232 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
off the cream or adding skimmed milk increases the spe- 
cific gravity, while the addition of water decreases it. It 
is not possible to detect these forms of adulteration from 
the change in specific gravity alone, on account of the 
wide range in the specific gravity of normal milk, but 
when considered in connection with the per cent. of fat 
and solids not fat the specific gravity is of great assist- 
ance. The specific gravity of skimmed milk may be 
lowered to normal by the addition of a suitable quantity 
of water. When this is suspected, 
the determination of the specific 
gravity of the dry matter or solids 
and the per cent. of fat in the total 
solids will throw further light on 
the subject. The test for nitrates 
and nitrites will assist in discover- 
ing the addition of water (see page 
247). The refraction number of 
the milk serum is also of value in 
this connection (see page 250). 
Fra. 32.—Westphal balance. 
From Chemical Testing of Mi i 
ioe neal Pevtag oleae It is necessary to refer to the 
U- 8. Dept. of Agriculture) New York Board of Health lac- 
tometer because it is still used to some extent in 
the East, although it is constructed on the incorrect 
theory that 1.029 is the lowest specific gravity of pure 
milk. Its scale is divided into 120 divisions. One hun- 
dred corresponds to 29 Quevenne degrees, or a specific 
gravity of 1.029. Milk testing 90 on this scale is sup- 
posed to be 90 per cent. pure, i.e., 10 per cent. of water 
is supposed to have been added, which, of course, is 
not always true. Readings on this scale may be con- 
verted into Quevenne degrees by multiplying by 0.29 
or the following table may be used: 
