REFRIGEEATION. 793 REFRIGERATION. effected, and the liquor resulting therefrom bein" naturally much diluted with water. Another serious result of the above defect was the accuum- lation of weak liquor in the refrigerator and the consequent necessity for constant additions of ammonia. By subsequent improvements, how- ever, made by Reece in 1867-70, by IMort in 1870 by Stanley in 1875, and by E. Carrg in 1876, by Beck in 1886, and by Mackay and Christiansen, Tomkins, and Pontifax in 1887, the distillate has been rendered nearly anhydrous and the absorp- tion machines have been brought to a very consid- erable degree of efficiency. The number of absorp- tion machines which have been invented is large, and they can be described in detail only in special but the same general process is followed by all machines. CoLi)-.iu Pboces.s. The cold-air process of re- frigeration is based on the principle that the com- pression of air or other gas generates heat and the subsequent expansion thereof generates cold, and coldair machines operate by first ioni- pressing air in a cylinder, passing it under pres- sure through cooler, and. finally allowing it to expand again in an expansion cylinder. The ad- vantage of coldair machines are that no chem- icals of any description arc required, that very low temperatures can be obtained rapidly by their use, that their construction is comparatively sim- ple and their application is easy, and that the en- Oenera+or. Condenser, Receiver. Cooler. Absorber. Ammonicx Pump. Fig. 4. DIAGRA5I SECTION OF REFRIGERATI.VO PLANT IN A.MXIONIA ABSORPTION SYSTEM. treatises. For a general explanation of the ab- sorption process the installation shown by Fig. 4 has been selected. Following first the course of the ammonia gas, w-e start with the generator and analyzer, which are filled with aqua-ammonia. This liquor is treated by the steam coil in the generator and the ammonia evaporates, the gas passing through the pipe A to the condenser, which is a cylindrical vessel containing a coil of pipe and filled with Avater. The upper coils of the con- denser pipe are provided with drips, a a, in which the water vapor which is mingled with the am- monia gas is condensed and led back to the gen- erator by the pipe B. The ammonia gas is cooled while passing down the condenser coil and finally liquefies at the bottom and runs through the pipe C into the receiver. From the receiver the liquid ammonia is led into the cooler, -where it changes into gas and abstracts heat from the coil of brine pipe. The gas then passes to the absorber, where it meets the weak ammonia solution from the generator and is reabsorbed. The liquor is then pumped from the absorber back into the generator, where it is again heated. When the liquor in the generator is released of its ammonia it passes by the iiipe D into the heater, and thence by the pipe E into the absorber, where it meets the ammonia gas from the cooler and reabsorbs it. The cooling or refrigerating is done by the brine which circu- lates through the cooler. The foregoing descrip- tion applies in detail only to one make of machine, tire machine is situated externally to the chamlwr or .store being cooled and is consequently accessi- ble at all times. The invention of the cold-air machine is ascribed to (iorric, who is said to have designed the first machine of this class in 1849, and improvements were made by Alexander Kirk in 186.3, by GilTard in 1873, and by Windhausen, Bell-Coleman, and several others. By these suc- cessive improvements the trouble from moisture and freezing had with the early machines has been largely overcome, and the present coldair machine is a valuable and efficient device, particu- larly for small installations. The purposes to which mechanical refrigera-' tion is applied are, as already stated, numerous. It .is possible to group them, however, under ii few general heads, and for the present occasion the following heads are selected: Cold storage, ice-making, marine refrigeration, and manufac- turing. Cold Rtokage. Cold storage includes practical- ly all applications of refrigeration to the preser- vation of foodstuffs. A cold-storage plant com- prises a refrigerating plant of one of the forms previouslv described and a store which is kept cold by the refrigerating plant and in which all the provisions to be preserved are placed. Cold stores vary in size from the single-room store used by the hotels, larger resideiices. butcher shops, etc., to larse buildings containing niimerous rooms for the storage of all kinds of provisions.
