NON-METALLIC ELEMENTS.
OXYGEN—SYMBOL =O=; ATOMIC WEIGHT 16.
Oxygen is certainly the most abundant element in nature. It exists all
around us, and the animal and vegetable worlds are dependent upon it.
It constitutes in combination about one-half of the crust of the earth,
and composes eight-ninths of its weight of water. It is a gas without
taste or colour. Oxygen was discovered by Priestley and Scheele, in
1774, independently of each other.
[Illustration: Fig. 333.—Oxygen from oxide of mercury.]
Oxygen can be procured from the oxides of the metals, particularly from
gold, silver, and platinum. The noble metals are reducible from their
oxides by heat, and this fact assists us at once. If we heat chlorate
of potash, mixed with binoxide of manganese, in a retort in a furnace,
the gas will be given off. There are many other ways of obtaining
oxygen, and we illustrate two (figs. 333, 335).
The red oxide of mercury will very readily evolve oxygen, and if we
heat a small quantity of the compound in a retort as per illustration
(fig. 333) we shall get the gas. In a basin of water we place a tube
test-glass, and the gas from the retort will pass over and collect in
the test tube, driving out the water.
The other method mentioned above,—viz., by heating chlorate of potash,
etc., in a furnace, is shown in the following illustration. Oxygen, as
we have said, is a colourless and inodorous gas, and for a long time
it could not be obtained in any other form; but lately both oxygen and
hydrogen have been liquified under tremendous pressure at a very low
temperature. Oxygen causes any red-hot substance plunged into it to
burn brightly; a match will readily inflame if a spark be remaining,
while phosphorus is exceedingly brilliant, and these appearances, with
many others equally striking, are caused by the affinity for those
substances possessed by the gas. Combustion is merely oxidation, just
as the process of rusting is, only in the latter case the action is so
slow that no sensible heat is produced. But when an aggregate of slowly
oxidising masses are heaped together, heat is generated, and at length
bursts into flame. This phenomenon is called “spontaneous combustion.”
Cases have been known in which the gases developed in the human body by
the abuse of alcoholic drinks have ended fatally; in like manner the
body being completely charred. (Combustion must not be confounded with
_ignition_, as in the electric light.) Oxygen then, we see, is a great
supporter of combustion, though not a combustible itself as coal is.
When the chemical union of oxygen with another substance is very rapid
an explosion takes place.
[Illustration: Fig. 334.—Showing retort placed in furnace.]
[Illustration: Fig. 335.—The generation of oxygen from oxide of
manganese and potash.]
Oxidation occurs in various ways. Besides those already mentioned,
all verdigris produced on copper, all decays of whatever kind,
disintegration, and respiration, are the effects of oxygen. The
following experiment for the extraction of oxygen directly from the air
was made by M. Boussingault, who passed the gas upon a substance at a
certain temperature, and released it at a higher. The illustration on
page 351 will show the way in which the experiment was performed.
Boussingault permitted a thin stream of water to flow into a large
empty flask, and by this water the air was gradually driven out into
a flask containing chloride of calcium and sulphuric acid, which
effectually dried it. This dry air then passed into a large tube inside
the reverberatory furnace, in which tube were pieces of caustic baryta.
Heated to a dull redness this absorbs oxygen, and when the heat is
increased to a bright red the superabundant gas is given off. Thus the
oxygen was permitted to pass from the furnace-tube into the receiving
glass, and so pure oxygen was obtained from the air which had been in
the glass bottle at first (fig. 338).
[Illustration: Fig. 336.—Phosphorus burning in oxygen.]
HYDROGEN—SYMBOL =H=; ATOMIC WEIGHT 1.
Hydrogen is abundant in nature, but never free. United with oxygen it
forms water, hence its name, “water-former.” It is to Parcelcus that
its discovery is due, for he found that oil of vitriol in contact with
iron disengaged a gas which was a constituent of water. This gas was
subsequently found to be inflammable, but it is to Cavendish that the
real explanation of hydrogen is owing. He explained his views in 1766.
Hydrogen is obtained in the manner illustrated in the cut, by means of
a furnace, as in fig. 339, or by the bottle method, as per fig. 340.
The first method is less convenient than the second. A gun-barrel or
fire-proof tube is passed through the furnace, and filled with iron
nails or filings; a delivery tube is at the farther end, and a flask
of water boiling at the other. The oxygen combines with the iron in
the tube, and the hydrogen passes over. The second method is easily
arranged. A flask, as in the cut, is provided, and in it some zinc
shavings are put. Diluted sulphuric acid is then poured upon the metal.
Sulphate of zinc is formed in the flask, and the hydrogen passes off.
Hydrogen being the lightest of all known bodies, its weight is put
as 1, and thus we are relatively with it enabled to write down the
weights of all the other elements. Hydrogen is fourteen-and-a-half
times lighter than atmospheric air, and would do admirably for the
inflation of balloons were it not so expensive to procure in such large
quantities as would be necessary. Ordinary coal gas, however, contains
a great deal of hydrogen, and answers the same purpose.
[Illustration: Fig. 337.—Magnesium wire burning in oxygen.]
A very pretty experiment may be made with a bladder full of hydrogen
gas. If a tube be fitted to the bladder already provided with a
stop-cock, and a basin of ordinary soap-suds be at hand, by dipping the
end of the tube in the solution and gently expressing the gas, bubbles
will be formed which are of exceeding lightness (fig. 341). They can
also be fired with a taper.
Another experiment may be made with hydrogen as follows:—If we permit
the gas to escape from the flask, and light it, as in the illustration,
and put a glass over it, we shall obtain a musical note, higher or
lower, according to the length, breadth, and thickness of the open
glass-tube (fig. 342). If a number of different tubes be employed, we
can obtain a musical instrument—a gas harmonium.
[Illustration: Fig. 338.—Extraction of oxygen from air.]
Hydrogen burns with a blue flame, and is very inflammable. Even water
sprinkled upon a fire will increase its fierceness, because the
hydrogen burns with great heat, and the oxygen is liberated. Being
very light, H can be transferred from one vessel to another if both
be held upside down. Some mixtures of H and O are very explosive. The
oxyhydrogen blow-pipe is used with a mixture of O and H, which is
forcibly blown through a tube and then ignited. The flame thus produced
has a most intense heating-power.
A very easy method of producing hydrogen is to put a piece of sodium
into an inverted cylinder full of water, standing in a basin of water.
The sodium liberates the hydrogen by removing the oxygen from the
liquid.
WATER—SYMBOL =H_{2}O=; ATOMIC WEIGHT 18.
At page 59 of this volume we said something about water, and remarked
(as we have since perceived by experiment) that “water is composed of
oxygen and hydrogen in proportions, by weight, of eight of the former
to one of the latter gas; in volume, hydrogen is two to one”; and we
saw that “volume and weight were very different things.” This we will
do well to bear in mind, and that, to quote Professor Roscoe, “Water is
always made up of sixteen parts of oxygen to two parts of hydrogen by
weight”; sixteen and two being eighteen, the combining weight of water
is eighteen.
[Illustration: Fig. 339.—Preparation of hydrogen with furnace.]
[Illustration: Fig. 340.—Apparatus for generating hydrogen by flask.]
We can prove by the Eudiometer that hydrogen when burnt with oxygen
forms water; and here we must remark that water is not a mere
mechanical mixture of gases, as air is. Water is the product of
chemical combination, and as we have before said, is really an oxide
of hydrogen, and therefore combustion, or electricity, must be called
to our assistance before we can form water, which is the result of an
explosion, the mixture meeting with an ignited body—the aqueous vapour
being expanded by heat.
The ancients supposed water to be a simple body, but Lavoisier and
Cavendish demonstrated its true character. Pure water, at ordinary
temperatures, is devoid of taste and smell, and is a transparent,
nearly colourless, liquid. When viewed in masses it is blue, as
visible in a marked degree in the Rhone and Rhine, at Geneva, and
Bâle respectively. Its specific gravity is 1, and it is taken as the
standard for Sp. Gravity, as hydrogen is taken as the standard for
Atomic Weight. The uses of water and the very important part it plays
in the arrangements of nature as a mechanical agent, geology can
attest, and meteorology confirm. It composes the greater portions of
animals and plants; without water the world would be a desert—a dead
planet.
[Illustration: Fig. 341.—Blowing bubbles with hydrogen gas.]
We sometimes speak of “pure” spring water, but such a fluid absolutely
pure can scarcely be obtained; and though we can filter water there
will always remain some foreign substance or substances in solution.
It is well known that the action of water wears away and rounds off
hard rocks, and this power of disintegration is supplemented by its
strength as a solvent, which is very great. Rain-water is purest in
the country as it falls from the clouds. In smoky towns it becomes
sooty and dirty. It is owing to the solvent properties of water,
therefore, that we have such difficulty in obtaining a pure supply.
There is _hard_ water and _soft_ water. The former is derived from the
calcareous formations, and contains lime, like the Kent water. This can
be ascertained by noticing the incrustations of the vessels wherein the
water is boiled. But water rising from hard rocks, such as granite, can
do little to disintegrate them at the moment, and therefore the water
rises purer. Springs from a great depth are warm, and are known as
“thermal springs”; and when they come in contact with carbonic acid and
some salts in their passage to the surface, they are known as “mineral
waters.” These waters hold in solution salts of lime and magnesia, or
carbonates of soda with those of lime and magnesia; salts of iron, and
compounds of iodine and bromine are found in the natural mineral waters
also, as well as sulphurous impregnations, instances of which will
occur to every reader.
[Illustration: Fig. 342.—Experiment with hydrogen.]
[Illustration: Fig. 343.—The composition of water.]
We mentioned the Eudiometer just now, and we give an illustration of
it. This instrument is used to ascertain the proportions in which the
elements of water are composed by _synthesis_, or a putting together of
the constituents of a body to make it up. This is distinguished from
_analysis_, which means separating the compound body into its elements,
as we do when we pass the electric current through water.
The Eudiometer consists of a stout glass tube sealed hermetically at
one end; two platinum wires are pushed in through the glass just before
the end is sealed. The tube is now filled with mercury, and inverted
in a bowl of the same metal. Hydrogen, and then oxygen, are admitted
through the mercury in the recognised proportions of two to one. By
the time the mercury is somewhat more than half displaced, the tube
should be held upon a sheet of india-rubber at the bottom of the
vessel to keep the metal in the tube, for when the necessary explosion
takes place the mercury might also be driven out. A spark from the
electrophorus or from a Leyden jar may now be passed through the gases
in the tube. The explosion occurs, and water is formed inside. If the
mercury be again admitted it will rise nearly to the very top of the
tube, driving the bubble up. Thus we find we have formed water from the
two gases.
The decomposition of water is easily affected by electricity, and if
a little sulphuric acid be added to the water, the experiment will
be thereby facilitated. Two wires from a battery should be inserted
through a glass filled with the water, and into two test tubes also
filled. The wires terminate in platinum strips, and are fastened at the
other end to the positive and negative poles of the galvanic battery.
The gases will collect in the test tubes, and will be found in proper
proportions when the current passes.
[Illustration: Fig. 344.—The Eudiometer.]
[Illustration: Fig. 345.—Decomposition of water.]
So much for water in its liquid state. The solid condition of water
(ice) is equally interesting. When we apply heat to water, we get a
vapour called “steam”; when we cool water to 32° Fahr., we get a solid
mass which weighs just the same as the liquid we have congealed, or the
steam we have raised from an equal amount of water. But water expands
while in the process of solidification, just as it does when it becomes
gaseous, and as we have remarked before, our water-pipes bear full
testimony to this scientific fact. When ice forms it has a tendency
to crystallize, and some of these ice crystals are, as we see, very
beautiful. Snow is only water in a nearly solid form, and the crystals
are extremely elegant, appearing more like flowers than congealed
water, in tiny six-pointed ice crystals. Many philosophers of late
years have written concerning these tiny crystals, which, in common
with all crystals, have their own certain form, from which they never
depart. Snowflakes are regular six-sided prisms grouped around a centre
forming angles of 60° and 120°. There are a number of forms, as will
be seen from the accompanying illustrations, and at least ninety-six
varieties have been observed. One snowflake, apparently so like all
other flakes that fall, can thus be viewed with much interest, and yet,
while so very various, snowflakes never get away from their proper
hexagonal structure. It has been remarked that snowflakes falling at
the same time have generally the same form.
Of the latent heat of ice, etc., we have already spoken in our article
upon Heat, and therefore it will be sufficient to state that the latent
heat of water is 79 thermal units, because when passing from the liquid
to the solid state a certain amount of water absorbs sufficient heat to
raise an equal quantity of the liquid 79°. This can be proved by taking
a measured quantity (say a pint) of water at 79° and adding ice of the
same weight to the water. The mixture will be found to be at zero.
Therefore the ice has absorbed or rendered latent 79° of heat which the
water possessed. If we melt ice until only a trace of it is left, we
shall still find the water as cold as the ice was; all the latent heat
is employed in melting the ice. So it will take as much heat to bring a
pound of ice at zero to a pound of water at zero, as it would to raise
79 pounds of water 1°. The same law applies to steam.
[Illustration: Fig. 346.—Snow crystals.]
Water can be distilled in small quantities by an apparatus, as figured
in the illustration, and by these means we get rid of all impurities
which are inseparable from the liquid otherwise. When it is desirable
to distil large quantities of water a larger apparatus is used, called
an “Alembic.” The principle is simply to convert the liquid by heat
into vapour, then cool it, by condensation, in another vessel.
[Illustration: Fig. 347.—Distilling water.]
The evaporation of water, with its effects upon our globe, belong more
to the study of Meteorology.
[Illustration: Fig. 348.—Distillation.]
Rain-water is the purest, as we have said, because it goes through the
process of distillation by nature. The sun takes it up, by evaporation,
into the air, where it is condensed, and falls as rain-water. Water
containing carbonate of lime will petrify or harden, as in stalactite
caverns. The carbonic acid escapes from the dripping water, the
carbonate in solution is deposited as a stalactite, and finally forms
pillars in the cave. Sea-water contains many salts; its composition is
as follows, according to Dr. Schwertzer, of Brighton:—
Water 964·74372 grains.
Chloride of sodium (salt) 28·05948 ”
Chloride of potassium 0·76552 ”
Chloride of magnesium 3·66658 ”
Bromide of magnesium 0·02929 ”
Sulphate of magnesia 2·29578 ”
Sulphate of lime 0·40662 ”
Carbonate of lime 0·03301 ”
(With traces of iodine and ammonia). --—--—----
1000·00000 grains.
[Illustration: Fig. 349.—Stalactite Cavern.]
There is much more oxygen in water than in air, as can be ascertained
by analysis of these compounds. This great proportion in favour of
water enables fish to breathe by passing the water through the gills.
Marine animals (not fishes), like the whale,—which is a warm-blooded
creature, and therefore not suited to exist without air,—are obliged
to come to the surface to breathe. The density of salt water is much
greater than that of fresh water, and therefore swimming and flotation
is easier in the sea than in a river. We shall have more to say of
water by-and-by.
NITROGEN—SYMBOL =N=; ATOMIC WEIGHT 14.
We have already made some reference to this gas when speaking of the
atmosphere and its constituents, of which nitrogen is the principal.
From its life-destroying properties it is called “azote” by French
chemists, and when we wish to obtain a supply of nitrogen all we have
to do is to take away the oxygen from the air by burning phosphorus
on water under a glass. Nitrogen is not found frequently in solid
portions of the globe. It is abundant in animals. It is without colour
or smell, and can be breathed in air without danger. It is heavy and
sluggish; but if we put a taper into a jar of nitrogen it will go out,
and animals die in the gas for want of oxygen, as nitrogen alone cannot
support life.
[Illustration: Fig. 350.—Obtaining nitrogen.]
The affinity of nitrogen for other substances is not great, but it
gives rise to five compounds, which are as below, in the order they are
combined with oxygen:—
Nitrous oxide (“laughing gas”) (Monoxide) N_{2}O.
Nitric oxide Dioxide N_{2}O_{2}.
Nitrous acid Trioxide N_{2}O_{3}.
Nitric peroxide Tetroxide N_{2}O_{4}.
Nitric acid Pentoxide N_{2}O_{5}.
These compounds are usually taken as representative examples of
combining weight, and as explanatory of the symbolic nomenclature of
chemistry, as they advance in such regular proportions of oxygen with
nitrogen. The combining weight of nitrogen is 14, and when two parts
combine with five of oxygen it makes nitric acid, and we put it down
as N_{2}O_{5}; on adding water, HNO_{3}, as we can see by eliminating
the constituents and putting in the proportions. Actually it is
H_{2}N_{2}O_{6}, or, by division, HNO_{3}.
Nitrogen plays a very important part in nature, particularly in the
vegetable kingdom. Nitric acid has been known for centuries. Geber,
the alchemist, was acquainted with a substance called “nitric,”
which he found would yield a dissolvent under certain circumstances.
He called it “dissolving fluid.” At the end of the twelfth century
Albert Magnus investigated the properties of this acid, and in 1235
Raymond Lully prepared nitre with clay, and gave the liquid the
name of “aqua-fortis.” But till 1849 nitric acid was only known as
a hydrate,—that is, in combination with water,—but now we have the
anhydrous acid.
[Illustration: Fig. 351.—Apparatus for obtaining nitrogen by using
metal to absorb the oxygen of the air.]
Oxygen and nitrogen combine under the influence of electricity, as
shown by Cavendish, who passed a current through an atmospheric
mixture of oxygen and nitrogen, in a tube terminating in a solution of
potash, lime, and soda. Every time the spark passed, the volume of gas
diminished, and nitric acid was formed, as it is in thunderstorms, when
it does not remain free, but unites with ammonia, and forms a highly
useful salt, which promotes vegetable growth. Here is another instance
of the usefulness of thunderstorms, and of the grand provisions of
nature for our benefit. Nitric acid is obtained by distilling nitre
with sulphuric acid. The liquid is, when pure, colourless, and is a
powerful oxidizer. It dissolves most metals, and destroys vegetable and
animal substances. By an addition of a little sulphuric acid the water
is taken from the nitric acid, and a very powerful form of it is the
result. The acid is of great use in medicine, and as an application
to bites of rabid animals or serpents. It converts cotton waste into
“gun-cotton” by a very simple process of steeping, washing, and
pressing. From the hydraulic press it comes in discs like “quoits,”
which will burn harmlessly and smoulder away, but if detonated
they explode with great violence. As a rule, when damp, it is not
dangerous, but it can be fired even when wet. It will explode at a less
temperature than gunpowder, and, moreover, yields no smoke, nor does
it foul a gun. Gun-cotton, when dissolved in ether, gives us collodion
for photographic purposes.
[Illustration: Fig. 352.—Nitric acid obtained from nitre and sulphuric
acid.]
In speaking farther of the compounds of nitrogen with oxygen, we will
limit ourselves to the monoxide, or laughing gas. This is now used
as an anæsthetic in dentistry, etc., and is quite successful, as a
rule. People afflicted with heart disease should not use it without
advice, however. When inhaled into the lungs it makes the subject very
hilarious, and the effect is rather noisy. It is obtained from the
nitrate of ammonia, which, on the application of heat, decomposes into
nitrous oxide and vapour. Warm water should be used for the trough. The
gas is a powerful supporter of combustion.
[Illustration: Fig. 353.—Cavendish’s experiment.]
Binoxide of nitrogen is of importance in the manufacture of sulphuric
acid.
Nitrogen combines with hydrogen, forming various compounds. These
are the “amines,” also ammonia, and ammonium. Ammonia possesses the
properties of a base. Its name is derived from Jupiter Ammon, near
whose temple it was prepared, from camels’ dung. But bodies containing
nitrogen give off ammonia in course of distilling, and hartshorn is
the term applied to horn-cuttings, which yield ammonia, which is a
colourless gas of strong odour and taste now obtained from gas-works.
[Illustration: Fig. 354.—Experiment to obtain nitric acid.]
[Illustration: Fig. 355.—Apparatus for obtaining laughing-gas.]
[Illustration: Fig. 356.—Inhaling laughing gas.]
[Illustration: Fig. 357.—Generation of ammonia.]
To obtain ammonia heat equal parts of chloride of ammonia (sal
ammoniac) and quick-lime powdered (_see_ fig. 357). The gas must be
collected over mercury, because it is very soluble in water. Ammonia
is useful to restore tipsy people and fainting ladies. A solution of
ammonia is used for cauteries. Ammoniacal gas is remarkable for its
solubility in water. To prepare the solution the gas is forced through
a series of flasks. The tubes carrying the gas should be continued to
the bottoms of the flasks, else the solution, being lighter than water,
the upper portion alone would be saturated. The tubes carrying away
the solution are raised a little, so that the renewal is continually
proceeding. The gas liquifies under a pressure of six atmospheres,
at a temperature of 10° Cent. This experiment can be artificially
performed by heating chloride of silver saturated with ammonia, and
the silver will part with the gas at a temperature of 40° C. The gas
will then condense in a liquid form in the tube. The experiment may
be facilitated by placing the other extremity of the tube in snow and
salt, and by the liquid we can obtain intense cold. This experiment
has been made use of by M. Carré in his refrigerator (which was
described in the Physics’ section), by which he freezes water. We may,
however, just refer to the process. Whenever the condition of a body
is changed from that of liquid to a gas, the temperature is greatly
lowered, because the heat becomes “latent.” The latest freezing machine
consists of an apparatus as shown in the illustrations herewith (figs.
359 and 360). The machine is of wrought iron, and contains, when
ready for action, a saturated solution of ammonia at zero. This is
in communication with another and an air-tight vessel, of which the
centre is hollow. The first process is to heat the solution, and the
gas escapes into the second “vase,” which is surrounded by cold water,
and quite unable to escape. A tremendous pressure is soon obtained, and
this, added to the cold water, before long liquifies the ammonia, and
when the temperature indicates 130° the hot vessel is suddenly cooled
by being put into the water. The gas is thus suddenly converted into
a liquid, the water in the second hollow vase is taken out, and the
bottle to be frozen is put into the cavity. The cold is so great, in
consequence of the transformation of the liquid ammonia into a gas,
that it freezes the water in any vessel put into the receiver. The
ammonia can be reconverted into liquid and back again, so no loss is
occasioned by the process, which is rapid and simple. This is how great
blocks of ice are produced in water-bottles.
[Illustration: Fig. 358.—Liquefaction of ammonia.]
[Illustration: Fig. 359.—Carré’s refrigerator (first action).]
The one important point upon which care is necessary is the raising of
the temperature. If it be elevated beyond 130° C., the pressure will be
too great, and an explosion will occur.
The abundant formation of ammonia from decaying animal matter is
evident to everyone, and depends upon the presence of moisture to a
great extent. Chloride of ammonia is called sal-ammoniac, and the
carbonate of ammonia crystallizes from the alkaline liquid produced by
the distillation of certain animal matter. The compounds of ammonia are
easily recognized by a certain sharp taste. They are highly valuable
remedial agents, acting particularly upon the cutaneous system, and
when taken internally, produce the effect of powerful sudorifics.
Their _volatility_, and the facility with which they are expelled from
other substances, render them of great importance in chemistry, and
peculiarly fit them for the purposes of many chemical analyses. The
ammonia compounds display a remarkable analogy to the corresponding
combinations of potash and soda. The compounds of ammonia are highly
important in their relation to the vegetable kingdom. It may be assumed
that all the _nitrogen_ of plants is derived from the ammonia which
they absorb from the soil, and from the surrounding atmosphere.
[Illustration: Fig. 360.—Carré’s refrigerator (second action).]
The similarity of ammonia to the metallic oxides has led to the
conjecture that all its combinations contain a _compound_ metallic
body, which has received the name _ammonium_ (NH_{4}); but no one has
yet succeeded in its preparation, although by peculiar processes it may
be obtained in the form of an amalgam.
Ammonias, in which one or more atoms of hydrogen are replaced by basic
radicals, are termed _Amides_, or _Amines_.