The condenser B is kept full of running water while the machine is in operation, and the action of the latter is regulated and kept under complete control by the aid of valves and stop-coeks.
The freezing-vessel shown at D contains cans, in which blocks of ice are produced ; these cans stand between hollow metallic partitions, through which the freezer passes. The vessel E, seen also in Fig. 833, is provided with receptacles for holding bottles, or other small vessels, around which the ether circulates. That at F is of conical form, and bag double walls for the passage of the ether.
Siddeley and Mackay'e refrigerating-machine, which has been already described under Carbolic Acid (p. 673), also works with ether.
An ice-making apparatus, in which ammonia is the medium used, constructed by the Boyle Ice Machine Co., of Chicago, Illinois, is shown in Fig. 834. On the left, are a steam-boiler and a combined engine and ammonia - pump ; in the centre, a pump for water supply for the gas condenser ; and on the right, a freez ing-tank. The am monia-pump is used for compressing the ammonia gas, which is liquefied in the con denser, and expanded in a freezing - tank seen on the right, in which the cold is pro duced. This freezing tank is provided with coils of iron pipe, in which the gas evapo rates ; they are placed at regular spaces apart, determined by the thickness of the ice required. Between the coils, are placed moulds or cans, containing the water to be frozen ; and the space about both moulds and coils is filled with strong brine. The pump being put in motion, a valve leading from the condenser to the evaporator-coils is opened, and the gas flows into the evaporator-coils. Meeting there with the heat in the salt water to be cooled, it expands very rapidly, taking up the heat which is in the brine, which, in turn, extracts the heat from the water in the moulds. The expanded gas is aspirated by the pump, and forced over into the condenser, where the heat is taken from it by a stream of water continually flowing over it, and where, under the pressure of the pump, it is reliquefied, and returns to be again expanded in the evaporator-coils. This process is continued until the water is frozen, when the mould is lifted from its place in the freezing-tank, and immersed in warmer water, which loosens the ice from the mould ; the latter, being refilled with water, is returned to the freezing-tank.
Carres intermittent portable apparatus, in which ammonia is employed, is shown in Fig. 835. A boiler k containing the ammonia is connected by the pipe r with the refrigerator t, into the well of which are put vessels z filled with water to be frozen. The boiler k is placed over a portable furnace, and the apparatus is purged of air, which is driven by the evolved gas out at the stop-cock m. This being closed, and
the refrigerator immersed in a tank of cool water, the tempera ture of the liquid ammonia is raised to 110°-115° (230°-240° F.), at which heat the ammonia is expelled, and condensed in a liquid form in the refrigerator t. The boiler being now removed from the furnace, and placed in the water-bath, the temperature of the water in it will fall, and the power of the water to dissolve ammonia will be restored. The gas will be rapidly re-dissolved, reducing the pressure, as the liquid ammonia will evaporate with corresponding rapidity, drawing for its latent heat upon the sensible heat of the water to be frozen. The result will be the complete evaporation of the liquefied ammonia, and the restoration of an aqueous solution in the boiler, of the original strength. Between the ice-pan and the well, is a body of alcohol, which will not freeze, but will act as a conductor. During the refrigeration, the vessel t has a non-conducting envelope.
Cures continuous process, shown in Figs. 836 and 837, also depends for its efficacy upon the evaporation of liquid ammonia. The boiler a is exposed to the heat of the furnace b; c is an indicator to show the level of the liquid; i is a tube conducting gas to the liquefier j; the vertical pipe above the branch i leads to a safety-valve ; and any escaping gas passes by pipe c to the 4 D water-tank e', where it is absorbed; f is a tube which brings back to the boiler saturated solution of ammonia from the absorbing-apparatus u ; this solution passes downward, trickling through the perforated trays g, while the ascending gas rises in a sinuous course, alternately around the edge of one tray and through a central hole in the next, and so on. This condenses and carries back the watery vapour which accompanies the gas. The latter passes by tube i to the liquefier j, through a box k, and a series of zigzag and spiral tubes in a bath of cold water, constantly renewed from reservoir a, which also supplies other parts of the apparatus. The tubes terminate in another box k', and the ammonia is by this time in a liquid state, under a pressure of 10 atmos., which is constantly maintained in the boiler. In the liquid state, the ammonia passes by the pipe / to the efflux regulator m, which is the dividing barrier between the part of the machine in which a regular pressure of 10 atmos. is maintained, and the following part where the pressure does not exceed l atmos. The regulating device is a floating cup, which opens or closes a hole of influx. The liquid passes from the regulator m by pipe n to the distributor p, the pipe n being wound spirally around the tube t, through which the vaporized ammonia is returning from the refrigerator q; the vapours serve to reduce the temperature of the liquid in n before it reaches the refrigerator.