32 



ones, or else enough better ones must be added to the herd to 

 bring up the average. Here is another use for the Babcock tester. 

 By testing the different cows in his herd, and by the use of a few 

 figures, the farmer can tell what to do to improve the quality of 

 the milli he sells, and, if necessary, to bring it up to the standard. 



To illustrate : suppose a farmer who is producing ten cans per 

 day for the Boston market gets word that his milk is down to 12 

 per cent. As we have said, there is usually no great variation in 

 the quality of the mixed milk of the same herd, and if the man 

 has been using the tester he knew even before the contractors that 

 he was running some risk in shipping such milk. But having re- 

 ceived this notice he starts at once to test the different cows of the 

 herd, and he finds at the outset that one large cow, in the flush of 

 new milk, is giving two cans per day, which has only 2 per cent 

 of fat. The approximate composition of her milk is fat, 2, solids 

 not fat, 8.50, total, 10.50. One hundred pounds of the mixed milk 

 of this herd giving 12 percent milk has of fat 3 pounds. The cow 

 whose milk has only 2 per cent of fat contributes one-fifth of the 

 whole supply, or 20 pounds. Her milk therefore contains of fat 

 one-fifth of 2 pounds, .40 pounds. The eighty pounds of milk 

 from the other cows therefore contains 2.60 pounds. Now if he 

 should replace that poorer milk with 20 pounds that has 4.50 per 

 cent of fat, this would contain .90 pounds. One hundred pounds 

 of that mixture would contain 3.50 pounds. This is 3.50 per cent, 

 and though such milk would not be safely over the danger line, an 

 improvement of three-fourths of one per cent would be shown (the 

 milk having gained from 12 to about 12.75 per cent of total solids) 

 and might be accepted. 



To illustrate this principle farther : suppose that a farmer has 

 100 pounds of milk which tests 3 per cent of fat, and he desires 

 to bring it up to 13 per cent of total solids. If he takes 50 pounds 

 of such milk it will have of fat 1.50 pounds. Fifty pounds of 5 

 per cent milk would have 2.50 pounds. A mixture of half and 

 half of 3 per cent and 5 per cent milk would contain 4 pounds. 

 This would test 4 per cent of fat, and have approximately 13.25 

 per cent of total solids. 



Again, suppose he takes one-third of the 5 per cent milk and 

 two-thirds of the 3 per cent. Sixty-six and two-thirds pounds of 

 3 per cent milk would have of fat 2 pounds, and 33^ pounds of 5 

 per cent milk would have 1.66 pounds, and 100 pounds of the 

 mixture would have 3.66 pounds. In other words the mixture 

 would have 3.66 per cent fat, and would have approximately 13 

 per cent of total solids. 



In institute work, when this principle is explained, the question 



