Lactometers 79 



pose ; but it was soon found that the percentage of 

 cream depends not so much upon the amount of fat 

 present in the milk as upon the size of the globules 

 and the conditions under which they are brought 

 to the surface, and that the percentage of cream 

 does not necessarily bear a constant relation to the 

 percentage of fat. 



Specific gravity. The determination of the spe- 

 cific gravity was next brought into use as a means 

 of determining the quality of milk. Inasmuch as 

 milk is slightly heavier than water, and as water is 

 the most common adulterant of milk, any addition 

 of water to it would serve to lessen its specific 

 gravity, and would easily be detected by a determi- 

 nation of the specific gravity. To determine the 

 specific gravity of milk, various forms of specific 

 gravity hydrometers, known as' lactometers, have 

 been devised. They were formerly very much more 

 depended upon as a test of the quality of milk than 

 at present, and though now we have learned that 

 under certain conditions a simple specific gravity 

 test may not only be inaccurate, but entirely mis- 

 leading, still they are "of considerable use for cer- 

 tain purposes and in connection with certain other 

 instruments. 



Lactometers. In devising the lactometer, it was as- 

 sumed that 1.029 was as low as the specific gravity of 

 any unadulterated milk would ever fall ; therefore a 

 hydrometer was devised, the scale of which was gradu- 

 ated from to 120, the marking the point of pure 

 water, or a specific gravity of 1.000, and 100 cor-. 



