The finest river silt, carefully separated from all the coarser
particles, and mixed with water, so as to have the consistency of
cream, is poured into the paper cylinder by small portions at a
time, carefully shaking the plant a little after each addition,
in order that its leaves may be covered, and that no bubbles of
air may be left. The plant and its mould are now allowed to dry,
and the yielding nature of the paper allows the loamy coating to
shrink from the outside. When this is dry it is surrounded by a
coarser substance; and, finally, we have the twig with all its
leaves embedded in a perfect mould. This mould is carefully
dried, and then gradually heated to a red heat. At the ends of
some of the leaves or shoots, wires have been left to afford
airholes by their removal, and in this state of strong ignition a
stream of air is directed into the hole formed by the end of the
branch. The consequence is, that the wood and leaves which had
been turned into charcoal by the fire, are now converted into
carbonic acid by the current of air; and, after some time, the
whole of the solid matter of which the plant consisted is
completely removed, leaving a hollow mould, bearing on its
interior all the minutest traces of its late vegetable occupant.
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