APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 



15 



salt' 5 upward until it cuts the curve, then read opposite on the ver- 

 tical line marked "Approximate temperature ° F., 11°." The curve 

 in figure 3 was plotted from the figures in Table VII, which gives 

 the approximate temperatures obtained with different proportions of 

 salt and ice. 



Table VII. 



-Approximate temperatures obtained with different proportions of salt and 

 ice. 



Per cent of 



Tempera- 



Per cent of 



Tempera- 



salt in 



ture of 



salt in 



ture of 



mixture. 



mixture. 



mixture. 



mixture. 





°F. 





T. 







32 



15 



11 



5 



27 



20 



1.5 



10 



20 



25 



—10 



One pound of ice, in melting, absorbs 144 B. T. U. This is known 

 as the latent heat of fusion of ice. Salt in dissolving also absorbs 

 heat, called the latent heat of solution, which varies in amount, 

 depending on the density and temperature of the resulting brine. 



The heat of solution of salt in water at 32° F. varies from 58 to 

 16 B. T. U., depending on the final strength of the brine obtained. 

 Table VIII gives the heat of solution of 1 pound of salt dissolved in 

 water at 32° F. up to the concentration given by the numbers of 

 pounds of salt dissolved in 100 pounds of water. 



Table VIII. — Refrigeration available vjith different proportions of ice and salt. 



Salt per 



100 pounds 



water. 



Heat of 

 solution. 



Total heat 



of resulting 



solution. 



Heat re- 

 quired per 

 pound of 

 mixture. 



Salt per 



100 pounds 



water. 



Heat of 

 solution. 



Total heat 



of resulting 



solution. 



Heat re- 

 quired per 

 pound of 

 mixture. 



Pounds. 



1 



5 



10 



15 



B. T. U. 

 58.0 

 49.7 

 40.5 

 33.0 



B.T.JJ. 



14, 458 

 14, 668 

 14, 806 

 14, 895 



B. T- U. 

 143.0 

 139.5 

 134.5 

 129.5 



Pounds. 



20 

 25 

 30 

 35 



B. T. U. 

 27.0 

 22.5 

 19.1 



16.4 



B. T- XT. 



14, 940 

 14, 962 



14. 973 



14. 974 



B. T. U. 

 124.5 

 119. 5 

 115.0 

 111.0 



The curve in figure 4, based on the percentage of salt, shows the 

 amount of refrigeration available per pounds of ice and salt mixture. 

 This curve was plotted from the figures given in Table VIII corrected 

 to a percentage basis, which were calculated from the melting of ice 

 at 32° F. into a liquid at the same temperature. If, however, the 

 salt is added to the ice at a temperature varying from 32° F. or, if the 

 resulting brine is allowed to escape at a temperature other than 32° F., 

 the amount of available refrigeration must be corrected accordingly. 

 These corrections are determined by multiplying weights, in pounds 

 of salt and brine, by their respective specific heats and by their dif- 

 ference in temperature from 32° F. The specific heat of dry salt may 

 be taken as 0.214, and as the specific heat of salt brine varies with 

 its density, it may be obtained from Table IX or from curve figure 5, 

 which is plotted from the figures contained in the table. 



