FROM THE PRACTICAL VIEWPOINT 



the heating surface. A thermostat attached to the 

 milk outlet pipe from the heater could be made 

 to control the steam which supplied the milk 

 pump. This would vary the speed of milk flow. 

 If milk flows by gravity to the heater, the ther- 

 mostat might be made to open or close a valve in 

 the feed pipe. 



The nearest approach to the use of this prin- 

 ciple occurs in some plants when the heated water 

 is kept at a uniform temperature by a thermostat, 

 and the milk flow is also constant. The heating 

 surface of the heater is so very large compared to 

 the amount of milk heated, that the water is never 

 more than 3 or 4 hotter than the milk, and 

 there is therefore no possibility of scorching the 

 milk. In these plants also the efficiency of the re- 

 generative principle is carried as near the theo- 

 retical limit of perfection as it seems possible. The 

 water leaving the heater is within a few degrees of 

 the temperature of the cold milk entering the ma- 

 chine. This cooled water is conveyed to the milk 

 cooler, where it is used for cooling the hot milk. 

 It becomes so heated when leaving the cooler that 

 it is but a few degrees lower than the hot milk. 

 It can be seen that but little steam is required to 

 139 



