74 MILK AND DAIRY PRODUCTS PART 



main divisions of the scale, and then, by holding the test-bottle 

 against the light, the height of the column of fat can be 

 accurately ascertained. The lowest point of the meniscus is 

 taken as the level when reading the upper surface of the fat in 

 a sample of whole milk, and the middle of the meniscus for 

 separated milk. 



If the column of fat is not clear and sharply defined, the 

 sample must be again whirled in the centrifuge. 



Each division on the scale is equivalent to 01 per cent., so it 

 is very easy to read to 0'05 per cent., or, with a lens, to 0'025 per 

 cent. If the number which is read off is multiplied by 01, 

 then the percentage quantity of fat in the milk is obtained, 

 e.g., if the number on the scale was 36"5, then the percentage of 

 fat is 3 '6 5 per cent. 



If a plug of material forms below the column of fat during 

 the centrifuging, it is a sign that the sulphuric acid is too 

 strong. Siegfeld l recommends in such cases that a weaker acid 

 (sp. gr. 1'800-1'810) should be used. A plug is often obtained 

 when the milk has been preserved with formalin, for this 

 combines with the casein to give a compound insoluble in 

 sulphuric acid. To prevent this, Siegfeld 2 recommends the 

 addition of 2 c.c. of hydroxylamine solution (1 part hydroxylamine 

 hydrochloride and 2 parts water) to 100 c.c. milk, a few 

 drops of ammonia also being added. The amount of fat must 

 then be calculated to the original volume of milk. 



If the temperature falls very much during the time the test- 

 bottles are being whirled in the centrifuge, all the fat does not 

 separate, so in such cases the centrifuge must be heated in 

 some way. The bottles are cleaned in the same way as those 

 of Babcock or Lindstrom. 



With whole milk, Gerber's test gives excellent results, which 

 agree very closely with those obtained by gravimetric methods 

 of analysis, and it has become almost universal (except in 

 North America) for estimating the percentage of fat in milk. 



For the analysis of cream Gerber has proposed the use of a 

 special form of butyrometer, which is open at both ends, and 

 serves also for the determination of fat in butter and cheese. 

 The results, however, which it gives are not reliable, and it is 



1 Molkerei-Zeitung, Hildesheim, 1901, p. 797. 



2 Zeitschrift f. Untersuchnny der Nahrungs- u. Genussmittel, 1903, p. 397. 



