Familiar Letters on Chemistry | Page 7

trace of
iron. Nothing could be discovered in it of the nature of a pigment,
nothing to which its blue colour could be referred, the cause of which
was searched for in vain. It might therefore have been supposed that the
analyst was here altogether at fault, and that at any rate its artificial
production must be impossible. Nevertheless, this has been
accomplished, and simply by combining in the proper proportions, as
determined by analysis, silica, alumina, soda, iron, and sulphur.
Thousands of pounds weight are now manufactured from these
ingredients, and this artificial ultramarine is as beautiful as the natural,
while for the price of a single ounce of the latter we may obtain many
pounds of the former.
With the production of artificial lapis lazuli, the formation of mineral
bodies by synthesis ceased to be a scientific problem to the chemist; he
has no longer sufficient interest in it to pursue the subject. He may now
be satisfied that analysis will reveal to him the true constitution of
minerals. But to the mineralogist and geologist it is still in a great
measure an unexplored field, offering inquiries of the highest interest
and importance to their pursuits.
After becoming acquainted with the constituent elements of all the
substances within our reach and the mutual relations of these elements,
the remarkable transmutations to which the bodies are subject under the
influence of the vital powers of plants and animals, became the

principal object of chemical investigations, and the highest point of
interest. A new science, inexhaustible as life itself, is here presented us,
standing upon the sound and solid foundation of a well established
inorganic chemistry. Thus the progress of science is, like the
development of nature's works, gradual and expansive. After the buds
and branches spring forth the leaves and blossoms, after the blossoms
the fruit.
Chemistry, in its application to animals and vegetables. endeavours
jointly with physiology to enlighten us respecting the mysterious
processes and sources of organic life.

LETTER II

My dear Sir,
In my former letter I reminded you that three of the supposed elements
of the ancients represent the forms or state in which all the ponderable
matter of our globe exists; I would now observe, that no substance
possesses absolutely any one of those conditions; that modern
chemistry recognises nothing unchangeably solid, liquid, or aeriform:
means have been devised for effecting a change of state in almost every
known substance. Platinum, alumina, and rock crystal, it is true, cannot
be liquified by the most intense heat of our furnaces, but they melt like
wax before the flame of the oxy-hydrogen blowpipe. On the other hand,
of the twenty-eight gaseous bodies with which we are acquainted,
twenty-five may be reduced to a liquid state, and one into a solid.
Probably, ere long, similar changes of condition will be extended to
every form of matter.
There are many things relating to this condensation of the gases worthy
of your attention. Most aeriform bodies, when subjected to
compression, are made to occupy a space which diminishes in the exact
ratio of the increase of the compressing force. Very generally, under a
force double or triple of the ordinary atmospheric pressure, they

become one half or one third their former volume. This was a long time
considered to be a law, and known as the law of Marriotte; but a more
accurate study of the subject has demonstrated that this law is by no
means of general application. The volume of certain gases does not
decrease in the ratio of the increase of the force used to compress them,
but in some, a diminution of their bulk takes place in a far greater
degree as the pressure increases.
Again, if ammoniacal gas is reduced by a compressing force to
one-sixth of its volume, or carbonic acid is reduced to one thirty-sixth,
a portion of them loses entirely the form of a gas, and becomes a liquid,
which, when the pressure is withdrawn, assumes again in an instant its
gaseous state--another deviation from the law of Marriotte.
Our process for reducing gases into fluids is of admirable simplicity. A
simple bent tube, or a reduction of temperature by artificial means,
have superseded the powerful compressing machines of the early
experimenters.
The cyanuret of mercury, when heated in an open glass tube, is
resolved into cyanogen gas and metallic mercury; if this substance is
heated in a tube hermetically sealed, the decomposition occurs as
before, but the gas, unable to escape, and shut up in a space several
hundred times smaller than it would occupy as gas under the ordinary
atmospheric pressure, becomes a fluid in that part of the tube which is
kept cool.
When sulphuric acid is poured upon limestone in an open vessel,
carbonic acid escapes with