The nature of the
black compound produced was examined by putting portions of it into
cylindrical jars, and observing the changes which they experienced
with respect either to the formation of mould, the deposition of their
contents, or any change of colour. The fluids were also compared by
dropping portions of them upon white tissue paper, in which way both
their colour and their consistence might be minutely ascertained. A
third method was, to add together the respective infusions, and the
solutions of the sulphate of iron, in a very diluted state, by which I
was enabled to form a more correct comparison of the quantity, and of
the state of the colouring matter, and of the degree of its solubility.
The practical conclusions that I think myself warranted in drawing
from these experiments, are as follow:--In order to procure an ink
which may be little disposed either to mould or to deposit its contents,
and which, at the same time, may possess a deep black colour, not liable
to fade, the galls should be macerated for some hours in hot water, and
the fluid be filtered; it should then be exposed for about fourteen days
to a warm atmosphere, when any mould which may have been produced must
be removed.
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