126 BUTTER-MAKING. 



impossible that under any circumstances there can be more 

 than a small fraction of a degree of difference between the 

 temperature of the fat and that of the milk serum. More- 

 over, with the limits of temperature practical for a creamery, 

 (90 to 40 F.), the coefficient of expansion of butter-fat is 

 more than three times - as great as that of water, so that in 

 order to maintain the same relative differen<^ in their specific 

 gravities when the temperature is falling, the milk serum must 

 cool nearly three times as quickly as the fat. In other words, 

 when the milk serum has cooled from 90 to 40, or 50 F., 

 the fat-glabules should have lost less than 17, and should 

 still have a temperature of over 70 F., a difference between 

 the temperature of milk serum and fat of more than 33. Such 

 a condition is manifestly impossible, but no less difference 

 than this would cause the fat to become relatively heavier 

 than at first, and would operate against the creaming." 



A low temperature increases the viscosity of the milk, 

 and consequently it would seem that the resistant force of 

 the fat-globules in their upward passage through the milk 

 serum would be increased, and thus retard the creaming. 

 Babcock maintains that fibrin is partially precipitated when 

 milk is allowed to stand at a medium high temperature. The 

 fibrin, when precipitated, forms a fine network of threads 

 permeating the milk in all directions, similar to the network 

 of fibrin in coagulated blood. It is possible to co'nceive that 

 such a network would interfere with the rising of the fat-glob- 

 ules, at comparatively high temperatures. The reason that 

 fat-globules will ri^e more quickly and more completely in the 

 deep-setting system than in the shallow-pan system, might 

 be explained on this fibrin theory \vere it not for the fact that 

 experiments conducted at the Cornell Experiment Station 

 show that the setting and cooling of milk may be delayed 

 long enough for this fibrin to form, without any effect upon 

 the separation when set and cooled. 



Probable Explanation. It is a well known fact in physics 

 that most liquids, when present in the form of drops, increase 



