STANDARDISATION . 



425 



constant temperature, because a purchaser is not in the habit of 

 reducing cream to a temperature of (say) 60 F. before passing 

 judgment on its thickness. 



At the same time that the viscosity is estimated a determina- 

 tion of the fat should be made by one of the methods recom- 

 mended (pp. 136, 146, 187, and 189). 



The relation between viscosity and fat can be calculated by the 

 approximate formula, which may be expressed, for practical use, as 



A standard viscosity must be fixed, which evidently must be 

 determined by each operator to suit his apparatus, and the con- 

 ditions under which it is necessary to work. 



The table below gives the values of &F for all viscosities likely 

 to be met with in practice, and the percentage of fat in the 

 standard cream can be calculated by multiplying the percentage 

 of fat determined by the value of &F corresponding with the 

 standard viscosity and dividing by that corresponding with the 

 viscosity actually found. 



TABLE CL. RELATION BETWEEN VISCOSITY AND FAT 

 IN CREAM. 



If a be the percentage of fat found in the cream, and 6 the 

 percentage of fat which will be contained in the cream of standard 

 viscosity, the cream may be reduced to standard viscosity by 



adding to each 100 parts 100 ( T ) P ar ts of separated milk, 

 or 100 L _ j.j parts of milk containing / per cent, of fat. The 

 figure 3-5 may generally be used for / without appreciable error. 



