METHODS OF QUANTITATIVE ANALYSIS. 



I. DETERMINATION OF SPECIFIC GRAVITY. 



For an absolutely accurate determination of specific 

 gravity, the pyknometer must be used. The pyknometer 

 is graduated for a definite temperature. The determina- 

 tion of specific gravity therefore must be made at that 

 degree. The milk and the instrument are brought to 

 the proper temperature by placing in warm water. Since 

 the cream readily separates from the milk, it is best to 

 mix the sample thoroughly by shaking before each de- 

 termination. 



The pyknometer is accurately tared, filled with milk and 

 weighed. If the capacity of the instrument be lo cc. and 

 if it weigh, when filled with milk, after deducting the tare, 

 0.1035 gram, the specific gravity of the milk would be 

 10X0.1035= 1.035.* 



For a less accurate determination of the specific grav- 

 ity one may use a good areometer (lactodensimeter). 

 On account of the rapid rise of the cream on milk, one 

 must read the scale as quickly as possible. An areometer 

 constructed especially for the examination of milk should 

 have a scale that will indicate the specific gravity accu- 

 rately to the fourth decimal place. The range of the 



*The pyknometers most commonly used at present, have a 

 capacity of about 50 cc. They are first dried and weighed; 

 then filled with distilled water at a chosen temperature (usually 

 17.5° C.) and weighed; and finally rinsed and filled with milk at 

 exactly the same temperature, and again weighed. 



Weight of milk divided by weight of water equals specific 

 gravity. — Translators. 



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