THE PASTEURIZATION OF MILK 



to circulate, usually by means of a pump. These 

 tanks have, extending through them in a horizon- 

 tal direction, some form of agitator. This may be 

 a tubular coil, as in Figs. 12, 13 and 14-B, or stir- 

 ring paddles, as in Fig. 15, or it may be coil sus- 

 pended from above, as in Fig. 16. Some of the 

 older forms have, instead of a coil of pipe, a series 

 of hollow screw-shaped discs. In some, as in Fig. 

 14, there is a tubular structure which is suspended 

 from the top of the tank and which swings back 

 and forth by means of a mechanical arrangement. 

 In operation, these tanks being filled with milk, 

 hot water is forced through the tubes or discs 

 above referred to. These coils rotate, keep the 

 milk mixed and, at the same time, heat it and thus 

 raise it to the desired temperature. The circulation 

 of water is maintained in some machines by means 

 of pumps, the steam for heating being admitted 

 into the return water shortly before it is again 

 forced through the coil. 



In other machines, as in Fig. 12, the admission 

 of air into the coil creates a suction which forces 

 the water through without the use of pumps. In 

 the form shown in Fig. 15, the heating is accom- 

 plished in a rather novel manner. In the space 

 70 



