CHAPTER II 



HEATERS 



In 1909 the New York City Department of 

 Health first adopted the rule which required that 

 milk could not be considered as pasteurized un- 

 less it had been heated to a definite temperature 

 and held at this temperature for a certain definite 

 length of time. New York was the pioneer in 

 requirements of this sort. 



At this time various forms of milk heaters were 

 on the market, but no device was available for 

 holding the heated milk. All heaters employed 

 a process which is known as the continuous or flash 

 process of heating. By this process the milk 

 flowed or was forced in a continuous stream 

 through the apparatus, where it was subjected to 

 an amount of heat which was not very definite, and 

 which was controlled by the hand of the operator. 

 The milk was then immediately cooled. 



Most of the forms of apparatus which were 



then on the market are still in use, and certain new 



forms of heaters have been invented. Certain new 



types of apparatus were devised as adjuncts of 



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