In the eleventh century, and during the reign of King Henry the First,
surnamed Beauclerk, or the fine scholar, there appeared for the first
time in certain books, professing to teach the art of making gold,
the words chemistry, chemist, derived from the Greek. Seven hundred
years and more have passed away, and that which was only the pursuit
of a shadow called alchemy, has resulted in the acquisition of a great
and noble science, now and again called chemistry. So it is with the
great edifice Chemistry; we may, in these brief pages, peep in at the
open door, but should we desire to go beyond the threshold, there are
numerous guides, such as Roscoe, Wilson, and Fownes, who will conduct
us through the mazes of the interior, and explain in elementary
language the beautiful processes which have become so useful to mankind.
Chemistry is one of the most comprehensive of all the sciences, and at
the same time one which comes home to us in the most ordinary of our
daily avocations. Most of the arts of life are indebted to it for their
very existence, and nearly all have been, from time to time, improved
by the application of its principles.
Chemistry is, in fact, the science which treats of the composition
of all material bodies, and of the means of forming them into new
combinations, and reducing them to their _ultimate elements_, as
they are termed; that is, bodies which we are unable to split up, as
it were, or separate into other bodies. To take a common substance
as an illustration; water, by a great number of processes, can be
separated into two other substances, called oxygen and hydrogen, in the
proportion by weight of 8 parts of the first to 1 of the second; but no
power that we at present possess can separate the oxygen and hydrogen
into any other bodies; they are therefore called ultimate elements, or
undecomposable bodies.
Again, sulphate of magnesia (common Epsom salts) can be very easily
separated into two other substances,--sulphuric acid and magnesia; and
in this instance, both these substances can again be subdivided--the
acid into sulphur and oxygen, and the magnesia into a metallic body
called magnesium and oxygen; but sulphur, oxygen, and magnesium are
incapable of further division, and are therefore called _ultimate
elements_.
These ultimate elements amount to 64 in number, according to the
present state of our knowledge, and may be arranged in various ways;
the simplest plan, perhaps, is dividing them into Non-metallic and
Metallic elements.
The Non-metallic elements are:--1. Oxygen. 2. Hydrogen. 3. Nitrogen. 4.
Chlorine. 5. Iodine. 6. Bromine. 7. Fluorine. 8. Carbon. 9. Sulphur.
10. Selenium. 11. Tellurium. 12. Silicon. 13. Boron. 14. Phosphorus.
The last-named element is the connecting link with the metals through
arsenic, which phosphorus closely resembles in its chemical properties.
The Metallic elements may be sub-divided into the metals of the
alkalies, the metals of the alkaline earths, the metals of the earths,
and the other metals sometimes called metals proper.
1st. The metallic bases of the alkalies:--potassium, sodium, lithium,
ammonium, cæsium, rubidium.
2d. The metallic bases of the alkaline earths:--calcium, strontium,
barium.
3d. The metallic bases of the earths:--aluminum, glucinum, zirconium,
thorium, yttrium, erbium, cerium, lanthanum, didymium.
4th. The metals proper, the most important of which are:--platinum,
gold, silver, mercury, copper, iron, tin, lead, nickel, zinc, bismuth,
antimony, manganese, cobalt, arsenic.
Now, from these elementary bodies, united together in various
proportions, is formed the infinite variety of substances around
us, whether animal, vegetable, or mineral; in fact, a few only are
generally employed:--in the case of animals and vegetables, oxygen,
hydrogen, carbon, nitrogen, with occasionally some sulphur, calcium,
phosphorus, and silicon, suffice for building up the beautiful forms
of animated nature; while the fabric of our globe itself consists for
the most part of the earths; silex, _i.e._, flint or crystal; lime,
in the shape of chalk, marble, or limestone, such as our flagstones
are composed of; slate and granite, which are compounds of aluminium,
silica, and small quantities of oxide of iron, and sometimes a little
potash, etc.; and through their masses are projected irregular
streams--veins as they are termed--of the metals, either in a pure
state, as is the case sometimes with gold, silver, platinum, mercury,
and perhaps one or two others; or combined with one of the non-metallic
elements, or with one another.
Late calculations have determined the composition of the earth’s solid
crust in 100 parts by weight to be:
Oxygen 44.0 to 48.7.
Silicon 22.8 “ 36.2.
Aluminium 9.9 “ 6.1.
Iron 9.9 “ 2.4.
Calcium 6.6 “ 0.9.
Magnesium 2.7 “ 0.1.
Sodium 2.4 “ 2.5.
Potassium 1.7 “ 3.1.
------ ------
100.0 100.0
------ ------
All these combinations are effected by certain powers, termed _forces_;
those which cause the union of the elements are called the forces of
attraction; those causing their separation, the forces of repulsion.
The force of attraction when exerted between masses of matter, is
termed gravitation; when it unites particles of matter of a similar
kind and produces masses, it is called the attraction of cohesion; when
the particles united are of a dissimilar character, it is then termed
chemical or elective affinity. For example, the crystals of Epsom salts
are formed from minute particles of the salt, united into a larger
or smaller mass by the attraction of cohesion, while the _elements_
of which each particle consists, namely, the sulphur, oxygen, and
magnesium, are united by the attraction of chemical affinity.
Cohesion thus unites particles of a similar kind; chemical affinity, of
a dissimilar nature. It is to cohesion that the existence of _masses_
of matter is owing, and its power increases as the squares of the
distances diminish, in an inverse ratio to the squares of the distances
of the particles on which it acts.
The power exerted by cohesion may be exhibited in various ways. This is
one: Procure two discs of glass about three inches in diameter, their
surfaces being ground extremely smooth; fix each into a square piece
of wood, taking care that they are placed accurately in the center;
then put them together by sliding their edges very carefully over each
other, so as to avoid any air getting between them, and you will find
a great force necessary to separate them. A hook should be fixed into
the center of each piece of wood, so that they may be suspended, and a
weight hung to the lower one. It is almost impossible for any one to
separate them by merely pulling them with both hands; a weight of many
pounds is required for that purpose. In like manner two freshly-cut
surfaces of caoutchouc will, on being squeezed together, cohere so
perfectly, that it is difficult to tear them asunder, and it is in this
way that tubes of caoutchouc may be rapidly prepared for experiments,
where little or no pressure is exerted.
Chemical affinity is sometimes called _elective_, or the effect of
_choice_, as if one substance exerted a kind of _preference_ for
another, and chose to be united to it rather than to that with which
it was previously combined; thus, if you pour some vinegar, which is
a weak acetic acid, upon some pearlash (a combination of potash and
carbonic acid), or some carbonate of soda (a combination of the same
acid with soda), a violent effervescence will take place, occasioned by
the escape of the carbonic acid, displaced in consequence of the potash
or soda preferring the acetic acid, and forming a compound called an
acetate. Then if some sulphuric acid be poured on this new compound,
the acetic acid will in its turn be displaced by the greater attachment
of either of the bases, as they are termed, for the sulphuric acid.
Again, if into a solution of blue vitriol (a combination of sulphuric
acid with oxide of copper) the bright blade of a knife be introduced,
the knife will speedily be covered with a coat of copper, deposited
in consequence of the acid _preferring_ the iron, of which the knife
is made, a quantity of it being dissolved in exact proportion to the
quantity of copper deposited.
It is on the same principle that a very beautiful preparation called a
silver-tree, or a lead-tree, may be formed thus:--Fill a wide bottle,
capable of holding from half a pint to a pint, with a tolerably strong
solution of nitrate of silver (lunar caustic), or acetate of lead, in
pure distilled water; then attach a small piece of zinc by a string
to the cork or stopper of the bottle, so that the zinc shall hang
about the middle of the bottle, and set it by where it may be quite
undisturbed; in a short time, brilliant plates of silver or lead, as
the case may be, will be seen to collect around the piece of zinc,
assuming more or less of the crystalline form. This at first is a
case of elective affinity; the acid with which the silver or lead was
united _prefers_ the zinc to either of those metals, and in consequence
discards them in order to attach the zinc to itself, subsequently a
voltaic current is set up between the two metals, and the process will
continue until almost the whole of the zinc is taken up, or nearly the
whole of the silver or lead deposited.
Again, many animal and vegetable substances consist for the most
part of carbon or charcoal, united with oxygen and hydrogen in the
proportion which forms water. Now oil of vitriol (strong sulphuric
acid) has so powerful an affinity, or so great a _thirst_ for water,
that it will abstract it from almost any body in which it exists; if
you then pour some of this acid on a lump of sugar, or place a chip of
wood in it, the sugar or wood will speedily become quite black, or be
_charred_, as it is called, in consequence of the oxygen and hydrogen
being removed by the sulphuric acid, and only the carbon, or charcoal,
left.
When Cleopatra dissolved pearls of wondrous value in vinegar, she was
exhibiting unwittingly an instance of chemical elective affinity; the
pearl being simply carbonate of lime, which was decomposed by the
greater affinity or fondness of lime for its new acquaintance (the
acetic acid of the vinegar) than for the carbonic acid, with which it
had been united all its life,--an example of inconstancy in strong
contrast with the conduct of its owner, who chose death rather than
become the mistress of her lover’s conqueror.
Gases.
The three permanent gaseous elements are oxygen, hydrogen, and nitrogen.
The compound gases are very numerous, some being combustible, and
others supporters of combustion.
Gases are for the most part transparent and colorless, with a few
exceptions, and of course, like the air of the atmosphere, invisible.
They are little affected by the attraction of cohesion, but rather, on
the contrary, the particles composing them have a constant tendency
to separate from each other, so that their force of expansion is
only limited by the pressure under which they may be kept, and the
temperature they may be exposed to. They have a tendency to _penetrate_
each other, as it were; for instance, if you take a jar of heavy gas,
such as carbonic gas, set it with its mouth upwards, then invert over
it another jar containing hydrogen, a gas nearly twenty-two times
lighter, in a very short time the two gases will have become thoroughly
mixed, the heavy carbonic acid having risen, and the light hydrogen
fallen, until the gases are thoroughly mixed, each jar containing an
equal quantity of each gas.
Oxygen Gas.
This gas, so named from two Greek words signifying the maker of acid,
was discovered by Dr. Priestly in 1774. He obtained it by heating
the red oxide of mercury in a glass retort, when the gas escaped in
considerable quantities. In the ensuing year Scheele obtained it by a
variety of methods, and a few years afterwards Lavoisier discovered
that it was contained in atmospheric air, where it exists in the
proportion of about one-fifth, the remaining four fifths being almost
entirely nitrogen.
Oxygen gas may be obtained for the purpose of experiment, by heating to
redness the black oxide of manganese in an iron bottle, to the mouth of
which a flexible tube is attached to convey away the gas as fast as it
is liberated from the manganese. The first portions should be allowed
to escape, being mixed with the air in the tubes and bottle, and the
remainder may be collected in a gasometer, or in glass jars inverted
over water.
Another method to obtain the gas, and one to be used only in the
absence of other ingredients, is to mix in a retort some of this same
oxide of manganese with about half its weight of strong sulphuric
acid, and apply heat to the retort, when the gas will come over in
considerable quantities; the first portions must be allowed to escape
as before.[1] If the gas is required very pure, a small quantity of the
salt called chlorate of potassa, may be heated in a retort, and oxygen
gas will be evolved, and may be collected as before. If you have an
iron bottle, the first mode is by far the cheapest, as the heat of a
bright fire is sufficient for the operation, and a large quantity of
gas is obtained in a short time from a very inexpensive material. The
most rapid and convenient process of all is to heat a mixture of two
parts chlorate of potash, and one of powdered black oxide of manganese,
in a common clean oil flask, to which a cork and bent tube has been
adapted. Care must be taken not to mistake sulphide of antimony for
black oxide of manganese, as very serious accidents have arisen from
this cause.
Oxygen is largely distributed over our globe, both in its uncombined
state, and in union with other substances. Besides forming one-fifth of
the atmosphere, it forms eight-ninths by weight of all the water in the
ocean, rivers, and springs on the face of the whole earth. It also, in
combination with various metals, forms the various earths and minerals
of which the crust of the earth consists, so that it is the most
abundant and widely distributed substance in nature, and in combination
with other elements, forms nearly half the weight of the solid earth.
In its uncombined state it is a colorless gas, somewhat heavier than
atmospheric air, without taste or smell. It is a powerful supporter of
combustion, and is absolutely necessary for the support of animal life,
which cannot exist for any time without a free supply of this gas,
which is constantly consumed in the act of breathing and is replaced
by an equivalent portion of carbonic acid gas. The want of oxygen is
partly the cause of the oppression felt in crowded rooms, where the
air cannot be renewed so fast as is required for the number of persons
who are constantly consuming the oxygen; and if an animal be confined
under a glass jar inverted over water, it will presently die, just for
the same reason that burning tapers are extinguished under similar
circumstances.
If a jet of this gas be thrown upon a piece of charcoal, sulphur, or
almost any combustible body in a state of ignition, it will make it
burn with great vividness and rapidity.