GRAVITY CREAJIING 153 



clusters of globules, in rising. It is a fair assumption that in the 

 experiment at the Cornell Station the milk was not held long 

 enough, before cooling, seriously to impair its ph}-sieal condi- 

 tion. 



The second \'er}' probable factor is that of the formation of 

 fat clusters, through large fat-globules rising faster and coming 

 into contact with smaller ones. These and other clusters would 

 continue to pick up isolated globules and smaller clusters, and so 

 the process would continue; clusters would, of course, rise more 

 readily than individual globules, and larger clusters would rise 

 more rapidly than smaller ones. The result would be that, 

 owing to the good phj'sical conrlition of the milk — the absence 

 of casein particles to ennresh the fat-globules and offer obstruc- 

 tion — practically all the fat-globules would find their way to the 

 top. 



Water-dilution Cream (Hydraulic.) — It was thought, at one 

 time, that a modification of the deep-setting system, through 

 the dilution of the milk with water to the extent of 25 per cent to 

 50 per cent, would greatly add to its efficienc}-, through reducing 

 the viscosity of the milk. The idea was. of course, commercial- 

 ized and a number of so-called " dilution cream separators " 

 were placed on the market. The method is still practiced 

 to some extent, but it is by no means as general as it was at one 

 time. 



While it is true that under ver\' exceptional conditions — such 

 as in setting the milk of an occasional indixiclual cow near the 

 end of her lactation period — some advantage may be gained, the 

 principle has no general application. It must be remembered 

 that, while the additiim of water to milk makes it more liquid, it 

 also reduces the difference in specific gravity between the m.ilk 

 serum and the butter-fat, and it is upon this dift'erence that we 

 depend to bring about a separation. 



Even though the skim-milk should, at times, show a lower 

 per cent of fat, this is only an apparent ach-antage, as there is a 

 much greater quantity of it. Wing' obtained the following 

 results with diluted and undiluted milk: 



' Jlilk and Its Products, p. 105. 



