CHAPTER XXXVII 



THE ADULTERATION OF MILK 



Because milk was for so long a time sold by the measure, 

 with no easy, accurate way of testing for quality, it is not sur- 

 prising that some men either skimmed or watered the milk they 

 sold. Of all forms of adulteration these two are most common 

 and in general most easily detected. 



Chemical analysis of the milk to detect adulterations is not 

 necessary since it has been discovered that the specific gravity 

 (weight per volume) of milk bears a definite and constant rela- 

 tion to the amount of solids contained in it. 



The Quevenne lactometer, which is the chief instrument 

 used in the detection of skimming or watering, is a glass tube 

 filled with air, weighted to float in milk, and graduated to indi- 

 cate the depth to which it sinks. Since any floating object sinks 

 until it displaces exactly its weight of liquid in which it is 

 floating, the lighter or thinner the milk, the deeper the instru- 

 ment will have to sink to balance. 



Influence of Temperature. — Water, milk and most other 

 liquids expand and become thinner or less dense upon becoming 

 warm, consequently, the milk to be tested must be brought to 

 a fixed temperature, 60 degrees or close to it. For every degree 

 in temperature above 60, one-tenth is added to the lactometer 

 reading; thus: if the lactometer, L = 31.5, at temperature 64, 

 the corrected reading would be 31.9, and likewise for every 

 degree below 60, one-tenth is subtracted from the lactometer 

 reading, thus if L = 32.4 temperature 55, the correct reading 

 would be 31.9. This rule for the correction does not hold true 

 above 70 degrees nor below 50 degrees, and preferably should 

 not be worked above 65 degrees nor below 55 degrees. The 

 sample should be brought to within a few degrees of 60 before 

 it is tested. 



Influence of Air. — On account of the fine bubbles of air or 

 other gas in freshly drawn milk, the lactometer cannot be ac- 



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