DAIRYING 215 



knows that, if water is poured on a grindstone, and the 

 stone turned rapidly, the water is thrown off. This indi- 

 cates that anything revolving has a tendency to be forced 

 away from the point around which it is revolving. 



Dr. Babcock made use of these two principles by de- 

 vising a machine in which bottles can be set and revolved 

 rapidly. To make the test, a certain amount of milk is 

 put in a test bottle and some sulphuric acid added. The 

 acid assists in breaking down the milk, and makes it easier 

 for the fat to be separated from it. The test bottles are 

 put in the machine, which is then turned at a given speed. 

 The cups in which the bottles are set swing outward, as the 

 speed increases, until the bottles are in a horizontal posi- 

 tion, with the bottoms the farthest away from the center, 

 around which they are revolving. This rapid revolving 

 tends to force all the milk into the bottom of the bottle, 

 just as turning the grindstone tends to throw water away 

 from it. Milk, being heavier than cream, is crowded with 

 more force into the bottom of the bottles, and the fat rises 

 into the necks. The acid added to the milk causes it to 

 turn dark, and the butter-fat is amber colored, so that 

 the fat is easily distinguished from the milk. The necks 

 of the bottles have scales on them, and as the cream is 

 forced into them, one notices how many spaces are filled 

 with fat. The number filled indicates the per cent of the 

 fat in the milk. If three spaces are filled, the milk tests 

 three per cent, and, if four and a half spaces are filled, the 

 milk tests four and a half per cent. See page 358. 



Milk Test. — If we say milk tests five per cent fat, we 

 mean that in one hundred pounds of milk there are five 

 pounds of butter-fat. One hundred pounds of six per cent 

 milk is worth twice as much at the creamery as one hundred 

 pounds of three per cent milk. 



At every creamery this test is used, and when a farmer 

 brings milk to the creamery, the butter maker weighs it, 

 takes a sample and tests it. The total weight multiplied 

 by the test of the milk and divided by one hundred, gives 

 the pounds of fat and affords the basis on which the milk 

 is paid for. Thus, if a farmer delivers one hundred and 

 seventy-five pounds of milk, and it tests four per cent, the 



