PASTEURIZATION 201 



the glands, if not to the bearings themselves. In the case of 

 the self-circulating system the water is heated in one of the 

 following three ways : 



Steam is blown into the water entering the shaft, through a 

 steam jet located at the front end of the vat. This is the most 

 objectionable manner df heating, usually causing the coil to be- 

 come excessively coated with burnt cream and making it exceed- 

 ingly hard to clean. In this method free steam is bound to 

 occasionally blow into and through the coil. 



Again, the water in some of the vats is heated by means of a 

 water heater of the McDaniels or Penberthy type, installed at 

 the back end of the pipe which returns the exhaust of the coil 

 to the head of the coil. This method gives the steam a some- 

 what better opportunity to be completely absorbed by the water, 

 but even in this case there is a spasmodic blowing of the steam 

 through the coil at times. 



In the third method of heating, a water heater is installed 

 in the ice-box at the rear end of the vat, all the water is heated 

 in the ice-box and from here, the hot water returns to the head 

 of the coil through the return pipe located under the vat. This 

 method precludes the blowing of steam through the coil and is, 

 from this point of view, the most satisfactory manner of heating 

 the water with the self-circulating system. By this method, how- 

 ever, the cream is not heated quite as rapidly as when the steam 

 is injected into the water in the return pipe or at the head of 

 the coil. 



In the positive circulating system, a separate tank is pro- 

 vided in which the water is heated with direct steam to the 

 desired temperature, from which it is pumped with a centrifugal 

 pump, attached to the tank, through the coil, and to which the 

 exhaust water of the coil returns. In this method the coil is 

 completely rilled with the hot water. It is obviously a very 

 reliable and rapid method of heating, but necessitates extra 

 equipment and additional space. 



The cooling is done in a similar manner as the heating, the 

 same system serving both. It is customary to use water for 

 the first cooling, lowering the temperature to about 70 F. and 

 then finish the cooling with brine or ice water. If ice water is 



