EVAPORATED M1LK—HoMOGENIZING 127 
Kinds of Homogenizers.—There are at this time three makes 
of homogenizers in use in this country, namely, the “Gaulin” 
homogenizer, the “Progress” homogenizer and the “ Viscolizer.” 
In the Gaulin homogenizer, the milk is forced, by means of 
single-acting pumps, against an agate valve which presses against 
a ground valve seat. The milk has to pass between the ground 
surfaces of this valve and valve seat. 
In the Progress homogenizer the homogenizing principle 
consists of forcing the milk, by means of single acting pumps, 
between a series of discs with ground surfaces. The discs lie 
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Fig. 49. 
Homogenizing discs 
Courtesy of Davis-Watkins Dairymen’s Mfg. Co. and screw 
mechanism 
Fig. 48. The Progress homogenizer 
flat one upon the other, they are enclosed in a cylinder and are 
held in place by a rod running through their center. The discs 
are pressed against each other by a heavy spiral screw, which 
regulates the pressure to which the milk is subjected. The milk 
passes from the center to the periphery of the discs. The discs 
used in this machine are of two types. One type has very fine 
irregular grooves. The milk shoots through these grooves 
against hard shoulders. The other type of discs has smooth 
surfaces but their area of contact is narrow. The milk passes 
through these smooth surfaces. 
