BEFRIGERATION. 795 REFRIGERATION. manufacture practiced commercially, and each of boiling, or frozen in a vacuum, or distilled. The these will be briefly described, and, afterwards, a vacuum system is but little used. In the other more detailed description will be presented of one systems the evaporated or distilled water is of the most popular ammonia compression can frozen either by the can system or plate svstem. systems employed in America. The great diffi- Turning now" to a specific example of ice-mak- culty in manufacturing artificial ice is that of producing a clear, transparent material, for, un- less special provisions arc made to get rid of it, the air in the water fails to escajw, because of the rapid freezing, and an opaque ice containing ^ir bubbles and of inferior keeping qualities is pro- duced. Five methods may be employed for pre- venting this opacity and forming clear crystal ice : ( 1 ) Freezing the water slowly at compara- tively high temperatures; (2) agitating the water in cans, molds, or cases during 'the process of freezing so as to admit of the escape of the im- prisoned air; (3) forming thin slabs of ice on what is known as the wall or plate system; (4) freezing the water in shallow stationaiy cells; and (5) de-aerating the water before placing it in the molds or cells. Freezing the water slowly at comparatively high temperatures is simply an imitation of the natural process, the water being exposed in well-insulated rooms to an atmosphere cooled below freezing point. The process is too slow to be successful commercially. In the can system, which is one of the most popular, metal cans are set in a tank containing chilled brine and these cans are filled with the water to be frozen. Extending down into the.se cans is a bar or rod of w'ood which is given a swinging motion by suitable mechanism. ing. Fig. 6 shows a plant for making ice on the ammonia compressor can system: The ammonia compressor plant has already been descriljed in a preceding section and will be neglected here. To follow now the water from the well to the loading platform, where it is delivered as ice, we tjegin with the well-water pump in the boiler house. Water from this pump splits into two currents, one of which rises to the top of the building, and discharges into the water-storage tank. This water, as shown by the pipes leading from the tank, flows over the gas and oil cooler and also over the ammonia condenser. From the pans, or cemented floor, on which these stand it flows Fie. 6. SECTIONAL DIAGBAM OF ARTIFICIAL ICE-MAKINli PLAST : DE LA VEBGSE BV9TEM. thus agitating the water, and facilitating the escape of the contained air. In the plate or wall system the water to be frozen is placed in a large refrigerator tank which is divided into compartments by a series of parallel hol- low partitions. In these hollow partitions brine is circulated, causing a sheet or plate of ice to freeze to both sides of each. When these ice plates have frozen to a thickness of 8 to 12 inches, the cold brine is drained from the partitions and replaced by warm brine, which causes the plates to melt loo'se, after which they are lifted from the tanks and sawed into blocks. The standard size of plate in the United States is 8 X 16 feet X II inches. As in the can system, agitators are em- ployed to expel the air from the water during freezing. In the stationary cell system a tank, as in the plate system, is divided by both transverse and longitudinal hollow partitions, so that the ice is frozen in rectangular blocks instead of in long flat plates. The "methods of freezing and freeing the ice and of agitating the water are the same as in the plate svstem. In the de-aerating system the water to hk frozen is either evaporated by Vol. XVI.— 51. to the floor below, where it enters the steam con- denser. After traversing the condenser it passes through the next floor, runs along the ceiling, and empties into the vertical standpipe (seen to the extreme left) connecting with the sewer. Water from the water storage also flows liy a pipe (hid- den by the ammonia condenser) to the condensed- water cooler, from the base of which it passes through the floor, runs along the ceiling of the first floor, and empties into the sewer standpipe. This disposes of one current from the well-water pump: the other passes through the sand filter, whence it rises to the third floor and passes through the heater. From this heater it again descends to the feed-water collector in the Iwiler house whence it is drawn ofl' by the boiler-feeil pump', and bv it sent into the boilers. It leaves the boilers iii the form of live steam. The pipe conveviiig this live steam has branches supplying the engine, the well-water pump, the boiler feed pump and is continued along the ceiling of the fir^t floor, rising to the third floor, where it is connected with the reboiler and also the steam filter. The purpose of it^s connection with the
