2                  Freezing Point Test for Buffalo's and Cow's Milk

                                    EXPERIMENTAL

Apparatus and method used for the determination of the freezing point of
milk.—A Beckmann freezing point apparatus as described by Andrew [1929]
was employed. This is a simple instrument capable of giving accurate and
reproducible results. In this apparatus the tube containing milk is separated
from the cooling mixture of ice and salt by an air space. Two thermometers
are used, the control and the regular. The latter, of Beckmann type, is gradu-
ated to hundredth of a degree centrigrade and it can be read to half a gradua-
tion. It is checked repeatedly at regular intervals by determining the freez-
ing point of fresh glass distilled water and chemically pure sucrose solution.

For the determination of the freezing point, the sample under test was
supercooled to —2°C. in a separate vessel and the tube containing the milk
was then wiped dry and transferred to the main apparatus. Stirring was
continued at an even rate. The mercury column after falling steadily suddenly
jumped up and remained constant for some time at a figure which was taken
as the freezing point.

This method was applied to a large number of samples of genuine milk
and then tested under various conditions of adulteration likely to occur in
practice as described below.

(i) Freezing point of cow's and buffalo's milk.—One hundred and fifty
samples of buffalo's milk and fifty of cow's milk were examined. The buffalo's
milk was obtained from animals of Murrah breed, that of cow's from Sindhi,
Gir and cross-bred animals. A few samples of buffalo's milk obtained from
animals kept under average village conditions were also included. All the
determinations on them were made within two or three hours of the milk being
drawn and for this the samples were kept in a cool and clean place to ensure
their remaining perfectly sweet. It was previously observed that at the pre-
vailing temperature (about 80°F.) no rise in acidity occurred until about six
hours after milking. The determinations were made on morning milk in the
case of buffaloes and on evening milk in the case of cows. A summary of
these results is given in Table I showing clearly the variations observed.

                                                                    TABLE I

                                                   Freezing point of buffalo's and cow's milk