CHEMISTRY AND ALCHEMY—CHEMICAL COMBINATIONS—THE ATMOSPHERIC AIR.
We have in the foregoing pages given some experiments, and considered
several of the metals, but there are numerous very interesting subjects
still remaining; indeed, the number is so great that we can only
pick and choose. All people are desirous to hear something of the
atmosphere, of water, and the earth; and as we proceed to speak of
crystals and minerals, and so on to geology, we shall learn a good
deal respecting our globe—its conformation and constituents. But the
atmospheric air must be treated of first. This will lead us to speak of
oxygen and nitrogen. Water will serve to introduce hydrogen with a few
experiments, and thus we shall have covered a good deal of ground on
our way towards various other elements in daily use and appreciation.
Now let us begin with a few words concerning CHEMISTRY itself.
At the very outset we are obliged to grope in the dark after the origin
of this fascinating science. Shem, or “Chem,” the son of Noah, has
been credited with its introduction, and, at any rate, magicians were
in Egypt in the time of Moses, and the lawgiver is stated by ancient
writers to have gained his knowledge from the Egyptians. But we need
not pursue that line of argument. In more modern times the search for
the Philosopher’s Stone and the Elixir of Life, which respectively
turned everything to gold, and bestowed long life upon the fortunate
finder, occupied many people, who in their researches no doubt
discovered the germs of the popular science of Chemistry in Alchemy,
while the pursuit took a firm hold of the popular imagination for
centuries; and even now chemistry is the most favoured science, because
of its adaptability to all minds, for it holds plain and simple truths
for our every-day experience to confirm, while it leads us step by step
into the infinite, pleasing us with experiments as we proceed.
Alchemy was practised by numerous quacks in ancient times and the
Middle Ages, but all its professors were not quacks. Astrology and
alchemy were associated by the Arabians. Geber was a philosopher who
devoted himself entirely to alchemy, and who lived in the year 730
A.D. He fancied gold would cure all disease, and he did
actually discover corrosive sublimate, nitric acid, and nitrate of
silver. To give even a list of the noted alchemists and magicians would
fill too much space. Raymond Sully, Paracelsus, Friar Bacon, Albertus
Magnus, Thomas Aquinas, Flamel, Bernard of Treves, Doctor Dee, with his
assistant Kelly, and in later times Jean Delisle, and Joseph Balsamo
(Cagliostro), who was one of the most notorious persons in Europe about
one hundred years ago (1765-1789), are names taken at random; and with
the older philosophers chemistry was an all-absorbing occupation—not
for gold, but knowledge.
The revelation was slow. On the temperature of bodies the old arts
of healing were based—for chemistry and medicine were allies. The
elements, we read, existed on the supposition “that bodies were hot
or cold, dry or moist”; and on this distinction for a long time “was
based the practice of medicine.” The doctrine of the “three principles”
of existence superseded this,—the principles being salt, mercury, and
sulphur. Metals had been regarded as living bodies, gases as souls or
spirits. The idea remained that the _form_ of the substance gave it its
character. Acid was pointed; sweet things were round.
Chemistry, then, has had a great deal to contend against. From the
time of the Egyptians and Chinese, who were evidently acquainted with
various processes,—dyeing, etc.,—the science filtered through the
alchemists to Beecher and Stahl, and then the principle of affinity—a
disposition to combine—was promulgated, supplemented in 1674 by
Mayow, by the theory of divorce or analysis. He concluded that where
union could be effected, separation was equally possible. In 1718 the
first “Table of Affinities” was produced. Affinity had been shown
to be _elective_, for Mayow pointed out that fixed salts chose one
acid rather than another. Richter and Dalton made great advances.
Before them Hales, Black, Priestley, Scheele, Lavoisier, and numerous
others penetrated the mysteries of the science whose history has been
pleasantly written by more than one author who we have not been able
to consult, and have no space to do more than indicate. In later days
Faraday, De la Rive, Roscoe, and many others have rendered chemistry
much more popular, while they have added to its treasures. The story
of the progress of chemistry would fill a large volume, and we have
regretfully to put aside the introduction and pass on.
Before proceeding to investigate the elements, a few words concerning
the general terms used in chemistry will be beneficial to the reader.
If we look at the list of the elements, pp. 308-9, we shall see
various terminations. Some are apparently named from places, some from
their characteristics. Metals lately discovered by the spectroscope
(and recently) end in _ium_; some end in “ine,” some in “on.” As far
as possible in late years a certain system of nomenclature has been
adhered to, but the old popular names have not been interfered with.
When elements combine together in certain proportions of each they
receive certain names. The following table will explain the terms used;
for instance, we find that—
Compounds of Oxygen are termed Oxides, as oxide of copper.
” Hydrogen ” Hydrides, as hydride of potassium.
” Chlorine ” Chlorides, as chloride of sodium.
” Nitrogen ” Nitrides, as nitride of boron.
” Bromine ” Bromides, as bromide of potassium.
” Iodine ” Iodides, as iodide of potassium.
” Sulphur ” Sulphides, or}
Sulphurets,} as sulphuret of lead.
” Selenium ” Selenides, as selenide of mercury.
” Carbon ” Carbides, or} as carbide of nitrogen,
Carburets,} and so on.
The above examples refer to the union in single proportion of each, and
are called Binary Compounds. When more than one atom of each element
exists in different proportions we have different terms to express
such union. If one atom of oxygen be in the compound it is called
a “monoxide” or “protoxide”; two atoms of oxygen in combination is
termed “dioxide” or “binoxide”; three, “trioxide,” or “tritoxide”;
four is the “tetroxide” or “per-oxide,” etc. When more than one
atom, but not two atoms is involved, we speak of the _sesqui_-oxide
(one-and-a-half),—“oxide” being interchangeable for “sulphide” or
“chloride,” according to the element.
There are other distinctions adopted when metals form two series of
combinations, such as _ous_ and _ic_, which apply, as will be seen, to
acids. Sulphur_ic_ and sulphur_ous_ acids, nitr_ic_ and nitr_ous_ acid
are familiar examples. In these cases we shall find that in the acids
ending in “ous” oxygen is present in less quantity than in the acids
ending in _ic_. The symbolic form will prove this directly, the number
of atoms of oxygen being written below,
Sulphurous Acid = H_{2} SO_{3}. Nitrous Acid = HNO_{2}.
Sulphuric Acid = H_{2}SO_{4}. Nitric Acid = HNO_{3}.
Whenever a stronger compound of oxygen is discovered than that
denominated by _ic_, chemists adopt the plan of dubbing it the _per_
(ὑπέρ over), as per-chloric acid, which possesses four atoms of oxygen
(HClO_{4}), chloric acid being HClO_{3}. The opposite Greek term,
ὑπὸ (_hupo_, below), is used for an acid with less than two atoms
of oxygen, and in books is written “hypo”-chlorous (for instance).
Care has been taken to distinguish between the higher and lower; for
“_hyper_” is used in English to denote excess, as hyper-critical; and
_hypo_ might to a reader unacquainted with the derivation convey just
the opposite meaning to what is intended.
While speaking of these terminations we may show how these distinctive
endings are carried out. We shall find, if we pursue the subject, that
when we have a salt of any acid ending in _ic_ the salt terminates in
“_ate_.” Similarly the salts of acids ending in _ous_, end in “_ite_.”
To continue the same example we have—
Sulphur_ous_ Acid, which forms salts called Sulph_ites_.
Sulphur_ic_ Acid, ” ” Sulph_ates_.
Besides these are sulph_ides_, which are results of the unions or
compounds of elementary bodies. Sulph_ites_ are more complicated
unions of the compounds. Sulphates are the salts formed by the union
of sulphuric acid with bases. Sulphides or sulphurets are compounds in
which sulphur forms the electro-negative element, and sulphites are
salts formed by the union of sulphur_ous_ acids with bases, or by their
action upon them.
[Illustration: Fig. 322.—Combinations of elements.]
The symbolical nomenclature of the chemist is worse than Greek to the
uninitiated. We frequently see in so-called popular chemical books a
number of hieroglyphics and combinations of letters with figures very
difficult to decipher, much less to interpret. These symbols take the
place of the names of the chemical compounds. Thus water is made up of
oxygen and hydrogen in certain proportions; that is, two of hydrogen to
one of oxygen. The symbolic reading is simple, H_{2}O, = the oxide of
hydrogen. Potassium again mingles with oxygen. Potassium is K in our
list; KO is oxide of potassium (potash). Let us look into this a little
closer.
The union of one particle of a simple body with a particle of another
simple body can be easily understood; but, as we have seen, it is
possible to have substances consisting of four or five different
particles, though the greater number of chemical combinations consist
of two or three dissimilar ones. In the diagram (fig. 322) we have some
possible combinations.
In these combinations we may have one particle of _a_ in combination
with one, two, three, four, or five of _b_, and many particles of _a_
can unite with various molecules of _b_. Suppose we have oxygen and
sulphur compounds as follows:—
Thus there are three different compounds of these two elements—SO,
SO_{2}, SO_{3} (without water).
[Illustration: (1) (2) (3)
Fig. 323.-(1) Hydrosulphurous Acid. (2) Sulphurous Acid. (3) Sulphuric
Acid.]
A compound body may combine with another compound body, and this
makes a complicated compound. Suppose we have a mixture of sulphuric
acid and potash. We have a sulphate of potassium (K_{2}SO_{4}) and
combinations of these combinations may likewise be formed. We must
read these symbols by the light of the combining weights given in the
table, and then we shall find the weight of oxygen or other elements
in combination. Thus when we see a certain symbol (Hg.S for instance),
we understand that they form a compound including so many parts of
mercury and so many of sulphur, which is known as vermilion. Hg.O is
oxide of mercury, and by reference to the table of Atomic Weights, we
find mercury is Hg., and its combining weight is 200; while oxygen is
O, and its weight is 16. Thus we see at once how much of each element
is contained in oxide of mercury, and this proportion never varies;
there must be 200 of one and 16 of the other, by weight, to produce the
oxide. So if the oxygen has to be separated from it, the sum of 216
parts must be taken to procure the 16 parts of oxygen. When we see, as
above, O_{2} or O_{3}, we know that the weight must be calculated twice
or three times, O being 16; O_{2} is therefore 32 parts by weight. So
when we have found what the compounds consist of, we can write them
symbolically with ease.
COMPOSITION OF THE ATMOSPHERIC AIR.
We have already communicated a variety of facts concerning the air.
We have seen that it possesses pressure and weight. We call the
gaseous envelope of the earth the atmosphere, and we are justified in
concluding that other planets possess an atmosphere also, though of a
different nature to ours. We have seen how easy it is to weigh the air,
but we may repeat the experiment. (_See_ illustration, fig. 45, page
50.) We shall find that a perfectly empty glass globe will balance the
weights in the scale-pan; admit the air, and the glass globe will sink.
So air possesses weight. We have mentioned the Magdeburg hemispheres,
the barometer, the air-pump, and the height and the pressure of the
atmosphere have been indicated. The density of the atmosphere decreases
as we ascend; for the first seven miles the density diminishes
one-fourth that of the air at the sea-level, and so on for every
succeeding seven.
In consequence of the equal, if enormous, pressure exercised in every
direction, we do not perceive the inconvenience, but if the air were
removed from inside of a drum, the parchment would quickly collapse.
We feel the air when we move rapidly. We breathe the air, and that
statement brings us to consider the composition of the atmosphere,
which, _chemically_ speaking, _may vary a little_ (as compared with
the whole mass) in consequence of changes which are continually taking
place, but to all intents and purposes the air is composed as follows,
in 100 parts:
Nitrogen 79 parts.
Oxygen 20 ”
Carbonic Acid .04 ”
with minute quantities of other ingredients, such as ammonia, iodine,
carbonetted hydrogen, hydrochloric acid, sulphuretted hydrogen, nitric
acid, carbonic oxide, and dust particles, as visible in the sunbeams,
added.
The true composition of the atmosphere was not known till Lavoisier
demonstrated that it consisted of two gases, one of which was the vital
fluid, or oxygen, discovered by Priestley. To the other gas Lavoisier
gave the name of Azote,—an enemy of life,—because it caused death if
inhaled alone. The carbonic acid in the air varies very much, and in
close, heated, and crowded rooms increases to a large quantity, which
causes lassitude and headache.
We can easily prove the existence of carbonic acid gas as exhaled
from the lungs. Suppose we take a glass and fill it partly with clear
lime-water; breathe through a glass tube into the water in the glass,
and very quickly you will perceive that the lime-water is becoming
cloudy and turbid. This cloudiness is due to the presence of chalk,
which has been produced by the action of the carbonic acid gas in the
lime-water. This is a well known and always interesting experiment,
because it leads up to the vital question of our existence, and the
functions of breathing and living.
A popular writer once wrote a book entitled, “Is Life Worth Living?”
and a witty commentator replied to the implied question by saying, “It
depends upon the _liver_.” This was felt to be true by many people who
suffer, but the scientific man will go farther, and tell you it depends
upon the air you breathe, and on the carbonic acid you can raise to
create heat,—animal heat,—which is so essential to our well-being.
We are always burning; a furnace is within us, never ceasing to burn
without visible combustion. We are generating heat by means of the
blood. We know that we inhale air into the lungs, and probably are
aware that the air so received parts with the oxygen to renew the
blood. The nitrogen dilutes the oxygen, for if we inhaled a less-mixed
air we should either be burnt up or become lunatics, as light-headed
as when inhaling “laughing-gas.” This beautifully graduated mixture is
taken into our bodies, the oxygen renews the blood and gives it its
bright red colour; the carbon which exists in all our bodies is cold
and dead when not so vivified by oxygen. The carbonic acid given off
produces heat, and our bodies are warm. But when the action ceases we
become cold, we die away, and cease to live. Man’s life exemplifies
a taper burning; the carbon waste is consumed as the wax is, and
when the candle burns away—it dies! It is a beautiful study, full of
suggestiveness to all who care to study the great facts of Nature,
which works by the same means in all matter. We will refer to plants
presently, after having proved by experiment the existence of nitrogen
in the air.
Rutherford experimented very cruelly upon a bird, which he placed
beneath a glass shade, and there let it remain in the carbonic acid
exhaled from its lungs, till the oxygen being at length all consumed
by the bird, it died. When the atmosphere had been chemically purified
by a solution of caustic potash, another bird was introduced, but
though it lived for some time, it did not exist so long as the first.
Again the air was deprived of the carbonic acid, and a third bird was
introduced. The experiment was thus repeated, till at length a bird
was placed beneath the receiver, and it perished at once. This is at
once a cruel and clumsy method of making an experiment, which can be
more pleasantly and satisfactorily practised by burning some substance
in the air beneath the glass. Phosphorus, having a great affinity for
oxygen, is usually chosen. The experiment can be performed as follows
with a taper, but the phosphorus is a better exponent.
Let us take a shallow basin with some water in it, a cork or small
plate floating upon the water, and in the plate a piece of phosphorus.
We must be careful how we handle phosphorus, for it has a habit, well
known, but sometimes forgotten by amateur chemists, of suddenly taking
fire. Light this piece of phosphorus,—a small piece will do if the jar
be of average “shade” size,—and place the glass over it, as in the
illustration (fig. 325). The smoke will quickly spread in the jar, and
the entry of air being prevented, because the jar is resting under
water, phosphoric acid will be formed, and the oxygen thereby consumed.
The water, meanwhile, will rise in the jar, the pressure of the air
being removed. The burning phosphorus will soon go out, and when the
glass is cool, you will be able to ascertain what is inside the jar.
Put a lighted taper underneath, and it will go out. The taper would
not go out before the phosphorus was burnt in the glass, and so now we
perceive we have azote in the receptacle—that is, nitrogen. The other,
the constituent of our atmosphere, carbonic acid, as we have seen, is
very injurious to the life of animals, and as every animal breathes
it out into the air, what becomes of it? Where does all this enormous
volume of carbonic acid, the quantities of this poison which are daily
and nightly exhaled, where do they all go to? We may be sure nature has
provided for the safe disposal of it all. Not only because we live and
move about still,—and of course that is a proof,—but because nature
always has a compensating law. Remember _nothing is wasted_; not even
the refuse, poisonous air we get rid of from our lungs. Where does it
go?
[Illustration: 324.—Rutherford’s experiment.]
It goes to nourish the plants and trees and vegetables that we delight
to look upon and to eat the fruit of. Thus the vegetable world forms a
link between the animals and the minerals. Vegetables obtain food, so
to speak, and nourishment from water, ammonia, and carbonic acid, all
compound bodies, but inorganic.
Water consists of oxygen and hydrogen, carbonic acid of carbon and
oxygen, and ammonia of hydrogen and nitrogen. Water and ammonia are
present in the air; so are oxygen and nitrogen. Water falls in the
form of rain, dew, etc. So in the atmosphere around us we find nearly
every necessary for plant-life; and in the ground, which supplies some
metallic oxides for their use, we find the remainder. From the air,
then, the plant derives its life.
[Illustration: Fig. 325—Drawing the oxygen from air by combustion.]
The vegetable kingdom in turn gives all animals their food. This you
will see at a glance is true. Certainly animals live on animals. Man
and wilder animals live on the beasts of the field in a measure, but
those beasts derive their nourishment from vegetables—the vegetable
kingdom. So we live on the vegetable kingdom, and it separates the
carbonic acid from the air, and absorbs it. What we do not want it
takes. What we want it gives. Vegetables give out oxygen, and we
consume it gladly. We throw away carbonic acid, and the plants take
it greedily; and thus the atmosphere is retained pure for our use. We
can, if desirable, prove that plants absorb carbonic acid and give
out oxygen by placing leaves of a plant in water, holding the acid in
solution, and let the sun shine upon them. Before long we shall find
that the carbonic acid has disappeared, and that oxygen has come into
the water.
Carbonic acid is sufficiently heavy to be poured from one vessel to
another; and if we have obtained some in a glass, we can extinguish a
taper by pouring the invisible gas on to the lighted taper, when it
will be immediately extinguished.
From the foregoing observations it will be perceived how very desirable
it is that ventilation should be attended to. People close up windows
and doors and fireplaces, and go to bed and sleep. In the morning
they complain of headache and lassitude; they wonder what is the
matter, and why the children are not well. Simply because they have
been rebreathing the carbonic acid. Go into a closed railway carriage
which is nearly filled (and it is astonishing to us how people can be
so foolish as to close every outlet), and you will recoil in disgust.
These travellers shut the ventilators and windows “because of the
cold.” A very small aperture will ventilate a railway carriage; but a
close carriage is sickening and enervating, as these kind of travellers
find out by the time they reach their journey’s end. Air was given us
to breathe at night as well as by day; and though from man’s acts or
omissions there may be circumstances in which “night” air may affect
the health, we maintain that air is no more injurious naturally than
“day” air. Colder it may be, but any air at night is “night” air, in
or out of doors at night; and we are certain that night air in itself
never hurt any healthy person. It is not nature’s plan to destroy, but
to save. If a person delicate in constitution gets hot, and comes out
into a colder atmosphere, and defy nature in that way, he (or she)
must take the consequences. But air and _ventilation_ (not draught)
are necessaries of health, and to say they injure is to accuse nature
falsely. There are many impurities in the air in cities, and in country
places sometimes, but such impurities are owing to man’s acts and
omissions. With average sanitary arrangements and appliances in a
neighbourhood no one need be afraid to breathe fresh air night or day;
and while many invalids have, we believe, been retarded in recovery
from being kept in a close room, hundreds will be benefited by plenty
of fresh air. We should not so insist upon these plain and simple
truths were there not so many individuals who think it beneficial to
close up every avenue by which air can enter, and who then feel ill and
out of spirits, blaming everything but their own short-sightedness for
the effect of their own acts. An inch or two of a window may be open
at night in a room, as the chimney register should be always fully up
in bedrooms. When there are fires the draught supplies fresh air to
the room with sufficient rapidity. But many seaside journeys might be
avoided if fresh air were insisted on at home.
There is another and an important constituent of the atmosphere called
OZONE, which is very superior oxygen, or oxygen in what is
termed the “Allotropic” state, and is distantly related to electricity,
inasmuch as it can be produced by an electrical discharge. This partly
accounts for the freshness in the air after a thunderstorm, for we
are all conscious that the storm has “cleared the air.” The fresh,
crisp ozone in the atmosphere is evident. Ozone differs from oxygen
in possessing taste and smell, and it is heavier by one-half than the
oxygen gas. There is a good deal of ozone in the sea breeze, and we
can, though not infallibly, detect its presence by test-paper prepared
with iodide of potassium, which, when ozone is present, will turn
blue. We have still something to learn about ozone, which may be
considered as “condensed oxygen.”
[Illustration: Fig. 326. Development of gas by combustion. Fig. 327.]
We have frequently mentioned “combustion,” and as under ordinary
circumstances such effects cannot take place without atmospheric air,
we will consider it. Combustion is chemical action accompanied by
light and heat. Chemical union is always attended by the development
of heat, not always by light, because the union varies in intensity
and quickness. But when a candle is burning we can study all the
interesting phenomena of combustion. We have already spoken of HEAT
and LIGHT, so we need only refer the readers to those subjects in the
former parts of this volume. Heat is referable to chemical action,
and varies according to the energy of union. Heat is always present,
remember, in a greater or less degree; and when visible combustion
takes place we see light. Invisible combustion goes on in our bodies,
and we feel heat; when we get cold we feed the fire by eating, or blow
it by exercise and air in our lungs.
[Illustration: Fig. 328.—Gas evolved from flame.]
We shall speak, however, of combustion now as it affects us in daily
life; our fires, our candles, gas, etc., and under these ordinary
circumstances hydrogen and carbon are present. (We shall hear more
about carbon presently.) These unite with the oxygen to form water and
carbonic acid; the water being visible as we first put the cold shade
upon the lighted lamp, and the carbonic acid renders the air impure.
In the case of a common candle, or lamp, combustion takes place in the
same way. The wick is the intermediary. The oil mounts in the lamp
wick, where it is converted into a gas by heat; it then “takes fire,”
and gives us light and heat. The candle-flame is just the same with
one exception: the burning material is solid, not liquid, though the
difference is only apparent, for the wax is melted and goes up as gas.
The burning part of the wick has a centre where there is no combustion,
and contains carbon. We can prove this by placing a bent tube, as in
the illustration (fig. 326), one end in the unburning part of the
flame. We shall soon see a dark vapour come over into the receiver.
This is combustible, for if we raise the tube without the glass we can
light the gas (fig. 327). If we insert the end of the tube into the
brilliant portion of the flame we shall perceive a black vapour, which
will extinguish the combustion, for it is a mixture of carbonic acid
gas and aqueous vapour, in which (fig. 328) particles of carbon are
floating.
[Illustration: Fig. 329.—Davy’s safety lamp.]
[Illustration: Fig. 330.—Davy lamp (section).]
When we proceed to light our lamps to read or to write by, we find some
difficulty in making the wick burn at first. We present to it a lighted
taper, and it has no immediate effect. Here we have oil and cotton,
two things which would speedily set a warehouse in flames from top to
bottom, but we cannot even ignite them, try all we can. Why?—Because we
must first obtain a gas, oil will not burn liquid; it must be heated
to a gaseous point before it will burn, as all combustion depends upon
that,—so flames mount high in air. Now in a candle-flame, as will be
seen in the diagram (fig. 331.), there are three portions,—the inner
dark core, which consists of unburnt gas; the outer flame, which gives
light; and the outside rim of perfect combustion non-luminous. In the
centre, A, there is no heat. If we place a piece of gauze wire over the
flame at a little distance the flame will not penetrate it. It will
remain underneath, because the wire, being of metal, quickly absorbs
the heat, and consequently there is no flame. This idea led to the
invention of the “safety” lamp by Sir Humphrey Davy, which, although it
is not infallible, is the only lamp in general use in mines (figs. 329,
330).
[Illustration: Fig. 331.—Construction of a candle flame.]
Mines must have light, but there is a gas in mines, a “marsh” gas,
which becomes very explosive when it mixes with oxygen. Of course the
gas will be harmless till it meets oxygen, but, in its efforts to meet,
it explodes the moment the union takes place; instead of burning slowly
like a candle it goes off all at once. This gas, called “fire damp,” is
carburetted hydrogen, and when it explodes it develops into carbonic
acid gas, which suffocates the miners.
[Illustration: Fig. 332.—Pouring carbonic acid on a lighted taper.]