(seq. 47)

38

Materia Alimentaria

Milk

corodes copper which it does not when sweet, from these facts I
am induced to believe the rancidity is owing to the presence of
an acid. During the process of churning I believe there is a
disengagement of carbonic acid, owing to a decomposition
of the milk. The Hottentots make their butter by pouring
their milk into leather bags made for the purpose and
shaking them until the butter is found. Sugar and Nitre
preserve it sweet for a long time, the acid found in butter
is the sebacic. Mr Russell tells of a plant in India which
deprives butter of its rancidity and when mixed with it
preserves it. Rennet is very often used to coagulate milk. Dr
Young thought this not to depend on an acid, for when
mixed with Volatile Alkali it still preserves this property, also
the liver and heart of a turkey, some live fish have this
property which they loose when dead, some vegitables will
likewise coagulate milk. The milk of herbivorous animals
is coagulated by the nitrous acid but that of the
carnivorous is not. Rennet I think coagulates milk by the acid
it contains, by the same means do children coagulate
milk, many authors suppose milk to be only renovated chyle,