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In the first case the solids-not-fat shows the presence of at least 6.2 per
cent. added water, while the freezing point shows none and points to the
possibility of the deficiency being due to natural causes. In the second case
the maximum of added water is obtained in both methods of calculation. In
the third case no added water is indicated by either test, although 6.2
per cent. is actually present. In the fourth case the solids-not-fat figure
satisfies the Regulations though 6.6 per cent. of added water is shown to be
present by the freezing point. The last example shows the necessity of
carrying out freezing point determinations although the sample is apparently
satisfactory from the chemical analysis.
Recently convictions have been obtained on the freezing point only, and
this figure is being accepted at the Thames Police Court. There is one
difficulty, however. In the case of any dispute as to the figure, the third part
of the sample could not be examined as the freezing point determination is only
correct when carried out on fresh milk. The above figures show that the
detection of about 5 per cent. of added water may be a matter of chance.
At any rate, the full amount present would rarely be detected, and, in my
opinion, in those cases where added water is definitely detected the amount
should be calculated from an average and not from a minimum figure. The
figures also show why the calculation of added water by both methods is
seldom likely to give the same figure.
Although wide variations are shown in the above hypothetical figures,
on an average the disagreement is not great. Out of 20 adulterated and poor
quality samples examined during the year, 11 samples gave by the Hortvet
calculation from 0.3 to 2.6 per cent. higher, and 9 samples from 0.1 to 1.8 per
cent. lower than the figure calculated from the 8.5 basis. The latter samples
were mainly obtained in those months in which the solids-not-fat is low, that
is, nearer to the minimum of 8.5 per cent. Both methods of calculation, of
course, give only the least amount of added water present, the Hortvet method
having the great advantage of proving that the milk is definitely adulterated
and not naturally deficient in solids-not-fat.
Notes on Table D.
In the case of sample X 113, which contained 5.2 per cent. of added
water, the defence produced a certificate of analysis showing a figure of 8.4
per cent. for the solids-not-fat and stating that the sample was "of poor
quality and doubtful purity."