ICE-MAKING AND MACHINE REFRIGERATION. 23 



the expansion coils in the freezing tank, and passes again through 

 the cycle of operations just described. The same ammonia is 

 thus used over indefinitely. The pressure to which the ammonia 

 is subjected in this apparatus ranges from one hundred and 

 twenty-five to one hundred and seventy-five pounds per square 

 inch. The pump, shown in the lower part of Fig. 2, is one of 

 several makes. It has two compression cylinders, seen at the 

 top of the tall A-shaped frame. The piston-rods work vertically 

 beneath these cylinders, and are connected by cranks and connect- 

 ing-rods to the piston working in the steam-cylinder seen at the 

 right. The use of the ammonia in making ice can be compared to 

 the use of a sponge in baling a boat. As the sponge soaks up wa- 

 ter from the bottom of the boat, and after being squeezed over the 

 side is ready to soak up more, so the ammonia soaks up, as it were, 

 heat from the water to be frozen ; and, after this has been squeezed 

 out by the compressor, the liquid is ready to take up more heat. 



The water from which the ice is made in the New York factory, 

 previously mentioned, is from the city supply (Croton). Before 

 being frozen it is purified by filtering and distillation. It is first 

 filtered, then converted into steam in vertical boilers about twenty 

 feet high; the steam is condensed and again filtered in steam 

 filters filled with coke. The condensation is effected by placing 

 the filters in the open air on the roof of one of the buildings, and 

 circulating around them water pumped from the river, near which 

 the factory is located. After leaving the steam filters and con- 

 densers, the water is further cooled by passing through a cooler 

 similar to the condenser used for the ammonia. After leaving 

 the cooler, the water is filtered through charcoal, and is then 

 ready to go into the cans. It is filled into them through a hose, 

 which ends in a long nozzle, containing a patented device that 

 prevents air from being carried down into the water. In order 

 to make clear ice, the formation of air-bubbles in it must be pre- 

 vented. "Water always contains some air, which is driven out by 

 boiling. When boiled water is frozen, the ice contains only what 

 little air is absorbed by the water while it is being cooled down to 

 the freezing-point. The artificial ice, therefore, is clear except a 

 thin layer running lengthwise through the middle of the cake 

 the part that freezes last. A very attractive exhibit for a market 

 is made by putting meat, fish, fruit, and flowers into cans of wa- 

 ter and freezing them into the clear ice. Articlgs having smooth 

 surfaces, and consequently few crevices in which air-bubbles can 

 cling, give the best results. 



It was mentioned early in this article that sulphurous oxide is 

 used as a cooling agent in making ice. This is the choking gas 

 that is formed when sulphur burns. An ice machine employing 

 anhydrous sulphurous oxide is made, which, as it works accord- 



