NON-METALLIC ELEMENTS (_continued_).
CHLORINE—BROMINE—IODINE—FLUORINE—CARBON—SULPHUR—PHOSPHORUS—SILICON—
BORON—TELLURIUM—ARSENIC.
Chlorine (Cl.) is usually found with sodium in the mineral kingdom, and
this chloride of sodium is our common salt. Chlorine can be obtained by
heating hydrochloric acid with binoxide of manganese. (Atomic weight
35·5.)
[Illustration: Fig. 361.—Generation of chlorine.]
Chlorine possesses a greenish-yellow colour, hence its name “Chloros,”
green. It should be handled carefully, for it is highly injurious and
suffocating. It possesses a great affinity for other substances, and
attacks the metals. For hydrogen it has a great affection, and when
hydrogen is combined with any other substances chlorine immediately
attacks them, and in time destroys them. But even this destructive
and apparently objectionable quality makes chlorine very valuable;
for if we carry the idea to its conclusion, we shall find that it
also destroys offensive and putrid matter, and purifies the atmosphere
very much. Most colouring matters include hydrogen, and therefore they
are destroyed by chlorine, which is a great “bleacher” as well as a
purifier. If we dip any vegetable dyes into a jar of chlorine, they
will become white if the dyed substances are damp.
Hydrochloric acid is known as muriatic acid and spirits of salt. It is
obtained when salt is treated with sulphuric acid and the gas comes
off into water. Equal parts of the acid and the salt are put into a
flask as in the cut (fig. 362), and diluted with water. The mixture is
then heated. The gas is condensed in the bottles half-full of water.
The result gives sulphate of soda and hydrochloric acid. This acid is
procured in soda manufactories, and with nitric acid is called “aqua
regia,” a solvent for gold. When chlorine and hydrogen are mixed
in equal proportions they explode in sunlight. In the dark or by
candle-light they are harmless. Dry chlorine gas can be obtained by
interposing a glass filled with some chloride of calcium. The gas being
heavier than air (about 2½ times), displaces it in the flask, and
when it is filled another can be placed in position. This mode causes a
little waste of gas, which should not be breathed.
[Illustration: Fig. 362.—Production of hydrochloric acid.]
Chlorine possesses a great affinity for certain bodies. If the gas be
thrown upon phosphorus, the latter will burn brilliantly. Arsenic,
tin, and antimony when powdered and poured from a shoot into a vase of
chlorine will burst into brilliant sparks, and other metals will glow
when introduced to this gas. Chlorine forms many unstable combinations
with oxygen. Its combination with hydrogen has already been referred to.
BROMINE is a rare element. (Symbol Br. Atomic weight 80.)
It is deep brownish red, very volatile, and of a peculiar odour.
Bromine unites with the elementary bodies, and forms some oxygen
compounds. It resembles chlorine in its properties, and is used in
medicine and in photography. It is found in saline springs and in salt
water, combined with soda and magnesium. The presence of bromine may
easily be detected in the strong smell of seaweed. Its combinations
with metals are termed bromides. It is a powerful poison.
IODINE is another relative of chlorine. It is found in
seaweed, which by burning is reduced to _kelp_. When iodine is heated
a beautiful violet vapour comes off, and this characteristic has given
it its name (“iodes,” violet). Iodine was discovered by Courtois, of
Paris, and in 1813, Gay Lussac made it a special study. It is solid
at ordinary temperatures, and assumes crystallized forms in plates
of metallic lustre. It is an excellent remedy in “goitre” and such
affections. (Symbol I. Atomic weight 127.)
FLUORINE is very difficult to prepare. Fluor spar is a compound of
fluorine and calcium. This element is gaseous, and combines so rapidly
that it is very difficult to obtain in a free state. Etching on glass
is accomplished by means of hydrofluoric acid, for fluorine has a
great affinity for silicic acid, which is contained in glass. The
glass is covered with wax, and the design is traced with a needle. The
acid attacks the glass and leaves the wax, so the design is eaten in.
(Symbol F. Atomic weight 19.)
[Illustration: Fig. 363.—Apparatus for obtaining dry chlorine gas.]
Chlorine, fluorine, bromine, and iodine are termed “Halogens”
(producers of salts). They appear, as we have seen, in a gaseous,
liquid, and solid form respectively.
CARBON is the most, or one of the most, largely diffused elements in
nature, and claims more than a passing notice at our hands, though
even that must be brief. We may put down carbon next to oxygen as the
most important element in the world. The forms assumed by carbon are
very variable, and pervade nature in all its phases. We have carbon in
crystals, in the animal and vegetable kingdoms, and amongst the chief
minerals a solid, odourless, tasteless, infusible, and almost insoluble
body. In various combinations carbon meets us at every turn; united
with oxygen it forms carbonic acid, which we exhale for the plants
to imbibe. We have it in coal, with hydrogen and oxygen. We have it
building up animal tissues, and it is never absent in two out of the
three great divisions of nature—the plants and the animals (Symbol C;
Atomic W. 12).
[Illustration: Fig. 364.—Facets of a brilliant.]
[Illustration: Fig. 365.—Facets of a rose diamond.]
We have carbon in three different and well-known conditions; as
the diamond, as graphite, or black-lead, and as charcoal. The
properties of the diamond are well known, and we shall, when we get
to Crystallography, learn the forms of diamond or crystals of carbon.
At present we give an illustration or two, reserving all explanation
for the present. Diamond cutting is a matter of some difficulty, and
it requires skill to cut in the proper direction. Diamonds are found
in India, Brazil, and at the Cape of Good Hope, in alluvial soil.
The identity of diamond and charcoal was discovered accidentally.
An experiment to fuse a few small diamonds resulted in their
disappearance, and when the residue was examined it was found that the
diamonds had been burned, that they had combined with oxygen and formed
carbonic acid, just as when coal burns. The diamond is the hardest of
all substances, the most valuable of gems, and the purest condition in
which carbon appears.
GRAPHITE (Plumbago) is termed “black-lead,” and is the next purest form
of carbon. It crystallizes and belongs to the primitive formations. In
Cumberland it is dug up and used to make pencils; the operations can be
seen at Keswick. It has other uses of a domestic character.
Charcoal is the third form of carbon, and as it possesses no definite
form, is said to be _amorphous_. Charcoal is prepared in air-tight
ovens, so that no oxygen can enter and burn the wood thus treated.
Coke is the result of the same process applied to coal. The gas
manufactories are the chief depôts for this article, and it is used in
locomotive engines. The various smokeless coals and prepared fuels,
however, are frequently substituted.
[Illustration: Fig. 366. —Coke ovens.]
Coke ovens were formerly much resorted to by the railway companies, who
found the ordinary coal too smoky for locomotive purposes, and apt to
give rise to complaints by passengers and residents near the line.
The origin of wood charcoal we have seen. All vegetable substances
contain carbon. When we burn wood, in the absence of air as far as
possible, oxygen and hydrogen are expelled. The wood is piled in layers
as in the illustration (fig. 368), covered over with turf and mould,
with occasional apertures for air. This mass is ignited, the oxygen
and hydrogen are driven off, and carbon remains. (Animal charcoal
is obtained from calcining bones). Wood charcoal attracts vapours,
and water, if impure, can be purified by charcoal, and any impure or
tainted animal matter can be rendered inoffensive by reason of charcoal
absorbing the gases, while the process of decay goes on just the same.
Housekeepers should therefore not always decide that meat is good
because it is not offensive to the olfactory nerves. Charcoal will
remove the aroma, but the meat may be nevertheless bad. The use of
charcoal in filters is acknowledged universally, and as a constituent
of gunpowder it is important.
[Illustration: Fig. 367.—Charcoal burning.]
Carbon is not easily affected by the atmospheric air, or in the
earth; so in many instances wood is charred before being driven into
the ground; and casks for water are prepared so. Soot is carbon in
a pulverised condition, and Indian ink is manufactured with its
assistance.
[Illustration: Fig. 368.—Wood piles of charcoal burners.]
The preparation of wood charcoal gives occupation to men who are
frequently wild and untutored, but the results of their labour are very
beneficial. Care should be taken not to sleep in a room with a charcoal
stove burning, unless there is ample vent for the carbonic acid gas,
for it will cause suffocation. Lampblack is obtained by holding a plate
over the flame of some resinous substance, which deposits the black
upon it. There is a special apparatus for this purpose.
[Illustration: Fig. 369.—Seltzer-water manufactory.]
Carbon combines with oxygen to make carbonic acid gas, as we have
already mentioned, and in other proportions to form a more deadly
compound than the other. The former is the dioxide (CO_{2}), the
latter the monoxide, or carbonic oxide (CO). The dioxide is the
more important, being held in the atmosphere, and combined with lime
in chalk. All sparkling beverages contain carbonic acid, to which
their effervescence is due. The soda and other mineral waters owe
their sparkle to this gas. Soda-water consists of a weak solution of
carbonate of soda and the acid. There is a vessel holding chalk and
water, and another containing some sulphuric acid. When the sulphuric
acid is permitted to unite with the chalk and water, carbonic acid
is liberated. A boy turning a wheel forces the gas into the water in
the bottles, or the water and carbonate of soda is drawn off thus
impregnated into bottles and corked down, in the manner so familiar to
all. The bottles are made of the shape depicted, so that the bubble
of air shall be at the top when the bottle lies down. If it be not
kept so, the air will eventually escape, no matter how tightly the
cork be put in. The ordinary “soda-water” contains scarcely any soda.
It is merely water, chalk, and carbonic acid. The “Gazogene” is made
useful for small quantities of soda-water, and is arranged in the
following manner. The appearance of it is familiar to all. It consists
of a double vessel, into the upper part of which a solution of any
kind—wine and water, or even plain water—is put, to be saturated with
carbonic acid, or “aerated,” and into the lower one some carbonate of
soda and tartaric acid. A tube leads from this lower to the top of the
upper vessel, which screws on and off. By shaking the apparatus when
thus charged and screwed together, some of the liquid descends through
the tube into the lower vessel and moistens the soda and acid, which
therefore act on each other, and cause carbonic acid to be disengaged;
this, rising up through the tube (which is perforated with small holes
at the upper part), disperses itself through the liquid in small
bubbles, and causes sufficient pressure to enable the liquid to absorb
it, which therefore effervesces when drawn off by the tap.
[Illustration: Fig. 370.—Gazogene.]
[Illustration: Fig. 371.—Soda-water apparatus.]
Carbonic acid can be liquified, and then it is colourless. In a solid
form it resembles snow, and if pressed with the fingers it will blister
them. Being very heavy the gas can be poured into a vase, and if there
be a light in the receptacle the flame will be immediately extinguished.
That even the gas introduced into seltzer-water is capable of
destroying life, the following experiment will prove. Let us place
a bird within a glass case as in the illustration (fig. 373), and
connect the glass with a bottle of seltzer-water or a siphon. As soon
as the liquid enters, the carbonic acid will ascend, and this, if
continued for a long time, would suffocate the bird, which soon begins
to develop an appearance of restlessness.
[Illustration: Fig. 372.—Pouring out the carbonic acid gas.]
[Illustration: Fig. 373.—Experiment with carbonic acid.]
We have already remarked upon the important part taken by this gas
in nature, so we need only mention its existence in pits and caves.
There are many places in which the vapour is so strong as to render
the localities uninhabitable. In the Middle Ages the vapours were
attributed to the presence of evil spirits, who were supposed to
extinguish miners’ lamps, and suffocate people who ventured into the
caves. In the Grotto Del Cane there is still an example, and certain
caves of Montrouge are often filled with the gas. A lighted taper
held in the hand will, by its extinction, give the necessary warning.
Oxygen and carbon are condensed in carbonic acid, for the gas contains
a volume of oxygen equal to its own. If we fill a glass globe, as per
illustration (fig. 374), with pure oxygen, and in the globe insert two
carbon points, through which we pass a current of electricity, we shall
find, after the experiment, that if the stop-cock be opened, there is
no escape of gas, and yet the mercury does not rise in the tube, so the
oxygen absorbed has been replaced by an equal volume of carbonic acid.
The other combination of carbon with oxygen is the carbonic oxide (CO),
and when a small quantity of oxygen is burnt with it it gives a blue
flame, as on the top of the fire in our ordinary grates. This gas is
present in lime kilns, and is a very deadly one. We must now pass
rapidly through the compounds of carbon with hydrogen, merely referring
to coal for a moment as we go on.
Coal, of which we shall learn more in Mineralogy and Geology, is
a combination, mechanical or otherwise, and is the result of the
decomposition of vegetable matter in remote ages,—the so-called
“forests,” which were more like the jungles than the woods of the
present day. Moss and fern played prominent parts in this great
transformation, as we can see in the Irish peat-bogs, where the first
steps to the coal measures are taken.
[Illustration: Fig. 374.—Experiment showing that carbonic acid contains
oxygen and carbon.]
The compounds of carbon with hydrogen are important. There is the
“light” carburetted hydrogen (CH_{4}), which is usually known as
fire-damp in coal mines. It is highly inflammable and dangerous. The
safety-lamp invented by Davy is a great protection against it, for as
the gas enters it is cooled by the wire, and burns within harmlessly.
The explosion warns the miner. “Heavy” carburetted hydrogen possesses
double the quantity of carbon (C_{2}H_{4}). It is also explosive when
mixed with oxygen.
[Illustration: Fig. 375.—Temperature reduced by contact with wire.]
The most useful compound is coal-gas, and though its principal function
appears to be in some manner superseded by electricity, “gas” is still
too important to be put aside. It can easily be obtained by putting
small fragments of coal in the bowl of a tobacco-pipe, closing the
bowl with clay, and putting it in the fire. Before long the gas will
issue from the stem of the pipe, and may either be lighted or collected
in a bladder. For the use of the “million,” however, gas is prepared
upon a very large scale, and is divided into three processes—its
“formation,” “purification,” and its “collection” for distribution to
consumers. The first process is carried on by means of retorts shown
in the illustration (fig. 376). The first portion of the next figure
is a section of a furnace, the other part shows two furnaces from the
front. The following is the mode employed. The coal is put into retorts
fitted to the furnace, so that they are surrounded by the flames, and
terminating in a horizontal tube called the hydraulic main, E, which is
in its turn connected with a pit or opening for the reception of the
tar and ammoniacal liquor, etc., which condenses from the gas. It then
passes up and down a series of tubes in water, called a “condenser,”
and in this are reservoirs or receptacles for any tar and ammonia
that remain. But sulphur is still present, so the gas is carried to
the purifying apparatus (D in fig. 378), which consists of a large
cylindrical vessel air-tight, with an inverted funnel, nearly filled
with a mixture of lime and water. The gas bubbles in, and the sulphur
unites with the lime, while the gas rises to the top (trays of lime
are used when the gas enters from the bottom). The Gasometer, a large
vessel closed at the top and open below, dips into a large trough of
circular shape. The gasometer is balanced by weights and chains, and
may be raised (_See_ fig. 379). When quite empty the top rests upon
the ground, and when the gas enters it is raised to the top of the
frame which supports it. We have now our Gasometer full. When the time
comes to fill the pipes for lighting purposes, some of the weights are
removed, the Gasometer falls down slowly, and forces the gas through
the tubes into the main supply to be distributed. About four cubic feet
of gas is obtained from every pound of coal. When gas and air become
mixed, the mixture is very explosive. In a house where an escape of
gas is detected let the windows be opened at the top, and no light
introduced for several minutes.
[Illustration: Fig. 376.—Retorts.]
[Illustration:
Fig. 377.—Section. Front view.]
[Illustration:
Fig. 378.—Condenser. Purifier. Gasometer.]
[Illustration: Fig. 379.—Gasometer.]
It has been calculated that one ton of good coal produces the
following:—
1 Chaldron of coke weighing 1,494 lbs.
12 Gallons of tar ” 135 lbs.
12 Gallons of ammoniacal liquor ” 100 lbs.
5,900 Cubic feet of gas ” 291 lbs.
Loss (water) ” 220 lbs.
----------
Total 2,240 lbs.
==========
[Illustration: Fig. 380.—Gasometer]
We can thus estimate the profits of our gas companies at leisure. The
analysis of gas made by Professor Bunsen is as under, in 100 parts.
Hydrogen 45·58
Marsh gas 34·90
Carbonic oxide 6·64
Olefiant gas 4·08
Butyline 2·38
Sulphide of hydrogen 0·29
Nitrogen 2·46
Carbonic acid 3·67
------
100·00
======
Gas, therefore, is very injurious, for it rapidly vitiates the
atmosphere it burns in, and is very trying to the eyes, as well as
destructive to gilt ornaments.
Tar is familiar to all readers, and though unpleasant to handle or
to smell, it produces the beautiful aniline dyes. Tar pills are very
efficacious for some blood disorders, and will remove pimples, etc.,
from the face, and cure “boils” effectually. If a dose of five be
taken first, in a day or two four, and so on, no second remedy need be
applied. We have known cases finally cured, and no recurrence of boils
ever ensued after this simple remedy.
[Illustration: Fig. 381.—Tar manufactory]
Tar is one of the results left in the distillation both of wood and
coal: in places where wood is plentiful and tar in request, it is
produced by burning the wood for that purpose; and in some of the pits
in which charcoal is produced, an arrangement is made to collect the
tar also. Coal-tar and wood-tar are different in some respects, and
are both distilled to procure the napthas which bear their respective
names. From wood-tar creosote is also extracted, and it is this
substance which gives the peculiar tarry flavours to provisions, such
as ham, bacon, or herrings, cured or preserved by being smoked over
wood fires. Tar is used as a sort of paint for covering wood-work and
cordage when much exposed to wet, which it resists better than anything
else at the same price; but the tar chiefly used for these purposes is
that produced by burning fir or deal wood and condensing the tar in a
pit below the stack of wood; it is called Stockholm tar, as it comes
chiefly from that place.
Carbon only combines with nitrogen under peculiar circumstances. This
indirect combination is termed _cyanogen_ (CN). It was discovered
by Gay-Lussac, and is used for the production of Prussian blue.
Hydrocyanide of potassium (Prussic acid) is prepared by heating cyanide
of potassium with sulphuric acid. It is a deadly poison, and found
in peach-stones. Free cyanogen is a gas. The bisulphide of carbon is
a colourless, transparent liquid. It will easily dissolve sulphur and
phosphorus and several resins. When phosphorus is dissolved in it, it
makes a very dangerous “fire,” and one difficult to extinguish. We must
now leave carbon and its combinations, and come to sulphur.
[Illustration: Fig. 382.—Sulphur furnace.]
SULPHUR is found in a native state in Sicily and many other localities
which are volcanic. It is a yellow, solid body, and as it is never
perfectly free from earthy matter, it must be purified before it can
be used. It possesses neither taste nor smell, and is insoluble in
water. Sulphur is purified in a retort, C D, which communicates with
a brick chamber, A. The retort is placed over a furnace, K, and the
vapour passes into the chimney through the tube, D, where it condenses
into fine powder called “flowers of sulphur” (brimstone). A valve
permits the heated air to pass off, while no exterior air can pass in,
for explosions would take place were the heated vapour to meet the
atmospheric air. The danger is avoided by putting an air reservoir
outside the chimney which is heated by the furnace. The sulphur is
drawn out through the aperture, _r_, when deposited on the floor of
the chamber. The sulphur is cast into cylinders and sold. Sulphur is
soluble in bisulphide of carbon, and is used as a medical agent.
The compounds of sulphurs with oxygen form an interesting series. There
are two anhydrous oxides (anhydrides),—viz., sulphurous and sulphuric
anhydride (SO_{2} and SO_{3}). There are two notable acids formed
by the combination with water, sulphurous and sulphuric, and some
others, which, as in the case of nitrogen, form a series of multiple
proportions, the oxygen being present in an increasing regularity of
progression, as follows:—
Name of Acid. Chemical Formula.
Hypo-sulphurous acid H_{2}SO_{2}
Sulphurous acid H_{2}SO_{3}
Sulphuric acid H_{2}SO_{4}
Thio-sulphuric, or hypo-sulphuric acid H_{2}S_{2}O_{3}
Dithionic acid H_{2}S_{2}O_{6}
Trithionic acid H_{2}S_{3}O_{6}
Tetrathionic acid H_{2}S_{4}O_{6}
Pentathionic acid H_{2}S_{5}O_{6}
The last four are termed “polythionic,” because the proportions of
sulphur vary with constant proportions of the other constituents.
[Illustration: Fig. 383.—Liquefaction of sulphuric acid.]
The sulphurous anhydride mentioned above is produced when we burn
sulphur in the air, or in oxygen; it may be obtained in other ways.
It is a colourless gas, and when subjected to pressure may be
liquified, and crystallized at very low temperature. It was formerly
called sulphuric acid. It is a powerful “reducing agent,” and a good
antiseptic. It dissolves in water, and forms the H_{2}SO_{3}, now known
as sulphurous acid.
[Illustration: Fig. 384.—Retorts and receivers for acid.]
Sulphuric acid is a most dangerous agent in wicked or inexperienced
hands, and amateurs should be very careful when dealing with it. It
takes the water from the moist air, and from vegetable and animal
substances. It carbonizes and destroys all animal tissues. Its
discovery is due to Basil Valentine, in 1440. He distilled sulphate
of iron, or green vitriol, and the result was “oil of vitriol.” It
is still manufactured in this way in the Hartz district, and the
acid passes by retorts into receivers. The earthen retorts, A, are
arranged in the furnace as in the illustration, and the receivers,
B, containing a little sulphuric acid, are firmly fixed to them. The
oily brown product fumes in the air, and is called “fuming sulphuric
acid,” or Nordhausen acid. Sulphuric acid is very much used in chemical
manufactures, and the prices of many necessaries, such as soap, soda,
calico, stearin, paper, etc., are in close relationship with the cost
and production of sulphur, which also plays an important part in the
making of gunpowder. The manufacture of the acid is carried on in
platinum stills.
[Illustration: Fig. 385.—Experiment to show the existence of gases in
solution.]
Sulphuretted hydrogen, or the hydric sulphide (H_{2}S), is a colourless
and horribly-smelling gas, and arises from putrefying vegetable and
animal matter which contains sulphur. The odour of rotten eggs is due
to this gas, which is very dangerous when breathed in a pure state in
drains, etc. It can be made by treating a sulphide with sulphuric acid.
It is capable of precipitating the metals when in solution, and so
by its aid we can discover the metallic ingredient if it be present.
The gas is soluble in water, and makes its presence known in certain
sulphur springs. The colour imparted to egg-spoons and fish-knives
and forks sometimes is due to the presence of metallic sulphides. The
solution is called hydro-sulphuric acid.
PHOSPHORUS occurs in very small quantities, though in the form of
phosphates we are acquainted with it pretty generally, and as such it
is absorbed by plants, and is useful in agricultural operations. In
our organization—in the brain, the nerves, flesh, and particularly in
bones—phosphorus is present, and likewise in all animals. Nevertheless
it is highly poisonous. It is usually obtained from the calcined bones
of mammalia by obtaining _phosphoric acid_ by means of acting upon the
bone-ash with sulphuric acid. Phosphorus when pure is colourless,
nearly transparent, soft, and easily cut. It has a strong affinity for
oxygen. It evolves white vapour in atmospheric air, and is luminous;
to this element is attributable the luminosity of bones of decaying
animal matter. It should be kept in water, and handled—or indeed not
handled—but grasped with a proper instrument.
Phosphorus is much used in the manufacture of lucifer matches, and we
are all aware of the ghastly appearance and ghostly presentment it
gives when rubbed upon the face and hands in the dark. In the ripples
of the waves and under the counter of ships at sea, the phosphorescence
of the ocean is very marked. In Calais harbour we have frequently
noticed it of a very brilliant appearance as the mail steamer slowly
came to her moorings. This appearance is due to the presence of
phosphorus in the tiny animalculæ of the sea. It is also observable in
the female glow-worm, and the “fire-fly.” Phosphorus was discovered by
Brandt in 1669.
[Illustration: Fig. 386.—Manufacture of sulphuric acid.]
It forms two compounds with oxygen-phosphorous acid, H_{2}PO_{4}, and
phosphoric acid, H_{3}PO_{4}. The compound with hydrogen is well marked
as phosphuretted hydrogen, and is a product of animal and vegetable
decomposition. It may frequently be observed in stagnant pools, for
when emitted it becomes luminous by contact with atmospheric air. There
is a very pretty but not altogether safe experiment to be performed
when phosphuretted hydrogen has been prepared in the following manner.
Heat small pieces of phosphorus with milk of lime or a solution of
caustic potash; or make a paste of quick-lime and phosphorus, and
put into the flask with some quick-lime powdered. Fix a tube to the
neck, and let the other end be inserted in a basin of water. (_See_
illustration, fig. 388.) Apply heat; the phosphuretted hydrogen will
be given off, and will emerge from the water in the basin in luminous
rings of a very beautiful appearance. The greatest care should be
taken in the performance of this very simple experiment. _No water
must on any account come in contact with the mixture in the flask._ If
even a drop or two find its way in through the bent tube a tremendous
explosion will result, and then the fire generated will surely prove
disastrous. The experiment can be performed in a cheaper and less
dangerous fashion by dropping phosphate of lime into the basin. We
strongly recommend the latter course to the student unless he has
had some practice in the handling of these inflammable substances,
and learnt caution by experience. The effect when the experiment is
properly performed is very good, the smoke rising in a succession of
coloured rings.
[Illustration: Fig. 387.—(Phosphuretted hydrogen and marsh gas)
Will-o’-the-Wisp.]
SILICON is not found in a free state in nature, but, combined with
oxygen, as _Silica_ it constitutes the major portion of our earth,
and even occurs in wheat stalks and bones of animals. As flint or
quartz (see _Mineralogy_) it is very plentiful, and in its purest
form is known as rock crystal, and approaches the form of carbon
known as diamond. When separated from oxygen, silicon is a powder of
greyish-brown appearance, and when heated in an atmosphere of oxygen
forms silicic “acid” again, which, however, is not acid to the taste,
and is also termed “silica,” or “silex.” It is fused with great
difficulty, but enters into the manufacture of glass in the form of
sand. The chemical composition of glass is mixed silicate of potassium
or sodium, with silicates of calcium, lead, etc. Ordinary window-glass
is a mixture of silicates of sodium and calcium; crown glass contains
calcium and silicate of potassium. Crystal glass is a mixture of the
same silicate and lead. Flint glass is of a heavier composition. Glass
can be coloured by copper to a gold tinge, blue by cobalt, green
by chromium, etc. Glass made on a large scale is composed of the
following materials, according to the kind of glass that is required.
Flint glass (“crystal”) is very heavy and moderately soft, very white
and bright. It is essentially a table-glass, and was used in the
construction of the Crystal Palace. Its composition is—pure white
sea-sand, 52 parts, potash 14 parts, oxide of lead, 34 parts = 100.
Plate Glass. Crown Glass. Green (Bottle) Glass.
Pure white sand 55 parts. Fine sand 63 parts. Sea sand 80 parts.
Soda 35 ” Chalk 7 ” Salt 10 ”
Nitre 8 ” Soda 30 ” Lime 10 ”
Lime 2 ”
--- --- ---
100 ” 100 ” 100 ”
The ingredients to be made into glass (of whatever kind it may be)
are thoroughly mixed together and thrown from time to time into large
crucibles placed in a circle, A A (fig. 389), in a furnace resting on
buttresses, B B, and heated to whiteness by means of a fire in the
centre, C, blown by a blowing machine, the tube of which is seen at D.
This furnace is shown in prospective in fig. 390. The ingredients melt
and sink down into a clear fluid, throwing up a scum, which is removed.
This clear glass in the fused state is kept at a white heat till all
air-bubbles have disappeared; the heat is then lowered to a bright
redness, when the glass assumes a consistence and ductility suitable to
the purposes of the “blower.”
[Illustration: Fig. 388.—Experiment with phosphuretted hydrogen.]
Glass blowing requires great care and dexterity, and is done by
twirling a hollow rod of iron on one end of which is a globe of
melted glass, the workman blowing into the other end all the time. By
reheating and twirling a sheet of glass is produced. Plate glass is
formed by pouring the molten glass upon a table with raised edges. When
cold it is ground with emery powder, and then polished by machinery.
[Illustration: Fig. 389.—Crucibles.]
Many glass articles are cast, or “struck-up,” by compression in moulds,
and are made to resemble cut-glass, but they are much inferior in
appearance. The best are first blown, and afterwards cut and polished.
Of whatever kind of glass the article may be, it is so brittle that the
slightest blow would break it, a bad quality which is got rid of by a
process called “annealing,” that is, placing it while quite hot on the
floor of an oven, which is allowed to cool very gradually. This slow
cooling takes off the brittleness, consequently articles of glass well
annealed are very much tougher than others, and will scarcely break in
boiling water.
[Illustration: Fig. 390.—Plate-glass casting—bringing out the pot.]
The kind generally used for ornamental cutting is flint-glass.
Decanters and wine-glasses are therefore made of it; it is very bright,
white, and easily cut. The cutting is performed by means of wheels of
different sizes and materials, turned by a treadle, as in a common
lathe, or by steam power; some wheels are made of fine sandstone, some
of iron, others of tin or copper; the edges of some are square,or
round, or sharp. They are used with sand and water, or emery and water,
stone wheels with water only.
[Illustration: Fig. 391.—Glass furnace. (_See_ also fig. 390 for
detail.)]
[Illustration: Fig. 392.—Glass-cutting.]
In a soluble form silicic acid is found in springs, and thus
enters into the composition of most plants and grasses, while the
shells and scales of “infusoria” consist of silica. As silicate
of alumina,—_i.e._, clay,—it plays a very important _rôle_ in our
porcelain and pottery works.
* * * * *
BORON is found in volcanic districts, in lakes as boracic acid, in
combination with oxygen. It is a brownish-green, insoluble powder, in
a free state, but as boracic acid it is white. It is used to colour
fireworks with the beautiful green tints we see. Soda and boracic acid
combine to make borax (or biborate of soda). Another and inferior
quality of this combination is _tinkal_, found in Thibet. Borax is much
used in art and manufactures, and in glazing porcelain. (Symbol B,
Atomic Weight 11).
SELENIUM is a very rare element. It was found by Berzilius in a
sulphuric-acid factory. It is not found in a free state in nature. It
closely resembles sulphur in its properties. Its union with hydrogen
produces a gas, seleniuretted hydrogen, which is even more offensive
than sulphuretted hydrogen. (Symbol Se, Atomic Weight 79).
TELLURIUM is also a rare substance generally found in combination with
gold and silver. It is like bismuth, and is lustrous in appearance.
Telluretted hydrogen is horrible as a gas. Tellurium, like selenium,
sulphur, and oxygen, combines with two atoms of hydrogen. (Symbol Te,
Atomic Weight 129).
[Illustration: Fig. 393.—Casting plate-glass.]
ARSENIC, like tellurium, possesses many attributes of a metal, and on
the other hand has some resemblance to phosphorus. Arsenic is sometimes
found free, but usually combined with metals, and is reduced from
the ores by roasting; and uniting with oxygen in the air, is known
as “white arsenic.” The brilliant greens on papers, etc., contain
arsenic, and are poisonous on that account. Arsenic and hydrogen unite
(as do sulphur and hydrogen, etc.), and produce a foetid gas of a most
deadly quality. This element also unites with sulphur. If poured into
a glass containing chlorine it will sparkle and scintillate as in the
illustration (fig. 395). (Symbol As, Atomic Weight 75).
Before closing this division, and passing on to a brief review of
the METALS, we would call attention to a few facts connected with
the metalloids we have been considering. Some, we have seen, unite
with hydrogen only, as chlorine; some with two atoms of hydrogen, as
oxygen, sulphur, etc., and some with three, as nitrogen and phosphorus;
some again with four, as carbon and silicon. It has been impossible
in the pages we have been able to devote to the Metalloids to do more
than mention each briefly and incompletely, but the student will find
sufficient, we trust, to interest him, and to induce him to search
farther, while the general reader will have gathered some few facts to
add to his store of interesting knowledge. We now pass on to the Metals.
[Illustration: Fig· 394—The manufacture of porcelain in China.]
[Illustration: Fig. 395.—Experiment showing affinity between arsenic
and chlorine.]