258 THE CHEMICAL CONTROL OF THE DAIEY. 



TABLE LXIII. 



The constant a depends on the follo-vving conditions : — 



1. Size of drum and thickness of the layer of milk. 



2. The specific gravity of the milk serum and of fat. 



3. The units in which the variables are expressed. 



The first condition is that -which can be varied by a difierence 

 in type of separator. 



The constant 6 chiefly depends on the viscosity (internal 

 ■friction) of the mill-;: serum ; also, to a slight degree, on the cubical 

 expansion of milk serum and milk fat, and on the friction of the 

 liquid against the drum. 



The constant c depends on the viscosity of cream and on the 

 friction of the cream against the sides of the outlet. 



It is naturally advantageous for a, 6, and c to be as low as 

 possible. 



To obtain a lo"w, the drum should be of large capacity and 

 the formation of currents in the milk should be prevented ; the 

 discs placed inside the drum in separators of the Alpha type 

 ensure the latter condition, and, therefore, decrease a. 



To obtain h lo-w, the exits, and especially the cream exit, 

 should be as large as compatible with the proper working of 

 the separator ; and the tubes, through which the skim milk and 

 cream leave the drum, as short and as straight as possible. 



To obtain c low, cooling of the cream inside the drum should 

 be avoided, and the cream exit large. Separators in which the 

 adjustment of the thickness of cream is performed at the cream 

 exit have a large c. 



It is more difficult to express by a definite formula the amount 

 of fat in skim milk obtained by allowing milk to stand. Here 

 we have not a definite space through which the globules of fat 



