USE OF LACTOMETER i8i 



adjusted, commencing with the largest rider, until the 

 beam is horizontal, as shown by the pointer attached to 

 the short arm, and the density of the milk is then read 

 off from the positions of the various riders. 



Westphal's balance allows of the rapid and accurate 

 determination of the specific gravities of milk samples. 

 The method, however, is purely empirical, and the beam 

 is always graduated in the first instance by means of the 

 specific-gravity bottle method (above). 



178. Determination of Specific Gravity 



by Lactometer. 



The lactometer is a special form of hydrometer graduated to 

 give readings in the neighbourhood of a density of 1-032, the 

 normal specific gravity of milk. 



The numbers on the lactometer scale represent the second and 

 third numbers after the decimal place, so that a reading of 30 

 corresponds to a specific gravity of 1-030, and a reading of 42 

 to 1-042. The lactometer is generally graduated for use at a 

 definite temperature, 15° C, but it is sufficiently accurate to allow 

 a latitude of 5° on each side of the standard temperature, the 

 density at 15° being then determined by means of tables. 



A well-mixed sample of milk is poured into a jar of 

 suitable diameter, and the lactometer, which must be 

 clean and dry, is held by the stem, and gently lowered 

 into the milk until the level is somewhere near the 

 reading to be expected. It is then released, and the 

 reading carefully taken when the instrument has come 

 to rest. 



The lactometer is easy to use, and affords a 

 means of rapid determination of the specific gravities 

 of a number of samples. Unless the instrument 

 is manufactured by a good maker, however, the 

 results are often not reliable, and should be compared 

 with those obtained by the specific-gravity bottle or 

 pyknometer. 



M 2 



