CHAPTER XVII. 



FREEZING THE MIX. 



Ice and Salt. Having held the cream at about 34 F., 

 for from 12 to 24 hours, and having added the sugar, 

 flavoring and binder, we are ready to strain and freeze 

 the mixture. 



A freezing mixture is made of ice and salt. The chief 

 cause of the freezing is the attraction of salt for water. 

 This causes the ice to melt rapidly and absorb heat. 

 Whenever a frozen solid is reduced to a liquid, heat is 

 absorbed, and when one pound of ice melts to water at 

 32 F., it absorbs 144 British Thermal Units (one B.T.U. 

 being the heat given up by i pound of water in cooling 

 i F.). This heat is absorbed, to a great extent, from 

 the cream mixture in the freezing can, and finally the 

 temperature is reduced below the freezing point. 



Cream may be frozen by packing the mixture of ice 

 and salt directly around the freezing can, or by making a 

 brine in a separate receptacle and circulating the brine 

 around the freezing can. 



On a small scale the tub freezer is commonly employed, 

 and the ice to be used should be finely crushed in order 

 to expose to the salt the greatest possible amount of sur- 

 face, and insure rapid freezing. When large chunks are 

 put into the freezer, they do not pack close, large air 

 spaces are formed, and the ice can not so well perform its 

 function of extracting the heat from the cream. Further- 

 more, large pieces of ice are likely to jam and dent the 



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