MILK 237 



longer, if they are oiled daily when in use. The bottles travel around 

 the circle 700 to 1,000 times a minute, moving about 40 miles per 

 hour. The machines are not all of the same size and some go faster 

 than others. A weight hung iby a string 22 inches long will swing 

 back and forth about 80 times per minute, or about 70 times if the 

 string be made 24 inches long. Such a pendulum, once adjusted to 

 the right length with the aid of a watch, is a help in running the 

 tester at the right speed. In large factories where many samples are 

 tested the centrifuges are run by steam or electric power. In such 

 cases a speed indicator is used to make sure that each machine runs 

 at the proper speed. Running faster than directed is likely to break 

 the bottles. 



The cover is opened when motion has stopped, and a small 

 amount of hot, soft water is added with the pipette to each bottle, 

 without taking it out of the pocket. The bottles are thus filled to the 

 bottom of the neck, and the machine is then closed and run at full 

 speed for another minute. More hot water is added with the pipette, 

 bringing the fat up into the neck, between the top and bottom of 

 the scale of figures, and the machine is closed and run another min- 

 ute or two, for the third and last time. 



Some operators prefer to add enough water after the first whirl- 

 ing to bring all the fat up into the neck and whirl the bottles only 

 two times in all. The bottles are then taken out of the machine and 

 the per cent of fat is read from the neck of each bottle, while still 

 hot, before the fat solidifies. To prevent the bottles cooling they 

 may be set in water at 130 or 140 degrees until each is read. 



Reading the Per Cent of Fat. In reading the per cent of fat 

 from the fat column in the neck of a milk test bottle, readings are 

 made at the extreme top and at the bottom of the fat column. Sub- 

 tracting the smaller of these figures from the larger gives the per 

 cent of fat in the milk. By the aid of a pair of dividers the subtrac- 

 tion is avoided, and the per cent of fat is read directly from the neck 

 of the bottle. 



To use the dividers adjust the points to the top and bottom of 

 the fat column as shown ; and then, without changing the distance 

 between them, place one point at the bottom of the scale of figures, 

 and read on the scale the position of the other point. This gives the 

 per cent of fat in the milk. 



Fat solidifies at about 100 degrees. Warming the fat in the 

 neck of a test bottle from 110 to 150 degrees makes it expand about 

 1.5 per cent of its volume. This expansion amounts to about .05 per 

 cent fat on a test reading 3.5 per cent fat, and hence is too small to 

 be of importance in milk testing. In cream testing it is necessary to 

 regulate the temperature with care. It is well to study the directions 

 and to repeat the entire process of sampling and testing on several 

 days, until thoroughly familiar with the work. 



Calculating Weight of Fat in Milk. To find the pounds of fat 

 in any quantity of milk it is necessary, first, to weigh the milk ; sec- 

 ond, to test the milk by the Babcock test to find the per cent of fat; 

 and, third, to multiply the weight of the milk by the per cent of fat 



