CHAPTER III. 



The lactometer and its use. 



This instrument, shown in Fig. 13, is used to determine 

 the specific gravity of milk. The stem has two scales 

 upon it, a thermometer scale at the upper end and a lac- 

 tometer scale at the lower. The latter scale reads from 

 fifteen to forty, being divided into twenty-five divisions, 

 each of which reads one lactometer degree. The lower 

 end of the instrument consists of two bulbs : an upper one 

 containing the mercury for the thermometer scale, and a 

 lower and larger one w^eighted with shot or mercury 

 which serves to immerse and to keep in an upright posi- 

 tion the large oblong bulb or float below the stem. 



Making the Test. In making a lactometer test the 

 sample of milk is carefully mixed and placed in the 

 lactometer cylinder. (Fig. 14.) The lactometer is now 

 carefully lowered into it and enough milk is added to the 

 cylinder to fill it brim full. Now place your eye in a hori- 

 zontal position with the surface of the liquid and read 

 down as far as the liquid w^ill permit. The reading thus 

 obtained is the correct lactometer reading, provided the 

 temperature as indicated by the thermometer scale is 60°. 



Corrections for Temperature. Lactometers are stan- 

 dardized at a temperature of 60° F. ; but, since it is diffi- 

 cult to have a sample always at this temperature, cor- 

 rections may be made for temperatures ranging from 50° 

 to 70°. As the temperature rises the liquid expands and 

 the specific gravity decreases. This decrease amounts to 



34 



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