Scientific Pursuits:
INCLUDING
ACOUSTICS.
AERONAUTICS.
CHEMISTRY.
ELECTRICITY.
GALVANISM.
HEAT.
HYDRAULICS.
MAGNETISM.
MECHANICS.
MICROSCOPE.
OPTICS AND OPTICAL ILLUSIONS.
PHOTOGRAPHY.
PNEUMATICS.
SPECTRUM.
ACOUSTICS.
Acoustics is the science relating to sound and hearing. Sound is heard
when any shock or impulse is given to the air, or to any other body
which is in contact directly or indirectly with the ear.
DIFFERENCE BETWEEN SOUND AND NOISE.
Noises are made by the cracks of whips, the beating of hammers, the
creak of a file or saw, or the hubbub of a multitude. But when a bell is
struck, the bow of a violin drawn across the strings, or the wetted
finger turned round a musical glass, we have what are properly called
sounds.
SOUNDS, HOW PROPAGATED.
Sounds are propagated on all bodies much after the manner that waves are
in water, with a velocity of 1,142 feet in a second. Sounds in liquids
and in solids are more rapid than in air. Two stones rubbed together may
be heard in water at half a mile; solid bodies convey sounds to great
distances, and pipes may be made to convey the voice over every part of
the house.
TO SHOW HOW SOUND TRAVELS THROUGH A SOLID.
Take a long piece of wood, such as the handle of a hair broom, and
placing a watch at one end, apply your ear to the other, and the
tickings will be distinctly heard.
TO SHOW THAT SOUND DEPENDS ON VIBRATION.
Touch a bell when it is sounding, and the noise ceases; the same may be
done to a musical string with the same results. Hold a musical
pitch-fork to the lips, when it is made to sound, and a quivering motion
will be felt from its vibrations. These experiments show that sound is
produced by the quick motions and vibrations of different bodies.
MUSICAL FIGURES RESULTING FROM SOUND.
Cover the mouth of a wine glass, having a foot-stalk, with a thin sheet
of membrane, over which scatter a layer of fine sand. The vibrations
excited in the air by the sound of a musical instrument, held within a
few inches of the membrane, will cause the sand on its surface to form
regular lines and figures with astonishing celerity, which vary with the
sound produced.
TO MAKE AN ÆOLIAN HARP.
This instrument consists of a long narrow box of very thin deal, about
six inches deep, with a circle in the middle of the upper side of an
inch and a half in diameter, in which are to be drilled small holes. On
this side seven, ten, or more strings of very fine catgut are stretched
over bridges at each end like the bridges of a fiddle, and screwed up or
relaxed with screw pins. The strings must all be tuned to one and the
same note,[5] and the instrument should be placed in a window partly
open, in which the width is exactly equal to the length of the harp,
with the sash just raised to give the air admission. When the air blows
upon these strings with different degrees of force, it will excite
different tones of sound. Sometimes the blast brings out all the tones
in full concert, and sometimes it sinks them to the softest murmurs.
[5] D is a good note for it. The upper string may be tuned to the
upper D, and the two lower to the lower D and D D. The “harmonics”
are the sounds produced.
A colossal imitation of the instrument just described was invented at
Milan in 1786, by the Abbate Gattoni. He stretched seven strong iron
wires, tuned to the notes of the gamut, from the top of a tower sixty
feet high, to the house of a Signor Moscate, who was interested in the
success of the experiment; and this apparatus, called the “giant’s
harp,” in blowing weather yielded lengthened peals of harmonious music.
In a storm this music was heard at a greater distance.
THE INVISIBLE GIRL.
[Illustration]
The facility with which the voice circulates through tubes was known to
the ancients, and no doubt has afforded the priests of all religions
means of deception to the ignorant and credulous. But of late days the
light of science dispels all such wicked deceptions. A very clever
machine was produced at Paris several years ago, and afterwards
exhibited in London under the name of the “Invisible Girl,” since the
apparatus was so constructed that the voice of a female at a distance
was heard as if it originated from a hollow globe, not more than a foot
in diameter. It consisted of a wooden frame something like a tent
bedstead, formed by four pillars _a a a a_, connected by upper cross
rails _b b_, and similar rails below, while it terminated above in four
bent wires _c c_, proceeding at right angles of the frame, and meeting
in a central point. The hollow copper ball _d_, with four trumpets _t
t_, crossing from it at right angles, hung in the centre of the frame,
being connected with the wires alone by four narrow ribbons _r r_. The
questions were proposed close to the open mouth of one of these
trumpets, and the reply was returned from the same orifice. The means
used in the deception were as follow: a pipe or tube was attached to one
of the hollow pillars, and carried into another apartment, in which a
female was placed; and this tube having been carried up the leg or
pillar of the instrument to the cross-rails, had an aperture exactly
opposite two of the trumpet mouths; so that what was spoken was
immediately answered through a very simple mode of communication.
VENTRILOQUISM.
This is an art by no means very difficult of acquirement, if the young
reader will take the pains. It is produced by a reflection of sound
within the mouth, the voice being brought to the lowest possible place
in the larynx. When the art is acquired by practice, the voice may be
made to appear as if coming from any part of a room, from up a chimney,
or from the depths of a cellar. The celebrated Dr. Wolcott, better known
as Peter Pindar, used to amuse his friends in a remarkable manner with
this art. He would represent his landlady as demanding payment of her
rent, and hold a colloquy with her, which would at last rise to terms of
reproach and fury, and end by a noise as if the landlady had been kicked
down stairs. The marvellous powers of Matthews, Le Lagg, Alexander, and,
lastly, Mr. Love, are familiar to most persons. To learn the art, the
young practitioner must have the power of enunciating well, and that
without motion of the lips,--of disguising the voice, so as to imitate
other sounds,--and of adapting the degree to the apparent source of the
sound. By practice this art is attainable by any person whose organs of
speech are completely and fully developed.
[Illustration]
[Illustration]
AERONAUTICS.
BALLOONS.
The art of sailing or navigating a body through the air is called
aëronautics. In remote ages, Icarus is said to have risen so high in the
air that the sun melted his wings, and he fell into the Ægean sea, and
was drowned; and there is reason to believe, from some figures that have
recently been discovered on Egyptian and Assyrian monuments, that the
ancients possessed means of rising in the air with which we are not now
acquainted.
The air-balloon, as now constructed, is a bag of silk of large
dimensions, usually cut in gores, and is, when expanded by gas, of a
pear-shape. It ascends in the atmosphere because its whole bulk is much
lighter than the air would be in the space it occupies. It is, in fact,
a vessel filled with a fluid which will float on another fluid lighter
than itself.
HOW TO MAKE AN AIR-BALLOON.
The best shape for an air-balloon, or rather a gas-balloon, is that of a
pegtop. And in preparing the gores proceed as follows: Get some close
texture silk, and cut it into a form resembling a narrow pear with a
very thin stalk. Fourteen of these pieces will be found to be the best
number; and, of course, the breadths of each piece must be measured
accordingly. When sewing them together, it will be of advantage to coat
the parts that overlap with a layer of varnish, as this will save much
trouble afterwards, and hold the silk firmer in its place during the
stitching. The threads must be placed very regularly, or the balloon
will be drawn out of shape, and it will be found useful if the gores are
covered with an interior coating of varnish before they are finally sewn
together. Take care not to have the varnish too thick. To the upper part
of the balloon there should be a valve opening inwards, to which a
string should be fastened, passing through a hole made in a small piece
of wood fixed in the lower part of the balloon, so that the aeronaut may
open the valve when he wishes to descend; and this should be imitated on
a small scale, so that the young aëronaut may be perfectly familiar with
the construction of a balloon. The gores are to be covered with a
varnish of India-rubber dissolved in a mixture of turpentine and
naphtha. Over the whole of the upper part should be a net-work, which
should come down to the middle with various cords, proceeding from it to
the circumference of a circle about two feet below the balloon. The
circle may be made of wood, or of several pieces of slender cane bound
together. The meshes should be small at top, against which part of the
balloon the inflammable air exerts the greatest force, and increase in
size as they recede from the top.
[Illustration]
The car is made of wicker-work; it is usually covered with leather, and
is well varnished or painted. It is suspended by ropes proceeding from
the net which goes over the balloon. Balloons of this kind cannot be
made smaller than six feet in diameter, of oiled silk, as the weight of
the material is too great for the air to buoy it up. They may be made
smaller of thin slips of bladder, or other membrane glued together, or
of thin gutta-percha cloth, which is now extensively used for this
purpose; with this they may be made a foot in diameter, and will rise
beautifully.
HOW TO FILL A BALLOON.
Procure a large stone bottle which will hold a gallon of water, into
this put a pound of iron filings, or granulated zinc, with two quarts of
water, and add to this by degrees one pint of sulphuric acid. Then take
a tube, either of glass or metal, and introduce one end of it through a
cork, which place in the bottle, then put the other end into the neck of
the balloon, and the gas will rise into the body of it. When quite full
withdraw the tube, and tie the neck of the balloon with strong cord very
tightly. If freed it will now rise in the air.
TO MAKE FIRE-BALLOONS.
[Illustration]
Cut the gores, according to the forms already given, from well-woven
tissue paper, paste the gores nicely together, and look well over the
surface of the paper for any small hole or slit, over which paste a
piece of paper, and let it dry. Pass a wire round the neck of the
balloon, and have two cross pieces at its diameter a little bent, so
that a piece of soft cotton dipped in spirits of wine may be laid on
them. When all is prepared let some one hold the balloon from its top by
means of a stick, while you dip the cotton in spirits of wine till it is
thoroughly saturated, place it under the balloon and set fire to it, but
be very careful you do not set fire to the balloon. When the air is
sufficiently heated within, the balloon will indicate a desire to rise,
and when it pulls very hard, let it go, and it will ascend to a great
height in the air, and at night present a very beautiful appearance.
PARACHUTES.
[Illustration]
These are easily made by cutting a piece of paper in a circular form,
and placing threads round the edges, which may be made to converge to a
point, at which a cork may be placed as a balance. They ascend by the
air getting under them, and are frequently blown to a great distance.
[Illustration: SCIENTIFIC PURSUITS.]
[Illustration]
CHEMISTRY.
In the eleventh century, and during the reign of King Henry the First,
surnamed Beauclerk, or the fine scholar, there appeared for the first
time in certain books, professing to teach the art making of gold, the
words chemistry, chemist, derived from the Greek χημεία. Seven hundred
years and more have passed away, and that which was only the pursuit of
a shadow called alchemy, has resulted in the acquisition of a great and
noble science, now and again called chemistry. When we go to the French
Exposition, we shall doubtless pass by much that is worthy of notice,
and bring away with us only a general impression of the wonders it
contains. So it is with the great edifice Chemistry; we may, in these
brief pages, peep in at the open door, but should we desire to go beyond
the threshold, there are numerous guides, such as Roscoe, Wilson, and
Fownes, who will conduct us through the mazes of the interior, and
explain in elementary language the beautiful processes which have become
so useful to mankind.
Chemistry is one of the most comprehensive of all the sciences, and at
the same time one which comes home to us in the most ordinary of our
daily avocations. Most of the arts of life are indebted to it for their
very existence, and nearly all have been, from time to time, improved by
the application of its principles.
Chemistry is, in fact, the science which treats of the composition of
all material bodies, and of the means of forming them into new
combinations, and reducing them to their _ultimate elements_, as they
are termed, that is, bodies which we are unable to split up, as it were,
or separate into other bodies. To take a common substance as an
illustration; water, by a great number of processes, can be separated
into two other substances, called oxygen and hydrogen, in the proportion
by weight of 8 parts of the first to 1 of the second; but no power that
we at present possess can separate the oxygen and hydrogen into any
other bodies; they are therefore called ultimate elements, or
undecomposable bodies.
Again, sulphate of magnesia (common Epsom salts) can be very easily
separated into two other substances,--sulphuric acid and magnesia; and
in this instance, both these substances can again be sub-divided--the
acid into sulphur and oxygen, and the magnesia into a metallic body
called magnesium and oxygen; but sulphur, oxygen, and magnesium are
incapable of further division, and are therefore called _ultimate
elements_.
These ultimate elements amount to 64 in number, according to the present
state of our knowledge, and may be arranged in various ways; the
simplest plan, perhaps, is dividing them into Non-metallic and Metallic
elements.
The Non-metallic elements are:--1. Oxygen. 2. Hydrogen. 3. Nitrogen. 4.
Chlorine. 5. Iodine. 6. Bromine. 7. Fluorine. 8. Carbon. 9. Sulphur. 10.
Selenium. 11. Tellurium. 12. Silicon. 13. Boron. 14. Phosphorus. The
last-named element is the connecting link with the metals through
arsenic, which phosphorus closely resembles in its chemical properties.
The Metallic elements may be sub-divided into the metals of the
alkalies, the metals of the alkaline earths, the metals of the earths,
and the other metals sometimes called metals proper.
1st. The metallic bases of the alkalies:--potassium, sodium, lithium,
ammonium, cæsium, rubidium.
2d. The metallic bases of the alkaline earths:--calcium, strontium,
barium.
3d. The metallic bases of the earths:--aluminium, glucinum, zirconium,
thorium, yttrium, erbium, cerium, lanthanum, didymium.
4th. The metals proper, the most important of which are:--platinum,
gold, silver, mercury, copper, iron, tin, lead, nickel, zinc, bismuth,
antimony, manganese, cobalt, arsenic.
Now, from these elementary bodies, united together in various
proportions, is formed the infinite variety of substances around us,
whether animal, vegetable, or mineral; in fact, a few only are generally
employed;--in the case of animals and vegetables, oxygen, hydrogen,
carbon, nitrogen, with occasionally some sulphur, calcium, phosphorus,
and silicon, suffice for building up the beautiful forms of animated
nature; while the fabric of our globe itself consists for the most part
of the earths; silex, _i. e._ flint or crystal; lime, in the shape of
chalk, marble, or limestone, such as our flagstones are composed of;
slate and granite, which are compounds of aluminium, silica, and small
quantities of oxide of iron, and sometimes a little potash, &c.; and
through their masses are projected irregular streams--veins as they are
termed--of the metals, either in a pure state, as is the case sometimes
with gold, silver, platinum, mercury, and perhaps one or two others; or
combined with one of the non-metallic elements, or with one another.
Late calculations have determined the composition of the earth’s solid
crust in 100 parts by weight to be
Oxygen 44·0 to 48·7
Silicon 22·8 „ 36·2
Aluminium 9·9 „ 6·1
Iron 9·9 „ 2·4
Calcium 6·6 „ 0·9
Magnesium 2·7 „ 0·1
Sodium 2·4 „ 2·5
Potassium 1·7 „ 3·1
----- -----
100· 100·
===== =====
All these combinations are effected by certain powers, termed _forces_;
those which cause the union of the elements are called the forces of
attraction; those causing their separation, the forces of repulsion.
The force of attraction when exerted between masses of matter, is termed
gravitation; when it unites particles of matter of a similar kind and
produces masses, it is called the attraction of cohesion; when the
particles united are of a dissimilar character, it is then termed
chemical or elective affinity. For example, the crystals of Epsom salts
are formed from minute particles of the salt, united into a larger or
smaller mass by the attraction of cohesion, while the _elements_ of
which each particle consists, namely, the sulphur, oxygen, and
magnesium, are united by the attraction of chemical affinity.
Cohesion thus unites particles of a similar kind; chemical affinity, of
a dissimilar nature. It is to cohesion that the existence of _masses_ of
matter is owing, and its power increases as the squares of the distances
diminish, in an inverse ratio to the squares of the distances of the
particles on which it acts.
The power exerted by cohesion may be exhibited in various ways. This is
one: Procure two discs of glass about three inches in diameter, their
surfaces being ground extremely smooth; fix each into a square piece of
wood, taking care that they are placed accurately in the centre; then
put them together, by sliding their edges very carefully over each
other, so as to avoid any air getting between them, and you will find a
great force necessary to separate them. A hook should be fixed into the
centre of each piece of wood, so that they may be suspended, and a
weight hung to the lower one. It is almost impossible for any one to
separate them by merely pulling them with both hands; a weight of many
pounds is required for that purpose. In like manner two freshly-cut
surfaces of caoutchouc will, on being squeezed together, cohere so
perfectly, that it is difficult to tear them asunder, and it is in this
way that tubes of caoutchouc may be rapidly prepared for experiments,
where little or no pressure is exerted.
Chemical affinity is sometimes called _elective_, or the effect of
_choice_, as if one substance exerted a kind of _preference_ for
another, and chose to be united to it rather than to that with which it
was previously combined; thus, if you pour some vinegar, which is a weak
acetic acid, upon some pearlash (a combination of potash and carbonic
acid), or some carbonate of soda (a combination of the same acid with
soda), a violent effervescence will take place, occasioned by the escape
of the carbonic acid, displaced in consequence of the potash or soda
preferring the acetic acid, and forming a compound called an acetate.
Then, if some sulphuric acid be poured on this new compound, the acetic
acid will in its turn be displaced by the greater attachment of either
of the bases, as they are termed, for the sulphuric acid. Again, if into
a solution of blue vitriol (a combination of sulphuric acid with oxide
of copper) the bright blade of a knife be introduced, the knife will
speedily be covered with a coat of copper, deposited in consequence of
the acid _preferring_ the iron, of which the knife is made, a quantity
of it being dissolved in exact proportion to the quantity of copper
deposited.
[Illustration]
It is on the same principle that a very beautiful preparation, called a
silver-tree, or a lead-tree, may be formed thus:--Fill a wide bottle,
capable of holding from half a pint to a pint, with a tolerably strong
solution of nitrate of silver (lunar caustic), or acetate of lead, in
pure distilled water; then attach a small piece of zinc by a string to
the cork or stopper of the bottle, so that the zinc shall hang about the
middle of the bottle, and set it by where it may be quite undisturbed;
in a short time, brilliant plates of silver or lead, as the case may be,
will be seen to collect around the piece of zinc, assuming more or less
of the crystalline form. This at first is a case of elective affinity;
the acid with which the silver or lead was united _prefers_ the zinc to
either of those metals and in consequence discards them in order to
attach the zinc to itself, subsequently a voltaic current is set up
between the two metals, and the process will continue until almost the
whole of the zinc is taken up, or nearly the whole of the silver or lead
deposited.
Again, many animal and vegetable substances consist for the most part of
carbon or charcoal, united with oxygen and hydrogen in the proportion
which forms water. Now oil of vitriol (strong sulphuric acid) has so
powerful an affinity, or so great a _thirst_ for water, that it will
abstract it from almost any body in which it exists; if you then pour
some of this acid on a lump of sugar, or place a chip of wood in it, the
sugar or wood will speedily become quite black, or be _charred_, as it
is called, in consequence of the oxygen and hydrogen being removed by
the sulphuric acid, and only the carbon, or charcoal, left.
When Cleopatra dissolved pearls of wondrous value in vinegar, she was
exhibiting unwittingly an instance of chemical elective affinity; the
pearl being simply carbonate of lime, which was decomposed by the
greater affinity or fondness of lime for its new acquaintance (the
acetic acid of the vinegar) than for the carbonic acid, with which it
had been united all its life,--an example of inconstancy in strong
contrast with the conduct of its owner, who chose death rather than
become the mistress of her lover’s conqueror.
GASES.
The three permanent gaseous elements are oxygen, hydrogen, and nitrogen.
The compound gases are very numerous, some being combustible, and others
supporters of combustion.
Gases are for the most part transparent and colourless, with a few
exceptions, and of course, like the air of the atmosphere, invisible.
They are little affected by the attraction of cohesion, but rather, on
the contrary, the particles composing them have a constant tendency to
separate from each other, so that their force of expansion is only
limited by the pressure under which they may be kept, and the
temperature they may be exposed to. They have a tendency to _penetrate_
each other, as it were; for instance, if you take a jar of heavy gas,
such as carbonic gas, set it with its mouth upwards, then invert over it
another jar containing hydrogen, a gas nearly twenty-two times lighter;
in a very short time the two gases will have become thoroughly mixed,
the heavy carbonic acid having risen, and the light hydrogen fallen,
until the gases are thoroughly mixed, each jar containing an equal
quantity of each gas.
OXYGEN GAS.
This gas, so named from two Greek words signifying the maker of acid,
was discovered by Dr. Priestly in 1774. He obtained it by heating the
red oxide of mercury in a glass retort, when the gas escaped in
considerable quantities. In the ensuing year Scheele obtained it by a
variety of methods, and a few years afterwards Lavoisier discovered that
it was contained in atmospheric air, where it exists in the proportion
of about one-fifth, the remaining four-fifths being almost entirely
nitrogen.
Oxygen gas may be obtained for the purpose of experiment, by heating to
redness the black oxide of manganese in an iron bottle, to the mouth of
which a flexible tube is attached to convey away the gas as fast as it
is liberated from the manganese. The first portions should be allowed to
escape, being mixed with the air in the tubes and bottle, and the
remainder may be collected in a gasometer, or in glass jars inverted
over water.
Another method to obtain the gas, and one to be used only in the absence
of other ingredients, is to mix in a retort some of this same oxide of
manganese with about half its weight of strong sulphuric acid, and apply
heat to the retort, when the gas will come over in considerable
quantities; the first portions must be allowed to escape as before.[6]
If the gas is required _very_ pure, a small quantity of the salt called
chlorate of potassa may be heated in a retort, and oxygen gas will be
evolved, and may be collected as before. If you have an iron bottle, the
first mode is by far the cheapest, as the heat of a bright fire is
sufficient for the operation, and a large quantity of gas is obtained in
a short time from a very inexpensive material. The most rapid and
convenient process of all is to heat a mixture of two parts chlorate of
potash, and one of powdered black oxide of manganese, in a common clean
oil flask, to which a cork and bent tube has been adapted. Care must be
taken not to mistake sulphide of antimony for black oxide of manganese,
as very serious accidents have arisen from this cause.
[6] Some _boiling_ water should be added to the mass left in the
retort directly the gas has ceased to come away, or it will adhere
to the glass so firmly, that the retort will certainly be spoilt.
Oxygen is largely distributed over our globe, both in its uncombined
state, and in union with other substances. Besides forming one-fifth of
the atmosphere, it forms eight-ninths by weight of all the water in the
ocean, rivers, and springs on the face of the whole earth. It also, in
combination with various metals, forms the various earths and minerals
of which the crust of the earth consists, so that it is the most
abundant and widely distributed substance in nature, and in combination
with other elements, forms nearly half the weight of the solid earth.
In its uncombined state it is a colourless gas, somewhat heavier than
atmospheric air, without taste or smell. It is a powerful supporter of
combustion, and is absolutely necessary for the support of animal life,
which cannot exist for any time without a free supply of this gas, which
is constantly consumed in the act of breathing, and is replaced by an
equivalent portion of carbonic acid gas. The want of oxygen is partly
the cause of the oppression felt in crowded rooms, where the air cannot
be renewed so fast as is required for the number of persons who are
constantly consuming the oxygen; and if an animal be confined under a
glass jar inverted over water, it will presently die, just for the same
reason that burning tapers are extinguished under similar circumstances.
If a jet of this gas be thrown upon a piece of charcoal, sulphur, or
almost any combustible body in a state of ignition, it will make it burn
with great vividness and rapidity. For a complete series of experiments
with oxygen see “The Boy’s Play-book of Science.”
EXPERIMENT.
But by far the most intense heat, and most brilliant light, may be
produced by introducing a piece of phosphorus into a jar of oxygen. The
phosphorus may be placed in a small copper cup, with a long handle of
thick wire passing through a hole in a cork that fits the jar. The
phosphorus must first be ignited; and, as soon as it is introduced into
the oxygen, it gives out a light so brilliant that no eye can bear it,
and the whole jar appears filled with an intensely luminous atmosphere.
It is well to dilute the oxygen with about one-fourth part of common air
to moderate the intense heat which is nearly certain to break the jar if
pure oxygen is used.
[Illustration]
EXPERIMENT.
If a piece of charcoal, which is pure carbon or nearly so, be ignited,
and introduced into a jar containing oxygen or common atmospheric air,
the product will be carbonic gas only, of which we shall speak
presently. As most combustible bodies contain both carbon and hydrogen,
the result of their combination is carbonic acid and water. This is the
case with the gas used for illumination; and in order to prevent the
water so produced from spoiling goods in shops, various plans have been
devised for carrying off the water when in the state of steam. This is
generally accomplished by suspending over the burners glass bells,
communicating with tubes opening into the chimney, or passing outside
the house.
To show that oxygen, or some equivalent, is necessary for the support
of combustion, fix two or three pieces of wax-taper on flat pieces of
cork, and set them floating on water in a soup-plate, light them, and
invert over them a glass jar; as they burn, the heat produced may
perhaps at first expand the air so as to force a small quantity out of
the jar, but the water will soon rise in the jar, and continue to do so
until the tapers expire, when you will find that a considerable portion
of the air has disappeared, and what remains will no longer support
flame; that is, the oxygen has been converted partly into water, and
partly into carbonic acid gas, by uniting with the carbon and hydrogen,
of which the taper consists, and the remaining air is principally
nitrogen, with some carbonic acid; the presence of the latter may be
proved by decanting some of the remaining air into a bottle, and then
shaking some lime-water with it, which will absorb the carbonic acid and
form chalk, rendering the water quite turbid.
NITROGEN.
This gas is, as its name implies, the producer of nitre, or at least
forms a portion of the nitric acid contained in nitre. It is rather
lighter than atmospheric air, colourless, transparent, incapable of
supporting animal life, on which account it is sometimes called
azote--an objectionable name, as it is not a poison like many other
gases, but destroys life only in the absence of oxygen. This gas
extinguishes all burning bodies plunged into it, and does not itself
burn. It exists largely in nature, for four-fifths of the atmosphere
consists of nitrogen gas. It is also an important constituent of animal
bodies, and is found in the vegetable world.
Nitrogen may be most easily obtained for experiment by setting fire to
some phosphorus contained in a porcelain or metallic cup, placed under a
gas jar full of air, and resting on the shelf of the pneumatic trough,
or in a soup-plate filled with water.
Nitrogen combines in five different proportions with oxygen, producing
five distinct chemical compounds, named respectively nitrous oxide,
nitric oxide, nitric tri-oxide, nitric tetr-oxide, nitric pent-oxide,
which last, united with water, forms nitric acid, now called hydric
nitrate, as nitrous acid is termed hydric nitrite.
[Illustration]
Nitrous oxide gas is generally known by the name of “laughing gas,” from
the jolly sensations experienced on inhaling it. It may be procured by
distilling in a glass retort a salt called nitrate of ammonia, which
yields the gas in considerable quantities, and it should be kept
standing in jars over water for some hours before it is used. It should
be transferred into a silk air-tight bag, furnished with a stopcock and
mouthpiece, from which the gas may be breathed; a little practice is
required to do this easily, and more resolution to desist when the gas
begins to produce its effects, as it appears to fascinate the
experimenter, and actual force is often necessary to remove the bag from
the mouth. The effects produced vary according to the temperament of the
person inhaling it; they are, however, always of a highly pleasurable
nature, muscular action being generally greatly exalted, compelling the
individual to race round the apartment and execute leaps and pirouettes
perfectly astounding. Some persons shout and sing, and I have seen one
expend his superfluous animation in twisting his features into such
ludicrous grimaces as would be the envy of the candidates at a grinning
match, and beat them all out of the field. Sir H. Davy was the
discoverer of this gas, and of its peculiar effects on the nervous
system, and a full account of it may be found in his “Researches on
Nitrous Oxide Gas.”
This gas is heavier than air, and supports combustion nearly as
energetically as oxygen, as may be shown by introducing a piece of
ignited phosphorus into a jar of this gas. It will not, however, support
the life of small animals, such as mice, which introduced into it die
very quickly.
[Illustration: PLAN OF PNEUMATIC TROUGH.]
[Illustration: SECTION OF PNEUMATIC TROUGH.]
The next compound of nitrogen with oxygen, when one proportion of
nitrogen unites with two of oxygen, is termed nit_ric_ oxide gas. It may
be easily procured by heating in a retort some copper turnings in dilute
nitric acid. It is colourless and transparent, and has the property of
combining with oxygen to form other compounds.
EXPERIMENT.
Into a jar of this gas standing over water pass some oxygen gas. The jar
will be filled with red fumes, which will be rapidly absorbed by the
water. If atmospheric air be used instead of oxygen, there will remain
in the jar the nitrogen of the air, amounting to four-fifths of the air
employed.
This gas is destructive to animal life, in consequence of its property
of uniting with the oxygen in the lungs, and producing the highly
corrosive nitrous acid gas. It will, however, support the combustion of
a few substances, phosphorus for instance, provided it is sufficiently
heated before being plunged into the gas.
We pass over the third and fourth compounds of nitrogen with oxygen, as
they are not calculated for amusing experiments. Nitric acid is easily
prepared on the small scale, by gradually heating equal parts by weight
of nitric and sulphuric acid in a retort to which a receiver has been
adapted. The receiver, which may be a clean oil flask, should be kept
cool with wetted blotting paper.
Nitrogen combines with chlorine and iodine, forming detonating
compounds, the former being so extremely dangerous that it will be
better to pass it by.
The compound with iodine, called iodide of nitrogen, may very easily be
made by pouring strong solution of ammonia (a compound of nitrogen and
hydrogen) upon some iodine in a phial, shaking them well together, and
after letting them stand for a few hours, pouring off the fluid; the
black powder remaining in the phial is the explosive compound, the
iodide of nitrogen. When dry, it is very apt to detonate spontaneously;
it should therefore be shaken out of the phial while _wet_, and spread
in very small quantities on separate pieces of blotting paper, which
should be kept apart from each other. When thoroughly dry, the slightest
touch with the point of a feather, shaking the paper on which it rests,
or even opening too rapidly the door of a closet where it has been put
to dry, will cause it to explode, producing a quantity of
violet-coloured fumes. The explosion is somewhat violent, producing a
sharp cracking noise; and the greatest care should be taken in
experimenting with it.
ATMOSPHERIC AIR.
As has been already mentioned, nitrogen is the principal constituent of
the air of the atmosphere which surrounds our globe, extending to a
height of about forty-five miles above it, and playing a most important
part in the economy of nature, inorganic as well as organic.
This atmospheric air consists by volume of nearly four-fifths of
nitrogen, and rather more than one-fifth of oxygen, viz. seventy-nine of
the former to twenty-one of the latter, or twenty-three parts by weight
of oxygen and seventy-seven of nitrogen; it generally contains also a
variable proportion of the vapour of water, and a very small quantity of
carbonic acid gas, being only about four volumes to 10,000 of air. Its
constituent parts are easily separated, as it is a mechanical mixture
and not a chemical compound, though the mixture by diffusion is so
complete that chemists have not been able to ascertain any difference in
the composition of air taken from all parts of the world, and from
different heights, up to the highest point which has to this time been
attained.
The atmosphere presses on the surface of the globe, and every being on
it, with a force of about fifteen pounds to every square inch of
surface, but as it presses equally in all directions, upwards as well as
downwards, its weight cannot be perceived unless the pressure be removed
from one surface by some artificial means.
Atmospheric air contains, besides the oxygen and nitrogen, its principal
constituents, a small proportion of carbonic acid gas, as has been
mentioned, and this may be shown by filling a tube about half full of
lime-water, and shaking it with the air contained in the other half,
when it will become slightly turbid from the insoluble carbonate of lime
formed.
When we consider that every living animal is constantly consuming
oxygen, and replacing it by carbonic acid gas, and that all burning
bodies, fires in our dwellings, furnaces, artificial lights of all
kinds, act in the same way in abstracting the oxygen from the air, and
replacing it by immense quantities of carbonic acid gas, which is a
poison to all animals who breathe, or attempt to breathe it, we must
wonder what becomes of this irrespirable gas, as it is found to exist in
the air in quantities so minute, and by what means the oxygen is
restored, and the air again made fit for respiration. This is effected
by one of those laws which the wisdom of the Creator has impressed upon
matter, by which one part of creation as it were balances another, and
all proceeds in an endless circle of change. This carbonic acid, which
is so poisonous to animal life, is the food of the vegetable world,
plants having the power of taking up the carbonic acid into their pores;
converting the carbon into their own substance, and rejecting the
oxygen, which is again respired by animals, &c. In the same way, all
animal refuse is the food of vegetables, and is used under the name of
manures.
The atmosphere contains also a variable quantity of vapour of water,
invisible as long as it is in the state of vapour, but it may be
rendered obvious by bringing any very cold body into warm air, when the
vapour will condense on the cold body in the form of small drops of
water. A tumbler of fresh-pumped water brought into a crowded room, is
almost immediately covered with moisture, and it may also be seen on
bottles of wine which have been put into ice before coming to table.
Fogs are occasioned by the condensation of vapour produced by mixing a
current of warm air with a colder air. The banks of Newfoundland are
notorious for dense fogs, occasioned by the warm air brought from the
south by the great Gulf stream, mixing with the cold air from the Arctic
regions, and thus precipitating the vapour in a visible form, rendering
everything but itself invisible. The famous London fogs depend upon the
same precipitation of the vapour of water, with the addition of the
smoke from the numerous sea-coal fires, which give it that interesting
yellow tinge for which it is so remarkable.
Aqueous vapour appears to impart a transparency to air, and permits
objects to be seen more distinctly in proportion to its quantity; hence,
when distant hills appear nearer, and objects upon them more distinct
than usual, rain may be expected, the air being fully charged with
vapour ready to be deposited on the slightest cause.
HYDROGEN.
[Illustration]
Hydrogen gas is the lightest substance known, being fifteen times
lighter than atmospheric air. It is colourless and transparent,
incapable of supporting combustion or respiration, but is itself
combustible. Hydrogen, as its name implies (being derived from two Greek
words, signifying the generator of water), is a constituent of water in
the proportion of one-ninth by weight, and is always obtained by
decomposing that fluid, by presenting to it some body to take up its
other ingredient, oxygen, and so set the hydrogen at liberty. If the
steam of water be passed through a red-hot gun barrel, containing iron
filings, the water is decomposed, the iron taking the oxygen, and the
hydrogen comes over in torrents; but as every one has not a gun barrel
and furnace to heat it, the usual mode is to employ dilute sulphuric
acid, and iron filings, or zinc, in small pieces, and it may be
collected over water by means of a bent tube issuing from the bottle in
which it is formed. It is so light that it was used to fill balloons
before coal gas was to be had, and if you procure a light air-tight bag
of silk, or thin membrane such as a turkey’s crop, and fill it with the
gas, it will ascend rapidly, and dance about the ceiling of a room.
EXPERIMENTS.
1. Attach a tobacco-pipe to a bladder filled with this gas, and blow
some soap-bubbles with it; they will rise very rapidly, and if a lighted
taper be applied to them they burn.
If you mix in a soda water bottle one-third of oxygen with two-thirds of
hydrogen, and apply flame, the mixture will explode with a sharp report.
Great care must be taken in all experiments with the mixed gases. To
avoid danger the gases are placed in separate india-rubber bags, and are
only brought together at the jet. This is an expensive apparatus, and
should only be used by experienced persons.
[Illustration]
2. If a jar of this gas be held with its mouth _downwards_, and a
lighted taper passed up well into the jar, the taper will be
extinguished, and the gas take fire, and burn quietly at the mouth of
the jar; if mixed with oxygen or atmospheric air, it will explode.
[Illustration]
Hold over the jet of hydrogen issuing from a small tube, hollow
cylinders of glass or earthenware, Florence flasks, or hollow glass
balls, and musical sounds will be produced, which were supposed to
depend on some peculiar property of hydrogen gas, until Mr. Faraday
tried flame from coal gas, olefiant gas, and even the vapour of ether,
when the sounds were still produced, and he attributed them to a
continuous explosion, or series of explosions, produced by the union of
oxygen with the hydrogen of the flames.
WATER.
With oxygen, hydrogen unites to form the important compound water, which
exists not only in the obvious form of oceans, rivers, lakes, rains,
dews, &c. &c. but is found intimately combined with many substances,
giving them some of their peculiar properties. Many crystals have a
definite proportion of water combined with them, and on losing this
water they lose their crystalline form. Many acids also cannot exist as
acids without water. The slaking of lime depends upon the union of water
with the lime, the dry powder resulting from the process being a
_hydrate_ of lime, the water having become _solidified_, and in passing
from the fluid to the solid state gives out its latent caloric,
producing the heat observed during the process. When a large quantity
of lime, a barge-load for instance, has got wetted by accident, the heat
evolved has been sufficient to set fire to the barge.
At the temperature of 32° of Fahrenheit’s thermometer, water loses its
fluid form, and becomes ice. As it solidifies, it starts into beautiful
crystals, which unite and cross each other at determinate angles. Ice is
lighter than the water on which it floats, forming a protection to the
water beneath, and preventing it from being frozen so rapidly; else, if
the ice were _heavier_ than water, and consequently sank as soon as
formed, each portion of water would be frozen in its turn, until rivers
became solid throughout, and every living creature in them must be
destroyed. Now, the temperature of the water under the ice is seldom
much below 40°, and if care be taken to break holes at intervals to
allow access to the air, the fish and other aquatic animals seldom
suffer even in our coldest winters.
Although it is impossible to raise ice even one degree above 32° without
thawing, it is not difficult to reduce water many degrees below that
point without freezing it.
[Illustration]
In order to obtain both the constituents of water in a separate state,
it must be decomposed by galvanism, each pole of a battery terminating
in a separate tube containing water, when the result will be that at the
positive pole oxygen gas will be evolved, and hydrogen at the negative,
the latter being double the quantity of the former. Now, if you mix the
gases thus obtained, introduce them into a vessel called a “Eudiometer,”
and pass an electric spark through them from a Leyden phial, a sudden
flash will be seen, and the gases will entirely disappear, being again
converted into water. If you have a mercurial trough, and perform this
experiment over mercury, the inside of the eudiometer will exhibit
minute drops of water. Thus you have proved both by _analysis_ and
_synthesis_, that water consists of oxygen and hydrogen, in the
proportion of one volume of the former to two of the latter.
EXPERIMENT.
Take some perfectly pure distilled water, filter it, surround it with a
mixture of light snow, or powdered ice, and salt, taking care to keep it
perfectly still, a thermometer having been previously placed in it. The
mercury will gradually sink many degrees below the freezing point 32°
(it has been reduced as low as 4°), the water still remaining fluid;
when all at once, either from shaking the table, or simply because the
reduction can be carried no further, it suddenly starts into ice, and
the thermometer jumps up at once to 32°, where it remains until the
whole is frozen, when the temperature gradually sinks to that of the
surrounding medium.
Now if you remove the glass of ice from the freezing mixture into the
apartment, and watch the thermometer, you will find it gradually rise to
32°, and there remain until all the ice is melted, when it will
gradually acquire the temperature of the room. The reason of this is,
that the water in passing from the solid to the fluid form absorbs, and
in passing from the fluid to the solid form gives out caloric, so
maintaining the temperature at 32°, the point at which the change of
form takes place, until it is completed.
Between the temperature of 32° and 212°, water exists in a fluid form,
under ordinary circumstances; but at the latter point it assumes the
form of vapour or steam, and acquires many of the properties of gases,
being indefinitely expansible by heat, the force increasing as the
temperature is raised, provided the steam be confined, until it becomes
irresistible,--witness the frequent explosions of steam-engines even in
this country; and in America, where the engines are worked at a high
pressure, accidents are of daily occurrence.
The temperature at which water boils is modified by the pressure applied
to it. Thus, as you ascend a mountain, and so pass through a portion of
the atmosphere, water boils at a lower temperature, until at great
heights it boils at so low a heat, that good tea cannot be made because
it is impossible to heat the water sufficiently. Under the exhausted
receiver of an air-pump, water boils at about 140°.
CHLORINE.
Another gaseous element, sometimes called a supporter of combustion, is
named chlorine, from a Greek word signifying yellowish green.
This gas was formerly called “oxymuriatic acid,” being supposed to be a
compound of oxygen and muriatic acid gases, until Sir H. Davy, in a
series of masterly experiments carried on during the years 1808-9-10 and
11, proved that it contained no oxygen or muriatic acid, and that it was
in fact a simple or undecompounded substance, and changed its name to
chlorine, which name was, after some discussion, accepted by the
scientific world, and is still in use.
This gas may be obtained for experiment, by gently heating in a retort a
mixture of muriatic or hydrochloric acid, hydrochloride, as it is now
called, with some black oxide of manganese: the muriatic acid, a
compound of chlorine and hydrogen, is decomposed, and so is the oxide of
manganese, giving out some of its oxygen, which takes the hydrogen from
the muriatic acid to form water, while the chlorine gas, with which the
hydrogen had been united, is set at liberty, and may be collected in
jars over water.
[Illustration]
Chlorine gas is transparent, of a greenish yellow colour, has a peculiar
disagreeable taste and smell, and if breathed even in small quantities,
occasions a sensation of suffocation, of tightness in the chest, and
violent coughing, attended with great prostration. I have been compelled
to retire to bed from having upset a bottle containing some of this gas.
It destroys most vegetable colours when moist, and is in fact the agent
now universally employed for bleaching purposes.
It has also the power of combining with and destroying all noxious
smells, and is invaluable as a purifier of foul rooms, and destroyer of
infection. For these latter purposes it is used in combination with
lime, either in substance or solution, under the name of “Chloride of
Lime.”
Sir W. Burnett has lately discovered that the chloride of zinc answers
the same purposes as the chloride of lime, and has the advantage of
being itself destitute of smell, and his fluid is frequently substituted
for the other.
Chlorine gas is a powerful supporter of combustion, many of the metals
taking fire spontaneously when introduced in a fine state of division
into the gas.
EXPERIMENTS.
1. Into a jar of chlorine gas introduce a few sheets of copper leaf,
sold under the name of Dutch foil, when it will burn with a dull red
light.
2. If some metallic antimony in a state of powder be poured into a jar
of this gas, it will take fire as it falls, and burn with a bright white
light.
3. A small piece of the metal potassium may be introduced, and will also
take fire.
4. A piece of phosphorus will also generally take fire spontaneously
when introduced into this gas. In all these cases direct compounds of
the substances with chlorine are produced, called chlorides.
5. If a lighted taper be plunged quickly into the gas, it will continue
to burn with a dull light, giving off a very large quantity of smoke,
being in fact the carbon of the wax taper, with which the chlorine does
not unite; while the other constituent of the taper, the hydrogen, forms
muriatic acid by union with the chlorine.
6. This substance has the property of destroying most vegetable colours,
and is used in large quantities for bleaching calico, linen, and the
rags of which paper is made. It is a curious fact that it shows this
property only when water is present, for if a piece of coloured cloth is
introduced dry into a jar of the gas, also dry, no effect will be
produced--wet the cloth, and reintroduce it, and in a very short time
its colour will be discharged.
7. Introduce a quantity of the infusion of the common red cabbage, which
is of a beautiful blue colour, into a jar of this gas, and it will
instantly become nearly as pale as water, retaining a slight tinge of
yellow. A solution of sulphate of indigo can always be obtained, and
answers well for this experiment.
MURIATIC ACID GAS, OR HYDRIC CHLORIDE.
With chlorine, hydrogen forms a compound called muriatic, or
hydrochloric acid gas. It cannot easily be formed by the direct union of
its elements, but is procured from some compound in which it exists
ready formed. Common salt (chloride of sodium) is generally employed;
and when acted on by strong sulphuric acid (or oil of vitriol), the gas
is disengaged in abundance. It must be collected over mercury, for water
absorbs it, forming the liquid muriatic, or hydrochloric acid.
A lighted taper plunged into this gas is instantly extinguished. It is
very dangerous to animal life if respired. It has the property of
destroying animal effluvia, and was once employed to purify the
cathedral of Dijon, which was so filled with putrid emanations from the
bodies buried in it, that it had been closed for some time. It perfectly
succeeded, but it is so destructive to all metallic substances that it
is not used now, for the chlorides of lime and zinc have since been
discovered to act more effectually than the muriatic acid gas, without
its inconvenience.
The compounds of hydrogen with iodine are passed over.
With nitrogen, hydrogen unites and forms one of the most extraordinary
compounds in the whole range of chemistry,--the gas called ammonia. This
is the only gas possessing what are called alkaline properties; _i. e._
it changes the blue colour of certain vegetables to green, yellow to
deep brown, and unites with the acids to form neutral compounds, just as
the other alkalies, potash and soda, which are oxides of metals. It may
be procured in abundance by heating the hydrochlorate of ammonia, or sal
ammoniac, as it is usually called, with quick-lime, which takes the
hydrochloric acid, and sets free this remarkable gas. It must be
received over mercury, as it is absorbed to almost any extent by water,
forming the fluid sold as “spirits of hartshorn” in the shops.
This gas is colourless and transparent, lighter than atmospheric air,
and will not support combustion; it has a very pungent but not
disagreeable smell. Under certain circumstances it is combustible.
EXPERIMENTS.
1. Take a bottle containing chlorine gas, and invert over its mouth
another filled with ammoniacal gas; then if the bottles be held in the
hand (guarded by a pair of gloves), and suddenly turned, so that the
chlorine be uppermost, the two gases will unite so rapidly that a white
flame fills the bottles for an instant.
2. Substitute for the chlorine of the last experiment a bottle of
carbonic or hydrochloric acid gas; in either case the gases disappear,
and a light white powder settles on the sides of the bottles, being the
carbonate or hydrochlorate of ammonia, according to the acid used.
Carbonate of ammonia is the substance sold for “smelling salts;” and the
hydrochlorate, or muriate of ammonia, is the salt called “sal ammoniac,”
whence the alkaline gas was first obtained, and from which it got its
name of ammonia. The salt itself was so called, because it was formerly
brought from the deserts near the ruins of the temple of Jupiter Ammon.
This salt is, as has been shown, a compound of muriatic acid gas and
ammoniacal gas, containing therefore only _three_ simple
elements--hydrogen, chlorine, and nitrogen, all gases, and known only in
the gaseous state, its symbol being NH₄Cl; yet they by union form a
solid body, resembling in all essential qualities the salts of potash
and soda, which are oxides of known metals. Moreover, if some mercury be
placed in a solution of this salt, and subjected to the action of
galvanism, the _negative_ pole being applied to the mercury, and the
positive to the sal ammoniac, the mercury presently loses its fluidity,
increases greatly in size, and in fact presents the same appearance as
when it is mixed with some metal, forming what is called an “amalgam.”
When the battery ceases to act, a succession of white films forms on the
surface of the amalgam, and the mercury soon returns to its original
state. How is this to be explained? Some chemists have supposed that
there must be a _base_ united to the mercury, and have named this
hypothetical substance “ammonium,” to correspond to potassium and
sodium, the bases of potash and soda, which resemble ammonia in so many
properties. But what is this ammonium? and how is it formed? for
hydrogen and nitrogen are simple elementary bodies. Are _all_ metals
compounds of gases? and are there but a few elements instead of the 64
now enumerated? This, however, is a difficult question, not fitted for
discussion here.
Carbonate of ammonia may be obtained by mixing together powdered chalk
(which is a carbonate of lime) and muriate of ammonia, and heating the
mixture in close vessels, when the salt in question will rise in fumes,
and be condensed in a mass in the upper part of the vessel. It is,
however, so largely produced in other manufactures, particularly in
gas-works, that there is no necessity to resort to the more expensive
and direct method. It is the well-known “smelling salts.”
The only other salt of ammonia worth our notice here is the nitrate,
from the destructive distillation of which is obtained the nitrous
oxide, or laughing gas, already mentioned.
IODINE.
On the coasts of certain islands belonging to the Duke of Argyll, vast
quantities of sea-weed are occasionally torn up from their ocean beds
and deposited on the shores. This weed, after being partially dried by
exposure to the sun and air, is burnt in a shallow pit; the ashes are
then collected, and form the commercial raw material called kelp, from
which iodine is procured by a gradual series of processes.
EXPERIMENTS.
Iodine has a beautiful metallic lustre, with a bluish black colour, and
should be kept in a well-stoppered bottle. A small quantity placed in a
clear flask and heated, affords a magnificent violet vapour, which may
be poured from the flask into another glass vessel, when it condenses
again into crystalline plates. The colour of the vapour originates the
name of this element, so called from the Greek Ἰώδης, violet-coloured.
If a little iodine be placed in contact with a thin slice of phosphorus,
the latter takes fire almost immediately.
BROMINE.
So called from the Greek βρόμος, a bad odour, is most intimately allied
with chlorine and iodine; like these elements it belongs to the sea, and
is a constituent of sea-water. Bromine is a very heavy fluid, and should
be preserved by keeping it covered with water in a stoppered-bottle.
Experiments with liquid bromine are not recommended, as all the most
interesting ones can be performed with the vapour, which is easily
procured by letting fall a few drops of bromine into a warm dry bottle.
EXPERIMENTS.
Pounded antimony sprinkled into the vapour takes fire immediately.
A thin slice of phosphorus placed in a deflagrating ladle and placed
into the vapour of bromine ignites very quickly.
A solution of sulphate of indigo, or an infusion of red cabbage, are
easily bleached by being shaken violently with the vapour of bromine.
FLUORINE.
In many parts of England, especially in Devonshire, Cornwall, and above
all in Derbyshire, is found a very beautiful mineral, known by the name
of Fluor Spar, Derbyshire Spar, and called by the miners Blue John, to
distinguish it from another mineral found, in the same locality, called
_Black Jack_. It occurs in very regular and frequently large crystals in
the form of cubes, and occasionally in octoëdra. It is a compound of
calcium with fluorine, and is very abundant in certain fossil bones.
This element, in combination with hydrogen and called hydrofluoric acid,
acts so energetically upon all substances containing silica, that it
cannot be preserved in vessels of glass or porcelain--very few of the
metals are capable of resisting its action, lead being nearly the only
common metal possessed of this power. Gutta percha may also be employed
for vessels to hold it.
This property of dissolving silica, has caused this acid to be used for
engraving on glass.
EXPERIMENT.
Mix one part of powdered fluor-spar, quite pure, with two parts of oil
of vitriol, in a saucer, and apply a gentle heat, when the acid will be
disengaged in the form of vapour. Prepare a piece of glass after the
manner of engraving on copper, by coating it with a thin covering of
wax, placing a paper over the wax, and then drawing any design with a
sharp-pointed instrument, when, on removing the paper, the wax-coating
will be found to be removed wherever the instrument has passed over it.
Now invert, this glass over the fumes of the acid for half an hour or
so, and then heat the glass so as to soften the coating, and wipe it
off; the design will then appear “bitten in” as the term is, that is,
the acid will have dissolved the glass wherever it was not protected by
the wax, and will exhibit the design indelibly fixed on the glass.
This acid requires the greatest care in handling, for it is extremely
corrosive, producing very troublesome ulcers if it comes in contact with
the skin; even the fumes will produce smarting if the skin is long
exposed to them.
CARBON.
The next substance in our list of elementary bodies is named carbon.
The purest form of carbon is the precious stone called diamond, which
consists entirely of carbon in a crystallized form. The French chemist
Lavoisier was the first who proved the combustibility of the diamond;
and Sir H. Davy found that when once set on fire it would continue to
burn in oxygen gas air, and that the product of the combustion was
carbonic acid gas, exactly equal in quantity to the gas produced by
burning an equal weight of pure charcoal, the most common form of
carbon.
Plumbago, or “black-lead,” as it is very improperly called, is also
nearly pure carbon, a very small quantity of iron being united with it.
By far the greater part of all vegetable, and a very large portion of
animal bodies consists of carbon; and in the state of carbonic acid in
combination with lime and some other earths, it forms nearly the half of
all the chalk, marble, and limestone of our hills; so that it is, in one
shape or other, one of the most widely diffused bodies in nature.
Carbon forms two gaseous compounds with oxygen; the first, called
carbonic oxide, is easily obtained by boiling oxalic acid with its own
bulk of sulphuric acid, in a flask to which a cork and bent tube is
attached. The gas comes over in large quantities, and must be collected
in a gas jar, or the pneumatic trough. It is inflammable, and burns with
a lambent blue flame.
The other compound, carbonic acid, is transparent, colourless, much
heavier than atmospheric air, has an agreeable taste, has the power of
irritating the mucous membrane of the nose, (as any one can tell who has
drunk soda-water), without possessing any particular odour, is absorbed
by water, does not support respiration, and extinguishes flame.
Carbonic acid gas may be obtained with the greatest facility by pouring
some muriatic or sulphuric acid, diluted with about six parts of water,
upon some pieces of marble or limestone in a bottle with a tube
attached, when the gas comes over in torrents. It may be collected over
water.
EXPERIMENTS.
[Illustration: STOPPERED BOTTLE FOR HOLDING GAS.]
1. To show the great comparative weight of this gas, place a lighted
taper at the bottom of a tall glass jar, then take a jar full of
carbonic acid gas, and pour it as you would pour water into the jar
containing the lighted taper; you will soon find the taper will be
extinguished as effectually as if you had poured water on it, and the
smoke of the taper will float on the surface of the gas in very
beautiful wavy forms.
2. Heat a piece of the metal potassium in a metal spoon (platinum is
best), and if introduced in a state of ignition into the gas, it will
continue burning brilliantly, producing a quantity of dense smoke, which
is the carbon from the carbonic acid, the potassium having seized the
oxygen and being converted by it into potash.
3. If a mouse, bird, or other small animal, be placed in a jar of this
gas, it becomes insensible almost immediately, but if speedily removed
it will occasionally recover.
4. Shake up some water with some of this gas in a bottle; the greater
part of the gas will be absorbed by the water, which acquires a
sparkling appearance and a pleasant sharp taste; with the addition of a
little soda this becomes the well-known beverage called soda-water, so
famous for removing the morning headaches caused by “_that salmon_”
having disagreed at yesterday’s dinner.
It is the presence of this gas which renders it so dangerous to descend
into deep wells, for by its great weight it collects at the bottom, and
instantly suffocates any unfortunate person who incautiously subjects
himself to it. Hence it is prudent always to let down a lighted candle
before any one descends into a well, or other deep excavation, and if
the candle is extinguished, it is necessary to throw down several pails
of water, lime-water if possible, and again to try the candle, which
must burn freely before it is safe for any one to descend.
It is this same gas under the name of “choke-damp,” which proves so
dangerous to miners, particularly after an explosion of “fire-damp,” for
it is the principal product of the explosion, and it is by no means an
easy matter to dislodge it.
Carbonic acid gas has been condensed into the fluid form by causing it
to be disengaged under great pressure; the fluid acid has the appearance
of water. When the pressure is removed, as by allowing some of the fluid
acid to escape from the vessel in which it has been condensed, it
instantly reassumes the gaseous form, and in so doing absorbs so much
latent caloric that a portion of the acid is actually solidified, and
appears in the shape of _snow_, which may be collected and preserved for
a short time. After a lecture by Mr. Addams before the Ashmolean Society
of Oxford, I carried a kind of _snowball_ of carbonic acid for a
distance of 500 or 600 yards, and placed it in a saucer in a room. It
evaporated very rapidly, and left no residue, not even a mark where it
had lain. It was too _cold_ to be touched by the naked hand without
pain.
Carbonic acid and lime are mutually tests for each other. If a jar
containing a little lime-water be put into a jar of this gas, it
speedily becomes turbid, the gas uniting with the lime, and producing
chalk (the carbonate of lime), which is insoluble in water.
This gas is produced in large quantities by the respiration of animals,
as may be proved by respiring through a tube immersed in lime-water,
when the water will be instantly rendered turbid from the formation of
chalk.
CARBON AND HYDROGEN.
To the combination of these elements in various proportions, and with
the occasional addition of other substances, we are indebted for all, or
nearly all, our means of obtaining light and heat. Coal, wood, spirit,
oil, and all the varieties of fats, are composed principally of carbon
and hydrogen, and may easily be converted into the gas with which our
houses and streets are lighted, which is nearly pure carburetted
hydrogen.
The two chief definite gaseous compounds of these two elements are the
light carburetted hydrogen, and the heavy carburetted hydrogen, or
olefiant gas. The first is easily procured by stirring the bottom of
stagnant water on a hot summer’s day, and collecting the bubbles in a
bottle filled with water and inverted over the place where the bubbles
rise. This gas burns with a yellowish flame, and when mixed with a
certain proportion of air, or oxygen gas, explodes with great violence
on the application of a flame. It is the much dreaded fire-damp
generated so profusely in some coal-mines, and causing such fearful
destruction to life and property when accidentally inflamed.
The other compound, the heavy carburetted hydrogen, forms part of the
gas used for illumination; and, in fact, whatever substance is employed
for artificial light, whether oil, tallow, wax, &c. &c. it is converted
into this gas by heat, and then furnishes the light by its own
combustion.
This gas has some very curious properties, and may be obtained nearly
pure by mixing in a retort, _very carefully_, one part of spirits of
wine and four of sulphuric acid. A lamp must be placed under the retort,
when the gas will be speedily disengaged, and come over in great
abundance; it may be collected over water.
This gas is transparent, colourless, will not support combustion, but is
itself inflammable, burning with a brilliant white light, and being
converted into carbonic acid and water. If mixed with three or four
times its bulk of oxygen, or with common atmospheric air in much larger
proportions, it explodes with great violence.
This gas is sometimes called “olefiant gas,” from the property it has of
forming an oily substance when mixed with chlorine.
[Illustration: JAR FOR COLLECTING GASES.]
EXPERIMENT.
Into a jar standing over water half full of this gas, pass an equal
quantity of chlorine gas. The gases will speedily unite and form an
oily-looking liquid, which may be collected from the sides of the jar as
it trickles down. By continually supplying the jar with the two gases as
they combine, a considerable quantity of this substance may be
collected. Care should be taken that the olefiant gas is rather in
excess.
The substance produced is insoluble in water, with which it should be
washed by shaking them together in a tube, and has a pleasant sweetish
taste and aromatic smell, somewhat resembling ether.
COAL GAS.
The gas so universally employed for the purposes of illumination is a
mixture of the carburetted and the bi-carburetted hydrogen, with minute
portions of other gases scarcely worth mentioning. It is procured by
submitting coals to a red heat in iron retorts, having a tube passing
from one end, along which passes all the fluid and gaseous matter
separated from the coal, namely, gas tar, ammoniacal liquor, and various
gases, carburetted hydrogen, carbonic acid, sulphuretted hydrogen, &c.
&c. The tar and ammoniacal liquor remain in the vessel in which the
tubes from the retorts terminate, and the gaseous productions are
conveyed through water and lime to separate the impurities; the
remaining gas, now fit for use, passes into large iron vessels, called
gasometers, inverted over water (like the jars in a pneumatic trough),
whence it is sent through pipes and distributed where required. What
remains in the retorts is called coke. It consists principally of
charcoal, mixed with the earthy and metallic particles contained in the
coal.
EXPERIMENT.
If you possess an iron bottle, fill it with powdered coal, and attach a
flexible tube to it, and put it in the fire: as soon as it becomes red
hot, large quantities of smoke will escape from the end of the tube,
being the gas mixed with all its impurities. By passing it through water
(if mixed with lime it will be better), the gas may be collected in jars
standing over water, and submitted to experiment. If you do not possess
a bottle, take a tobacco-pipe with a large bowl, (a “churchwarden” for
example); fill the bowl with small coal, cover it with clay or putty,
and when dry put it into the fire, and the gas will soon appear at the
other end of the pipe, when it may be lighted, or the gas may be
collected over water, as in the former experiment.
The light carburetted hydrogen contained in this gas is given off
spontaneously in some coal-mines, and as it forms explosive mixtures
with atmospheric air, the mines where it abounds could not be worked
except at the greatest risk until about the beginning of the present
century, when Sir H. Davy, while prosecuting some researches on the
nature of flame, found that flame would not pass through metallic tubes,
and he gradually reduced the length of the tubes, until he found fine
iron wire gauze formed an effectual barrier against the passage of
flame. He then thought that if the light in a lantern were surrounded
with this gauze, it might safely be used in an inflammable atmosphere,
where a naked light would instantly cause an explosion. Upon submitting
the lamp to experiment, he found that by passing coal gas by degrees
into a vessel in which one of his lamps was suspended, the flame first
became much larger, and then was extinguished, the cylinder of gauze
being filled with a pale flame, and though the gauze sometimes became
red-hot, it did not ignite the gas outside. As the supply of coal gas
was diminished, the wick of the lamp was rekindled, and all went on as
at first. A coil of platinum wire was afterwards suspended in the lamps,
which becomes intensely heated by the burning gas, and gives out
sufficient light to enable the miner to see to work. As long as the
gauze is perfect it is almost impossible for the external air to be
kindled by the wick of the lamp, but the miners are so careless that
they will often remove the gauze to get a better light, to look for a
tool, or some cause equally trivial, and many lives have been lost in
consequence of such carelessness.
The effect of fine wire gauze in preventing the passage of flame may be
shown by bringing a piece of the gauze gradually over the flame of a
spirit-lamp, until it nearly touches the wick, when the flame will be
nearly extinguished, but the vapour of the spirit passes through, and
may be lighted on the upper side of the gauze, which will thus have a
flame on either side, though totally unconnected with each other. The
flame from a gas-burner will answer as well as the spirit-lamp.
Nearly all the fluids, and solids also, used for procuring artificial
light, such as naphtha, various oils, tallow, wax, spermaceti, spirits
of wine, ether, &c. &c. are compounds of carbon and hydrogen in
different proportions, with the occasional addition of some other
elements, especially oxygen and hydrogen, in the proportions to form
water; as a general rule, those bodies containing the greatest
proportion of carbon give the most light, though not necessarily the
most heat.
PHOSPHORUS.
The next body we have to notice is phosphorus, a most remarkable
substance, procured from the earthy part of bones by a process not worth
detailing here. It should be _always_ kept under water, and the naked
fingers should not be allowed even to touch it, for the smallest piece
getting under the nail will inflame the first time the hand comes near
the fire, and produce a sore very painful and difficult to heal. It
should be cut under water by a knife or scissors, and removed with a
pair of forceps. Its combustible properties have been frequently
mentioned. It has also the property of shining in the dark, so that if
you write on a wall with a solution of phosphorus in oil, the letters
will appear luminous in the dark--there is no danger, excepting from the
greasiness of the oil.
Of the compounds of phosphorus with oxygen we have nothing to do here,
but it forms with hydrogen a very curious gaseous compound, which takes
fire spontaneously on the contact of air, or almost any gas containing
oxygen.
EXPERIMENTS.
It may be procured in either of two ways, according to the purpose for
which it is wanted. The simplest way is to put a lump or two of
phosphuret of lime into a saucer, about two inches in depth, containing
some very diluted hydrochloric acid; bubbles of gas will speedily arise,
and bursting on the surface of the fluid will burn with a slight
explosion, and a circular wreath of smoke will rise into the atmosphere,
enlarging as it rises, and wreathing itself round and round in the most
elegant forms. Care must be taken that the phosphuret is _fresh_, and
has been kept in a well-closed bottle, or the experiment will fail. The
apartment must be free from draughts. If you desire to collect the gas,
another method must be employed.
[Illustration]
Fill a small retort _quite full_, neck and all, of a solution of caustic
potash, drop five or six pieces of phosphorus into it, place the finger
on the end of the retort, and immerse it in a basin also containing a
_hot_ solution of potash, remove the finger, and on applying the heat of
a lamp to the retort, the gas will soon be disengaged rapidly, and drive
out the fluid in the retort; it then escapes into the air, when it
inflames with the same appearances as before described. Or it may be
collected in gas jars filled with the potash solution, and held over the
mouth of the retort. The object in using _hot_ solution of potash in the
basin is, that when the gas ceases to be given off, and the heat of the
lamp is withdrawn, the hot fluid may gradually fill the vacuum which
will form in the retort, and so prevent its being broken.
This gas is transparent and invisible, like most other gases. It is very
poisonous if inhaled. If kept for any time, it loses its property of
spontaneous inflammation, and must therefore be made at the time it is
required.
SULPHUR.
Sulphur, or brimstone, as it is frequently called, is sold in the form
of sticks, or _roll_ brimstone, or in fine powder called flowers of
brimstone.
It is capable of showing electric phenomena when rubbed, giving out
slight sparks, and first attracting and then repelling light bodies,
such as small pieces of paper, &c. It is so bad a conductor of heat,
that if grasped suddenly in a hot hand, it will crack and split into
pieces just as glass does when suddenly heated or cooled--of course I am
speaking of the roll brimstone. Water has no effect on it, as may be
seen in the pans placed for pet dogs to drink out of, where the same
piece of brimstone lies for years entirely unaltered, though it is
supposed to prevent the dogs from having the mange!
Sulphur is largely used in the arts, principally in the manufacture of
gunpowder, and fireworks of various kinds.
It combines with hydrogen, and forms a gaseous compound called
sulphuretted hydrogen, which is almost the most poisonous of all the
gases. It fortunately has so abominable smell, that due notice is given
of its presence. Rotten eggs, a dirty gun-barrel, cabbage water, putrid
animal and vegetable matter, &c. are indebted to this gas for their
inviting odour; and it is found in certain mineral springs, as at
Harrogate, where the water contains a considerable quantity of this gas,
and is found useful in many diseases of the skin. It is also given off
in a gaseous form by some volcanoes.
This gas may be obtained by pouring dilute hydrochloric acid upon a
metallic sulphuret, such as that called crude antimony, being a native
sulphuret of that metal. The gas may be kept for a short time over
water. It is colourless and transparent, inflammable, but quite
irrespirable, a small bird dying instantly when placed in air containing
only 1/1500th of this gas. Its most remarkable property perhaps is the
effect it has on certain metallic oxides, and other metallic salts,
blackening them instantly. White paint is easily stained by this gas,
and it will darken the colour of a metal in a solution, especially of
lead, even when diluted with 20,000 times its weight of water. By way of
experiment, slips of riband, silk, or even paper, may be wetted with
various metallic solutions, such as silver, mercury, lead, &c. or words
may be written with the solutions, and on holding them over a stream of
this gas they will be instantly darkened.
If this gas be collected in the pneumatic trough, which is usually
painted _white_, you will have the pleasure of seeing the colour changed
to a very dark brown, when your experiments are finished. With this very
limited description of some of the non-metallic elements and their
combinations, we must, for want of space, take leave of this division of
chemistry; “the beginning of which is pleasure, its progress knowledge,
its objects truth and utility.”--(_Davy._)
METALS.
We have a few words to say about a class of bodies called metals, which
are of the utmost importance to mankind, and indeed without some of
them, especially iron, few of the arts of civilized life could exist.
Fifty substances are now included in the list of metals; some of them,
however, are only _supposed_ to exist, such as _ammonium_, the supposed
base of ammonia; and very many are to be viewed rather in the light of
chemical curiosities, as from their great rarity they are too expensive
for use, even if possessed of valuable properties of which others might
be destitute.
Several metals have been known from the earliest period of which we have
any record; such were iron, gold, silver, copper, lead, tin, mercury,
and probably zinc, or at least its ores; for brass, which is an alloy of
copper and zinc, is frequently mentioned in the early part of the Old
Testament. In the sixteenth century others were discovered, such as
antimony and bismuth. In the last century, cobalt, arsenic, platinum,
nickel, manganese, and chromium, together with several unimportant
metals, were discovered by various philosophers; while in the present
century, Dr. Wollaston discovered rhodium, the hardest and nearly the
most indestructible of all the metals; and a few years later, Sir
Humphry Davy found that the alkalies, potash, and soda, with many of the
earths as they were called, had each a metal for its base, to which he
gave the Latin name of the alkali or earth, with the termination _um_,
as potassi_um_, the base of potassa, sodi_um_ of soda, calci_um_ of calx
(lime), &c.
Until Sir H. Davy’s discovery of the metals of the alkalies, great
specific gravity was regarded as one of the most striking
characteristics of a metal, the lightest of them being much heavier than
the heaviest earth; but potassium is very much lighter than water, and
not much heavier than spirits of wine. The other metals vary from a
specific gravity of nearly twenty-one--or twenty-one times heavier than
an equal bulk of water--that of platinum, to somewhat less than seven,
which is the specific gravity of antimony.
When pure, they all have a lustre, differing indeed among themselves,
but so peculiar that it is called the metallic lustre, for instance,
gold and copper are yellow and red--nearly all the others white, but of
a different shade; still there is no mistaking their metallic character,
no other substances at all equalling them in this respect. They are also
opaque, although some, like gold, when reduced to thin films, allow
light to pass through them. They are all good conductors of heat and
electricity, though some possess that property to a greater extent than
others.
Many of them are what is called malleable, that is, may be extended or
spread out by rolling, or beating them with a hammer; and ductile, or
have the property of being drawn out into wire. Gold, silver, copper,
and iron, are the most remarkable in this respect.
All the metals are fusible, but some require very different degrees of
heat to render them fluid,--platinum requiring the heat of the
oxy-hydrogen blowpipe, while tin melts in the flame of a candle, and
mercury is fluid at all temperatures in this climate, but becomes solid
at 40° Fahr. below 0,--a temperature occasionally experienced in the
Arctic regions, where the mercurial thermometer is useless, the mercury
becoming solid.
They are all excellent conductors of heat and electricity, and have the
property of reflecting light and forming mirrors; for looking-glasses
owe their power of reflecting objects principally to what is called the
“silvering;” that is, a mixture of mercury and tin spread over the back
of the glass, which being transparent, allows the image reflected from
the metal to pass through it.
The following classification is most instructive, because it suggests to
the young student that there must be identical properties in the metals
thus placed together:--
_Class 1._ Ammonium, cæsium, lithium, potassium, sodium.
_Class 2._ Calcium, barium, strontium.
_Class 3._ Aluminium, cerium, didymium, erbium, glucinium, lanthanum,
thorium, yttrium, zirconium.
_Class 4._ Zinc class: cadmium, magnesium, zinc.
_Class 5._ Iron class: cobalt, chromium, indium, iron, manganese,
nickel, uranium.
_Class 6._ Tin class: niobium, tantalum, tin, titanium.
_Class 7._ Tungsten class: molybdenum, tungsten, vanadium.
_Class 8._ Arsenic class: antimony, arsenic, bismuth.
_Class 9._ Lead class: lead, thallium.
_Class 10._ Silver class: copper, mercury, silver.
_Class 11._ Gold class: gold, iridium, osmium, palladium, platinum,
rhodium, ruthenium.
POTASSIUM.
Potassium was discovered by Sir H. Davy in the beginning of the present
century, while acting upon potash with the enormous galvanic battery of
the Royal Institution, consisting of 2,000 pairs of 4-inch plates. It is
a brilliant white metal, so soft as to be easily cut with a penknife,
and so light as to swim upon water, on which it acts with great energy,
uniting with the oxygen, and liberating the hydrogen, which takes fire
as it escapes.
EXPERIMENT.
Trace some continuous lines on paper with a camel’s-hair brush dipped in
water, and place a piece of potassium about the size of a pea on one of
the lines, and it will follow the course of the pencil, taking fire as
it runs, and burning with a purplish light. The paper will be found
covered with a solution of ordinary potash. If turmeric paper be used,
the course of the potassium will be marked with a deep brown
colour.--_Corollary._ Hence, if you touch potassium with _wet_ fingers
you will burn them!
If a small piece of the metal be placed on a piece of ice, it will
instantly take fire, and form a deep hole, which will be found to
contain a solution of potash.
In consequence of its great affinity for oxygen, potassium must be kept
in some fluid destitute of that element, such as naphtha.
_Caution!_--As the globules of potassium after conversion into potash,
when thrown on ice or water burst, strewing small particles of caustic
hot potash in every direction, the greatest care should be taken to
keep at a sufficient distance whilst performing the above experiment.
Saltpetre, or nitre, is a compound of this metal (or rather its oxide)
with nitric acid. It is one of the ingredients of gunpowder, and has the
property of quickening the combustion of all combustible bodies.
Mix some chlorate of potash with lump sugar, both being powdered, and
drop on the mixture a little strong sulphuric acid, and it will
instantly burst into flame. This experiment also requires caution.
Want of space precludes us from considering the individual metals and
their compounds in detail; it must suffice to describe some experiments
showing some of their properties.
The different affinities of the metals for oxygen may be exhibited in
various ways. The silver or zinc tree has already been described, page
357.
EXPERIMENTS.
1. Into a solution of nitrate of silver in distilled water immerse a
clean plate or slip of copper. The solution, which was colourless, will
soon begin to assume a greenish tint, and the piece of copper will be
covered with a coating of a light grey colour, which is the silver
formerly united to the nitric acid, which has been displaced by the
greater affinity or _liking_ of the oxygen and acid for the copper.
2. When the copper is no longer coated, but remains clean and bright
when immersed in the fluid, all the silver has been deposited, and the
glass now contains a solution of _copper_.
Place a piece of clean iron in the solution, and it will almost
instantly be coated with a film of _copper_, and this will continue
until the whole of that metal is removed, and its place filled by an
equivalent quantity of _iron_, so that nitrate of _iron_ is found in the
liquid. The oxygen and nitric acid remain unaltered in quantity or
quality during these changes, being merely transferred from one metal to
another.
A piece of zinc will displace the iron in like manner, leaving a
solution of nitrate of zinc.
Nearly all the colours used in the arts are produced by metals and their
combinations; indeed, one is named _chromium_, from a Greek word
signifying colour, on account of the beautiful tints obtained from its
various combinations with oxygen and the other metals. All the various
tints of green, orange, yellow, and red, are obtained from this metal.
Solutions of most of the metallic salts give precipitates with solutions
of alkalies and their salts, as well as with many other substances, such
as what are usually called prussiate of potash, hydro-sulphuret of
ammonia, &c.; and the colours differ according to the metal employed,
and so small a quantity is required to produce the colour that the
solutions before mixing may be nearly colourless.
EXPERIMENTS.
1. To a solution of sulphate of iron add a drop or two of a solution of
prussiate of potash, and a blue colour will be produced.
2. Substitute sulphate of copper for iron, and the colour will be a rich
brown.
3. Another blue, of quite a different tint, may be produced by letting a
few drops of a solution of ammonia fall into one of sulphate of
copper--a precipitate of a light blue falls down, which is dissolved by
an additional quantity of the ammonia, and forms a transparent solution
of the most splendid rich blue colour.
4. Into a solution of sulphate of iron let fall a few drops of a strong
infusion of galls, and the colour will become a bluish-black--in fact,
_ink_. A little _tea_ will answer as well as the infusion of galls. This
is the reason why certain stuffs formerly in general use for dressing
gowns for gentlemen were so objectionable; for as they were indebted to
a salt of iron for their colour, buff as it was called, a drop of tea
accidentally spilt produced all the effect of a drop of ink.
5. Put into a largish test tube two or three small pieces of granulated
zinc, fill it about one-third full of water, put in a few grains of
iodine and boil the water, which will at first acquire a dark purple
colour, gradually fading as the iodine combines with the zinc. Add a
little more iodine from time to time, until the zinc is nearly all
dissolved. If a few drops of this solution be added to an equally
colourless solution of corrosive sublimate (a salt of mercury) a
precipitate will take place of a splendid scarlet colour, brighter if
possible than vermilion, which is also a preparation of mercury.
CRYSTALLIZATION OF METALS.
Some of the metals assume certain definite forms in returning from the
fluid to the solid state. Bismuth shows this property more readily than
most others.
EXPERIMENT.
Melt a pound or two of bismuth in an iron ladle over the fire; remove it
as soon as the whole is fluid; and when the surface has become solid
break a hole in it, and pour out the still fluid metal from the
interior; what remains will exhibit beautifully formed crystals of a
cubic shape.
Sulphur may be crystallized in the same manner, but its fumes when
heated are so very unpleasant that few would wish to encounter them.
One of the most remarkable facts in chemistry, a science abounding in
wonders, is the circumstance, that the mere contact of hydrogen, the
_lightest_ body known, with the metal platinum, the heaviest, when in a
state of minute division, called spongy platinum, produces an intense
heat, sufficient to inflame the hydrogen: of course this experiment
must be made in the presence of atmospheric air or oxygen.
Time and space (or rather the want of them) compel us to conclude with a
few experiments of a miscellaneous character.
TO FORM A SOLID FROM TWO LIQUIDS.[7]
Prepare separately, saturated solutions of sulphate of magnesia (Epsom
salts) and carbonate of potash. On mixing them the result will be nearly
solid.
[7] Saturated solutions are made by adding the salt to _boiling_ water
until it will take up no more, letting it stand till cold and then
pouring off the liquid.
Solutions of muriate of lime and carbonate of potash will answer as
well.
TO FORM A LIQUID FROM TWO SOLIDS.
Rub together in a Wedgewood mortar a small quantity of sulphate of soda
and acetate of lead, and as they mix they will become liquid.
Carbonate of ammonia and sulphate of copper, previously reduced to
powder separately, will also, when mixed, become liquid, and acquire a
most splendid blue colour.
The greater number of salts have a tendency to assume regular forms, or
become _crystallised_, when passing from the fluid to the solid state;
and the size and regularity of the crystals depends in a great measure
on the slow or rapid escape of the fluid in which they were dissolved.
Sugar is a capital example of this property; the ordinary loaf-sugar
being rapidly boiled down, as it is called: while to make sugar-candy,
which is nothing but sugar in a crystallized form, the solution is
allowed to evaporate slowly, and as it cools it forms into those
beautiful crystals termed sugar-candy. The threads found in the centre
of some of the crystals are merely placed for the purpose of hastening
the formation of the crystals.
EXPERIMENTS.
1. Make a strong solution of alum, or of sulphate of copper, or blue
vitriol, and place in them rough and irregular pieces of clinker from
stoves, or wire-baskets, and set them by in a cool place, where they
will be free from dust, and in a few days crystals of the several salts
will deposit themselves on the baskets, &c.; they should then be taken
out of the solutions, and dried, when they form very pretty ornaments
for a room.
2. Fill a Florence flask up to the neck with a strong solution of
sulphate of soda, or Glauber’s salt, boil it, and tie the mouth over
with a piece of moistened bladder while boiling, and set it by in a
place where it cannot be disturbed. After twenty-four hours it will
probably still remain fluid. Pierce the bladder covering with a
penknife, and the entrance of the air will cause the whole mass
instantly to crystallize, and the flask will become quite warm from the
latent caloric, of which we have spoken before, given out by the salt in
passing from the fluid to the solid state. It is better to prepare two
or three flasks at the same time, to provide against accidents, for the
least shake will often cause crystallization to take place before the
proper time.
CHANGES OF COLOUR PRODUCED BY COLOURLESS LIQUIDS.
Make a strong infusion of the leaves of the red cabbage, which will be
of a beautiful _blue_ colour; drop into it a few drops of dilute
sulphuric acid, and the colour will change to a bright red; add some
solution of carbonate of potash, or soda, and the red colour will
gradually give way to the original blue; continue adding the alkaline
solution, and the fluid will assume a bright _green_ colour. Now resume
the acid, and as it is dropped in, the colour will again change from
green to blue, and from blue to red. Now this simple experiment
illustrates three points: first, that acids change the colour of most
vegetable blues and greens to red; second, that alkalies change most
blues and reds to green; and third, that when the acid and alkali are
united together, they both lose their property of changing colour, and
become what is called a _neutral_ salt, _i. e._ a compound possessing
the properties of _neither_ of its constituents.
[Illustration]
ELECTRICITY.
No branch of science is more capable of affording amusement, combined
with instruction, than electricity, and there are few sciences in which
the experiments are more easily performed. We would therefore especially
recommend it to our young friends.
The term electricity is derived from the Greek word _electron_,
signifying amber, because electrical attraction was first discovered
from its being noticed that when amber was rubbed into a certain degree
of warmth, it had the power of attracting small bodies to itself.
Electricity therefore primarily treats of the phenomena and effects
produced by the friction or rubbing together of certain bodies called
electrics. These consist of glass, amber, resinous matters, silks, hair,
wool, feathers, various vegetable substances, and atmospheric air, and
the electricity so obtained is usually called Frictional Electricity, to
distinguish it from that produced by chemical action, and called Voltaic
Electricity.
SIMPLE MEANS OF PRODUCING ELECTRICITY.
To show the nature of electrical action, rub a piece of sealing-wax or
amber upon the coat-sleeve, and it will attract light bodies, such as
straws or small pieces of paper. If a clean glass tube be rubbed several
times through a silken or leather cloth, and presented to any small
substances, it will immediately attract and then repel them; and if a
poker suspended by a dry silk string be presented to its upper end, then
the lower end of the poker will exhibit the same phenomena as the tube
itself, which shows that the opposite electrical condition may be
induced upon other bodies by the mere neighbourhood and approach of
another electrified body, and the effect so produced is called induced
electricity.
[Illustration]
When an electrified conductor is supported by non-conductors, so that
the electric fluid cannot pass from the conductor to the earth, it is
said to be insulated: thus the human body is a conductor of
electricity--but if a person standing on a glass stool (as represented
in the drawing) be charged with electricity, the electric fluid cannot
pass from him to the earth, and he is said to be _insulated_; and if he
be touched by another person standing on the ground, sparks will be
exhibited at the point of contact, where also the person touching will
feel a pricking sensation.
[Illustration]
ATTRACTION AND REPULSION EXHIBITED.
[Illustration]
In order to illustrate certain remarkable facts in this science of an
amusing character, attention must be directed to the figure A B, which
is a metal stand; C is a small piece of cork or pith, which is suspended
from the hook by a dry silken thread. Having rubbed an electric, as a
dry rod of glass, and presented it to C, the ball will be
instantaneously attracted to the glass and will adhere to it. After they
remain in contact for a few seconds, if the glass be withdrawn without
being touched by the fingers, and again presented to the ball, the
latter will be _repelled_ instead of attracted, as in the first
instance. By being touched with the finger, the ball can be deprived of
its electricity, and if after this has been done we present a piece of
sealing-wax in the place of the glass formerly employed, the very same
phenomena will take place. On the first application the ball will be
_attracted_, and on the second _repelled_.[8]
[8] For a more complete account of this interesting science we would
refer the young reader to “The Boy’s Playbook on Science,” or, if
more advanced, to “Noad’s Manual of Electricity.”
Before the young reader can perform any very important experiments with
electricity, he must become possessed of an ELECTRICAL MACHINE, which is
an instrument contrived for the purpose of rubbing together the surfaces
of glass and leather. They generally consist of a cylinder, or plate of
glass, and a piece of silk or leather for it to rub against, covered
with an amalgam, the method of preparing which we shall hereafter
describe.
HOW TO MAKE AN ELECTRICAL MACHINE.
[Illustration]
It is very easy to make a glass machine of the cylindrical form, if the
maker cannot afford to buy one. First procure a common wine bottle of
good dimensions, and thickish glass. Drill a hole through its bottom,
with a file moistened with dilute sulphuric acid. A blacksmith, if
supplied with the acid, would undertake to do this part of the work.
Through this hole and the mouth pass a spindle, as represented in the
cut. The end of B should be squared to fix a handle on, and the spindle
should be fixed firmly in the bottle. The bottle is then to be fixed in
a frame in the following manner: the end of the spindle C passes through
a hole at B; and the other end at C has the handle for turning the
machine.
[Illustration]
Next make a cushion of wash-leather stuffed with wool, and fastened to
the top of a frame of the following figure. This frame is to be of such
a height that the cushion shall press against the sides of the bottle,
and a piece of black silk is sewn on to the top of the cushion, and
hangs over the bottle D. The cushion should be smeared with an amalgam,
formed by melting together in the bowl of a tobacco-pipe one part of tin
with two of zinc; to which, while fluid, should be added six parts of
mercury. These should be stirred about till quite cold, and then reduced
to a fine powder in a mortar, and mixed with a sufficient quantity of
lard to form a thickish paste. When all is done, the machine is
complete.
[Illustration: CUSHION.]
THE CONDUCTOR.
The electricity being generated by the friction produced between the
rubber and the bottle from the motion imparted by the handle, it is
necessary to draw it off for use. This is performed by what is called a
conductor. This is made by covering a cylinder of turned wood six inches
long and two and a half inches in diameter, and nicely rounded at the
ends, with tinfoil, which is then mounted on a stand on a glass rod.
When used, it is to be placed in the direction of the length. In it some
pins are inserted, with the points outside, in a line even with, and
about half an inch from, the bottle, and it should be of such a height
as to come just below the silk apron. When it is wished to charge a
Leyden jar, it is to be placed at the round end of the conductor. By
these simple means a great variety of pleasing experiments may be
performed; but to show the various phenomena connected with this
interesting study, we shall now describe an electrical machine of the
newest construction, and perform our experiments with it.
THE PLATE ELECTRICAL MACHINE.
[Illustration]
Formerly the electrical machine was made in the form of a cylinder, but
now it consists of a plate A, as seen in the engraving. The plate is
turned by the handle F through the rubber B B, which diffuses the
excitement over the glass. The points or balls at each side of the plate
carry off a constant stream of positive electricity to the prime
conductor C. Negative electricity is generated by insulating the
conductor to which the cushion is attached, and continuing the prime
conductor with the ground, so as to carry off the fluid collected from
the plate.
HOW TO DRAW SPARKS FROM THE TIP OF THE NOSE.
If the person who works the machine be supported on a stool having glass
legs, and connected with the conductor by means of a glass rod, the
electricity will pass from the conductor to him, and as it cannot get
away, owing to the glass on which he stands being a non-conductor, any
person on touching him can draw the electricity from him, which will
exhibit itself in small sparks as it passes to the person who touches
him. If touched on the nose, sparks of fire will issue from it.
HOW TO CHARGE A LEYDEN JAR.
[Illustration]
A most useful piece of electrical apparatus is called the Leyden jar,
here represented. It is employed for the purpose of obtaining a quantity
of electricity, which may be applied to any substance. It consists of a
glass jar, coated both inside and without, four-fifths of the way up,
with tinfoil. A knob rises through a wooden top communicating with the
inside of the jar. When it is wished to charge the jar, this knob is
applied to the prime conductor of the electrical machine when in action,
and a quantity of electricity being given off, the jar will remain
charged with it till a connexion is made, by some good conductor of
electricity, between the knob and the outside tinfoil. A piece of brass
chain must hang from the stem that carries the knob, and connect it with
the interior of the jar.
THE ELECTRICAL BATTERY.
[Illustration]