368 MILK AND MILK PRODUCTS 
attention cannot be paid to this important step. The larger portion 
from which the sample is taken should be thoroughly stirred. If the 
sample is collected in a bottle, the contents should be very thoroughly 
mixed. 
Specific Gravity. This may be determined by any of the usual 
methods. Hydrometers are convenient and, in this form, are known as 
lactometers. They are of different types. The New York Board of 
Health has an arbitrary scale. This is divided into 120 parts with zero 
equal to the specific gravity of water and 120 equal to the specific gravity 
of 1.029. The length is usually about 12ins. The Quevenne lactometer 
is graduated in accordance with the specific gravity scale with the first 
two figures omitted for sake of convenience (1.029 sp. gr.=29 Que- 
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Fia. 66-—-Types of Lactometers. 
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venne). They are now made with blue and yellow columns. The 
fractions in the blue column indicate the percentage of water in the 
skimmed milk, and in the yellow column, in whole milk. 
Determination of Ash in Milk. Weigh about 20 gms. of milk in a 
tared dish and, after adding 6 c.c. of nitric acid, evaporate to dryness, 
ignite just below redness. 
Determination of Fat in Milk. Babcock Test. This rests on the 
fact that concentrated sulphuric acid will dissolve the solids not fat 
in milk. The fat is unchanged and may be separated in a centrifuge 
as follows: Special bottles are necessary and into each should be placed 
18 gms. (17.6 ¢.c.) of the well-shaken sample of milk. By means of a 
special pipette add 17.5 ¢.c. of commercial sulphuric acid with a spe- 
cific gravity of about 1.83. During the addition of the sulphuric acid, 
the contents of the bottle should be constantly shaken. The bottle 
should now be placed in a centrifuge and whirled for five minutes at 
about 1000 r.p.m. After this, boiling water should be added to the 
Babcock bottle, in order to raise the fat column into the neck of the 
