TESTING BUTTER 635 



bottle to the bottom of the neck with water, immediately after the 

 acid has been added and mixed. 



The danger of violent foaming and expulsion of a portion of 

 the sample is minimized materially, if not entirely prevented, by 

 adding the acid very slowly, in numerous installments and mix- 

 ing thoroughly after each addition. 



2. The experimental error in a product containing so high a 

 percentage of the ingredient to be determined as is the case with 

 fat in butter (butter contains 80 or more per cent fat) is naturally 

 proportionally great, and the causes which introduce the experimen- 

 tal error are fixed and cannot be removed. Thus, in estimating fat 

 by volume, it must be assumed that the butterfat has a definite spe- 

 cific gravity, that is, that a given weight occupies a definite volume. 

 This is not the case. Butterfat represents a compound of several 

 fats, varying widely in specific gravity and the proportion in which 

 these different fats are present in the mixed butterfat varies consid- 

 erably with breed, period of lactation and feed, as determined by 

 locality and season of the year. While the variations in the specific 

 gravity of the mixed butterfat are not large, yet, with butter con- 

 taining 80 per cent fat or over, they do affect the volume of the fat 

 column and therefore the accuracy of the reading. This one factor 

 is entirely beyond the control of the operator. 



Again, the temperature of the fat column when read is another 

 factor introducing experimental error. By the intelligent use of 

 the water bath, the temperature can be controlled within reasonable 

 limits, thus minimizing the effect of this interfering factor to a con- 

 siderable extent. 



The modified Babcock tests for butter which have been devised 

 are those in the operation of which the Hepburn bottle, the Wagner 

 bottle and the Wright bottle are used. They are briefly described in 

 the following paragraphs. 



Hepburn 1 Test Bottles. 



Two types of bottles have been designed by Hepburn, namely, 

 the 9 inch, 9 gram, 90 per cent bottle, and the 6 inch, 6 gram, 90 per 

 cent bottle. 



The 9 inch, 9 gram, 90 per cent bottle. The graduated por- 

 tion has a capacity of 90 per cent of the sample tested. 90 per 



1 Hepburn, A Modified Babcock Method for Determining Fat in Butter. 

 Thesis for Degree of Ph.D., Cornell, 1918. 



