The Gerber Butyrometer.-Special forms of tester, test-bottle, etc., are used. The test uses II cc. of milk, 10 cc. of sulphuric acid (1.825 specific gravity), ———— THE W.C NEW YO FIG. 28 AUTOMATIC "RUSSIAN" PIPETTE FIG. 28a "RUSSIAN" TEST-BOTTLE and I cc. of amyl alcohol. The operations are carried out about the same as in the Babcock test. The "Sinacid" (no acid) Test.—The distinctive feature of this test is that, in place of sulphuric acid, it uses a patented mixture, consisting of sodium phosphate and citrate, which, unlike sulphuric acid, is entirely free from any dangerous properties; it uses also a colored alcoholic solution. After mixing the "sinacid" liquid with the milk, the mixture is heated to 200° F. for 5 minutes before being whirled in the tester. The results do not always appear to agree closely with those given by other tests, according to the reports of some operators. There is, moreover, some natural prejudice against using a process, any part of which is patented. Gerber's "Sal" Test.-Gerber has just published a method in which no acid is used. The full details are not given, since the method is to be patented. Good results are reported. CHAPTER V Method of Testing Cream by the Babcock Test The Babcock test can be used in ascertaining the amount of fat in cream, but certain precautions and modifications are necessary to insure correct results. A special form of test-bottle is generally used. Special pains must be taken in sampling cream. For strictly accurate work, the cream sample must be weighed for testing. USE OF MILK TEST-BOTTLES IN TESTING CREAM Test-bottles used in testing milk can be used in testing cream only under special conditions. Cream containing over ro per cent. of fat will fill the neck of the test-bottle too full for measurement, when we take 18 grams (about 17.5 cc.) to test. This difficulty may be overcome in two ways: (1) By using a sample of cream less than 18 grams, and (2) by dividing an 18-gram sample in roughly equal parts between two or more bottles, according to its richness in fat. In the former case the per cent. of fat read is increased by a correction to be considered later. In the second case, the tests are made as in case of milk and the percentages found in the different bottles are added, the sum being the per cent. of fat in the cream tested. The volume of cream in each test-bottle is always made up to about 17.5 cc. by adding water to the cream and mixing before adding acid. SPECIAL CREAM-TESTING BOTTLES To test in one bottle an 18-gram sample of cream containing over 10 per cent. of fat, the neck must be made to hold more than the neck of a milk-bottle, that is, more than 2 cc. This additional space must be obtained (1) by using a neck of larger diameter, keeping the length the same as in the milk-bottle or (2) by making the neck longer, keeping the diameter the same. There is this objection to making the necks of test-bottles too large in diameter, that the divisions on the scale come nearer together and the reading of the results is less accurate. If the neck is made long enough to allow as fine graduation as in the milk-testing bottles, then the bottles are too long to use in an ordinary tester. Bulb-necked cream-bottle. - Both of the difficulties mentioned above are overcome by having a bulb made in the neck of the bottle (Fig. 29). In this cream-testing bottle the graduation is as fine as in the milk-testing bottles, the smallest division representing .2 per cent., and the scale ex FIG. 29 BULB-NECKED CREAM-BOTTLE tends from o to 25 per cent. Hence, in these bottles we can use 18 grams of cream, provided the cream does not contain over 25 per cent. of fat, while, with cream testing over 25 and up to 50 per cent., a 9gram sample can be used for the test. In using this form of bottle, care must be observed when water is added near the close of the test. Neither the lower nor the upper surface of the fat-column must be allowed to come in the bulb, since, obviously, it is impossible then to read the results. This style of bottle is also made with a scale measuring 50 per cent., the smallest divisions being .25 per cent. FIG. 30 STRAIGHT-NECKED CREAM-BOTTLE Straight-necked cream-bottles. The other varieties of cream-testing bottles are straight-necked, varying in respect to (1) diameter, (2) length of neck, and (3) fineness of graduation. These vary in length from the ordinary size to 9 and 10 inches, the longer sizes requiring special testers. In capacity, the necks vary from 6 to 20 cc., which is equivalent to 30 to 100 per cent., when an 18-gram sample of cream is used. In fineness of graduation, the smallest divisions vary in different bottles from 2 to I per cent. One type of straight-necked bottle is shown in Fig. 30. For strictly accurate work, bottles graduated to .2 per cent. should be used; and the use of bottles whose finest division is more than .5 per cent. should be condemned, except for rough work. |