METHODS OF EXAMINING MILK 237 
moved from the centrifuge, the bottle is placed in water 
at a temperature of 135° to 140° F. (57° to 60° C.) 
and submerged to a point above the fat column for 15 
minutes, after which the per cent. of fat is read off from 
the scale. The reading is taken from the bottom of the 
lower meniscus to the bottom of the upper one. It is 
recommended that the upper meniscus be destroyed by 
dropping a few drops of glymol 
(liquid petrolatum, white min- 
eral oil) into the test bottle and 
the reading taken from the bot- 
tom of the lower meniscus to 
the line between the glymol and 
the fat. 
Gerber Test.—(Fig. 36.) 
This test is used almost exclu- 
sively in Europe and to some ex- 
tent in this country. The prin- 
ciple is the same as in the Bab- 
cock test, except that the fat is 
not only liberated from its emul- 
sion by sulphuric acid but is 
also dissolved in amyl alcohol. 
The apparatus required con- 
<i - Fria. 36.—Bottle and pipettes used in 
sists of a special type of bottle Gerber test. 
(G) known as an acido-butyrometer, which has a long 
neck containing a scale graduated in tenths, each division 
representing 0.1 per cent. of fat, and an opening in the 
bottom which may be closed with a rubber stopper; also 
three pipettes: 1 of 11 c.c. capacity to measure the milk 
(K), an acid pipette holding 10 cc. (H), and a 1 c.c. 
pipette for the amyl alcohol (I). The chemicals used 
are commercial sulphuric acid of a specific gravity of 
