31 



met or float. The weights in terms of spe- 

 cific gravity represent unity, tenths, hun- 

 dred ths, thousandths, and ten thousandths. 

 With no weight on the beam it balances 

 when the plummet floats in air. When 

 the unit weight is in position, it balances 

 when the plummet floats in pure water at 

 the proper temperature. When the plum- 

 met is submerged in a liquid heavier than 

 water, such as milk, additional weights are 

 required to bring the instrument to equi- 

 librium. The specific gravity is read off 

 directly from the value of the weights and 

 their position on the beam. Detailed direc- 

 tions usually accompany the instrument. 



Lactometers. Most lactometers are not 

 sensitive enough for determining the speci- 

 fic gravity of milk if more than approximate 

 figures are required. The use of either the 

 Westphal balance or the special lactom. 

 eter, previously mentioned, is advised. 

 If, however, only approximate results are 

 required the ordinary lactometer, of which 

 there are several types on the market, will 

 suffice. 



The lactometer (fig. 29) is used exactly in 

 the same manner as is the hydrometer in 

 testing sulphuric acid, directions for which 

 are given on page 12. Care must be taken 

 that the milk is at the temperature at which 

 the lactometer is standardized and that the 

 lactometer floats freely in the cylinder. 

 The specific gravity of milk can not be 

 taken until the milk is three or four hours 

 old. The point on the scale of the lactome- 

 ter where the surface of the milk intercepts 

 represents the specific gravity which is 



ft 



02 



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