Cream Testing. 75 



of 25 per cent, cream is measured into an ordinary Bab- 

 cock test bottle, it follows that there will be 18 x. 25 =4.5 

 grams (or ~ = 5 cc. ) of pure butter fat in the bottle. 

 It is shown, however, (p. 38), that the space from to 

 10 in the neck of these bottles holds exactly 2 cc. The 

 neck of the milk test bottles will not therefore be large 

 enough to show the per cent, of fat in a sample of cream 

 if 18 grams are taken for testing, so that less cream must 

 be measured out, or special forms of test bottles used (89). 

 86. Errors of measuring cream. Several factors tend 

 to render inaccurate the measuring of cream for the Bab- 

 cock test, and in exact work it is recommended to weigh 

 the amount taken for a test. If a 17.6 cc. pipette is used 

 for measuring the cream, it will not deliver 18 grams of 

 cream, as it will of milk, for the following reasons: 



1. The specific gravity of cream is lower than that of 

 milk; if a certain quantity of milk weighs 1030 Ibs., the 

 same quantity of cream will weigh from 1020 Ibs. to 

 below 1000 Ibs., the weight being determined by the rich- 

 ness of the cream; the more fat the cream contains, the 

 less a certain quantity of it, e. g., a gallon will weigh. 1 



2. Cream is thicker (more viscous) than milk at the 

 same temperatures, and more of it will adhere to the 

 sides of the measuring pipette than in case of milk. This 

 is of special importance in testing very rich or sour 

 cream. 



3. In case of separator cream, more or less air will 

 become incorporated with the cream during the process 

 of separation. In the ripening of cream, the fermenta- 

 tion gases developed are held in the cream in the same 

 way as bread dough holds the gases generated by yeast. 



i For specific gravity of cream of different richness, see table on p. 76. 



