METHODS OF EXAMINING MILK 239 
power machine making 800 to 1000 revolutions per min- 
ute 3 to 4 minutes is sufficient. When the bottles are 
removed from the centrifuge they should be submerged 
in an upright position, with the stopper downward, in 
a water bath at 60° C. (140 ° F.) until the reading is 
taken, unless the samples are so few that they can all be 
read in a few seconds. The fat collects in 
a clear, yellow column at the top of the 
fluid in the neck. The stopper is turned 
sufficiently to bring the lower border of 
the fat column on a level with one of the 
main divisions of the scale and the per 
cent. of fat is then read off. The read- 
ing is taken from the bottom of the fat 
column to the lower border of the menis- 
cus at the top. After the reading is taken 
the bottle should be emptied at once and 
cleaned as directed for the Babcock bottle. 
A special bottle is made for testing 
cream. The cream placed in the bottle is 
weighed; otherwise the per cent. of fat in 
cream is determined in the same manner 
as that in milk. 
Lactoscope Test.—It was proposed 
some time ago to determine the per cent. : 
. « Fia. 37.—Feser’s 
of fat in milk by measuring its transpar- _lsctoscope. 
ency. Several forms of apparatus have been devised for 
this purpose, the simplest being Feser’s lactoscope (Fig. 
37). This is a glass tube, contracted towards the bot- 
tom. A vertical white-glass column, which is encircled 
by six blaek horizontal lines, projects upward into the 
contracted part. On the surface of the upper part of the 
tube there is a graduated scale with a column of figures 
