THE SPECIFIC-GRAVITY TEST. 209 



It is evident, from the well-known influence which 

 11 still-slops " and other exceedingly succulent food have 

 in increasing the amount of water in the milk, that adul- 

 teration may be effected by means of the food, as well 

 as by addition of water to the milk itself. It is evident, 

 too, on a moment's reflection, that the specific gravity 

 of pure milk must vary exceedingly, as it comes from 

 different cows, or from the same cow at different times. 

 This variation reached to the extent of twenty-three 

 degrees in the milk of forty-two different cows, or from 

 one thousand and eight to one thousand and thirty-one ; 

 but so great a variation is very rare, and not to be 

 expected. 



No reliable conclusion, as to whether a particular 

 specimen of milk has been adulterated or not, can there- 

 fore be drawn from the differences in specific gravity 

 alone. A radical difficulty attending this test arises 

 from the fact that the specific gravity both of water and 

 cream is less than that of pure milk. If, therefore, the 

 hydrometer sinks deeper into the fluid than would be 

 expected in ordinary pure milk, how is it 

 possible, unless the variation is very large, to 

 tell whether it is due to the richness of the 

 milk in cream, or to the water ? I have, 

 for instance, two instruments, each labelled 

 " Lactometer," but both of which are simple 

 hydrometers (Fig. 71), or specific gravity 

 testers, one of which is graduated with the 

 water-mark and that of pure milk 20° ; the 

 water-mark of the other being 0, like the 

 first, and that of pure milk 100°. Both are 

 the same in principle, the only difference 

 being in the graduation. On the former, 

 graduated for pure milk at 20°, it is difficult 

 to tell with accuracy the small variations in 

 Fig. n. 1 $* 14 



