The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1838-10-02 00:00:00

LIVERPOOL MECHANICS' INSTITUTION.

LECTURES ON CHEMISTRY APPLIED TO THE ARTS.

On Saturday evening, Dr. Robert Kane, A1.R.1.A., de-
livered his second lecture, upon the processes and substances
employed in bleaching.
On Wednesday evening, said the lecturer, owing to the
breakage of the stopper of a bottle in which sulphuret of car-
bon was contained, I was obliged to omit a little experiment
which was connected with our subject, therefore before com-
mencing this evening's lecture I will bring it before you. 1
have here a glass jar filled with nitric oxide, lot') which I
shall pour a little of the sulphuret of carbon, and apply a
taper to the mixture, o hen it will instantly ignite, and pro-
duce a flame of an exceedingly beautiful blue colour, and the
interior surface of the jar become coated with a deposit of sul-
phur. Sulphuret of carbon is composed of sulphur and char-
coal, of which the latter enters into combination with the ni-
tric oxide during combustion, and the former is disengaged
in a pure form.
I have to-night to bring before you the process used in one
of the most important branches of art—that of bleaching, by
which we are enabled to deprive various fabrics of their co-
louring matters and other impurities with which they are
combined. In the natural condition of wool, flax, cotton,
and silk, they are contaminated with foreign matters which
are not absolutely colourless, and in the passage of these ar-
ticles from the natural condition of their texture to their ul-
timate state, it is necessary to withdraw all such substances
as are calculated to injure their appearance. We are there-
fore obliged to bleach them in order to make them white.
The operation of bleaching is, in fact, analagous to or-
dinary combustion. It is less perfect and rapid, but we do
not violate the rules of scientific reasoning when we state
that we may reduce its operations to the state of a slow com-
bustion. In place of the whole of the material being burned,
we arrange matters so cautiously that the foreign impurities
only are burned away and consumed, whilst the vegetable
or animal fibres remain as nearly as possible uninjured. We
have in the science of bleaching a very nice office to perform.
It is necessary for the bleacher to arrange his materials as
nearly as possible in strength so as to eat away the colouring
matter only, and yet to leave the fibre undestroyed. This
is a very difficult art to obtain, and it has only been by the
great advancement of science that the present perfection of
bleaching has been arrived at.

In the infancy of the art of bleaching the processes were
of the most lengthened nature, in consequence of which the
manufacturer had to employ an infinitely greater amount of
capital than is now necessary. He was likewise subjected
to meteorological and atmospher►cal influences, by which the
process was limited to those countries in which the atmosphere
was favourable But when the present system was discovered,
the manufacturer became altogether independent of local in-
fluences, and if he understood the principles of the science
was enabled to bleach himself.

The most important substance employed in the operation of
bleaching is water. Flom the earliest periods of philosophy,
water was ranked as one of the elements; and we must look
upon the discovery of its true composition, by Cavendish, to
be one of the greatest discoveries in science which has ever
been made. This philosopher proved, by several conclusive
experiments, that it was a combination of oxygen and hydro-
gen. In order to obtain pure hydrogen, we have recourse to
a vast variety of methods, all of which, however, are based
upon the decomposition of water, and the abstraction of its
oxygen. 'l'he constituents of water are bound together with
a very powerful force; but if we bring water into contact
with some substance which has a greater attraction foroxygen
than hydrogen, decomposition will be effected, and the hy-
drogen set free. The most beautiful illustration of this is by
means of the metals sodium and potassium; but for practical
purposes, hydrogen is obtained through the decomposition of
water, by means of iron or zinc. Hydrogen itself does not
enter into the processes of the arts, and therefore we shall not
dwell long upon it. Like the atmospheric air, it is com-
pletely colourless; but it differs from it inasmuch as it is re-
markably combustible, and it extinguishes flame; that is to
say, it will not allow any body to burn in it. Hydrogen gives
out very little light, but very great heat. If perfectly pure,
its flame will be almost invisible. In order to show the little
light which.hvdrogen gives out, it is only necessary to take
a jar full, and apply a light to it, and you will perceive that
it will inflame with a slight explosion, and that the inte-
rior of the glass will be covered with dew, resulting from the
burning of the hydrogen. It is specifically the lightest body
in nature. If we take a gallon of hydrogen, we shall find
that it will weigh less than the same quantity of any other
substance. On account of this principle it is applied to bal-
loons, which it raises through the atmosphere upon the same
principle by which a cot k rises to the surface of water. This
levity of hydrogen is completely illustrated by the manner in
which it burns. Thus, when the jar is inverted, it takes fire
with a flash, and the flames rapidly ascend ; but if the jar is
inflamed beneath, the gas burns slowly at the mouth until the
whole of it is consumed, the interior of the jar, in the mean-
while, remaining full of the hydrogen. The composition of
water might be proved by a very great variety of experi-
ments. It consists of oxygen and hydrogen. Thus, if we
take zinc, it has a snore powerful affinity fur oxygen than
hydrogen, and the hydrogen is liberated, and we can set
fire to it. if we simply take water and zinc, we shall
have a very small quantity of hydrogen. The oxide of
zinc is a very white powder, and it forms a varnish over
time zinc, so as to prevent the further action of the water
upon it ; but if we take a little sulphuric acid, it will unite
with the oxide of zinc, and keep the metal clear, so that
the action of the water upon it will go on constantly. By
lighting the hydrogen as it issues from a small glass tube,
and placing a larger tube over the jet, sve shall observe
two phenomena. The external tube will have its interior
surface bedewed with water, anti we shall hear a remarkable
sound, which varies with the diameter of the tube employed.
The phenninena of flame are very remarkable : the gas by
which it is produced mixes with the atmospheric air sur-
rounding the point from whence it issues, and its combus-
tion is accompanied by a series of explosions. In fact, all
bete is made up out of a number of petty explosions so
rapidly succeeding each other, that our ear become accus-
touted to them. But if we confine the combustion of gas
within a given column of air, these explosions cause it to
vibrate in the same manner as the air in the tube of an
organ. The consequence of this is, that you might take a
number of tubes and construct an organ by means of the
ignition of hydrogen gas; indeed, several philosophers of
Germany have done so. The flame of hydrogen in oxygen
has been employed for the purposes of intense heat and light,
under the name of the oxyhydroeen jet. The season why
hydrogen produces so little lig,ht is, because its products are
gt.se,,os; but it au, au:id 60• I,•
•we shall find
that the flame becomes immensely bright. Experiments of
this kind can be usefully carried on by a little instrument
called the oxyhvdrogen blow-pipe. In order to show the
great necessity for caution in affairs of this kind, I shall in-
flame a mixture of the two gases in the proportions in which
they are calculated to afford the greatest light and heat.—
[Dr. Kane then set fire to the contents of a small bladder,
which exploded with fearful violence.]—Nlany accidents have
occurred to chemists enraged in these kind of experiments,
from the explosion of large quantities of mixed gases. It is
evident, that if so powerful an explosion can ensue from the
combustion of such a small amount of gas, that a very great
explosion must accompany the combustion of a large quan-
tity. The most convenient and the safest anode of using
these gasses, is by means of a blow-pipe, invented by Mr.
Hemming, a geutleman who has distinguished himself by se-
veral very remarkable improvements in chemistry. 'lhe
mixed gases pass from a bladder through a cylinder, tightly
stuffed with a great number of the finest wires. Where three
of these wires touch there is a small triangular tube formed. '
Now, no body can inflame unless it is above a red heat;
therefore, if we can take any bony which is on fire and cool
it below redness, the flame will be extinguished. lithe flame
of the gas attempts to pass through these tubes it will be di-
vided into a number of small jets, and in passing through be
cooled by contact with such a mass of cold metal, and ex-
tinguished. Admitting, however, for argument, that the
flame did pass through, it could do no serious injury beyond
exploding the small bladder. By means of the hydrogen
blow-pipe we can burn iron wire with amazing brilliancy. In
this way a heat can be obtained far exceeding the most vio.
lent which can be excited in our most powerful furnaces
By urging the flame of these gases upon a piece of lime, we
can produce a light almost rivalling in intensity the solar
rays, which has been applied by Lieutenant Drummond to
the illumination of light-houses. Thus we see that the flame
of the oxyhydroe'en blow-pipe has been applied to two of the
most important put poses for which flame is required.
The process of moistening fabrics, and exposing them to
the atmosphere, required to be practised over and over again
for a considerable period before the requisite degree of white-
ness was obtained. Now water consists of eight parts of
oxygen gas and one part of hydrogen. Thus if we take nine
parts of water, we shall find eight of them to consist of oxy-
gen. But under peculiar circumstances the hydrogen is able
to take twice es much oxygen as it otherwise possesses, and
in this form is called the deutoxide of hydrogen. This sub
stance is characterised by some properties of an interesting
nature, of which I shall only be able to bring before you one
or two on the present occasion. It is characterised by the
great ease with which it gives out its additional dose of oxy-
gen; indeed, so readily does this take place, that it is with
difficulty we can preserve a quantity of oxygenated water for
any length of time. If we put into it a portion of the black
oxide of manganese, we shall find that bubbles of oxygen
are expelled, which may be collected at the top. Whenever
we expose water to the atmosphere, we find that it dissolves
a quantity of oxygen, and this is what gives to ordinary
going water its pleasing taste. If we boil water, this air is
expelled from it. In fact, water analyses the air, as it takes
from it the most salubrious principle, and allows the nitrogen
to remain behind. If we introduce any colouring matter
into this oxygenated water, we shall find that the oxygen
will go to the colouring matter. Thus' if we impart oxygen
to indigo, we destroy its colour; and there are few bodies
which do this more readily than oxygenated water. Water
is employed in Holland for the purpose of bleaching; but
the process is so slow that it requires six or seven months to
complete it. The office of the water is to take oxygen from
the atmosphere, and to hand it over to the colouring matter,
the water merely acting the part of a go-between to the at-
mosphere and the colouring matter. This you will recollect
is the theory of all sorts of bleaching. Science has afforded
our bleachers inure rapid methods of accomplishing this office.
They can now bleach their fabrics, as well as ever it could
be done under the old system, in a thousand times less time.
Before proceeding to illustrate the present mode of conduct-
ing the process of bleaching, I shall bring before you what
might appear a perfect paradox if not carefully explained.
I have here a glass containing a quantity of flowers of a very
deep red colour. Beneath this glass I shall place a tray
containing some sulphur, which I shall set fire to. Sulphur
when thus burned forms sulphurous acid, and this sulphurous
acid is well known as one of the substances employed in
bleaching. Bleaching by this agent is the reverse of all
that has been said with respect to bleaching; in fact, sul-
phurous acid does not bleach at all; it does not remove the
colouring matter, but unites with it and forms a white com-
pound,
und so that the colouring matter can be got back again,
and there is no proper bleaching. Sulphurous acid is used
in bleaching earn in stores, which is done by putting sulphur
upon the fire which is used• to dry the corn. l'he corn is
stored upon a succession of perforated floors one above the
other, and in the lowest story are a number of fires, upon
which the sulphur is thrown, and the fumes, passing up with
the hot air, bleach the corn, and give to it a much better
appearaoce than it would otherwise possess. In bleaching
silks and straw bonnets, the same process is resorted to; but
the only effect of the sulphurous acid is, that it combines
with the colouring matter and generates a third body; but
the colouring matter is brought back if we withdraw the
sulphurous acid. After a few months' exposure, all articles
bleached by this agent again become yellow, and must again
undergo the bleaching if required to be white.
I shall now bring Lefore you a substance used in bleaching,
which is well calculated to explain the principle of the art.
It is called chromate of potash, of which the beautiful crys-
tals before yen are from the manufactory of Mr. Kurtz, of
this town. Chromate of potash consists of chromic acid and
potash, and chromic acid consists of two parts of oxygen and
one of chrome. If we we place chromate of potash in con-
tact. with vegetable or organic colouring matter' and add
an acid, we shall have this result. The acid will combine
with the potash, and one portion of the chromic acid with the
colouring matter. By this action the colouring matter will
be bleached and the chromate of potash converted into a
green oxide of chrome. If a little organic matter, say spirits
of wine, be poured into a solution of chromate of potash, and
then a little oil of vitriol added, we shall tind that a violent
action ensues, and that the red colour of the chromate of
potash will immediately disappear. The addition of a little
water will turn the colour of the mixture completely green,
and the spirits of wine will be found to have been converted
into vinegar by the addition of the oxygen. Upon this prin-
ciple we could turn ale into vinegar. Chromate of potash is
a beautiful example on account of the rapidity of the decom-
position. It is used in a variety of processes in the arts
where it is necessary to bleach -locally; but, generally, it is
inferior to one of the elements which far surpasses any which
has been introduced into the arts, namely, chlorine. We
owe the discovery of this substance to the celebrated Swedish
chemist, Scheele. Chlorine is a body remarkably different
froth hydrogen, inasmuch as it is a supporter of combustion