Theory of Deep Setting System 169 



ture of about 40 F., and held at that temperature 

 for twelve to twenty - four hours, not only could 

 the depth be increased from 4 to 20 inches, but the 

 separation was much more complete in a shorter 

 time. In order to bring about quick cooling, ves- 

 sels not more than a foot in diameter were used, and 

 water, either from cold springs or containing ice, 

 was used as the refrigerant. Two essentials, then, 

 for complete creaming by this system are the rapid 

 and immediate cooling of the milk to 40 F., and 

 a sufficient supply of ice to maintain this tempera- 

 ture for twenty - four hours. Under these condi- 

 tions the fat may be so completely separated that 

 not more than .2 of 1 per cent of fat is left in the 

 skimmed milk. Various devices have been used, 

 the best known of which is the Cooley system, in 

 which the cans are not only surrounded by ice- 

 cold water, but completely submerged in it, the 

 chief effect of the submerging being to guard the 

 milk against contamination through the atmosphere. 

 The same conditions as to the character of the milk 

 affect completeness of separation in both the shallow 

 pan and deep setting systems, but no completely 

 satisfactory explanation has ever been assigned as a 

 reason why the fat globules should rise more 

 rapidly and more completely through 20 inches of 

 milk at a temperature of 40 F. in the deep setting 

 system, than through 4 inches at a temperature of 

 60 -70 F. in the shallow pan system. 



It has been asserted that because water is a 

 better conductor of heat than fat, it will cool more 

 rapidly than the fat, and will increase in density 



