28 DAIRY CHEMISTRY 



or other soft water or condensed steam is preferable. 

 When water containing lime is used, bubbles of gas 

 are given off, causing foam when the hot water is 

 added to the test bottles containing the acid. The 

 presence of foam in the graduated stem of the test 

 bottle prevents accurate reading of the fat. Some 

 hard waters are suitable for use provided a few drops 

 of sulphuric acid are added before heating. If this 

 is done, of course the water cannot be heated or used 

 in ordinary metal boilers and receptacles. When a 

 large number of tests are to be made, a suitable out- 

 fit should be provided for the addition of hot water 

 to the test bottles ; a pail suspended three or four 

 feet above the tester with a rubber tube, a pinch 

 cock, and a glass tube drawn to a point, will be found 

 suitable for this purpose. 



28. Care of Test Bottles and Apparatus. The 

 rims on the necks of test bottles are easily nicked 

 and broken, and in handling bottles, care should be 

 exercised to prevent this being done. Some bottles 

 are provided with ground or roughened places for 

 labeling or marking with pencil, while others have 

 numbered copper or metal " collars." In making the 

 test, the numbers should be carefully checked, and 

 the proper entries made as to the sample and the fat 

 content. Many conveniences in the way of home- 

 made racks and devices for holding the apparatus 

 will suggest themselves. In milk testing, cleanliness 

 and accuracy in all the manipulations are the main 

 essentials for securing correct results. 



