APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 3 



cific heat may be had by studying the diagram in figure 9, on page 24, 

 which shows graphically the relation of heat to temperature. 



Ton refrigeration.^ — Refrigeration, or ice-melting capacity, is a term 

 applied to represent the cold produced, and is measured by the latent 

 heat of fusion of ice, which is 144 B. T. U. per pound. In other words, 

 it is the heat required to melt 1 pound of ice at 32° F. into water at 

 the same temperature. The capacity of a machine in tons of u ice 

 melting" or "refrigeration" does not mean that the machine would 

 make that amount of ice, but that the cold produced is equivalent to 

 the melting of the weight of ice at 32° into water at the same tem- 

 perature. Therefore 1-ton refrigeration is equal to 144 X 2,000, or 

 288,000 B. T. U. A 1-ton refrigerating machine is a machine that has 

 a capacity sufficient to extract from an insulated bath of brine 200 

 B. T. U. per minute, 12,000 B. T. U. per hour, or 288,000 B. T. U. 

 per 24 hours. 



Absolute pressure. — Absolute pressure is pressure reckoned from a 

 vacuum. Pressure gauges in general use are arranged to indicate 

 pressure in pounds per square inch above atmospheric. To convert 

 gauge pressure to absolute pressure, 14.7 pounds, the weight per 

 square inch of air pressure at sea level, must be added. 



CHANGES IN MILK CAUSED BY TEMPERATURE AND TIME. 



PHYSICAL CHANGES IN MILK AT LOW TEMPERATURES. 



During the last decade the progress made in the physical, chemical, 

 and bacteriological studies of milk and its products has greatly mod- 

 ified the various dairy operations and has led to improved methods 

 of treating and handling dairy products, based mainly on the appli- 

 cation of the two extremes, heat and cold. The preservation of milk 

 and its products depends almost entirely on the use made of these 

 two factors. In this bulletin, however, we will discuss only the use 

 of refrigeration as a means of preserving dairy products. Before dis- 

 cussing the practical application of refrigeration to the dairy industry 

 it is advisable to make a short summary of the data at hand relating 

 to the physical, chemical, and bacteriological changes and modifica- 

 tions which the action of cold produces in milk. 



SPECIFIC HEAT. 



In view of the wide variations in the specific heat of milk and cream, 

 as found in the limited amount of literature on the subject, the United 

 States Bureau of Standards was requested to make determinations of 

 the specific heat of whole milk and single and double cream. Sam- 

 ples of milk and cream, approximating average conditions, were pre- 

 pared by the Dairy Division laboratories and forwarded to the Bureau 

 of Standards in the afternoon, placed in the calorimeter and packed 



