THE TESTING OF MILK AND CREAM 137 



instrument 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 lactom- 

 eter scale with numbers ranging from 15 to 45, the lowest 

 readings being at the upper end of the scale. One may obtain 

 the specific gravity reading by prefixing 1.0 before the lactom- 

 eter reading. Thus, if the instrument gives a reading of 33, 

 the specific gravity would be 1 .033 . The fact that the Quevenne 

 lactometer 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 lactometers 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° F., we would add 

 .6 (.1 X 6) to the lactometer reading, making the corrected or 

 true reading 32.6. In this case the specific gravity would be 

 1.0326. 



The Board of Health lactometer is an instrument giving 

 arbitrary readings and must be changed to equivalent Quevenne 

 readings in order to obtain the specific gravity. It is of the 

 same general shape as the Quevenne, except that the thermom- 

 eter scale is usually on the opposite side of the stem from the 

 lactometer scale. The instrument is graduated from to 120, 

 and one degree Board of Health equals .29 of one degree Que- 

 venne. In order, therefore, to change from Board of Health 

 to Quevenne, the Board of Health reading is multiplied by .29. 

 Vice versa, to change from Quevenne to Board of Health read- 

 ing, the Quevenne reading is divided by .29. Like the Quevenne, 



