92 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 before the sample is taken so as to allow the air 

 to escape. 



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.^ The read- 

 ings must be taken as soon as the whirl- 

 ing is completed, since owing to the con- 

 traction of the liquid by cooling, the fat 

 will otherwise adhere 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,' is made 

 especially for measuring small quantities 

 of fat and gives fairly satisfactory results 

 in testing skim milk and butter milk. 

 Bach division of the scale in these bottles 

 represents five-hundredths of one per fiq.^stT The 

 cent., and the marks are so far apart that sum'^mi?/ \of- 



,, 11 J! i 1 1, •! ..tie (sometimes 



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

 mated to single hundredths of one per bottle). 



• See Wis. exp. station, report 17, p. 81. 



'First constructed by Mr. J. J. Nussbaumer, of Illinois; now manu- 

 factured by various flrroa. 



