The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1838-10-12 00:00:00

LIVERPOOL MECHANICS' INSTITUTION.

LECTURES ON CHEMISTRY, AS APPLIED TO THE ARTS.

On Saturday evening Dr. Kane delivered his fourth lec-
ture, upon the manufacture of glass and porcelain.
The substances used in the manufacture of glass and por-
celain, are metals united with oxygen; but their affinity for
it is so strong and powerful, that under all circuinstauces
they exist in nature in an oxydized form, and it is one of the
most difficult of chemical operations to separate them from
oxygen, so as to exhibit them in an uncombined form. he
substances which I allude to are the alkaline bases and the
base of silica, the metallic properties of which may be some-
what doubted, but which agree with those of the others;
therefore I have no hesitation in classing it as a metal. The
chemists of former days considered that there were only three
alkalies, and that they belonged to the three different king-
doms, namely, the vegetable, mineral, and the animal. The
vegetable alkali was potash, so called from its being derived
in large quantities from the ashes of vegetables; soda was
called the mineral alkali, in consequence of its existing in
large quantities in salt; and ammonia, in consequence of its
being an animal, product, was called the animal alkali, or
the volatile alkali, because of its gas-like form when uncom-
blued. At present we shall have nothing to do with ammo-
nia, but with potash and soda. The names which were given
to these alkalies are not correct; because potash, although
the most abundant source of it is the ashes of wood, yet it is
also found in felspar and a great variety of minerals con-
tained in the earth. In like manner, soda is found to exist
in all vegetables which grow in the neighbourhood of the
sea, and even at considerable distances from the sea, pro-
vided they are exposed to winds which pass over the sea.
Whole classes of marine plants, growing upon the shores
where they are washed by the waters of the ocean, contain
a great quantity of common salt; and by the collection and
the burning of these plants, were obtained the different vari-
eties of kelp and barilla, which, in the less advanced state of
science, gave to the manufacturers their whole amount of
soda. One of the most remarkable steps made in science
was by Sir flumphry Davy, when he discovered that the
alkalies were but peculiar combinations of various metals
with oxygen, metals possessing characteristics so totally dif-
ferent from those which we are accustomed to expect, that
at first sight it can be very well understood how they were
not sooner discovered. 'We find that they are the lightest
bodies in nature, and difficult to preserve; we shall likewise
find them to be amongst the most tender substances with
which we have to deal. In accordance with-the rule which
I laid down at the commencement of these lectures, I shall
not dwell upon the means of preparing these substances,
because they are merely of use in a scientific point of view,
the manufacturer never preparing potassium for his opera-
tions. _ .

Potassium is lighter than water, and its colour is a pale
blue, somewhat inferior in brilliancy to silver. When cut, it
presents a very beautiful metallic appearance, but it speedily
becomes covered over with a white crust, which is potash.—
In fact, so great is its affinity for oxygen, that we are obliged
to keep it in naptha, a substance which contains no oxygen.
When placed upon the surface of water its action is most
violent, as it decomposes the water, unites with its oxygen,
and sets fire to its hydrogen, which burus with a vivid, violet-
coloured flame. Potassium melts when heated, and if heated
in contact with the atmosphere it burns,and is converted into
potash; but at ordinary temperatures it combines with the
oxygen of the atmosphere without any appearance of flame.
When forty grains of potassium are converted into potash
they will absorb eight of oxygen, so that forty-eight is taken
as the equivalent of potash which unites with the different
acids. Potassium will burn with great rapidity and splen-
dour in oxygen, although it will not do so in atmospheric air,
owing to the oxygen of the atmosphere causing a crust of
potash to surronad it, which defends it from further oxidation
of a sufficiently rapid nature to suppoir combustion. The
product of its combination with oxygen we have stated to be
potash. In order to prepare potash we get the potash of com-
merce, which is combined with carbonic acid, and by dissolv-
ing it with lime and crystallizing it, we obtain the dry caus•
tic potash of the shops. AlthoUgh considered as dry, yet in
strict chemical language it is not so, as it contains a quantity
of water of crystallization, which cannot be expelled. The
alkaline properties of potash are readily shown by its brown-
ing turmeric paper and turning red cabbage liquor green.
The second substance, sodium, is derived from the alkali