Familiar Letters on Chemistry | Page 9

varies with different kinds of charcoal: it is
possessed in a higher degree by those containing the most pores, i.e.
where the pores are finer; and in a lower degree in the more spongy
kinds, i.e. where the pores are larger.
In this manner every porous body--rocks, stones, the clods of the fields,
&c.,--imbibe air, and therefore oxygen; the smallest solid molecule is
thus surrounded by its own atmosphere of condensed oxygen; and if in
their vicinity other bodies exist which have an affinity for oxygen, a
combination is effected. When, for instance, carbon and hydrogen are
thus present, they are converted into nourishment for vegetables,--into
carbonic acid and water. The development of heat when air is imbibed,

and the production of steam when the earth is moistened by rain, are
acknowledged to be consequences of this condensation by the action of
surfaces.
But the most remarkable and interesting case of this kind of action is
the imbibition of oxygen by metallic platinum. This metal, when
massive, is of a lustrous white colour, but it may be brought, by
separating it from its solutions, into so finely divided a state, that its
particles no longer reflect light, and it forms a powder as black as soot.
In this condition it absorbs eight hundred times its volume of oxygen
gas, and this oxygen must be contained within it in a state of
condensation very like that of fluid water.
When gases are thus condensed, i.e. their particles made to approximate
in this extraordinary manner, their properties can be palpably shown.
Their chemical actions become apparent as their physical characteristic
disappears. The latter consists in the continual tendency of their
particles to separate from each other; and it is easy to imagine that this
elasticity of gaseous bodies is the principal impediment to the operation
of their chemical force; for this becomes more energetic as their
particles approximate. In that state in which they exist within the pores
or upon the surface of solid bodies, their repulsion ceases, and their
whole chemical action is exerted. Thus combinations which oxygen
cannot enter into, decompositions which it cannot effect while in the
state of gas, take place with the greatest facility in the pores of platinum
containing condensed oxygen. When a jet of hydrogen gas, for instance,
is thrown upon spongy platinum, it combines with the oxygen
condensed in the interior of the mass; at their point of contact water is
formed, and as the immediate consequence heat is evolved; the
platinum becomes red hot and the gas is inflamed. If we interrupt the
current of the gas, the pores of the platinum become instantaneously
filled again with oxygen; and the same phenomenon can be repeated a
second time, and so on interminably.
In finely pulverised platinum, and even in spongy platinum, we
therefore possess a perpetuum mobile--a mechanism like a watch which
runs out and winds itself up--a force which is never

exhausted--competent to produce effects of the most powerful kind,
and self-renewed ad infinitum.
Many phenomena, formerly inexplicable, are satisfactorily explained
by these recently discovered properties of porous bodies. The
metamorphosis of alcohol into acetic acid, by the process known as the
quick vinegar manufacture, depends upon principles, at a knowledge of
which we have arrived by a careful study of these properties.

LETTER III

My dear Sir,
The manufacture of soda from common culinary salt, may be regarded
as the foundation of all our modern improvements in the domestic arts;
and we may take it as affording an excellent illustration of the
dependence of the various branches of human industry and commerce
upon each other, and their relation to chemistry.
Soda has been used from time immemorial in the manufacture of soap
and glass, two chemical productions which employ and keep in
circulation an immense amount of capital. The quantity of soap
consumed by a nation would be no inaccurate measure whereby to
estimate its wealth and civilisation. Of two countries, with an equal
amount of population, the wealthiest and most highly civilised will
consume the greatest weight of soap. This consumption does not
subserve sensual gratification, nor depend upon fashion, but upon the
feeling of the beauty, comfort, and welfare, attendant upon cleanliness;
and a regard to this feeling is coincident with wealth and civilisation.
The rich in the middle ages concealed a want of cleanliness in their
clothes and persons under a profusion of costly scents and essences,
whilst they were more luxurious in eating and drinking, in apparel and
horses. With us a want of cleanliness is equivalent to insupportable
misery and misfortune.

Soap belongs to those manufactured products, the money value of
which continually disappears from circulation, and requires to be
continually renewed. It is one of the few substances which are entirely
consumed by use, leaving no