Ice-making and cold storage depend upon the scientific principle that ammonia evaporates readily and absorbs a great deal of heat in passing from a liquid to a gaseous state. Apparatus for the manufacture of artificial ice consists of a large cylinder containing liquid ammonia. Attached to the cylinder is a vat containing brine or salt water with coils of pipes passing through from the cylinder which holds the liquid ammonia. The ammonia flows from the cylinder to the coils. The vat is filled with galvanized iron boxes, the size of an ordinary cake of ice, and the boxes are filled with distilled water. A pump exhausts air from the coils, which in turn causes the ammonia to evaporate quickly. As the ammonia passes through the coils the latter attract the heat from the surrounding bodies to the extent of freezing the water.
Fig. 56. - General Arrangement of Refrigerating Plant.