THE THICKNESS OF CREAM. 



271 



The volume of fat ia 100 volumes of cream may be calculated 

 from the percentage of fat (by weight) by the following formula — 



1',= 



1-07527 Fx 100 

 O-llF + 96-5 



This is true at a temperature of 60° F. (15-5° C), and may be 

 used without appreciable error at other temperatures. 



The following two series will illustrate the exactitude with 

 which the formula agrees : — 



TABLE LXVI. 



Series I. 



The agreement is within the limits of experiim-ntal error. 



Instead of the formula given above, which includes a calcula- 

 tion of the percentage by volume of fat, the followiiii]! approxi- 

 mate formula may be used — 



V = lO^.F-^-' 



where F is the percentage of fat by weight. For small differ- 

 ences the results by the two formulse agree sufficiently well. 



A practical method for the dilution of cream to constant 

 thickness may be founded upon the above formula. To take the 

 viscosity of a cream, a 10 c.c. pipette with a fairly wide opening, 

 marked with distinct lines both above and belo-w the bulb, may 

 be employed ; it should be surrounded by a water-jacket made 

 of glass to ensure a constant temperature ; and the end should 

 not project far beyond the jacket. Care must be taken that its 

 position is always vertical during the test ; this may usually be 

 ensured by clamping the jacket firmly in position and fixing 

 the pipette by rubber corks. The position should be tested by 

 a plumb line, made of cotton, passing through the pipette. 



The " viscosity " of the cream is represented by the number of 



