We have up to now (he writes) understood by organised matter something
of which _carbon_, combined with hydrogen, nitrogen, and other
elements, is the principal chemical component. Carbon is the essential
constituent; organic chemistry is the chemistry of carbon. We do
not know any other substance which would allow of such an array of
combinations, but the possibility of such a body cannot be denied.
While on Earth all life is bound up with carbon compounds, one may
suppose that in entirely different circumstances another element
might show itself capable of supporting the conditions of life in
combinations which might resist greater heat without decomposition or
greater cold without becoming torpid. A few years ago we seemed to be
on the track of something like that. _Silicon_ is the element
which has the greatest chemical analogy to carbon, and in combination
with oxygen it is found in enormous quantities in the form of silica,
and all its combinations have very characteristic properties. Just as
in organic matter every being forms itself into cells by fission or
conjugation, so also can we produce from combinations of silicic acid a
cell from which under our eyes an object develops which has a vegetable
appearance. This experiment, easy to make, is perhaps unknown to many
of our readers, and therefore we must say a little more about it.
Most combinations of silicic acid with metals are insoluble in water.
Some, however, and especially a combination with potassium known by the
name of water-glass, occurs in a soluble form. If into such a solution
we introduce a small quantity of any soluble metallic salt such as
chloride of copper or silver nitrate, decomposition takes place and the
chloride of copper is converted into silicate of copper and chloride of
potash. A very curious phenomenon then takes place. At the moment when
the first traces of the metallic salt are dissolved, the decomposition
mentioned above takes place and the molecule of salt is covered with
an extremely fine skin of insoluble silicate. It is across this skin
that the liquids are then exchanged by a process of osmosis which, as
we know, plays a great part in the life of plants and animals and which
here takes place as follows: