PHYSICAL PROPERTIES OF MILK 97 



The ratio between the number of calories required to raise a 

 given weight of a substance through a given temperature in- 

 terval, and the number of calories required to raise the same 

 weight of the standard substance through the same temperature 

 interval is called the "specific heat" of the substance. Water 

 is always the standard substance, and so the specific heat of a 

 substance is the number of calories required to raise one gram 

 or one pound one degree C. or F. respectively. 



The heat capacity of a substance is obviously its specific 

 heat multiplied by the quantity of the substance. 



It is particularly important to bear in mind that the specific 

 heat of a substance is not the same at all temperatures, though 

 for most substances the changes are not great so long as the 

 substance remains in the same physical state. 



Persons interested in milk and milk derivatives who have to 

 deal with great quantities of these materials upon narrow mar- 

 gins, both financially and in the matter of temperature control, 

 face the necessity of a knowledge of all factors of any consid- 

 erable magnitude. 



In pasteurizing it is desirable to know the amount of heat 

 required to bring a definite amount of milk or cream from the 

 temperature at which it has been delivered or held up to the 

 temperature used in pasteurizing, as well as the amount of re- 

 frigeration required to cool the same material down to a tem- 

 perature satisfactory for storage or for inoculation. Although 

 the losses which constantly occur, and which depend on a num- 

 ber of factors, prevent the exact computation of the amount of 

 heat or refrigeration through a knowledge of specific heats alone, 

 still, the exact experimental values are of great importance in 

 calculating the cost of pasteurization, particularly when large 

 quantities of material are being handled. The increasing use of 

 pasteurization, both in plants selling milk, and in plants manu- 

 facturing butter or ice cream from pasteurized cream, makes 

 the specific heat values of increasing importance. In calculat- 



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