20 THE POPULAR SCIENCE MONTHLY. 



containing water is kept wet on the outside with ether, the evap- 

 oration will chill the water and eventually freeze it. This is 

 essentially the process by which the carafes f rappees of French 

 restaurants are produced. The decanters filled with fresh water 

 are set in shallow tanks containing brine, which remains liquid 

 below the temperature at which fresh water freezes. In contact 

 with these tanks are receivers, which can be kept charged with 

 newly formed ether vapor. The chilling vapor cools the brine, 

 and this in turn takes heat from the water in the decanters, which 

 soon freezes. 



In making ice on the large scale, either ammonia or sulphur- 

 ous oxide is used instead of ether, because these substances are 

 cheaper and are not inflammable. Ammonia is a gas or vapor at 

 ordinary temperatures. What is commonly called ammonia, or, 

 more properly, ammonia water, is water with several hundred 

 times its volume of this gas dissolved in it. For ice-making, 

 anhydrous ammonia that is, ammonia perfectly free from water 

 is used. The first thing to do is to get the ammonia into the 

 liquid form. There are two ways of condensing a vapor to a 

 liquid by cold and by pressure. Practically it can be done easi- 

 est by combining the two. The ammonia gas is subjected to 

 pressure, and forced through a coil of pipe called a condenser, 

 where it is cooled by water from any convenient supply running 

 down over the pipes. By this means the latent heat in the gas 

 is pressed out, and is taken up and carried away by the water. 

 After being liquefied in the condenser the ammonia is forced into 

 pipes larger than the liquid can fill, where it immediately expands 

 into a vapor and exerts its chilling effect. 



Two methods of making ice, which differ, however, in only one 

 step of the process, are now in use. In a factory established last 

 year in New York city, which the writer has been permitted to 

 go through, the "compression system" is used, with anhydrous 

 ammonia as the cooling agent. The machinery employed con- 

 sists of a powerful pump driven by steam, with which is con- 

 nected the necessary condensers, piping, etc. Liquid ammonia is 

 supplied by the makers of ice machines in strong iron drums. 

 The ammonia is run into a cylindrical iron tank, from which it is 

 allowed to pass through a small orifice into the coils of pipe in 

 the freezing tank. In this factory the freezing tanks are of iron, 

 about twenty by fifty feet in size, and four feet deep. Over them 

 is a floor, which is cut up into rows and lines of rectangular cov- 

 ers. Each of these lifts up, showing a can under it, twenty-two 

 by eleven inches in size, and forty-four inches deep. The tank 

 contains a brine of regulated strength, and the cans when filled 

 with the water to be frozen float in this brine, coming within an 

 inch or two of the bottom of the tank. Back and forth across the 



