COMPRESSION PROCESS. The system of absorb ing heat and thus producing cold partly by vap orization and subsequent liquefaction, and partly by compression and cooling, is in accordance with the well-known law of physics that all substances during the process of passing from a liquid to a gaseous state are bound to absorb a certain amount of beat, and while returning from a gase ous to a liquid state to give up or throw off the same amount of heat. Whatever the refrigerat ing or heat-absorbing agent that may be used, the following cycle of operations is obligatory in all machines working upon this principle: (1) Compression, that is the refrigerating agent in gaseous form is subjected to a pressure sufficient to reduce it to a liquid form, this pressure vary ing with the nature of the agent and the tempera ture of the condensing water. During this com pression a degree of heat is developed in accord ance with the amount of pressure to which the gas is subjected or to the volume to which it has to be reduced relatively to that of the gas in order to produce liquefaction. (2) Condensa tion, during which process the heat developed during the compression of the gas is carried away by forcing the latter through water-cooled pipes, the heat being transferred to the cooling water. At this point the gas is ready to assume the liquid form, in doing which an additional amount of heat is given off to the water. (3) Expansion, during which the liquefied gas is admitted to series of coils of pipe, and being suddenly relieved of pressure, instantly flushes or expands into gaseous form, in doing which, according to the above mentioned law of physics, it is forced to take a quantity of heat which it draws from the surrounding objects, first, of course, the pipes wherein it is confined, and second, such substances as may be in contact with the pipes and which it is desired to cool, as air, water, and brine. The amount of heat thus abstracted or absorbed is equal to that previously given np to the cooling water in the condenser. This cycle of compression, condensation, and ex pansion having been completed. the refrigerating agent is in its first state again and is ready for another cycle. The three operations described being essential, all machines operating according to the compression process, however much they may differ in more or less important details, must consist of these main parts. as shown by the diagram Fig. 1: (1 , A compressor. A, in which the gas is compressed in some convenient and suitable manner: (2) a condensing side or condenser. B, in which the gas circulates through water-cooled pipes or coils or their equivalent and liquefaction takes place; (3) an expansion side, C. consisting of pipes or coils or other space wherein the gas can reexpand and perform its work of cooling or refrigerating by abstracting heat from the surrounding objects. In Fig. 1 D is a regulating valve. E is the low-pressure gauge, and F the high-pressure gauge.
Only those liquids are capable of being used as refrigerating agents which possess vapors capa ble of being liquefied under pressure at ordinary temperatures. There are several such liquids, but those most used in refrigeration are anhydrous extracting the heat from the gas during com pression by the simple device of injecting into the compressor at each stroke a certain quantity of a special quality oil. Fig. 2 shows diagram matically a De La Vergme refrigerating plant with all machinery in place. It consists of two sets of apparatus, one set being that required to compress, condense, and expand the ammonia gas and the other set being that required for hand ling the sealing and cooling oil. Following first the path taken by the ammonia in order to pro duce the refrigerating effect, there is the compres sion cylinder. which is of the double-acting type, and the steam-engine cylinder, which is horizon tal. The pipe through which the gas is drawn or sucked from the evaporating coils into the compression cylinder is also shown. The gas is discharged by the action of the compressor through the pipe into the pressure tank. From the pressure tank the gas, which still retains the ammonia. ether, methyl chloride, sulphurous acid. and carbonic acid. The first compression refrigerating machine was invented by Jacob Perkins in 1834. Subsequent improvements were made by Professor Twining in 1S50. by James Harrison in 1856, by Charles Tether a few years later. and by Van der Weyde. Pictet,- and Wind hausen at still later dates. The modern refrig erating agent which is most used is anhydrous ammonia, which boils at 40' F. There are numerous ammonia refrigeratine machines in use, but they differ from each other only in de tails, the general construction being the same in all. As an illustration of the general compres sion process and of the machinery and apparatus employed in conducting it a refrigerating plant on the De La Vergue ammonia compression sys tem may be described. Its characteristic feature consists in the patented system for preventing the occurrence of any leakage of gas taking pile.. past the stuffing box, piston, and valves. and of heat due to compression. passes upward through the pipe into the bottom or lower pipe of the condenser, wherein by the cooling action of the cold water running over the pipes the heated gas is first cooled and then liquefied. The am monia in this Ihmid condition is then led by the small liquid pipes through the liquid header into the storage tank, whence it flows through into the lower part of the separator, which is constantly maintained at least full. By reason of the pressure to which it is now subjected, the liquid aminonia is forced In the expansion cock or valve. through which it is injected into the evaporating or expansion coil which is situated in the room or chamber to be refrigerated or cooled.