228 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
DETERMINATION OF SPECIFIC GRAVITY 
The specific gravity of milk is determined by means 
of Quevenne’s lactometer (Fig. 31) or modifications of 
this apparatus. 
After being thoroughly mixed, some of the milk to 
be tested is poured into a high glass cylinder and the 
lactometer is slowly and carefully lowered 
into the fluid until it floats. Care should 
be taken not to mix air with the milk. 
This can be avoided by pouring the milk 
against the side of the vessel. The lacto- 
meter must not be permitted to touch 
the side of the cylinder. When the 
lactometer has become stationary, the 
specific gravity is indicated by the 
figures on the scale in the stem of the 
lactometer. The reading is taken from 
the line in the scale which is on a level 
with the surface of the milk. The stem 
of the lactometer draws the milk up 
around it, forming a slight meniscus 
which obscures the line at the surface of 
the milk. The reading should not be 
taken from the top of this meniscus, but 
at the surface of the milk, the depth of 
,. the meniscus being estimated. The 
Fia. 31.—Quevenne’s 
lactometer. figures on the lactometer scale do not ex- 
press the specific gravity but Quevenne degrees. By 
dividing Quevenne degrees by 1000 and adding 1, the 
specific gravity is obtained. 
The temperature of the milk should be 15° C. (60° 
F.) when the specific gravity is taken, and the tempera- 
ture should be taken with an accurate thermometer after 
