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Hospital, 47 samples of milk were taken on delivery for chemical examination from
etc., 6 institutions in the Borough. All the samples were genuine. The average
Samples. composition of the milk was:—Fat 3.49 per cent. and solids-not-fat 8.70 per
cent.
School 110 samples of milk were taken on delivery at 75 schools in the Borough.
Samples. of these samples 13 were reported as being of poor quality and two samples
were found to be adulterated. The average composition of all the samples
was:—Fat, 3.47 per cent, and solids-not fat 8.60 per cent.
The Hortvct The determination of the freezing point of milk by means of the Hortvet
Ctyoscope. apparatus, affords useful information in doubtful and other cases of adulteration.
The method is based on the fact that the freezing point of milk depends
on the osmotic pressure and as the osmotic pressure is for biological reasons
practically constant, the freezing point of genuine milk varies only within a
limited range.
The freezing point of milk which is naturally deficient in solids-not-fat will
fall within this range. It therefore becomes possible to say definitely from the
freezing point, without reference to the presumptive standard of 8.5 per cent.
solids-not-fat that a milk containing an appreciable amount of added water,
has been adulterated.
The freezing point of milk is unaffected by sterilisation, pasteurisation or
variations in the percentage of milk fat but the method can only be used when
the milk is fresh; a preservative solution of a certain strength can however be
added so as to keep the sample sufficiently long for a determination to be
made.
The freezing point of milk as determined by means of the Hortvet
apparatus ranges from —0.535°C to — 0.560°C, an extreme difference of onefortieth
of a degree, A depression of less than 0.530°C may be regarded as
definite proof of adulteration.
Some of the results obtained are given below; an average figure of 0.54°C
has been taken as a basis for calculation.