28 A DAIRY LABORATORY GUIDE 



Health (commonly called the B. of H. lactometer). 



The Quevenne lactometer has a long, narrow- 

 stem which is extended into a hollow glass tube of 

 much larger diameter than the stem itself. At the 

 lower end of the instrument is a bulb of mercury 

 which causes the lactometer to sink in the liquid 

 to its proper level. The upper part of the stem 

 contains a thermometer scale, as it is important to 

 know the temperature of the milk when the lac- 

 tometer reading is taken. This scale does not re- 

 cord high temperature, and, therefore, the instru- 

 ment should never be placed in hot liquids. In 

 order to clean the lactometer wash in cool water 

 and wipe with a dry cloth. Immediately below the 

 thermometer scale is a lactometer scale with num- 

 bers ranging from 15 to 45, the lowest readings 

 being at the upper end of the scale. One may ob- 

 tain the specific gravity reading by prefixing i.o 

 before the lactometer reading. Thus, if the in- 

 strument gives a reading of 33, the specific gravity 

 would be 1.033. The fact that the Quevenne lac- 

 tometer gives specific gravity readings directly is 

 one of its chief advantages. 



Temperature affects the density of liquids. The 

 colder the milk the more dense it is, and the warmer 

 the milk the less dense it is. For this reason lac- 

 tometers are standardized to give readings at a 

 temperature of 60° F. When milk is warmer or 

 colder than 60° F. a correction must be made, and 

 this correction for the Quevenne is .1 of a lactometer 

 degree for every degree in temperature that the 

 sample is above or below the standard temperature. 

 When we cool the milk down we add ; when we 

 warm the milk we subtract. For example, if a 

 lactometer gave a reading of 32 at a temperature 

 of 66° P., we would add .6 (.1X6) to the lactometer 



