixed air, or carbonic acid gas, we introduce our article on the subject in this place; and as the manufacture of these liquids has of late years become of considerable extent, owing to their agreeable as well as medicinal properties, we purpose describing several ingenious apparatuses that have been used, or are still employed, for the purpose. Water absorbs under the natural pressure of the atmosphere about its own bulk or volume of carbonic acid gas. If a pressure be applied equal to two atmospheres, the water will absorb double its own volume, its absorbing power increasing as the pressure. Water thus impregnated acquires a pleasant acid taste, to which is usually added a small quantity of potash or soda, and such flavouring or other ingredients as may be required to imitate the natural mineral waters. Nooth's apparatus was one of the earliest contrivances, and is adapted to the preparation of smallquantitie3 of aerated water.

It is represented in the subjoined cut, and consists of three vessels; the lowest a, is flat and broad, so as to form a good basis; in this is put a quantity of chalk or pounded marble, and some dilute muriatic or other acid is introduced through a screwed stopper b. The gas being thus generated, passes through the tube c, in which a glass valve opens upwards into d, which contains the water or solution to be impregnated, and is provided with a stop-cock to draw off the liquid. The tube of the uppermost vessel e, dips into d, occasioning therein some pressure; and the gas which is not absorbed in the latter, passes up into e, which being provided with a heavy stopper, acts as a valve, and causes a considerable pressure of the gas upon the water within it. The gas which is not absorbed by the water in c or d, escapes by the aperture at top. Another apparatus of great simplicity, and adapted to operating upon a more extended scale, is delineated in the following cut.

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A is a strong plank on which the vessels are fixed; B is a bottle, containing a quantity of pulverised carbonate of lime or chalk; C is the tubulure and stopper of the bottle; D a bent tube for conveying the gas into the bellows E, which are supported by the upright stand F; G is a stop-cock connected with the tube D, which passes from thence into the strong iron-hooped air-tight barrel H, suspended by its axis on the upright pillars I I. In using this apparatus, the cask is to be half filled with distilled or spring water; the hole K is then to be stopped air-tight with a good bung, which is to be fastened down by means of the jointed strap or hasp L, being passed over the staple, and secured by a bolt or key put through the same. Then pour through the tubulure of the bottle some sulphuric acid, diluted with five or six times its weight of water, over the chalk, and close the aperture by the screw-stopper C. Having taken off the weight from the bellows, the carbonic acid extricated from the chalk by the action of the acid passes out of the bottle into the bellows through the tube D, which has an orifice opening under them.

When the bellows are fully distended, the cock G is to be turned, and the weight being placed upon the bellows, the gas is thereby pressed downwards into the barrel, and is there absorbed by the water, which is accelerated by giving the barrel a few quick turns by the winch J. The contents of the barrel may then be drawn off into stone bottles, which should be quickly corked, and bound down with copper wire, to be preserved for use.

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A very complete machine, invented by Mr. Cameron, of Glasgow, calculated to offer a strong resistance to the pressure of the gas, and force a considerable quantity into water, is shown below. The gas generator a, is made of cast iron, three quarters of an inch thick, and lined interiorly with sheet lead, (of 9 lbs. weight to the foot,) to prevent the action of the acid upon the iron. This vessel contains about 15 gallons, and is filled up to the dotted line by a mixture of whiting and water; it has an agitator b, also lined with sheet lead, and which works on a pivot at the bottom, the axis passing through the stuffing-box c, at the top of the vessel. The acid holder e, is formed of lead, of the capacity of two gallons, and is filled with oil of vitriol up to the dotted line. The acid is kept from running down into the generator by means of the conical plug /, which fits into a conical opening in the leaden pipe g. This plug is attached to a rod, and moves up and down through the stuffing-box h, and is prevented from turning round by means of a pin k, moving in a slit in the bridle I, and the screw-nut m is riveted loose into the top of the bridle.

The pipe n, which forms a communication between the top of the acid-holder e, and the pipe s, in which the plug-rod moves, preserves an equilibrium of pressure, so as to prevent the acid from rising higher in the pipe s than the level of the acid in the acid-holder, by which means the brass work of the stuffing-box is preserved from injury. To prevent any of the sulphuric acid from being carried over by the effervescence, an intermediate vessel o, containing about three gallons, is formed either of thick sheet lead alone, or of cast iron, lined with lead. This intermediate vessel is filled with water up to the dotted line. The impregnator v should contain about 16 gallons. It may be made either of copper tinned, or of cast iron, lined with sheet-lead; and the agitator m may either be of tinned copper, or of maple-wood; which last, giving no taste to the water, is for that reason preferable. This impregnator is filled up to the dotted line with water, to which, in making saline waters, the proper proportion of sesqui-carbonate of soda, carbonate of magnesia, or other ingredient, is to be added. A pressure-gauge t, of quicksilver, is to be placed at a little distance, and connected by means of a leaden pipe. The" operation of this apparatus is very simple.

By turning the nut m the plug is raised, allowing the sulphuric acid to run down into the generator o, where it acts upon the whiting, disengaging the carbonic acid gas in proportion to the quantity of sulphuric acid admitted at a time. The nut m being turned the other way, lowers the plug, and stops the descent of the sulphuric acid, thus regulating the disengagement of the gas, and preventing too violent an effervescence. The disengaged gas passes through the intermediate vessel into the impregnator v, where it is absorbed by the water. The impregnated water is then drawn off into strong half-pint bottles, by means of a cock, which descends to the bottom of the bottle; on withdrawing the bottle, it should be instantly corked, and the corks be wired or tied down.

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A patent has just been granted to Mr. F. C. Bakewell, of Hampstead, for a very compact and ingenious apparatus for the preparation of aerated waters, the peculiarity of which consists in the gas-generating and the gas-impregnating apparatus being inclosed in the same vessel, and in the whole operation being effected by a simple oscillating motion. A correct idea of this machine may be formed by the annexed figure, (representing a vertical section of its principal parts,) together with the subjoined explanation, a a exhibits an external section of a cylindrical form, with spherical ends, made strong enough to resist the prossure of several atmospheres; b is a partition, about two-thirds from the top of the vessel, separating it into two parts. The bottom part c is a receptable for the chalk, or other suitable material, mixed into a pasty consistency with water; d is a vessel containing dilute muriatic or sulphuric acid, which is made to pass out in small quantities, as required, at the aperture e into the vessel c; f is a guard to prevent the aperture e from being choked up; g is a pipe, of the form of a truncated cone inverted, being about an inch diameter at bottom, and two inches at the top.

This pipe is fitted into an aperture in the partition b, and is closed at the upper end; its object is for the ascent of the gas as it is generated, which passes from the top down an external pipe, into the lower part of a vessel k, and through a small aperture the tenth of an inch diameter, (or through several apertures whose total areas do not exceed the tenth of an inch,) through the partition into the upper part of the vessel h. This vessel, which is denominated the washing vessel, is furnished with two shelves, sloping in opposite directions near its top, to detain the gas longer in its passage through the aperture b to an external pipe, furnished with a perforated rose, for distributing the gas as it escapes into the water to be impregnated, contained in the vessels oo; p is a stop-cock for drawing off the impregnated water as required; q is an aperture for the introduction of the chalk and water; r, another for the introduction of the acid; and s, another for the water to be aerated: each of these apertures is provided with a screwed cap, to stop them securely after the respective vessels have been charged. The apparatus is made to swing on two pivots, one of which is shown in section at t.

When the chalk and acid receptacles are to be supplied with those ingredients, the apparatus is to be turned on its pivots to a horizontal position, with the aperture r upwards, and a funnel or hopper, with a bent stem, is to be employed in filling the vessel c c; n is an end view of a pendulum or agitator, of the form of an arc of a circle, extending across the bottom of the vessel, and suspended at its two extremities; one of the suspension wires is shown in the drawing. The apparatus having been charged as above described, it is to be put into vibration on its pivots, by which the chalk and water will be effectively agitated by the motion of the pendulum, while a small portion of acid will escape from the vessel d into the vessel e, to keep up the generation of the gas as it passes off to the water in a, which will, at the same time, by the vibration of the apparatus, be thoroughly mixed with the gas as it escapes through the rose n. An elegant apparatus, adapted for saturating liquids with the carbonic acid, as well as other gases, was invented by M. Clement, for which see the article Absorbing and Productive Cascade.

Some manufacturers of aerated waters employ mechanical means to force the gas into the water, by the use of a transferring pump or syringe, which is connected at one end with a bladder, or other reservoir of the gas, and at the other, with a vessel, or single bottle of water; the up-stroke of the pump extracting the gas from the bladder, and the down-stroke transferring it into the water.

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