[1] 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.
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.
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 niter, or at least
forms a portion of the nitric acid contained in niter. It is rather
lighter than atmospheric air, colorless, 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 tetroxide, nitric pent-oxide,
which last, united with water, forms nitric acid, now called hydric
nitrate, as nitrous acid is termed hydric nitrite.
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
stop-cock and mouth-piece, 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.
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.
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 colorless 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 a strong solution of ammonia (a compound of nitrogen
and hydrogen) upon some iodine in a vial, shaking them well together,
and after letting them stand for a few hours, pouring off the fluid;
the black powder remaining in the vial 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 vial 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-colored 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 vapor 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 vapor of water,
invisible as long as it is in the state of vapor, but it may be
rendered obvious by bringing any very cold body into warm air, when
the vapor 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 vapor 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 vapor in a visible form,
rendering everything but itself invisible. The famous London fogs
depend upon the same precipitation of the vapor 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 vapor 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 vapor ready to be deposited on the slightest cause.
Hydrogen.
Hydrogen gas is the lightest substance known, being fifteen times
lighter than atmospheric air. It is colorless 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
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.
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.
Hold open 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 vapor 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.
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 vial, 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 vapor 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 in this
country, where the engines are worked at a high pressure.
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.
Chlorine gas is transparent, of a greenish yellow color, 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 colors 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.”
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 colors
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 colored 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 color will be discharged.
7. Introduce a quantity of the infusion of the common red cabbage,
which is of a beautiful blue color, 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 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 color 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 colorless 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 NH_{4}C_{2}; 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 simply 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--Bromine--Fluorine.
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 luster, with a bluish black color, and
should be kept in a well-stoppered bottle. A small quantity placed in a
clear flask and heated, affords a magnificent violet vapor, which may
be poured from the flask into another glass vessel, when it condenses
again into crystalline plates. The color of the vapor originates
the name of this element, so called from a Greek word, meaning
violet-colored. If a little iodine be placed in contact with a thin
slice of phosphorus, the latter takes fire almost immediately.
Bromine.
From the Greek, signifies a bad odor, and 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 vapor, which is easily
procured by letting fall a few drops of bromine into a warm dry bottle.
Experiments.
Pounded antimony sprinkled into the vapor takes fire immediately.
A thin slice of phosphorus placed in a deflagrating ladle and placed
into the vapor 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 vapor 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 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 vapor. 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, colorless, 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 odor, 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.
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.
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
carbureted hydrogen.
The two chief definite gaseous compounds of those two elements are
the light carbureted hydrogen and the heavy carbureted 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 carbureted hydrogen, forms part of the
gas used for illumination; and, in fact, whatever substance is employed
for artificial light, whether oil, tallow, wax, etc., etc., 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, colorless, 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
proportion, 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.
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 carbureted and the bi-carbureted 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, carbureted hydrogen, carbonic acid, sulphureted
hydrogen, etc., etc. 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,
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 carbureted 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 the 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 vapor 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 naptha, various oils, tallow, wax, spermaceti, spirits
of wine, ether, etc., 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.
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, etc. 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
sulphureted hydrogen, which is almost the most poisonous of all the
gases. It fortunately has so abominable a smell that due notice is
given of its presence. Rotten eggs, a dirty gun-barrel, cabbage water,
putrid animal and vegetable matter, etc., are indebted to this gas for
their inviting odor; 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 colorless 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 color 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 ribbon, silk, or even
paper, may be wetted with various metallic solutions, such as silver,
mercury, lead, etc., 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 color 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.”
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), etc.
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 luster, differing indeed among themselves,
but so peculiar that it is called the metallic luster; 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 equaling 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 degrees Fahrenheit 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. 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
color.--_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.
Saltpeter, or niter, 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.
Experiments.
1. Into a solution of nitrate of silver in distilled water immerse a
clean plate or slip of copper. The solution, which was colorless, will
soon begin to assume a greenish tint, and the piece of copper will
be covered with a coating of a light gray color, 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 the 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 colors used in the arts are produced by metals and
their combinations; indeed, one is named _chromium_, from a Greek word
signifying color, 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, etc.; and the colors differ according to
the metal employed, and so small a quantity is required to produce the
color that the solutions before mixing may be nearly colorless.
Experiments.
1. To a solution of sulphate of iron add a drop or two of a solution of
prussiate of potash, and a blue color will be produced.
2. Substitute sulphate of copper for iron, and the color will be a rich
brown.
3. Another blue, of quite a different tint, may be produced by letting
a few drops or 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 color.
4. Into a solution of sulphate of iron let fall a few drops of a strong
infusion of galls, and the color 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 color, 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
color, 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
colorless solution of corrosive sublimate (a salt of mercury) a
precipitate will take place of a splendid scarlet color, 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.
Prepare separately, saturated solutions of sulphate of magnesia (Epsom
salts) and carbonate of potash. On mixing them the result will be
nearly solid.
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 color.
The greater number of salts have a tendency to assume regular forms, or
become _crystallized_, when passing from the fluid to the solid state;
and the size and regularity of the crystals depend 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 center
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, etc.; 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 Color Produced by Colorless Liquids.
Make a strong infusion of the leaves of the red cabbage, which will
be of a beautiful _blue_ color; drop into it a few drops of dilute
sulphuric acid, and the color will change to a bright red; add some
solution of carbonate of potash, or soda, and the red color will
gradually give way to the original blue; continue adding the alkaline
solution, and the fluid will assume a bright _green_ color. Now
resume the acid, and as it is dropped in, the color will again change
from green to blue, and from blue to red. Now this simple experiment
illustrates three points: first, that acids change the color 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 color, and
become what is called a _neutral_ salt, _i.e._ a compound possessing
the properties of _neither_ of its constituents.