ZAL R. KOTHAVALLA, J. S. BHALLA & N. D. LAVANGIA 11
Eighty-five determinations were made on samples of buffalo's milk adul-
terated with 5, 10, 20 and 50 per cent water, in order to determine to what
extent adulteration percentage calculated by various methods from the freez-
ing'point of watered samples agreed with the true figure. The percentage of
added water was calculated by employing the formula of Hortvet [1921],
both by using the actual value obtained for unwatered and watered samples
and by taking the freezing point of unwatered milk as —0.530°C. These
results were also compared with the values obtained from the tables of Winter
[1914] and Leather [1914]. It was observed that in practically all cases the
difference never exceeded 2 to 3 per cent by Leather method. It was reduced
to about half a per cent when calculated according to Leather's method.
The freezing point of separated milk was found to be the same as that of
the whole milk from which it was obtained. Pasteurized milk (flash method,
175°F.) showed a very slight depression of about —0.005°C. in the freezing-
point and in some cases no change was observed. In the case of milk subject-
ed to first boil the range of depression observed was from —0.025° to —0.030°C.
Two drops of saturated aqueous mercuric perchloride solution added to 100
ml. of milk were found sufficient to preserve a sample for the determination
of freezing point for 24 hours. With larger amounts the samples could be
kept for as long as two weeks without any change occurring, beyond an initial
fall of about —0.005°C. in the freezing point. Other preservatives which
were tried failed to give satisfactory results.
Freezing point determinations were made on the foremilk and strippings,
as well as on milk obtained from stripper cows and it was found that the values
remained within the normal range of whole milk in all such cases.
A preliminary study of the day to day variations in the freezing point of
milk of individual animals showed that the value did not remain constant,
but sometimes varied by as much as 0.030°C. in 24 hours. In spite of these
variations the values were no doubt within normal limits. This fact is of
considerable significance when one considers the very small number of animals
kept by the average milkman in this country.
In conclusion it might be said that provided the freezing point determina-
tions are made on fresh samples no other test offers a more reliable indication
of the genuineness or otherwise of a milk sample than the freezing point
determination and this method is therefore recommended as a routine standard
test, both for cow and buffalo milk. The freezing point is useful not only for
confirming the addition of water, but also for proving the purity of genuine
milk when the solids-not-fat fall below minimum legal limits.
REFERENCES
Andrew, R. L. (1929). Analyst, 54, 210
Elsdon, G. D. and Stubbs, J. R. (1931). J. Soc. Chem. Ind. 50, 135T
—
(1933). Analyst, 58, 7
Handbook of the Association of Official Agri. Chemists, 1940
Hortvet, J. (1921). Ind. Eng. Chem. 13, 198
Keister, J. T. (1917). Ind. Eng. Chem. 9, 862
Leather, J. W. (1914). Analyst, 39, 432
Parker, A. J. and Spackman, L. S. (1929). Analyst, 54, 217
Winter, T. (1914). Chem. News 170, 283