AERATED WATERS. Dr. Venables, in a recent work on aerated waters, describes the operation of Bakewell's patent apparatus, and the composition necessary for the production of different varieties of these liquids. The ; aeration is not confined to mere cooling drinks . such as soda water, but is applicable to all cases where water is to have an effervescing quality given to it, whether for aperient, tonic, diuretic, antacid, lithotriptic, or pectic pur poses. The principal feature of the process is the forced combination of a gas with pure water ; and in the case of soda-water this gas is the result of chemical action between sulphuric acid and carbonate of soda.
Bakewell's apparatus consists of an upright vessel supported on a stand, and furnished with pipes and valves. In the lower part of the apparatus is a vessel called the generator, divided into two compartments by a horizontal partition. Sulphuric acid is placed in the uppermost of these compartments, and the carbonate of soda in the lower; and while the vessel is at rest, the two substances are kept wholly separate ; but when a working motion is given to it by making it oscillate on two pivots whereby it is suspended, the acid drops at regular intervals through a hole in the side of the upper compartment, and falls into the lower one, where it mixes with the carbonate. A chemical interchange imme diately takes place ; the soda leaves the car bonic acid and combines with the sulphuric ; so that instead of sulphuric acid and carbonate of soda we have carbonic acid and sulphate of soda. The carbonic acid assumes the gaseous form, and ascends to an earthen ware vessel in the upper part of the appa ratus. This vessel contains water ; and as
the apparatus is kept oscillating, the water is sufficiently agitated to absorb the gas passed up into it. With a small apparatus capable of holding a gallon at a time, a quarter of an hour's oscillation will suffice to impregnate the water with gas to a pressure of five at mospheres. The apparatus must of course be strong to resist this pressure ; it is made of iron, and there is a pressure gunge at the top, to measure the amount of the pressure. There is a tap for draining off the aerated liquids. Dr. Venables states that for a gallon of water to be impregnated to the extent of five at mospheres, would require about six ounces of carbonate (or rather sesqni-carbonate) of soda and four ounces of sulphuric acid. The appa ratus admits of being used in many ways ; for the aerator or upper vessel may be either filled with pure water, and modified only by the gas which ascends from the generator; or the water may previously be made acid or alka line, and receive a further change by the aera tion. The resulting beverage will thus depend, not only on the aeration, but also on the state of the water before aeration.
Messrs, Knight patented an air-tight stopper, in 1811, for flasks intended to contain the aerated water, when required. to keep it some time for further operations ; or to transfer it to the common glass-bottles. It is an inge nious piece of apparatus, strong enough to resist the expansive force of the gas, yet easily adjusted for the entrance or exit of liquids.