140 Repobt of the Bacteriologist of this 



Sleam pressure. — The pasteurizer was connected bv a f-inch 

 pipe directly to the high-pressure steam pipe. As will be noticed 

 in the diagram Plate II, the steam had a free outlet at a point 

 nearly opposite to the inlet, so that there was at no time any ap- 

 preciable pressure on the pasteurizer itself. On the contrary, the 

 steam was nearly all condensed and there was rarely any waste, 

 even when the steam valve was opened to its full capacity. 



The steam pressure given in the tables is that in the 30 horse- 

 power boiler and was noted as one of the possible factors in the 

 great variation in rate of operation on different days. 



Bate. — The amount of milk which a pasteurizer will heat to a 

 given temperature in a given time is important from the practical 

 standpoint. 



In order to minimize the variation in temperature to which the 

 milk was exposed and to determine the rate more accurately, it 

 was our custom to add water to the supply tank and when every- 

 thing was running at full speed and the last of the water was leav- 

 ing the tank to add the milk and note the time. After all of 

 the milk had been added and just as the last was leaving the tank 

 the time was again noted. The interval was taken as the time 

 required to handle the milk. Since the amount of milk at any 

 one time between the milk valve and the milk outlet was only 

 about 5 pounds, the error was not great. 



As one would expect, the rate varies with the pasteurizing tem- 

 perature. The machine was expected to handle 2,500 pounds an 

 hour at 70° C. (158° F.), and would do even more under favorable 

 conditions. In our experience, it did not much exceed 2,100 at 

 80° C. (170° F.), and handled less at 85° C. (185° F.). It will 

 be noticed that the rate at 80° C. ranged from as low as 900 to a 

 little over 2,100 pounds per hour. This extreme variation is due 

 to a number of factors, among which are variations in steam 

 pressure and initial temperature and the cooking of the milk on to 

 the walls of the pasteurizer. Tbis layer of cooked material not 



