90 



Testing Milk and Its Products. 



both. The test should be repeated in such cases, using 

 more acid and whirling for full five minutes. Sepa- 

 rator skim milk should be allowed to stand 10 to 15 min- 

 utes for the air to escape before the sample is taken. 



In order to bring as much fat as possible into the 

 neck of the bottles in testing skim milk, it is advisable 

 to add somewhat more acid than when 

 whole milk is tested, viz., about 20 cc., 

 and to whirl the bottles at full speed for 

 at least five minutes, keeping the tester as 

 hot as possible the whole time. 1 The read- 

 ings must be taken as soon as the whirl- 

 ing is completed, as owing to the contrac- 

 tion of the liquid by cooling, the fat oth- 

 erwise adheres to the inside of the neck 

 of the test bottle as a film of grease which 

 cannot be measured by the scale. 



99. The double-necked test bottle, 

 (fig. 37), suggested by one of us, 2 is made 

 especially for measuring small quantities 

 of fat and gives fairly satisfactory results 

 in testing skim milk and butter milk. 

 Each division of the scale in these bottles 

 represents five-hundredths of one per 



FlG . 



The 



/ ,, , double-necked 



cent, and the marks are so far apart that skim miik bot- 



., . th> (sometimes 



the small fat column can be easily esti- called the ohi- 



son or B. & W. 



mated to single hundredths of one per bottle.) 



cent. In the first forms, now out of use, the neck was 



graduated to hundredths of one per cent. 



1 See Wis. exp. station, report XVII, p. 81. 



2 First constructed by Mr* J. J. Nussbaurner, of Illinois; now man- 

 ufactured by various firms. 



