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104
Hot Milk.—Seven samples of hot milk, as served in restaurants, cafes,
etc., were submitted for analysis during the year, and of these no less than
five were found to be not genuine, either by reason of the abstraction of fat
or the addition of water.
Four prosecutions were successfully taken against the vendors of the
adulterated samples, and the attention of other vendors should be called to
the fact that milk may not be skimmed or contain water when sold as hot milk,
any more than when it is sold as cold milk.
It is, of course, well known that some of the fat in milk may be removed
in the form of skin when the milk is heated and poured off into a glass; but
the proportion that may unavoidably be removed in this way is comparatively
small, and would be taken into consideration before condemning a sample of
heated milk.
If a method of heating is adopted whereby a large amount of fat rises
and is separated as a skin, as, for example, if the milk is kept hot for some
hours in an urn without mixing and then drawn off from the bottom for serving,
the customer is obviously prejudiced by getting an article not of the quantity
demanded, and the method of heating should be improved.
Apart from the question of cream, added water was found in some of
the samples of heated milk, and in this connection a point of considerable
scientific interest arose.
It is widely known that natural variations occur in the composition of
milk and that the percentage of solids-not-fat in the milk from individual
cows and sometimes even from herds of certain breeds may occasionally fall
below 8.5; in such a case added water would be presumed under the Sale of
Milk Regulations to be present, and a prosecution might be taken against a
person who had sold poor but genuine milk.
Now, it has been shown that the secretion of fluids in the body of an
animal depends upon a factor known as their "osmotic pressure" and the
osmotic pressure of a particular fluid secreted by a particular animal must
accordingly, for physiological reasons, be a constant. As the freezing and
boiling points of solutions are related to their osmotic pressures, these properties
are also practically constant for a particular secretion, as, for example, cows'
milk; the exact determination of the freezing point of a sample of milk has
in the past been an extremely difficult matter, but the introduction in the
last few years of the Hortvet Cryoscope and the general adoption of a standard
technique, has made the accurate determination of a freezing point possible
for any qualified analyst.