Canadian Dept. Agr. 1915, Report of the dairy and cold storage commissioner. Dominion of Canada, Census and Statistics office, Rept. 1915. CHAPTER XIX _TESTING_ In connection with marketing, a certain amount of testing of the products should be practiced, to determine exactly the results and grades of products. This includes the testing of the whole milk, whey and cheese for fat, the milk for casein, and the cheese for moisture. In factories in which the milk is bought on the fat basis, it is necessary to test each patron's milk for fat. If there is a cheese-moisture law in the state, it is necessary to test for moisture. The whey should be tested to learn the loss of fat in the manufacturing process and to ascertain whether the losses have been reduced to the minimum. +308. The fat test.+--The test commonly used to determine the fat in milk is known as the Babcock. The principle of this test is as follows: Fat exists in the form of very small globules. Because the fat globules are lighter than the other milk constituents, under the influence of the force of gravity most of them rise to the surface. There, mixed with the other milk substances, these globules form a layer of cream. Babcock found that by adding to the milk sulfuric acid of proper strength and temperature, the casein, the milk-sugar and the albumin are decomposed and the sticky quality of the milk is destroyed. The acid does not decompose the fat but leaves it free to come to the surface of the mixture. Under centrifugal force, this fat is quickly brought to the surface. By using a known quantity of milk and having a scale graduated in percentage of the amount of milk, the percentage of fat can be determined. Fig. 69 shows the necessary equipment. [Illustration: FIG. 69.--Apparatus necessary to test milk and whey for fat and total solids.] There are three kinds of bottles employed in making the test, one with a very large neck which is used when testing materials high in fat-content such as cream, butter and cheese. This is generally called a cream-test bottle. It is graduated from 0 to 50 per cent. When testing materials with a small amount of fat such as whey, skim-milk and buttermilk, a test bottle with two necks is used, one with a small bore for the fat and the other neck with a larger bore to add the milk, acid, water. It is graduated from 0 to 0.5 of 1 per cent. There is a third bottle between the other two to test whole milk. This is known as a whole-milk bottle. It is graduated from 0 to 8 per cent. All of the glassware should comply with the laws.