ring like a
mixture of grease and water, and produce no foam, or but very little.
Genuine butter boils with less noise and produces an abundance of foam.

Waterhouse Test.--Into a small beaker pour 50 cc. of sweet milk. Heat
nearly to boiling and add from 5 to 10 gms. of butter or oleomargarine.
Stir with a glass rod until fat is melted. Then place the beaker in cold
water and stir the milk until the temperature falls sufficiently for the
fat to congeal. At this point the fat, if oleomargarine, can easily be
collected into one lump by means of the rod; while if butter, it will
granulate and cannot be collected.

(From Farmers' Bul. 131, U. S. Dept. of Agriculture.)

1. Name two simple tests for distinguishing butter and oleomargarine. 2.
Describe these tests. 3. Why do butter and oleomargarine respond
differently to these tests? 4. Are these tests based upon chemical or
physical properties of the fats?

Experiment No. 20

Testing for Watering or Skimming of Milk

_a._ Fat Content of Milk by Means of Babcock Test.--Measure with
pipette into test bottle 17.6 cc. of milk. Sample should be carefully
taken and well mixed. Measure with cylinder 17.5 cc. commercial
H_{2}SO_{4} and add to milk in test bottle. (See Fig. 25.) Mix acid and
milk by rotating the bottle. Then place test bottles in centrifugal
machine and whirl 5 minutes. Add sufficient hot water to test bottles to
bring contents up to about the 8th mark on stem. Then whirl bottles 2
minutes longer and read fat. Read from extreme lowest to highest point.
Each large division as 1 to 2 represents a whole per cent, each small
division 0.2 of a per cent.

_b._ Determining Specific Gravity by Means of Lactometer.--Pour 150
cc. of milk into 200 cc. cylinder. Place lactometer in milk and note
depth to which it sinks as indicated on stem. Note also temperature of
milk. For each 10 deg. above 60 deg. F. add 1 to the lactometer number,
in order to make the necessary correction for temperature. For example, if
milk has sp. gr. of 1.032 at temperature of 70 deg., it will be equivalent
to sp. gr. of 1.033 at 60 deg. Ordinarily milk has a sp. gr. of 1.029 to
1.034. If milk has sp. gr. less than 1.029, or contains less than 3 per
cent fat, it may be considered watered milk. If the milk has a high sp.
gr. (above 1.035) and a low content of fat, some of the fat has been
removed.

(For extended direction for milk testing see Snyder's "Dairy Chemistry.")

Experiment N