PHYSICAL AND CHEMICAL EXAMINATION OF MILK 147 



The following example will illustrate the method of reading : 



The 5.0 rider is on notch 10. Therefore this is 1 by 5 = 6.000 

 The 0.5 rider is on notch 0.3. Therefore this is 0.5 by 0.3 = 0.150 

 The 0.05 rider is on notch 0.1. Therefore this is 0.05 by 0.1 = 0.005 

 The 0.005 rider is on notch 0.4. Therefore this is 0.005 by 0.4 = 0.002 



Total, 5.157 



As the plummet displaces 5 grams water and 5.157 grams milk, 

 the specific gravity of the milk is 5.157 divided by 5, which equals 

 1.0314. The specific gravity can also be read directly from the 

 beam. 



The Determination of Fat 



The percentage of fat may be determined by three different 

 methods, namely: 1, ether extraction; 2, centrifugation, and 3, 

 refraction. The ether extraction and centrifugation methods are 

 commonly employed, while the refraction method is used only 

 exceptionally. By ether extraction more accurate results are 

 obtained than by centrifugation, but this latter method, if car- 

 ried out with care, gives sufficiently accurate results for practical 

 purposes and takes much less time. 



By ether extraction the fat is determined according to official 

 and provisional methods of analysis as follows: 



"Make rolls of thick filter paper, cut into strips of 6.25 by 62.5 

 cm., and thoroughly extract with ether and alcohol, or correct 

 the weight of the final fat extract by a constant obtained for the 

 paper. From a weighing bottle or weighing pipet transfer about 

 5 grams of milk to the coil, dry end down on a piece of glass, at 

 the temperature of boiling water for one hour, or, better, in 

 hydrogen at the temperature of boiling water; transfer to an ex- 

 traction apparatus and extract with absolute ether or petroleum 

 ether boiling at about 45° C; dry the extracted fat and weigh." 



Leach gives the following method (Adams Method): 



A fat-free strip of filter paper which can be purchased 

 (Schleicher and Schiill) about 2^ inches wide and 22 inches long 

 is rolled into a coil and held in place by a wire. About 5 c.c. of 

 milk are placed in a beaker and the beaker and the milk weighed. 

 The coil of filter paper is then brought in contact with the milk 

 until as much of the milk as possible has been absorbed by the 

 paper. The beaker is weighed again and the exact amount of 

 milk absorbed by the paper coil calculated. 



The milk on the coil is then dried, first in the air and then in 

 an oven at a temperature not to exceed 100° C. The coil is trans- 

 ferred to a Soxhlet ether extraction apparatus (Fig. 40) and 

 extraction continued until the ether has siphoned over at least 

 twenty times, which occupies about two hours. The ether is 



