228 DOMESTIC ANIMALS, DAIRYING, ETC. 



of construction. It is not practical to put ice in such a trench, how- 

 ever, and a temperature cannot be secured below that of the spring. 



As in the case of the shallow-pan system, the efficiency of this 

 system of separation depends principally upon the temperature of 

 the milk. Under the best conditions, milk can be separated with this 

 system leaving only about .3 per cent of butter fat in the separated 

 milk. Under favorable conditions .5 per cent, or more, will be left. 



The Dilution System. Another system which, fortunately, is 

 not found very frequently, is known as the dilution system. The so- 

 called separators which are sold to cream milk in this way are essen- 

 tially tin cans of varying capacities in which milk and water are 

 mixed. Sometimes tubes are run through them in different direc- 

 tions, helping to make the purchasers believe they are purchasing a 

 machine, but they do not add to the efficiency of the system. Usually 

 these tin cans have been sold to the farmer with the statement that 

 they have some of the virtues of the centrifugal machine and are 

 much cheaper. The fact is they do not have in the remotest sense 

 the characteristics of a centrifugal separator. They are not so effec- 

 tive, even, as the shallow-pan system. Repeated tests have shown that 

 they leave .7 per cent of butter fat in the skim milk under the best 

 conditions and often leave as high as 1.5 per cent. The manufac- 

 turers of these tin cans have traded upon the reputation achieved by 

 the centrifugal machines, by calling them separators, but no farmer 

 should buy one with the idea that he is securing anything but a tin 

 can, and should not use one, or the same method with home-made 

 cans, without expecting to lose even more butter than he would with 

 the pans. 



The Centrifugal System. The most efficient method of sepa- 

 rating milk yet devised is the centrifugal machine. This is a ma- 

 chine which revolves a bowl very rapidly. Milk is introduced into 

 the bowl at the center while the bowl is revolving. The milk is 

 thrown to the sides of the bowl with a great deal of force. The sepa- 

 rated milk being heavier than the cream, goes to the outside, the 

 cream staying in the center. Spouts draw off the separated milk and 

 the cream, the cream spout entering the center of the bowl and the 

 separated milk spout entering the outer part. 



This system involves the purchase of a very carefully constructed 

 machine, which must of necessity cost the farmer a considerable 

 amount of money, more than would be expended with any of the 

 other methods described, and he should expect better results. Any of 

 the standard makes of machines on the market will leave as little as 

 .02 per cent of butter fat in the separated milk under the best condi- 

 tions, and the farmer should expect to secure a separation averaging 

 as close as .05 per cent. (Va. B. 186.) 



The Hand Separator. The following is a summary of results of 

 a trial made to compare the efficiency of several hand separators: 



These trials show very little, if any, difference in completeness 

 of skimming and the total amount of fat recovered in the cream be- 

 tween the different makes of separators used. 



