General Properties of Gases
Ammonia gas is liquefied by strong pressure and low temperature and is then allowed to flow into pipes which run through tanks containing salt water. The reduction of pressure causes the liquid to evaporate or turn to a gas, and the fall of temperature which always accompanies evaporation means a lowering of the temperature of the salt water to 16° or 18° below zero. But immersed in the salt water are molds containing pure water, and since the freezing point of water is 0° C, the water in the molds freezes and can be drawn from the mold as solid cakes of ice.
Ammonia gas is driven by the pump C
into the coil D
under a pressure strong enough to liquefy it, the heat generated by this compression being carried off by cold water which constantly circulates through B
. The liquid ammonia flows through the regulating valve V
into the coil E
, in which the pressure is kept low by the pump C
. The accompanying expansion reduces the temperature to a very low degree, and the brine which circulates around the coil E
acquires a temperature below the freezing point of pure water. The cold brine passes from A
to a tank in which are immersed cans filled with water, and within a short time the water in the cans is frozen into solid cakes of ice.
FIG. - Apparatus for making artificial ice.