There remains now only the reading of the record. On the neck of each bottle there are marks to measure the amount of fat. If the fat inside the tube reaches only from the lowest mark to the second mark, then there is only one per cent of fat in this cow's milk. This means that the owner of the cow gets only one pound of butter-fat from each hundred pounds of her milk. Such a cow would not be at all profitable to a butter-seller. If the fat in another test-bottle reaches from the lowest mark to the fourth mark, then you put in your record-book that this cow's milk contains four per cent of butter-fat. This record shows that the second cow's milk yields four pounds of fat to every hundred pounds of milk. This cow is three times more valuable to a butter-maker than the first cow. In the same way add one more per cent for each higher mark reached by the fat. Four and one-half per cent is a good record for a cow to make. Some cows yield as high as five or six per cent but they do not generally keep up this record all the year. [Illustration: FIG. 274. BABCOCK TESTER AND HOW TO USE IT The tester, acid, acid measure, test-bottle, and thermometer at bottom; filling the pipette on right; adding the acid and measuring the fat at top] The Babcock tester shows only the amount of pure butter-fat in the milk. It does not tell the exact amount of finished butter which is made from 100 pounds of milk. This is because butter contains a few other things in addition to pure butter-fat. Finished and salted butter weighs on an average about one sixth more than the fat shown by the tester. Hence to get the exact amount of butter in every 100 pounds of milk, you will have to add one sixth to the record shown by the tester. Suppose, for example, you took one sample from 600 pounds of milk and that your test showed 4 per cent of fat in every 100 pounds of milk. Then, as you had 600 pounds of milk, you would have 24 pounds of butter-fat. This fat, after it has been salted and after it has absorbed moisture as butter does, will gain one sixth in weight. As one sixth of 24 is 4, this new 4 pounds must be added to the weight of the butter-fat. Hence the 600 pounds of milk would produce about 28 pounds of butter. EXERCISE 1. Find the number of pounds of butter in 1200 pounds of milk that tests 3 per cent of butter-fat. 2. A cow yields 4800 pounds of milk in a year. Her milk tests 4 per cent of butter-fat. Find the total amount of butter-fat she yields. Find also the total amount of butter. 3. The milk of two cows was tested: one yielded in a year 6000 pounds of milk that tested 3 per cent of fat; the other yielded 5000 pounds that tested 4 per cent. Which cow yielded the more butter-fat? What was the money value of the butter produced by each if butter-fat is worth twenty-five cents a pound? CHAPTER XII MISCELLANEOUS SECTION LXIV. GROWING FEED STUFFS ON THE FARM