QrA\T/TA T1VE AGRICULTURAL ANALYSIS
of the stoppered tube. Add 10 cc of 95-per cent alcohol and ink again.
Add 25 CT of dlivl t'ther, stopper the tube and shake vigorously for 30
M'ronds, tlien add 25 cr of petroleum ether (distilled below 60°) and stopper
siml shake again for 30 seconds. Let stand until the bubbles of air have
disappeared from die lower layer. Both layers should be clear and free
from suspended particles. Draw off most of the upper layer of ether-fat
solution by opening the stop cock and tipping slightly to make the separation
more complete, but without removing any of the lower layer. The fat
solution is run through a small (about 5 cm), dry filter, into a dried and
weighed fat flask. Repeat the extraction, using 15 cc of each ether as
before. Wash the tip of the outlet tube, the funnel and the filter with a
small amount of the ether mixture, then evaporate the ether from the fat
and ether mixture.
Dry the flask at 100°, coo! and weigh. Calculate the per cent of fat in
the sample.
Babcock Method.—This method is rapid and convenient for
genera! dairy control testing. The test is based upon the fact
that concentrated sulphuric acid will dissolve all proteins in
milt or cream and thus enable the fat to separate when whirled
rapidly in a centrifuge. When the acid is added to the milk,
the casein, is first precipitated and then dissolved in the excess of
acid. The solution darkens because of the charring of the milk
sugar, due to the heat of reaction.
It is important that the acid should have a specific gravity
of 1,82 to 1.83. If the acid is too dilute the fat will have a white
appearance with gray particles beneath it, while if too concen-
trated the fat Trill be dark colored with black charred particles
beneath. The temperature of the fat should be about 60°
(140° F.) when the fat reading is made. Appreciable errors will
result from volume changes if the temperature of reading is
allowed to vary more than 10° (18° F.) either way. The fat
should have a clear, golden 3rellow color and it should be separated
clearly from the chocolate-colored acid solution beneath.
Standard Babcock Test Bottles.1—The standard Babcock test
bottles for milk and cream are as follows:
1. Eigkt-per cent, 18-gram, 6-ni. Milk Test Bottle.—The total
per cent graduation is 8. The total height of the bottle is 150
to 165 mm. The capacity of the bulb up to the junction with
the neck is not less than 45 cc. The graduated portion of the
neck has a length of not less than 63.5 mm, and the neck 19
1 Assoc. Off. Agr. Chemists, "Methods of Analysis/' 227 (191S).