COLD STORAGE 171 



salt dissolves in the ice water. If there is enough salt, a 

 saturated solution of salt is formed. Now a saturated solu- 

 tion of salt will not freeze at a temperature above 7F. In 

 the ice cream freezer we have a mixture of the three sub- 

 stances, salt, ice, and a nearly saturated solution of salt. 

 As long as the supply of salt and ice holds out, the ice con- 

 tinues to melt and absorb heat; the temperature of the 

 mixture, therefore, tends to fall toward the freezing point of 

 the salt solution, 7F. 



199. Other Freezing Mixtures. Many other substances 

 have the same effect upon ice that salt has. For example: 

 If 1 part of common sal ammoniac be mixed with 4 parts of 

 broken ice, the mixture has a melting point (or freezing 

 point) of about 4F. If equal weights of sulphuric acid and 

 crushed ice be mixed, the mixture has a melting point (or 

 freezing point) of 35F. A mixture of calcium chloride and 

 ice has a melting point of 55C. Still lower temperatures 

 are obtained by using other mixtures. 



DEFINITION. A freezing mixture is a mixture of two or 

 more substances of such a nature that they act upon each other 

 in such a manner as to absorb heat, or to produce cold. 



III. COLD STORAGE 



200. Effect of Cold Storage on Modern Life. The develop- 

 ment of plants for the production of cold by artificial means 

 has not only given us ice in greater abundance and in greater 

 purity, but it has also made possible the construction of 

 many enormous COLD STORAGE PLANTS. In these cold storage 

 plants, the surplus of perishable produce, such as eggs, butter, 

 poultry, beef, fruits, and vegetables is stored during the 

 seasons of abundance. In cold storage this perishable 

 produce is preserved for weeks, or even months, much of it 

 suffering but little deterioration. Before the establishment 

 of cold storage plants, the markets were often flooded with 

 certain fruits for a short period ; in a few weeks, however, the 

 entire year's supply of these fruits was either consumed or 



