PRESERVATION OF MILK AND ITS TREATMENT 91 



that plate counts show apparently more bacteria than before 

 cleaning. The best results are got with the so-called cleaning 

 separator (Fig. 57), which first whirls out the coarser and 

 heavier particles in the form of slime, and then removes the finer 

 particles (but also a number of fat globules if the milk is cold), by 

 pressing the milk through a filter cloth which is stretched out in 

 the form of a cylindrical bag. As the illustration shows, the bowl 

 of the centrifuge is comparatively large in diameter and the 

 filtration cylinder is supported by a truncated cone through the 

 bottom of which the milk enters. Laval has constructed a clean- 

 ing centrifuge with plates which acts only by separating the slime 



FIG. 57. Heine's Cleaning Separator. 



(Fig. 58). The milk enters under the bottom plate into the 

 large slime chamber, and then passes in between the plates to the 

 outer side of the outlet pipe along which it is discharged from the 

 top. 



After cleaning the milk is cooled to a few degrees above C. 

 on surface coolers through which brine is circulated from the 

 refrigerator, after which it is run into well- cleaned cans or bottles 

 and kept cold. In summer it is necessary to use ice on the carts 

 from which the milk is retailed. Obviously, the necks of the 

 bottles must be free from cracks, holes or crevices in which dirt 

 may collect. The bottles are best closed by aluminium caps, 

 pressed on by machinery so that they can only be removed by 

 breaking them. Stoppers which can be removed and replaced at 

 will must have a proper seal ; they have the advantage that they 



