6o 



MILK AND DAIRY PRODUCTS 



PART 



operation of filling the testers must be performed as rapidly as 

 possible, otherwise the fat will rise to the surface, and unsatis- 

 factory results will be obtained. 



The testers, after being filled, are put into the disc, and if 

 they do not fill all the places they should be so arranged that 

 they lie opposite to one another. Should there be an unequal 

 number of testers, the disc will not rotate evenly, so it is best 

 to make up an equal number with the help 

 of a tester filled with water. When the 

 testers are in position, water is poured into 

 the bottom of the disc so as to bring about an 

 opposing hydrostatic pressure, and the disc is 

 at once set in motion, steam being blown in 

 to bring the temperature to 60 C. When 

 the speed reaches 5,000-7,000 revolutions 

 per minute, this rate is maintained for 4 or 

 5 minutes. 



When the testers are taken from the disc, 

 the small hole in the upper part is closed 

 with the finger, the tester held against the 

 light, and the height of the column of fat read 

 off upon the scale (see Fig. 24). Each division 

 of this is equivalent to 01 per cent, fat, so 

 that the percentage weight can be read off 

 directly. At the open end of the fat column 

 is a meniscus, and the reading is taken from 

 the lowest point of this. 



The testers are cleaned most easily by 

 washing with weak soda lye and warm water, 

 after which a dry cotton cord should be drawn 

 through the capillary. 



The lactocrite method gives results with 

 whole milk which agree very closely with those 

 got by the gravimetric form of analysis, as the investigations of 

 L. F. Nilson 1 show, and so can be used where accuracy is 

 essential. Those methods which will now be described, and 

 which depend upon the use of a centrifuge for the estimation 

 of the fat in milk, are really only modifications of de Laval's 

 original method. 



1 Chem. Zeitung, 1891, No. 37. 



FIG. 23. Boiling 

 Tube for the Lac- 

 tocrite Method. 



