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75
The freezing point of milk as determined by means of the Hortvet
apparatus ranges from —0.530° C. to —0.560° C. and the freezing points of
all normal samples and of those naturally deficient in solids-not-fat will fall
within this range. When the milk is adulterated with water the depression
of the freezing point is lessened, and it is therefore possible to say definitely
that the sample has been adulterated, and that the deficiency of solids-notfat
is not due to any abnormality.
Unfortunately, owing to the range of freezing points in genuine milk the
method may not always detect small amounts of added water, as a sample
of freezing point —0.560° C. could be watered down to —0.530° C. and would
still be regarded as genuine.
In America, where the method is official, the added water is calculated on
an average figure of —0.55° C. and a tolerance of 3 percent. of added water
allowed unless this figure is exceeded; this is the same as fixing a limit figure
of —0.533° C., with the advantage that the amount of added water so
calculated will more nearly agree with the actual amount added than if the
limiting figure of —0.533° C. had been taken as a basis of calculation.
In the following table a freezing point of —0.530 ° C. has been used as
the basis, and the figures so obtained represent the least amount of added
water present in the sample.
Freezing
point of
Milk