74 MODERN METHODS OF TESTING MILK 



WHY USE OF PIPETTE IS INACCURATE FOR 

 CREAM 



The use of a pipette in measuring cream samples 

 is inaccurate for the following reasons : { i ) More fat 

 adheres to the inside of a pipette than in case of 

 milk, the error increasing with the thickness of cream. 

 (2) The weight of cream decreases as the per cent, 

 of fat in cream increases, since milk-fat is lighter 



than the other 

 constituents 

 of cream. The 

 scale of the test-bottle is 

 based on the use of 18 

 grams of material, but the 

 amount of cream that oc- 

 FiG. 33 cupies the volume filled by 



CREAM-SAMPLIXG SIEVE jg ^^.^,^^5 ^f ^^^-^^^ ^ j^ - ^^^ ') 



is found to be more or less below i8 grams according 

 to the increased percentage of fat in the cream, run- 

 ning even below 17 grams in very rich cream. (3) 

 Separator cream is more or less filled with bubbles of 

 air, and ripened cream contains gases produced by 

 fermentation. These decrease the weight of a given 

 volume of cream. 



For the preceding reasons, the result of trying to 

 measure by pipette a sample of cream to be used for 

 testing its fat content is that less cream will be used 

 than should be, and therefore the results will be too 

 low. Any system of volumetric measurement pro- 

 posed is open to some uncertainty and inaccuracy. 

 The use of a pipette in testing cream is justifiable only 

 for work that is not expected to be strictly accurate. 



