144 MANAGEMENT OF DAIRY PLANTS 



It has been the experience of the writer that under ordinary 

 creamery conditions when a steam-gauge pressure of from 40 

 to 80 pounds is maintained it is reasonably safe to figure that a 

 pound of steam will yield about 900 B. T. U. of heat. From 

 this estimated heat value of steam the amount of steam re- 

 quired for pasteurization may be quite accurately determined. 

 As the difference in amount of heat required to raise a pound of 

 water one degree on different parts of the thermometer scale is 

 very slight, when considering the range of temperatures made 

 use of in pasteurization, it will be safe in this connection to 

 consider a B. T. U. as the amount of heat required to heat one 

 pound of water any one degree on the Fahrenheit thermometer 

 scale. 



Example: How much steam is required to heat 10,000 



pounds of milk from 60° F. to 185° F.? 



10,000 X .94 ' X (iSi^ — 60) ^ , , 



Answer: ^ = 1,305.6 pounds of 



900 



steam. 



1. Method by Which to Determine the Heating Value of Steam. 

 — More accurate determination of steam required for heating 

 may be obtained by determining the heating value of the 

 steam. This determination may be made as follows: Admit 

 live steam into a known amount of water held in an insulated 

 container; weigh the water after it has been heated to the de- 

 sired temperature — the increase in weight is due to amount of 

 steam condensed. 



Example: 80 pounds of water are heated from 60° F. to 180° 

 F. The water has increased in "weight 10 pounds. How much 

 heat has been obtained from a pound of steam? 



Answer: Let y stand for amount of latent heat obtained 

 from each pound of condensed steam used. Then, 



io\y-\- (212 - 180) ] = 80 (180 — 60); y = 928 B. T. U. 



The total amount of heat obtained from each pound of steam 

 used is equal to 928 -f 32 = 960 B. T. U. 



2. Weighing the Condensed Steam. — The amount of steam 

 required for doing a definite amount of work is determined in 



' Spedfic heat of milk. 



