gh the
pipette.

The next step is to add a strong, biting acid known as sulphuric acid to
the test-bottle into which you have just put the milk. A glass marked to
show just how much acid to use also comes with the machine. Fill this
glass measure to the mark. Then pour the acid carefully into the
test-bottle. Be sure not to drop any of the acid on your hands or your
clothes. As the acid is heavier than the milk, it will sink to the
bottom of the bottle. With a gentle whirling motion, shake the bottle
until the two fluids are thoroughly mixed. The mixture will turn a dark
brown and become very warm.

Now fill the other bottles in the same way with samples drawn from
different cows. Treat all the samples precisely as you did the first. Do
not forget to put on each sample the name of the cow giving the milk and
on each test-bottle a number corresponding to the name of the cow.

You are now ready to put the test-bottles in the sockets of the machine.
Arrange the bottles in the sockets so that the whirling frame of the
machine will be balanced. Fit the cover on the machine and turn the
handle slowly. Gradually gain in speed until the machine is whirled
rapidly. Continue the turning for about seven minutes at the speed
stated in the book of directions.

After this first turning is finished, pour enough hot water into each
test-bottle to cause the fat to rise to the neck of the bottle. Re-cover
the machine and turn for one minute. Again add hot water to each bottle
until all the fat rises into the neck of the bottle and again turn one
minute.

There remains now only the reading of the record. On the neck of each
bottle there are marks to measure the amount of fat. If the fat inside
the tube reaches only from the lowest mark to the second mark, then
there is only one per cent of fat in this cow's milk. This means that
the owner of the cow gets only one pound of butter-fat from each
hundred pounds of her milk. Such a cow would not be at all profitable to
a butter-seller. If the fat in another test-bottle reaches from the
lowest mark to the fourth mark, then you put in your record-book that
this cow's milk contains four per cent of butter-fat. This record shows
that the second cow's milk yields four pounds of fat to every hundred
pounds of milk. This cow is three times more valuable to a butter-maker
than the first cow. In the same way add one more per cent for each
higher mark reached by the fat. Four and one-half per cent