78 Testing Milk and Its Products. 



The figures in the table show plainly the variations 

 in the specific gravity of cream of different richness 

 and the error of making tests of cream by measuring it 

 with a 17.6 cc. pipette, especially if the pipette is not 

 rinsed and the washings added to the test bottle. If the 

 cream to be sampled is fresh separator cream testing 

 over 30 per cent., less than 17.0 grams of cream will be 

 delivered into the test bottle, and the results of the 

 reading will be at least one-eighteenth too low (since 

 the bottles are graduated for 18 grams), or about 1.6 

 per cent, too low in the case of a 30 per cent, cream. If 

 the cream is sour, the error will of course be still greater. 



It should be remembered that the specific gravities 

 of the cream given in the table refer to fresh separator 

 cream only. Considerable air is incorporated during 

 the separation, and cream of this kind is therefore lighter 

 than gravity cream of corresponding fat contents. 



Babcock has calculated the specific gravity of cream 

 containing different percentages of butter fat, and the 

 weight of one gallon of each; see table XVI in the 

 Appendix. (Hoard's Dairyman, Jan. 10, 1910.) 



88. Weighing cream for testing. For the reasons 

 stated in the preceding, accurate tests of cream can 

 only be made by weighing the cream into the Babcock 

 test bottles. 1 



The simplest method is to weigh 9 or 18 grams of the 

 samples on a small cream-weighing scale (see p. 81) into 

 one of the special forms of cream-test bottles. 



1 This is recognized by a law passed by the Wisconsin legislature in 

 1903, which requires cream to be weighed for testing where it is sold 

 on the basis of its fat content. (Chapter 43, laws of 1903, an act to 

 prescribe the standard measures for the use of the Babcock test in de- 

 termining the per cent, of butter fat in milk or cream.) 



