The two large pumps detailed in Fig. 840, communicate with pipe H from the cylinder, through inwardly-opening cheek-valves I, located in the branches of the pipe. These pipes are also pro vided with a gravity cup-shaped valve J, which is of greater diameter than the pisten-cylinder, and TS 9 plays between the cylinder-head and the flange of the body of the cylinder, upon which it is seated, being guided in its movement by ribs in the enlarged cavity of the cylinder-head. On the descent of the piston, the gas is drawn through the pipe H, the check-valves I are opened, and the pump cylinder is filled. But when the piston rises, the check-valves are closed, and the compressed gases above the piston lift the valve J, and allow the gas to pass out into the pipe, and thence to the condenser through K. As, however, the gases contained in the portion of the pipe between the pump-cylinder and the check are compressed, but not forced out, if the piston should descend with this pressure of gas contained here, the gas would expand, and, by partially filling the chamber, prevent the perfect exhaustion of the gas-cylinder. To provide for this, the piston in its upward stroke passes the orifices of pipe El, so that the compressed charge of gas is held in the confined space, and is liberated beneath the piston, and, upon its descent, is driven out through the valve L at the bottom into a pipe that communicates with K. The face of the piston, in rising, strikes against the bottom of the cup-valve and lifts it, and, upon the reverse stroke, the valve seats itself upon the lenge of the cylinder, while the plain ground face of the piston departs from the plain ground bottom of the valve, producing as nearly a perfect vacuum as it is possible to attain in a pump, there being practically no cushion of gas left between the valve and piston.
As the gas is delivered to the condenser, it is made to traverse coils, and is cooled by the circulation of water of the normal temperature which passes through the condenser. As the gss is liquefied, it passes into the receiver, where it accumulates, and is fed from time to time back into the refrigerator-cylinder. As the non-congealable liquid in the coil of the refrigerator circulates, it passes out through the pipe F to the distributing-pan M, where its temperature is to be trans ferred to the air circulating in the subjacent case N. The upper case is provided with a dis tributing-pan, into which the cooled liquid is admitted. The hottom of the pan hes perforations, which are arranged in rows immediately above a series of vertical partitions of wire gauze, between which are arranged the vertical baffle-plates. As the cooled liquid drops through the perforations in the pan, it falls upon the wire partitions, and being retarded in its descent, trickles slowly down, while the current of sir driven through the case by the blower is made to penetrate all parts by reason of the baffle-plates, and io so doing, takes on the temperature of the non-congealablo liquid, which is below the freezing-point of water, passes into the congealing-case at and through pipe P, then traverses the pans in the congealing-case to freeze the water therein contained, and after having done its duty, passes up through the blower and pipe Q, to be again reduced in temperature. The congealing-case has doors R at each end, and is provided With supporting rollers, upon which the pans S are fed in at one end and removed at the other.
This apparatus was first designed solely for reducing the temperature of liquids, such as beer when the liquid to be cooled is allowed to trickle down over the refrigerating-coil. It has been widely adopted in American breweries. For the production of ice, additional plant is necessary, consisting of a large tank, and suitable receptacles for the water.
A novelty in Holden's arrangement is that the water-holding vessels are introduced at one end of the tank and removed at the other, passing through a progressively increasing degree of Cold.
Sulphuric acid is employed in E. Canes apparatus, Fig.
841. It consists of a large vessel a, for holding the concentrated sulphuric acid ; an air-pump p, with tube-connections r adapted to the mouths of the decanters f; and a mechanism by which the lever h of the air-pump keeps the acid in continual motion ; 1 is a stop-cock. This apparatus is useful for cooling drinks.
One of the most important machines for producing a low temperature is that introduocd by Raoul Pictet, of Paris, in which anhydrous sulphurous acid (SOO, also called sulphur dioxide, sulphurous acid, sulphurous oxide, or sulphurous anhydride, is employed. Its arrangement is shown in Figs. 812 and 843. The valves of the compression-pump D are so disposed that at one stroke the sulphurous oxide is aspirated through the tube d, and, in return, is compressed through the tube e. The tube d connects with the refrigerator A, placed in the sheet-iron vat B, lined with non-conducting material ; the tube e, with the conductor E. The oxide is introduced at the plug cock 0, and is drawn by the pump in the direction of the arrow into the copper-tubular refrigerator A, the liquid filling the space between the tubes. Here takes place vaporization, with the con sequent production of intense cold, and the temperature of the non-congealable mixture of glycerine and water surrounding the refrigerator is so far reduced that water placed in the metallic vessels c, immersed in the tank, rapidly becomes frozen. The propeller-wheel f sends a current of the glycerine solution through the tubes, and thus hastens the refrigeration. The vapour of the oxide is drawn out of the refrigerator by the pump, and forced into the space between the tubes of the condenser E. Through these tubes, a stream of cold water is constantly forced ; this determines the condensation of the vapours, and the re-liquefied oxide passes into the admission-pipe, and enters again into circulation. A saturated solution of chloride of magnesium gives better results than the glycerine mixture. The tension of the oxide vapour varies from about 14.7-13 lb; on the return stroke, the gas is compressed to its original volume, having its temperature raised to 93° (200° F.). The cold water current reduced this temperature to about 16° (61° F.) at the outlet ; and under a pressure of 3-3i atmos., the gas resumes a liquid state. It is claimed that 1 lb. of acid produces nearly 1 lb. of ice; and that with a consumption of 22i tons of coal, 250 tons of ice can be made every 24 hours. The cost is said not to exceed lc. a kilo. (say id. a lb.). The system is largely adopted in skating-rinks, breweries, &c.