122 



MODERN METHODS OF TESTING MILK 



body. Thus it sinks deeper in a light liquid than in 

 a heavy one, because it takes a larger volume of the 

 light liquid to equal the weight of the floating body. 

 Such an instrument is graduated as the re- 

 sult of extensive experiments, so that the 

 specific gravity of the liquid in which the 

 hydrometer is placed can be read at the 

 point where the scale is even with the upper 

 surface of the liquid. A hydrometer is cor- 

 rect only for the temperature used in stand- 

 ardizing it. Wlien a hydrometer has a 

 scale specially adapted to the limits of the 

 specific gravity of milk, it is called a lactom- 

 eter. Of the various lactometers made, only 

 /^IJX two are sufficiently used to deserve atten- 

 tion: (i) The Quevenne, -and (2) the New 

 York Board of Health, lactometers. 



THE QUEVENNE LACTOMETER 



Description. — This instrument (Fig. 48) 

 is a hydrometer the scale of which is di- 

 vided into 25 equal parts, going from 15 

 to 40. Each division is called a degree, and 

 FIG. 48 every fifth degree is numbered on the scale. 

 LACTOMETER ^^^^ poiut marked 15 corresponds to the 

 point marked specific gravity T.015 on an 

 ordinary hydrometer, and is the point to which it will 

 sink when placed in li(|uids whose specific gravity is 

 1.015. The 40 degree mark on the Ouevenne lactom- 

 eter corres])onds to the specific gravity 1.040 mark 

 on a hydrometer. The relation between specific grav- 



