THE PASTEURIZATION OF MILK 



the milk from sticking to the heated surface. 

 There is difficulty in keeping the cord clean and 

 sanitary. 



Third Type. The tubular type of heater is 

 manufactured and sold by several concerns. In 

 all of these forms, the milk flows through tubes, 

 which are themselves surrounded by some heating 

 medium, usually hot water. In the form shown 

 in Fig. 7 the milk tube is enclosed by a larger 

 tube, through which hot water flows in a direction 

 opposite to the milk flow. In forms which are 

 illustrated by Figs. 8, 9 and 10 the heating water 

 is contained in boiler-like structures, through 

 which the tubes extend. Care must be exercised 

 in order to make sure that there can be no leak- 

 age between the milk tubes and the water con- 

 tainers. In Fig. 7 the couplings between the vari- 

 ous milk pipes in the series are outside of and 

 beyond the water couplings, so that no mixing of 

 the milk and water can occur unless there is a 

 broken milk pipe. In Figs. 8, 9 and 10 the milk 

 tubes are either braized or expanded into the heads, 

 and the danger of leakage is slight. Of course, 

 when heat is applied to these tubes, the tendency 

 is for them to expand and so become more tightly 

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