COLD STORAGE 1 49 



based upon the vaporization of ammonia, and kept con- 

 stant in spite of great changes in the temperature of the 

 air outside. Cold-storage plants are a modern device, 

 and only within comparatively recent years have they 

 come to be used to any considerable extent for the pres- 

 ervation of food. They are now found in all our large 

 cities, and they are being utilized more and more each 

 year, producing profound modifications of the conditions 

 of civilized life. By means of them a large variety of 

 foods can be preserved for many months without any 

 tendency toward putrefaction and decay, and may be used 

 at any time with the confidence that they have been kept 

 in a perfectly good condition. The cold-storage plants 

 make it possible to keep fresh for winter or spring use a 

 large quantity of the perishable products which previously, 

 if not capable of preservation by canning, it was necessary 

 to throw away because of the certainty of putrefaction and 

 decay. Such devices are producing a far more equitable 

 condition in the food supply of modern communities. It 

 is now possible to have fresh at any season of the year 

 the perishable food products produced at almost any other 

 season, provided we take the trouble to preserve them in 

 cold-storage plants, and our city markets can furnish fresh 

 fruits at almost any time. 



The length of time during which food can be preserved 

 by cold storage depends upon the temperature. If actually 

 frozen, as is commonly the case with fish, fowl, and flesh 

 generally, food may be preserved indefinitely. Frozen 

 food in the arctic regions keeps for years, and will indeed 

 keep as long as it remains frozen. The same would be 

 true of frozen food in cold storage. But some kinds of 



