24 



by reading from the bottom of the lower meniscus to the 

 top of the upper one. In skim milk, however, since most 

 of the globules are small, a greater proportion of them fail 

 to be driven into the neck of the test bottle ; consequently 

 the reading is too low and does not give the true percent- 

 age of fat. The skim-milk test is valuable for testing the 

 completeness of the skimming, but its re- 

 sults must not be interpreted too strictly. 



The skim-milk test bottle differs from 

 the whole-milk test bottle in having two 

 necks, one of small bore graduated to read 

 hundredths per cent for the fat column, 

 and one extending nearly to the bottom of 

 the bottle for filling. (See fig. 21.) 



Seventeen and one-half cubic centime- 

 ters of the skim milk is placed in the test 

 bottle by means of the filling tube. Twen- 

 ty cubic centimeters of sulphuric acid is 

 added in two portions of 10 cubic centime- 

 ters each, shaking after each addition. 

 Great care must be taken while shaking 

 to be sure that no particles reach the fat 

 tube; otherwise it will become plugged 

 and the test ruined. The test bottles are 

 placed in the tester with the filling tubes 

 toward the center. The first whirling is 

 continued one or two minutes longer than 

 when testing whole milk. As in whole-milk 

 testing, hot water is added in two portions, 

 the second one bringing the fat about half way up the tube. 

 The reading should be made immediately after the final 

 whirling. If the fat is in the lower part of the tube it may 

 be forced into the graduated part by the pressure of the 

 finger at the mouth of the filling tube. Some skim-milk 

 test bottles have the mouth of the fat tube enlarged to 

 receive a rubber stopper which may be used to adfust the 

 fat column for reading. 



FIG. 21. 



