MILK 



29 



above, for otherwise particles of dirt could not sink to the 



bottom. The figures which are obtained for the amount of 



dirt in milk ought not to have too much importance attached 



to them. A not unimportant part of the original dirt dissolves 



in the milk, and so escapes ; another 



portion adheres to the particles of 



fat, and is carried away with them 



instead of sinking with the other 



sediment. There is some further 



loss, too, during the treatment with 



alcohol and ether on the filter. 



The determination of the dirt 

 has, however, a relative value, for 

 it serves as an indication of the 

 care with which the milk has 

 been handled. According to Renk, 

 1 litre of good, pure milk ought, 

 after standing two hours in a 

 vessel with transparent bottom, to 

 show no traces of deposit. 



Quantitatively, a milk which has 

 been carefully and cleanly obtained 

 will contain 3-10 mg. dirt per FlG- 8 .-Spath's Sedimentation 

 litre, whilst those samples which Glass. 



are taken in the ordinary way of 



trade often contain considerably more. The amount of 

 dirt in a milk should be expressed in mg. per litre. 



FIG. 9. Bernstein's Dirt Tester. 



If there is no need to make a quantitative estimation of the 

 dirt in a sample of milk, then, by filtration through a thin layer 



