72 DAIRY LABORATORY GUIDE 



EXERCISE 13 



THE SPECIFIC GRAVITY OF MILK 



Object: To determine the specific gravity of milk by 

 means of the Quevenne lactometer. 



Apparatus: Samples to be tested, eight-inch cylinder, 

 thermometer, Quevenne lactometer, and Babcock testing 

 outfit. 



Steps: 1. Test the sample for butter-fat; then fill the 

 cylinder nearly full of the sample to be tested. 



2. Take the temperature of the sample, and record. 



3. Float the lactometer in the sample and observe the 

 exact point on the scale where it cuts the surface of the liquid, 

 and record the reading. Care is necessary in putting the lac- 

 tometer into the milk not to let it drop to the bottom of the 

 cylinder, as it is very easily broken. 



4. The scale of the Quevenne lactometer is divided into 

 25 equal parts, ranging from 15 to 40. Each division is called 

 a degree, and is divided into fifths. If the instrument floats 

 at 18, for example, it indicates a liquid whose specific gravity 

 is 1.018. 



5. Corrections for temperature: The lactometer is 

 standardized at 60 F.; so corrections need to be made in 

 reading if the temperature of the sample varies from 60 F. 

 For each degree above 60 add one-tenth to the lactometer 

 reading; for each degree below 60 subtract one-tenth from 

 the lactometer reading. It is a good plan to bring the tem- 

 perature of the sample within the extremes of 50 and 70F., 

 as the rules are only approximately correct. 



