62 



ANALYSIS OF MILK. 



the tV rider is kung, tlie third decimal from the ^^^ rider, and 

 the fourth decimal from the -,-^00 rider. 



This method has the advantage of being somewhat more rapid 

 than the use of the Sprengel tube, but is not quite so accurate, 

 as the adjustment of riders and balance cannot practically be 

 performed with very great accuracy. 



In dairy work the lactometer is generally used. From a 

 strictly scientific point of view, there are many objections to 

 lactometers, but their practical convenience is so great that they 

 are instruments of extreme value. 



T?ig. 3. — Westphal Balance. 



The faults of lactometers are : — (1) They do not indicate 

 true specific gravities, but the inverse of this — specific volumes ; 

 consequently, the scale is not divided into equal parts. The 

 divergence from equality is, however, so small in a lactometer, 

 which has only a limited range, as to render it practically 

 admissible to treat the smaller divisions as equal. 



(2) The exact point at which the level of the liquid cuts the 

 stem of the lactometer cannot be ascertained, as, owing to surface 

 energy, the liquid is attracted to a higher level round the stem 

 of the lactometer than the surface of the liquid ; moreover, the 

 height to which the liquid is attracted varies with the nature 



