FROM THE PRACTICAL VIEWPOINT 



a revolving arm, which extends into the milk space 

 between the inner and the outer water chambers. 

 In Fig. 5, the inner cylinder revolves and the nar- 

 row corrugation which extends in a spiral form 

 around the cylinder forces the milk upward. The 

 shaft which operates these stirring devices in some 

 instances comes in contact with the milk, and in 

 order to prevent leakage, it is necessary to pro- 

 vide some sort of packing or stuffing box. This 

 is a disadvantage, since nearly all packing is some- 

 what porous, and it is difficult to keep clean. 



Heaters constructed in this general form have 

 been found to be effective in operation, and good 

 results have been obtained by their use. They 

 have been found to be durable as well. Some in- 

 dividual machines have been in use for ten years, 

 which indicates the carefulness with which they 

 have been constructed. Those forms of_heaters 

 are the most satisfactory in which the greatest 

 amount of heating surface is available, and where 

 the amount of hot water which circulates through 

 the apparatus is relatively large. These conditions 

 render it possible to use water which has a com- 

 paratively low temperature. 



Some of these heaters employ what is known 

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