Principles of Milk Preservation. 



113 



f orated steam pipes. To facilitate the heating of the 

 milk, both the milk and water reservoirs are supplied 

 with agitators having a to and fro movement. The milk 

 stirrers are perforated so as to give an up and down 





FIG. 26. Russell's pasteurizing vat. 



movement, thus preventing the cream from rising to the 

 top of the vat during the operation. The milk is with- 

 drawn from the vat by means of a stop- cock that is 

 placed inside of the water chamber. This cock has a 

 circular bore so that when open, the outlet tube presents 

 a continuous passage that can be easily and thoroughly 

 cleaned. Placing the stop-cock within the water chamber 

 prevents the accumulation of unpasteurized milk in the 

 outlet tube at a point not reached by the heated water, 

 and where it would contaminate the whole vat when the 

 milk was withdrawn. 



The Potts pasteurizer is another machine of the inter- 

 mittent type that has recently been introduced that con- 

 forms to the necessary biological conditions. This ap- 

 paratus has a central milk chamber that is surrounded 

 with an outer shell containing hot water. The whole 

 machine revolves on a horizontal axis, and the cream or 

 milk is thus thoroughly agitated during the heating pro- 

 cess. 

 8 B. 



