The ammonia gas resulting from the expansion and evaporation of the liqui I ammonia in the evaporating or expansion coil. having absorbed or taken up the heat from the surrounding atmos plwre, passes away hack into the compression cylinder, and the cycle of operations just de scribed is again performed. Following now the course of the sealing and cooling oil, which, as previously mentioned. is heated with the gas during compression, this oil is passed from the compression cylinder mingled with ammonia 'gas into the pressure tank, where most of it separates from the gas and falls to the tank bottom. The heated oil is then conducted through a pipe to the lowermost pipe of the oil cooler, which is similar in construction and operation to the ammonia, condenser. After being sufficiently re duced in temperature in the oil cooler the oil flows through the strainer into the oil pump, which is so constructed that it delivers the cooled oil into the compression cylinder, dis tributing it to either side of the piston o• plunger during its compression stroke when it is being compressed and heated. From the compression cylinder the oil proceeds again through the cycle just described. Most of the oil separates from the ammonia gas in the tank, but any small amount that passes on is taken out when it reaches the separating tank. The three salient parts of the apparatus described are the com pressor, the condenser, and the expansion coil.
There are numerous compressors of other makes, all of which differ structurally from the De La Verg,ne and from each other. Condensers are of two general types, surface condensers and submerged condensers. In submerged condensers the pipe coils are submerged in the cooling water, and Fig. 3 shows a vertical section of such a construction. In surface condensers the cooling water is simply allowed to trickle from above onto the pipe coils, whence it falls into a basin and is conducted away. The condensers shown in Fig. 2 are of the surface type. Expansion
coils are simply coils of pipe of such section as will give a large amount of radiating surface. Their arrangement depends upon the purpose for which refrigeration is to be employed, whether for cold storage or ice-making or other purposes. Systems of refrigeration which use other refrig erating agents than ammonia differ from the am monia system chiefly in the character and con struction of the compressor. They all have the same cycle of operations—namely, compression, condensation. and expansion—which is constantly repeated. The advantages and disadvantages of ammonia and of the other eooling agents used in refrigeration by the compression system may be briefly summarized as follows: The chief ad vantages of anhydrous ammonia (see AMMONIA) are its possession of greater heat-absarbing power than that of any of the others, that it liquefies at a comparatively low temperature, and that it is not as explosive no• as inflammable as ether. The advantage of ether as a refrigerating agent is that it liquefies at low pressure and comparatively high temperature, which adapts it for hot climates. Its disadvantages are that an ether compressor is about seventeen times as large as an ammonia compressor of the same capacity, and that ether is a highly inflammable and explosive gas when mixed with air. The advantage of sulphurous acid or sulphur dioxide is that it liquefies at a low pressure—not so low as ether, but consider ably lower than ammonia. Its chief disadvantage is that it is liable to form sulphuric acid on ex posure to air, which acid rapidly destroys iron. Carbon dioxide has the advantages of being non inflammable and having a high specific gravity, which renders its heat of vaporization for a given volume much higher than that of ammonia ; it also has no corrosive action on copper. Its dis advantages are the high pressure required to liquefy it and its fatality to animal life when present in air in any quantity.