CHEMICAL PHENOMENA.
Water--Its Constituents--Oxygen--Hydrogen--Peroxide
of Hydrogen--Physical Property of Water--Ice--Sea
Water--Chlorine--Muriatic Acid--Iodine--Bromine--Compounds
of Hydrogen with Carbon--Combustion--Flame--Safety
Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic
Acid--Influence of Plants on the Air--Chemical Phenomena of
Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c. &c.
Without attempting anything which shall approach even to the character
of a sketch of chemical science, we may be allowed, in our search
after exalting truths, to select such examples of the results of
combination as may serve to elucidate any of the facts connected with
natural phenomena. In doing this, by associating our examination with
well-known natural objects or conditions, the interpretation afforded
by analysis will be more evident, and the operation of the creative
forces rendered more striking and familiar, particularly if at the same
time we examine such physical conditions as are allied in action, and
are sufficiently explanatory of important features.
A large portion of this planet is covered by the waters of the ocean,
of lakes and rivers. Water forms the best means of communication
between remote parts of the earth. It is in every respect of the
utmost importance to the animal and vegetable kingdom; and, indeed, it
is indispensable in all the great phenomena of the inorganic world.
The peculiarities of saltness or freshness in water are dependent
upon its solvent powers. The waters of the ocean are saline from
holding dissolved various saline compounds, which are received in
part from, and imparted also to, the marine plants. Perfectly pure
water is without taste: even the pleasant character of freshly-drawn
spring-water is due to the admixture of atmospheric air and carbonic
acid. The manner in which water absorbs air is evidently due to a
peculiar physical attractive force, the value of which we do not at
present clearly perceive or correctly estimate. It is chemically
composed of two volumes of hydrogen gas--the lightest body known, and
at the same time a highly inflammable one--united with one volume of
oxygen, which excites combustion, and continues that action,--producing
heat and light,--with great energy. By weight, one part of hydrogen
is united with eight of oxygen, or in 100 parts of water we find 88·9
oxygen, and 11·1 of hydrogen gas. That two such bodies should unite to
furnish the most refreshing beverage, and indeed the only natural drink
for man and animals, is one of the extraordinary facts of science.
Hydrogen will not support life--we cannot breathe it and live; and
oxygen would over-stimulate the organic system, and, producing a kind
of combustion, give rise to fever in the animal frame; but, united,
they form that drink, for a drop of which the fevered monarch would
yield his diadem, and the deprivation of which is one of the most
horrid calamities that can be inflicted upon any living thing. Water
appears as the antagonist principle to fire, and the ravages of the
latter are quenched by the assuaging powers of the former; yet a
mixture of oxygen and hydrogen gases, in the exact proportion in which
they form water, explodes with the utmost violence on the contact of
flame, and, when judiciously arranged, produces the most intense degree
of heat known;--such is the remarkable difference between a merely
mechanical mixture and a chemical combination. Beyond this, we have
already noticed the remarkable fact that water deprived of air is
explosive at a comparatively low temperature, less than 300°; gunpowder
requiring a temperature of nearly 1000° F.
If we place in a globe, oxygen and hydrogen gases, in the exact
proportions in which they combine to form water, they remain without
change of state. They appear to mix intimately; and, notwithstanding
the difference in the specific gravities of the two gases, the lighter
one is diffused through the heavier in a curious manner, agreeably to
a law which has an important bearing on the conditions of atmospheric
phenomena.[212] The moment, however, that an incandescent body, or
the spark from an electric machine, is brought into contact with the
mixed gases, they ignite, explode violently, and combine to form water.
The discovery of the composition of water was thus synthetically made
by Cavendish--its constitution having been previously theoretically
announced by Watt.[213]
If, instead of combining oxygen and hydrogen in the proportions in
which they form water, we compel the hydrogen to combine with an
additional equivalent of oxygen, we have a compound possessing many
properties strikingly different from water. This--peroxide of hydrogen,
as it is called--is a colourless liquid, less volatile than water,
having a metallic taste. It is decomposed at a low temperature, and,
at the boiling point, the oxygen escapes from it with such violence,
that something like an explosion ensues. All metals, except iron, tin,
antimony, and tellurium, have a tendency to decompose this compound,
and separate it into oxygen and water. Some metals are oxidized during
the decomposition, but gold, silver, platinum, and a few others,
still retain their metallic state. If either silver, lead, mercury,
gold, platinum, manganese, or cobalt, in their highest states of
oxidation, are put into a tube, containing this peroxide of hydrogen,
its oxygen is liberated with the rapidity of an explosion, and so
much heat is excited that the tube becomes red hot. These phenomena,
to which we have already referred in noticing catalysis, are by no
means satisfactorily explained, and the peculiar bleaching property
possessed by the peroxide of hydrogen sufficiently distinguishes it
from water. There are few combinations which show more strikingly than
this the difference arising from the chemical union of an additional
atom of one element. Similar instances are numerous in the range
of chemical science; but scarcely any two exhibit such dissimilar
properties. During the ordinary processes of combustion, it has been
long known that water is formed by the combination of the hydrogen of
the burning body with the oxygen of the air. The recent researches of
Schönbein have shown that a peculiar body, which has been regarded as
a peroxide of hydrogen, to which he has given the name of OZONE, is
produced at the same time, and that it is developed in a great many
ways, particularly during electrical changes of the atmosphere. Thus
we obtain evidence that this remarkable compound, which was considered
as a chemical curiosity merely, is diffused very generally through
nature, and produced under a great variety of circumstances. During
the excitation of an electrical machine, or the passage of a galvanic
current through water by the oxidation of phosphorus, and probably
in many similar processes--in particular those of combustion, and we
may therefore infer also of respiration--this body is formed. From
observations which have been made, it would appear that, during the
night, when the activity of plants is not excited by light, they act
upon the atmosphere in such a way as to produce this ozone; and its
presence is said to be indicated by its peculiar odour during the
early hours of morning. We are not yet acquainted with this body
sufficiently to speculate on its uses in nature: without doubt, they
are important, perhaps second to those of water only. It is probable,
as we have already had occasion to remark, that ozone may be the active
agent in removing from the atmosphere those organic poisons to which
many forms of pestilence are traceable; and it is a curious fact, that
a low electrical intensity, and a consequent deficiency of atmospheric
ozone, marks the prevalence of cholera, and an excess distinguishes the
reign of influenza.[214]
Some interesting researches appear to show the probability that ozone
is simply oxygen in a state of high activity. It has been found,
indeed, that perfectly dry oxygen, which will not bleach vegetable
colours in the dark, acquires, by exposure to sunshine, the power of
destroying them. Becquerel has proved that this ozonous state may be
produced in dry oxygen by passing a succession of electric sparks
through it. Fremy passed the electric sparks on the outside of a tube
which contained perfectly dry oxygen, and it was found to have acquired
the properties of ozone. In this case, and probably in the experiments
of Becquerel, the light of the spark, rather than the electricity,
appears to have been the active agent in producing this change.
Schönbein himself does not appear disposed to regard ozone as being
either peroxide of hydrogen, or an allotropic oxygen. He leans to his
first view of its being an entirely new chemical element. The energy
of this ozone is so great, that it has been found to destroy almost
instantaneously the Indian-rubber union joints of the apparatus in
which it is formed.[215]
Water, from the consideration of which a digression has been indulged
in, to consider the curious character of one of its elements,--water is
one of the most powerful chemical agents, having a most extensive range
of affinities, entering directly into the composition of a great many
crystallizable bodies and organic compounds. In those cases where it is
not combined as water, its elements often exist in the proportions in
which water is formed. Gum, starch, and sugar, only differ from each
other in the proportions in which the elements of water are combined
with the carbon.
In saline combinations, and also in many organic forms, we must regard
the water as condensed to the solid form; that is, to exist as ice. We
well know that, by the abstraction of heat, this condition is produced;
but, in chemical combinations, this change must be the result of the
mechanical force exerted by the power of the agency directing affinity.
In the case of water passing from a liquid to a solid state, we have a
most beautiful exemplification of the perfection of natural operations.
Water conducts heat downwards but very slowly; a mass of ice will
remain undissolved but a few inches under water, on the surface of
which, ether, or any other inflammable body, is burning. If ice (solid
water) swam beneath the surface, the summer sun would scarcely have
power to thaw it; and thus our lakes and seas would be gradually
converted into solid masses at our ordinary winter temperatures.
All similar bodies contract equally during the process of cooling,
from the highest to the lowest points to which the experiments have
been carried. It has been thought that if this applied to water,
the result would be the sudden consolidation of the whole mass. A
modification of the law has been supposed to take place to suit the
peculiar circumstances of water. Nature never modifies a law for a
particular purpose; we must, therefore, seek to explain the action of
the formation of ice, as we know it, by some more rational view.
Water expands by heat, and contracts by cold; consequently, the
coldest portions of this body occupy the lower portions of the fluid;
but it must be remembered that these parts are warmed by the earth.
Ross, however, states that at the depth of 1,000 fathoms the sea
has a constant temperature of 39°. Water is said to be at its point
of greatest density at 40° of Fahrenheit’s thermometer; in cooling
further, this fluid appears to expand, in the same way as if heated:
and, consequently, water colder than this point, instead of being
heavier, is lighter, and floats on the surface of the warmer fluid.
It does not seem that any modification of the law is required to
account for this phenomenon. Water cooled to 40° still retains its
peculiar corpuscular arrangement; but immediately it passes below that
temperature, it begins to dispose itself in such a manner that visible
crystals may form the moment it reaches 32°. Now, if we conceive
the particles of water, at 39°, to arrange themselves in the manner
necessary for the assumption of the solid form, by the particular
grouping of molecules in an angular instead of a spheroidal shape,
it will be clear, from what we know of the arrangement of crystals
of water--ice--that they must occupy a larger space than when the
particles are disposed, side by side, in minute spheres. Even the
escape of air from the water in which it is dissolved is sufficient to
give an apparent lightness to the colder water. This expansion still
goes on increasing, from the same cause, during the formation of ice,
so that the specific gravity of a mass of frozen water is less than
that of water at any temperature below 40°. It must not be forgotten
that ice always contains a large quantity of air, by which it is
rendered buoyant.
Water, at rest, may be cooled many degrees below the freezing point
without becoming solid. This is easily effected in a thin glass flask;
but the moment it is agitated, it becomes a firm mass. Here we have the
indication of another cause aiding in producing crystals of ice on the
surface of water, under the influence of the disturbance produced by
the wind, which does not extend to any depth.
As oxygen and hydrogen gases enter largely into other chemical
compounds besides water, it is important to consider some of the forms
of matter into the composition of which these elements enter. To
examine this thoroughly, a complete essay on chemical philosophy would
be necessary; we must, therefore, be content with referring to a few of
the more remarkable instances.
The waters of the ocean are salt: this arises from their holding, in
solution chloride of sodium (_muriate of soda_--_common culinary salt_)
and other saline bodies. Water being present, this becomes muriate of
soda,--that is, a compound of muriatic acid and soda: muriatic acid
is hydrogen, combined with a most remarkable gaseous body, called,
from its yellow colour, _chlorine_; and soda, oxygen in union with
the metal sodium,--therefore, when anhydrous, culinary salt is truly
a chloride of sodium. Chlorine in some respects resembles oxygen; it
attacks metallic bodies with great energy; and, in many cases, produces
the most vivid incandescence, during the process of combination. It
is a powerful bleaching agent, is destructive to animal life, and
rapidly changes all organic tissues. There are two other bodies in
many respects so similar to chlorine, although one is at the ordinary
temperatures solid, and the other fluid, and which are also discovered
in sea-water, or in the plants growing in it, that it is difficult to
consider them otherwise than as different forms of the same principle.
These are iodine and bromine, and they both unite with hydrogen to
form acids. The part which chlorine performs in nature is a great and
important one. Combined in muriate of soda, we may trace it in large
quantities through the three kingdoms of nature, and the universal
employment of salt as a condiment indicates the importance to the
animal economy of the elements composing it. Iodine has been traced
through the greater number of marine plants, existing, apparently as
an essential element of their constitution; in some land plants it has
also been found, particularly in the Armeria maritima, when this plant
grows near the sea:[216] it has been detected in some mineral springs,
and in small quantities in the mineral kingdom[217] combined as iodide
of silver, and in the aluminous slate of Latorp in Sweden.[218] Bromine
is found in sea-water, although in extremely minute quantities, in a
few saline springs, and in combination with silver; but we have no
evidence to show that its uses are important in nature.
Hydrogen, again, unites with carbon in various proportions, producing
the most dissimilar compounds. The air evolved from stagnant water,
and the fire-damp of the coal mine, are both carburetted hydrogen; and
the gas which we employ so advantageously for illumination, is the
same, holding an additional quantity of carbon in suspension. Naphtha,
and a long list of organic bodies, are composed of these two chemical
elements.
These combinations lead us, naturally, to the consideration of the
great chemical phenomena of combustion, which involve, indeed, the
influences of all the physical powers. By the application of heat,
we produce an intense action in a body said to be combustible; it
burns,--a chemical action of the most energetic character is in
progress, the elements which constitute the combustible body are
decomposed, they unite with some other elementary principles, and new
compounds are formed. A body burns--it is entirely dissipated, or it
leaves a very small quantity of ashes behind unconsumed, but nothing
is lost. Its volatile parts have entered into new arrangements, the
form of the body is changed, but its constituents are still playing an
important purpose in creation.
The ancient notion that fire was an empyreal element, and the Stahlian
hypothesis of a phlogistic principle on which all the effects of
combustion depended,[219] have both given way to the philosophy of the
unfortunate Lavoisier--which has, indeed, been modified in our own
times--who showed that combustion is but the development of heat and
light under the influence of chemical combination.
Combustion was, at one period, thought to be always due to the
combination of oxygen with the body burning, but research has shown
that vivid combustion may be produced where there is no oxygen. The
oxidizable metals burn most energetically in chlorine, and some of
them in the vapour of iodine and bromine, and many other unions take
place with manifestations of incandescence. Supporters of combustion
were, until lately, regarded as bodies distinct from those undergoing
combustion. For example, hydrogen was regarded as a combustible body,
and oxygen as a supporter of combustion. Such an arrangement is a
most illogical one, since we may _burn_ oxygen in an atmosphere of
hydrogen, in the same manner as we burn hydrogen in one of oxygen; and
so, in all the other cases, the supporter of combustion may be burnt
in an atmosphere formed of the, so called, combustible. The ordinary
phenomena of combustion are, however, due to the combination of oxygen
with the body burning; therefore every instance of oxidization may be
regarded as a condition of combustion, the difference being only one of
degree.
Common iron, exposed to air and moisture, _rusts_; it combines with
oxygen. Pure iron, in a state of fine division, unites with oxygen so
eagerly, that it becomes incandescent, and in both cases oxide of iron
is formed. This last instance is certainly a case of combustion; but
in what does it differ from the first one, except in the intensity of
the action? The cases of spontaneous combustion which are continually
occurring are examples of an analogous character to the above.
Oxygen is absorbed, it enters more or less quickly, according to
atmospheric conditions, into chemical combination; heat is evolved, and
eventually,--the action continually increasing,--true combustion takes
place. In this way our cotton-ships, storehouses of flax, piles of
oiled-cloth, sawdust, &c., frequently ignite; and to such an influence
is to be attributed the destruction of two of our ships of war, a few
years since, in Devonport naval arsenal.[220]
In the economic production of heat and light, we have the combination
of hydrogen and carbon with the oxygen of common air, forming water
and carbonic acid. In our domestic fires we employ coal, which is
essentially a compound of carbon and hydrogen containing a little
oxygen and some nitrogen, with some earthy matters which must be
regarded as impurities; the taper, whether of wax or tallow, is made up
of the same bodies, differing only in their combining proportions, and,
like coal gas, these burn as carburetted hydrogen. All these bodies
are very inflammable, having a tendency to combine energetically with
oxygen at a certain elevation of temperature.
We are at a loss to know how heat can cause the combination of those
bodies. Sir Humphry Davy has shown that hydrogen will not burn, nor
a mixture of it with oxygen explode, unless directly influenced by a
body heated so as to _emit light_.[221] May we not, therefore, conclude
that the chemical action exhibited in a burning body is a development
of some latent force, with which we are unacquainted, produced by the
absorption of light;--that a repulsive action at first takes place,
by which the hydrogen and carbon are separated from each other;--and
that in the nascent state they are seized by the oxygen, and again
compelled, though in the new forms of water and carbonic acid, to
resume their chains of combining affinity?
Every equivalent of carbon and of hydrogen in the burning body unites
with two equivalents of oxygen, in strict conformity with the laws
of combination. The flame of hydrogen, if pure, gives scarcely any
light, but combined with the solid particles of carbon, it increases
in brightness. The most brilliant of the illuminating gases is the
olefiant gas, produced by the decomposition of alcohol, and it is
only hydrogen charged with carbon to the point of saturation. Flame
is a cone of heated vapour, becoming incandescent at the points of
contact with the air; a mere superficial film only being luminous. It
is evident that all the particles of the gas are in a state of very
active repulsion over the surface, since flame will not pass through
wire gauze of moderate fineness. Upon this discovery is founded the
inimitable safety-lamp of Davy, by means of which the explosive gases
of a mine are harmlessly ignited within a cage of wire gauze. This
effect has been attributed to a cooling influence of the metal; but,
since the wires may be brought to a degree of heat but little below
redness without igniting the fire-damp, this does not appear to be the
cause. The conditions of the safety lamp may be regarded as presenting
examples exactly the converse of those already stated with reference to
the spheroidal state of water; and it affords additional evidence that
the condition of bodies at high temperatures is subject to important
physical changes.
The principle upon which the safety lamp is constructed is, that a
mixture of the fire-damp and atmospheric air in certain proportions
explodes upon coming in contact with a flame.
This mixture passes readily through a wire gauze, under all
circumstances, and it, of course, thus approaches the flame of the lamp
enclosed within such a material, and it explodes. But, notwithstanding
the mechanical force with which the exploding gas is thrown back
against the bars of its cage, it cannot pass them. Consequently, the
element of destruction is caught and caged; and notwithstanding its
fierceness and energy, it cannot impart to the explosive atmosphere
without, any of its force. No combustion can be communicated through
the wire gauze.
The researches which led to the safety-lamp may be regarded as among
the most complete examples of correct inductive experiment in the range
of English science, and the result is certainly one of the proudest
achievements of physico-chemical research. By merely enveloping the
flame of a lamp with a metallic gauze, the labourer in the recesses of
the gloomy mine may feel himself secure from that outpouring current
of inflammable gas, which has been so often the minister of death; he
may walk unharmed through the explosive atmosphere, and examine the
intensity of its power, as it is wasted in trifling efforts within the
little cage he carries. Accidents have been attributed to the “Davy,”
as the lamp is called among the colliers; but they may in most cases be
traced to carelessness on the part of those whose duty it has been to
examine the lamps, or to the recklessness of the miners themselves.
That curious metal, platinum, and also palladium, possesses a property
of maintaining a slow combustion, which the discoverer of the
safety-lamp proposed to render available to a very important purpose.
If we take a coil of platinum wire, and, having made it red-hot, plunge
it into an explosive atmosphere of carburetted hydrogen and common
air, it continues to glow with considerable brightness, producing,
by this very peculiar influence, a combination of the gases, which
is discovered by the escape of pungent acid vapours. Over the little
flame of the safety-lamp, it was proposed by Davy to suspend a coil
of platinum which would be thus kept constantly at a red heat. If the
miner became accidentally enveloped in an atmosphere of fire-damp,
although the flame of his lamp might be extinguished, the wire would
continue to glow with sufficient brightness to light him from his
danger, through the dark winding passages which have been worked in the
bed of fossil fuel. This very beautiful arrangement has not, however,
been adopted by our miners.
It is thus that the discoveries of science, although they may appear
of an abstract character, constantly, sooner or later, are applied to
uses by which some branch of human labour is assisted, the necessities
of man’s condition relieved, and the amenities of life advanced.
The respiration of animals is an instance of the same kind of chemical
phenomena as we discover in ordinary combustion. In the lungs the blood
becomes charged with oxygen, derived from the atmospheric air, with
which it passes through the system, performing its important offices,
and the blood is returned to the lungs with the carbonic acid formed
by the separation of carbon from the body which is thrown off at every
expiration. It will be quite evident that this process is similar to
that of ordinary combustion. In man or animals, as in the burning
taper,--which is aptly enough employed by poets as the symbol of
life,--we have hydrogen and carbon, with some nitrogen superadded; the
hydrogen and oxygen form water under the action of the vital forces;
the carbon with oxygen produces carbonic acid, and, by a curious
process, the nitrogen and hydrogen also combine, to form ammonia.[222]
All the carbon which is taken into the animal economy passes, in
the process of time, again into the atmosphere, in combination with
oxygen, this being effected in the body, under the _catalytic_ power of
tissues, immediately influenced by the excitation of nervous forces,
which are the direct manifestations of vital energy. The quantity of
carbonic acid thus given out to the air is capable of calculation,
with only a small amount of error. It appears that upwards of fifty
ounces of carbonic acid must be given off from the body of a healthy
man in twenty-four hours. On the lowest calculation, the population of
London must add to the atmosphere daily 4,500,000 pounds of carbonic
acid. It must also be remembered that in every process for artificial
illumination, and in all the operations of the manufactures in which
fire is used, and also in our arrangements to secure domestic comfort,
immense quantities of this gas are formed. We may, indeed, fairly
estimate the amount, if we ascertain the quantity of wood and coal
consumed, of all the carbon which combines with oxygen while burning,
and escapes into the air, either as carbonic acid or carbonic oxide.
The former gas, the same as that which accumulates in deep wells
and in brewers’ vats, is highly destructive to life, producing very
distressing symptoms, even when mixed with atmospheric air, in but
slight excess over that proportion which it commonly contains. The
oppressive atmosphere of crowded rooms is in a great measure due to the
increased proportion of carbonic acid given off from the lungs of those
assembled, and collected in the almost stagnant air of badly ventilated
apartments. It will be evident to every one, that unless some provision
was made for removing this deleterious gas from the atmosphere as
speedily as it formed, consequences of the most injurious character to
the animal races would ensue. It is found, however, that the quantity
in the atmosphere is almost constantly about one per cent. The peculiar
properties of carbonic acid in part ensure its speedy removal. It is
among the heaviest of gaseous bodies, and it is readily absorbed by
water; consequently, floating within a short distance from the surface
of the earth, a large quantity is dissolved by the waters spread
over it. A considerable portion is removed by the vegetable kingdom;
indeed, the whole of that produced by animals, and by the processes
of combustion, eventually becomes part of the vegetable world, being
absorbed with water by the roots, and separated from the air by the
peculiar functions of the leaves. However, this heavy gas unites with
the lighter atmospheric fluid in obedience to that law which determines
the diffusion of different specific gravities through each other.
The leaves of plants may be regarded as performing similar offices
to the lungs of animals. They are the breathing organs. In the animal
economy a certain quantity of carbon is necessarily retained, in
combination with nitrogen and other elements, to form muscle; but this
is constantly undergoing change; the entire system being renewed within
a comparatively limited period. The conditions with plants are somewhat
different. For instance, the carbon is fixed in a tree, and remains
as woody fibre until it decays, even though the life of the plant may
extend over centuries.
Animals, then, are constantly supplying carbonic acid; plants are as
constantly feeding on it; thus is the balance for ever maintained
between the two kingdoms. Another condition is, however, required to
maintain for the uses of men and animals the necessary supply of oxygen
gas. This is effected by one of those wonderful operations of nature’s
chemistry which must strike every reflecting mind with admiration.
During the night plants absorb carbonic acid; but there is a condition
of repose prevailing then in their functions, and consequently their
powers of effecting the decomposition of this gas are reduced to their
minimum. The plant sleeps, and vital power reposes; its repose being as
necessary to the plant as to the animal. With the first gleam of the
morning sun the dormant energies of the plant are awakened into full
action; it decomposes this carbonic acid, secretes the carbon, to form
the rings of wood which constitute so large a part of its structure,
and pour out oxygen gas to the air. The plant is, therefore, an
essential element in the conditions necessary for the support of animal
life.
The animal produces carbonic acid in an exact proportion to the
quantity of carbonaceous matter which it consumes. Fruit and herbage
contain a small quantity of carbon in comparison with muscle and fat.
But let us confine our attention to the human race. Man within the
Tropics, where the natural temperature is high, does not require so
great an amount of chemical action to go on within him for the purpose
of maintaining the requisite animal heat; consequently his Maker has
surrounded him with fruits and grains which constitute his food.
As we advance to the colder regions of the earth man becomes a
flesh-eater, and his carnivorous appetite increases as the external
temperature diminishes. Eventually we reach the coldest zones, and the
human being there devours enormous quantities of fat to supply the
necessities of his condition.
It must necessarily follow, that the inhabitants of the tropics do not
produce so much carbonic acid as those who dwell in colder regions. In
the first place, their habits of life are different, and they are not
under the necessity of maintaining animal heat by the use of artificial
combustion, as are the people of colder climes. The vegetation of
the regions of the tropics is much more luxuriant than that of the
temperate and arctic zones. Hence an additional supply of carbonic acid
is required between the torrid zones, and a less quantity is produced
by its animals. These cases are all met by the great aërial movements.
A current of warmed air, rich in oxygen, moves from the equator towards
the poles, whilst the cooler air, charged with the excess of carbonic
acid, sets in a constant stream towards the equator. By this means the
most perfect equalization of the atmospheric conditions is preserved.
The carbonic acid poured out from the thousand mouths of our fiery
furnaces,--produced during the laborious toil of the hard-working
artizan,--and exhaled from every populous town of this our island
home,--is borne away by this our aërial currents to find its place
in the pines of the Pacific Islands, the spice-trees of the Eastern
Archipelago, and the cinchonas of Southern America. The plants of
the valley of the Caucasus, and those which flourish amongst the
Himalayas, equally with the less luxuriant vegetation of our temperate
climes, are directly dependent upon man and the lower animals for their
supply of food.
If all plants were removed from the earth, animals could not exist.
How would it be if the animal kingdom was annihilated?--would it
be possible for vegetation to continue? This question is not quite
so easily answered; but, if we suppose all the carbon-producing
machines--the animals--to be extinct, from whence would the plants
draw their supply? It has been supposed that during the epoch of
the coal formation a luxuriant vegetation must have gone on over
the earth’s surface, when the existence of animal life was regarded
as problematical. It is supposed that the air was then charged with
carbonic acid, and that the calamites, lepidodendra, and sigilaria,
were employed to remove it, and fit the earth for the oxygen-breathing
races. The evidence upon these points is by no means satisfactory; and
although at one time quite disposed to acquiesce in a conjecture which
appears to account so beautifully for the observed geological phenomena
of carboniferous periods, we do not regard the necessities for such
a condition of the atmosphere as clearly made out.[223] Geological
research, too, has shown that the immense forests from which our coal
is formed teemed with life. A frog as large as an ox existed in the
swamps, and the existence of insects proves the high order of organic
creation at this epoch.
In all probability the same mutual dependence which now exists between
the animal and vegetable kingdoms existed from the beginning of time,
and will continue to do so under varying circumstances through the
countless ages of the earth’s duration.
There is yet another very important chain of circumstances which binds
these two great kingdoms together. This is the chain of the animal
necessities. A large number of races feed directly upon vegetables;
herbs and fruits are the only things from which they gain those
elements required to restore the waste of their systems.
These herbivorous animals, which must necessarily form fat and muscle
from the elements of their vegetable diet, are preyed on by the
carnivorous races; and from these the carbon is again restored to the
vegetable world. Sweep off from the earth the food of the herbivora,
they must necessarily very soon perish, and with their dissolution,
the destruction of the carnivora is certainly ensured. To illustrate
this on a small scale, it may be mentioned that around the coasts of
Cornwall, pilchards were formerly caught in very great abundance, in
the shallow water within coves, where these fish are now but rarely
seen. From the investigations of the Messrs. Couch, whose very accurate
observations on the Cornish fauna have placed both father and son
amongst the most eminent of British naturalists,[224] it appears that
the absence of these fish is to be attributed entirely to the practice
of the farmers, who cut the sea-weed from the rocks for the purpose
of manuring their lands. By this they destroy all the small crustacea
inhabiting these immature marine forests feeding on the algæ, and as
these, the principal food of the pilchards, have perished they seek
for a substitute in more favourable situations. Mr. Darwin remarks,
that if the immense sea-weeds of the Southern Ocean were removed by any
cause, the whole fauna of these seas would be changed.
We have seen that animals and vegetables are composed principally of
four elementary principles,--oxygen, hydrogen, nitrogen, and carbon.
We have examined the remarkable manner in which they pass from one
condition--from one kingdom of nature--into another. The animal,
perishing and dwindling by decomposition into the most simple forms of
matter, mingling with the atmosphere as mere gas, gradually becomes
part of the growing plant, and by like changes vegetable organism
progresses onward to form a portion of the animal structure.
A plant exposed to the action of natural or artificial decomposition
passes into air, leaving but a few grains of solid matter behind it.
An animal, in like manner, is gradually resolved into “thin air.”
Muscle, and blood, and bones, having undergone the change, are found to
have escaped as gases, leaving only “a pinch of dust,” which belongs
to the more stable mineral world. Our dependency on the atmosphere
is therefore evident. We derive our substance from it--we are, after
death, resolved again into it. We are really but fleeting shadows.
Animal and vegetable forms are little more than consolidated masses of
the atmosphere. The sublime creations of the most gifted bard cannot
rival the beauty of this, the highest and the truest poetry of science.
Man has divined such changes by the unaided powers of reason, arguing
from the phenomena which science reveals in unceasing action around
him. The Grecian sage’s doubts of his own identity, were only an
extension of a great truth beyond the limits of our reason. Romance and
superstition resolve the spiritual man into a visible form of extreme
ethereality in the spectral creations, “clothed in their own horror,”
by which their reigns have been perpetuated.
When Shakespeare made his charming Ariel sing--
“Full fathom five thy father lies,
Of his bones are coral made,
Those are pearls that were his eyes:
Nothing of him that doth fade,
But doth suffer a sea change
Into something rich and strange,”
he painted, with considerable correctness, the chemical changes
by which decomposing animal matter is replaced by a siliceous or
calcareous formation.
But the gifted have the power of looking through the veil of nature,
and they have revelations more wonderful than even those of the
philosopher, who evokes them by perpetual toil and brain-racking
struggle with the ever-changing elements around him.
The mysteries of flowers have ever been the charm of the poet’s song.
Imagination has invested them with a magic influence, and fancy has
almost regarded them as spiritual things. In contemplating their
surpassing loveliness, the mind of every observer is improved, and
the sentiments which they inspire, by their mere external elegance,
are great and good. But in examining the real mysteries of their
conditions, their physical phenomena, the relations in which they stand
to the animal world, “stealing and giving odours” in the marvellous
interchange of carbonic acid and ammonia for the soul-inspiring
oxygen--all speaking of the powers of some unseen, in-dwelling
principle, directed by a supreme ruler--the philosopher finds subjects
for deep and soul-trying contemplation. Such studies lift the mind into
the truly sublime of nature. The poet’s dream is the dim reflection of
a distant star: the philosopher’s revelation is a strong telescopic
examination of its features. One is the mere echo of the remote whisper
of nature’s voice in the dim twilight; the other is the swelling music
of the harp of Memnon, awakened by the sun of truth, newly risen from
the night of ignorance.
To return from our long, but somewhat natural digression, to a
consideration of the chemical phenomena connected with the atmosphere,
and its curious and important element, nitrogen, we must first examine
the evidence we have of the condition of the air itself.
The mean pressure exerted upon the surface of the earth, as indicated
by the barometer, is equal to a column of mercury thirty inches
high; that is, the column of air from the surface of the ocean to
its highest limits exactly balances that quantity of mercury. If our
tube of mercury had the area of one square inch, the columns would
weigh fifteen pounds, which represents a pressure of fifteen pounds
upon every square inch of the earth’s surface. This pressure, it must
be remembered, is the compound weight of the gaseous envelope, and
the elastic force of the aqueous vapour contained in it.[225] If the
atmosphere were of uniform condition, its height, as inferred from
the barometer, would be about five miles and a half. The density of
the air, however, diminishes with the pressure upon it, so that at the
height of 11,556 feet, the atmosphere is of half density; or one volume
of air, as taken at the surface of the earth, is expanded into two at
that height. Thus the weight is continually diminishing; but this is
regularly opposed by the decreasing temperature, which diminishes the
rate of about one degree for every 352 feet of ascent, although in all
probability it is less rapid at great distances from the earth.
It has been calculated from certain phenomena of refraction, that our
atmosphere must extend to about forty miles from the surface of the
earth. It may, in a state of extreme tenuity, extend still further;
but it is probable that the intense cold produced by rarefaction sets
limits to any extension much beyond this elevation.
The uses of the atmosphere are many. It is the medium for regulating
the dispersion of watery vapours over the earth. If there were no
atmosphere, and that, as now, the equatorial climes were hot and the
poles cold, evaporation would be continually going on at the equator,
and condensation in the colder regions. The sky of the tropical climes
would be perpetually cloudless, whilst in the temperate and arctic
zones we should have constant rain and snow. By having a gaseous
atmosphere, a more uniform state of things is produced; the vapours
arising from the earth become intimately mixed with the air, and are
borne by it over large tracts of country, and only precipitated when
they enter some stratum much colder than that which involves them.
There are opposite tendencies in an atmosphere of air and one of
vapour. The air circulates from the colder to the warmer parts, and
the vapour from the warmer to the colder regions; and as the currents
of the air, from the distribution of land and sea--the land, from its
low conducting power, being more quickly heated than the sea--are
very complicated, and as some force is employed in keeping the vapour
suspended in the air, water is less suddenly deposited on the earth
than it would have been, had not these tendencies of the air and its
hygrometric peculiarities been such as we find them.
The blue colour of the sky, which is so much more agreeable to the eye
than either red or yellow, is due to a tendency of the mixed gas and
vapour to reflect the blue rays rather than red or yellow. The white
light which falls upon the surface of the earth, without absorption or
decomposition in its passage from the sun, is partially absorbed by,
and in part reflected back from, the earth. The reflected rays pass
with tolerable freedom through this transparent medium, but a portion
of the blue rays are interrupted and rendered visible to us. That it
is reflected light, is proved by the fact of its being in a polarized
state.[226] Clouds of vapour reflect to us again, not isolated rays,
but the undecomposed beam, and consequently they appear white as snow
to our vision.
The golden glories of sunset,--when, “like a dying dolphin,” heaven
puts on the most gorgeous hues, which are continually changing,--depend
entirely upon the quantity of watery vapour which is mixed with air,
and its state of condensation. It has been observed, that steam at
night, issuing into the atmosphere under a pressure of twenty or thirty
pounds to the square inch, transmits and reflects orange-red light.
This we may, therefore, conclude to be the property of such a condition
of mixed vapour and air, as prevails when the rising or the setting
sun is shedding over the eastern or the western horizon the glory of
its coloured rays.[227]
Thus science points out to us the important uses of the air. We learn
that life and combustion are entirely dependent on it, and that it
is made the means for securing greater constancy in the climates
of the earth than could otherwise be obtained. The facts already
dwelt upon are sufficient to convince every thinking mind that the
beautiful system of order which is displayed in the composition of
the atmosphere, in which the all-exciting element, oxygen, is subdued
to a tranquil state by another element, nitrogen, (which, we shall
have presently to show, is itself, under certain conditions, one of
the most energetic agents with which we are acquainted,) indicates a
supreme power, omniscient in the adaptation of things to an especial
end. Oxygen and nitrogen are here _mixed_ for the benefit of man;
man _unites_ them by the aid of powers with which he is gifted, and
the consequences are of a fatal kind. The principles which the great
Chemist of Nature renders mild are transformed into sources of evil by
the chemist of art.
Beyond all this, the atmosphere produces effects on light which add
infinitely to the beauty of the world. Were there no atmosphere, we
should only see those objects upon which the sun’s rays directly fell,
or from which they were reflected. A ray falling through a small hole
into a dark room, illuminating one object, which reflects some light
upon another, is an apt illustration of the effect of light upon
the earth, if it existed without its enveloping atmosphere. By the
dispersive powers of this medium, sunlight is converted into daylight;
and instead of unbearable, parallel rays illuminating brilliantly,
and scorching up with heat those parts upon which they directly
fall, leaving all other parts in the darkness of night, we enjoy the
blessings of a diffusion of its rays, and experience the beauties of
soft shades and slowly-deepening shadows. Without an atmosphere, the
sun of the morning would burst upon us with unbearable brilliancy, and
leave us suddenly, at the close of day, at once in utter darkness. With
an atmosphere we have the twilight with all its tempered loveliness,--a
“time for poets made.”
In chemical character, atmospheric air is composed of twenty-one
volumes of oxygen, and seventy-nine volumes of nitrogen: or one hundred
grains of air consist of 23·1 grains of the former, and 76·9 grains
of the latter. Whether the air is taken from the greatest depths or
the most exalted heights to which man has ever reached, an invariable
proportion of the gases is maintained. The air of Chimborazo, of the
arid plains of Egypt, of the pestilential delta of the Niger, or
even of the infected atmosphere of an hospital, all give the same
proportions of these two gases as we find existing on the healthful
hills of Devonshire, or in the air of the city of London. This
constancy in constitution leads to the supposition that the oxygen
and nitrogen are chemically combined; but many eminent philosophers
have contended that they are merely mechanically mixed; and they have
shown that some peculiar properties prevail amongst gaseous bodies,
which very fully explain the equal admixture of two gases the specific
gravities of which are different. This is particularly exemplified in
the case of carbonic acid, of which gas one per cent. can be detected
in all regions of the air to which the investigations of man have
reached. This gas, although so heavy, is, by the law of diffusion,
mixed with great uniformity throughout the mass.[228] Every exhalation
from the earth, of course, passes into the air; but these are generally
either so light that they are carried into the upper regions, and
there perform their parts in the meteorological phenomena, or they
are otherwise very readily absorbed by water or growing plants, and
thus is the atmosphere preserved in a state of purity for the uses of
animals. Again, the quantity of oxygen contained in the air, and its
very peculiar character, ensures the oxidation of all the volatile
organic matters which are constantly passing off,--as the odoriferous
principles of plants, the miasmata of swamps, and the products of
animal putrefaction; these are rapidly converted into water, carbonic
acid, or nitric acid, and quickly enter into new and harmless
combinations. The elements of contagion we are unacquainted with; but
since the attention of inquirers has been of late directed to this
important and delicate subject, some light may possibly be thrown upon
it before long.
Nothing, shows more strikingly the admirable adaptation of all things
for their intended uses than the atmosphere. In it we find the source
of life and health; and chemistry teaches us, most indisputably,
that it is composed of certain proportions of oxygen and nitrogen
gases; and experience informs us that it is on the oxygen that we
are dependent for all that we enjoy. So beautifully is the atomic or
molecular constitution ordered, that it is impossible to produce any
change in the air without rendering it injurious to the vegetable and
animal economy. It might be thought, from the well-known exhilirating
character of oxygen gas, that, if a larger quantity existed in the
atmosphere than that which we find there, the enjoyments of life would
be of a more exciting kind; but the consequences of any increase would
be exceedingly injurious; and, by quickening all the processes of life
to an unnatural extent, the animal fabric would soon decay: excited
into fever, it would be destroyed by its own fires. Chemistry has made
us acquainted with six other compounds of oxygen and nitrogen, neither
of them fitted for the purposes of vitality, of which the following are
the most remarkable:--
Nitrous oxide, or the, so called, _laughing gas_, which contains two
volumes of nitrogen to one of oxygen, would prove more destructive than
even pure oxygen, from the delirious intoxication which it produces.
Nitric oxide is composed, according to Davy, of two volumes of nitrogen
and two of oxygen. It is of so irritating a nature, that the glottis
contracts spasmodically when any attempt is made to breathe it; and the
moment it escapes into the air it combines with more oxygen, and forms
the deep red fumes of nitrous acid.
Nitrous acid and the peroxide of nitrogen each contains an additional
proportion of oxygen, and they are still more destructive to all
organization.
Nitric acid contains five volumes of oxygen united to two of nitrogen;
and the well-known destructive properties of aqua fortis it is
unnecessary to describe.
The atmosphere, and these chemically active compounds, contain the same
elements, but their mode of combining is different; and what is, in the
one case, poisonous to the highest degree, is, in the other, rendered
salubrious, and essential to all organized beings.
Nitrogen gas may be regarded in the light of a diluent to the oxygen.
In its pure state it is only characterised by its negative properties.
It will not burn, or act as a supporter of combustion. Animals speedily
perish if confined in it; but they die rather through the absence
of oxygen than from any poisonous property of this gas. Yet, in
combination, we find nitrogen exhibiting powers of a most energetic
character. In addition to the fulminating compounds and the explosive
substances already named, which are among the most remarkable instances
of unstable affinity with which we are acquainted, we have also the
well-known pungent body, ammonia. From the analogous nature of this
volatile compound, and the fixed alkalies soda and potash, it was
inferred that it must, like them, be an oxide of a metallic base. Davy
exposed ammonia to the action of potassium, and to the influence of the
voltaic arc produced from 2,000 double plates, without at all changing
its character. From its slight tendency to combination, and from its
being found abundantly in the organs of animals feeding on substances
that do not contain it, it is, however, probably a compound body. A
phenomenon of an obscure and mysterious character is presented in the
formation of the “ammoniacal amalgam,” as it is called.
Mercury, being mixed with an ammoniacal salt, is exposed to powerful
galvanic action; and a compound, maintaining its metallic appearance,
but of considerable lightness and very porous, presents itself.[229]
This preparation has been carefully examined by Davy, Berzelius, and
others. It is always resolved into ammonia and mercury; and, although
the latter chemist is strongly inclined to regard it as affording
evidence of the compound nature of nitrogen,--and he has, indeed,
proposed the name _nitricum_ for its hypothetical base,--yet, to the
present time, we have no satisfactory explanation of this apparent
metallization of ammonia.
No attempt will be made to describe the various elementary substances
which come under the class of metallic bodies, much less to enumerate
their combinations. Many of the metals, as silver and copper, are found
sometimes in a native state, or nearly pure; but, for the most part,
they exist, in nature, in combination with oxygen or sulphur; gold
furnishing a remarkable exception. They are occasionally found combined
with other bodies,--as oxidized carbon, phosphorus, chlorine, &c.; but
these cases are by no means so common. Those substances called metals
are generally found embedded in the rocks, or deposited in fissures
formed through them; but it is one of the great discoveries of modern
science, that those rocks themselves are metallic oxides. With metals
we generally associate the idea of great density; but potassium and
sodium, the metallic bases of potash and soda, are lighter than water,
and they consequently float upon that fluid. We learn, therefore, from
the researches of science, that the crust of this earth is composed
entirely of metals, combined with gaseous elements; and there is
reason for believing that one, or perhaps two, of the gases we have
already named are also of a metallic character. Strange as it may
appear, there is nothing, as will be seen on attentive consideration,
irrational in this idea. Many of the metals proper, under the influence
of such heat as we can, by artificial means, command, are dissipated
in vapour, and may be maintained in this state perfectly invisible.
Indeed, the transparent space above the surface of the mercury in the
tube of a barometer, known as the Torricellian vacuum, is filled with
the vapour of mercury. There is, therefore, no reason why nitrogen,
or even hydrogen, should not be metallic molecules kept by the force
of the repulsive powers of heat, or some other influence, at a great
distance from each other. The peculiar manner in which nitrogen unites
with mercury, and the property which hydrogen possesses of combining
with antimony, zinc, arsenic, potassium, sodium, and possibly other
metals, besides its union with sulphur and carbon--in all which cases
there is no such change of character as occurs when they combine with
oxygen--appear to indicate bodies which, chemically, are not very
dissimilar to those metals themselves, although, physically, they have
not the most remote resemblance.
“We know nothing,” says Davy, “of the true elements belonging to
nature; but, so far as we can reason from the relations of the
properties of matter, hydrogen is the substance which approaches
nearest to what the elements may be supposed to be. It has energetic
powers of combination, its parts are highly repulsive as to each
other, and attractive of the particles of other matter; it enters into
combination in a quantity very much smaller than any other substance,
and in this respect it is approached by no known body.”[230]
Many of the elements are common to the three kingdoms of nature:
most of those found in one condition of organization are discovered
in another. The carbonates are an abundant mineral class. In the
vegetable kingdom we find carbon combining with oxygen, hydrogen, and
nitrogen: these elements, also, constitute the substance of animals,
the proportion of nitrogen being, however, much larger. If one element,
more than another, belongs especially to the animal economy, it is
phosphorus, although this is not wanting in the vegetable world; and
it is not uncommon in the mineral. Sulphur is common to the three
kingdoms: it is abundant in the mineral, being one of the products of
volcanic action; it is united with the metals, forming sulphurets;
and is found in our rocks in the state of sulphuric acid or oxidized
vapour, combined with the metallic bases of lime and other earths. In
the vegetable kingdom we discover sulphur in all plants of the onion
kind, in the mustard, and some others; it enters into the composition
of vegetable albumen, and appears always combined with albumen,
fibrine, and caseine, in the animal economy.
Chlorine is found most abundantly in combination with sodium, as common
salt: in this state, in particular, we may trace it from the depths
of the earth, its waters, and its rocks, to the plants and animals
of the surface. Iodine is most abundant in marine plants; but it has
been found in the mineral world, traced to plants, and it is indicated
in the flesh of some animals. Bromine is known to us as a product of
certain saline waters, and a few specimens of natural bromide of silver
have been examined. Fluorine, the base of the acid which, combining
with lime, forms fluor-spar, is found to exist to some considerable
extent in bones; it has been discovered in milk and blood; and
investigations have proved its existence in the vegetable world. It
must not be forgotten that the earths, lime and magnesia, enter into
the composition of the more solid parts of plants and animals. Lime is
one of the principal constituents of animal bone and shells, and it is
found in nearly all vegetables.
Silica, or the _earth_ of flints, is met with in beautiful transparent
crystals, in the depths of the mine; in all rock and soils we find it.
In the bark of many plants, particularly the grasses, it is discovered,
forming the hard supporting cuticle of the stalk, in wheat, the Dutch
rush, the sugar-cane, the bamboo, and many other plants.
It is thus that we find the same elementary principle presenting itself
in every form of matter, under the most Protean shapes. Numerous
phenomena of even a more striking character than those selected, are
exhibited in every department of chemistry; but within the limits of
this essay it is impracticable to speak of any beyond those which
directly explain natural phenomena.
The chemical elements, which actually exist in nature as simple
bodies, are probably but few. Most of the gases are in all probability
compounds of some ethereal ultimate principles; and with the advance of
science we may fairly hope to discover the means of reducing some of
them to a yet more simple state.
Curious relations, which can be traced through certain bodies, lead us
to believe that they may be only modified conditions of one element.
Flint and charcoal do not at first appear allied; but carbon in some
of its states approaches very near to the condition of silicon, the
metallic base of flint. When we remember the differences which are
evident in three forms of one body--coke, graphite, and diamond--the
dissimilitude between flint, a quartz crystal, and carbon, will cease
to be a strong objection to the speculation.
Phosphorus, sulphur, and selenium, have many properties in common.
Iodine, bromine, chlorine, and fluorine, appear to belong to the same
group. Iron and nickel, and cobalt, have a close relation. Silver and
lead are usually combined, and exhibit a strong relationship. Gold,
platinum, and the rarer metals, have so many properties in common, that
they may form a separate group from all the others.
Indeed, a philosophical examination of the elements now supposed to
constitute the material world, enables us to divide them into about six
well-defined groups. Wide differences exist within these groups; but
still we find a sufficient number of common properties to warrant our
classing them in one family.
The dream of the alchemists, in the vain endeavour to realise which
they exhausted their lives and dissipated their wealth, had its
foundation in a natural truth. The transmutation of one form of matter
into another may be beyond the power of man, but it is certainly
continually taking place in the laboratory of nature, under the
directing law of the great Creator of this beautiful earth.
The speculations of men, through all ages, have leaned towards this
idea, as is shown by the theory of the four elements,--Air, Fire,
Earth, and Water,--of the ancients, the three,--Salt, Sulphur, and
Mercury,--of the alchemists, and the refined speculations of Newton
and Boscovich on the ultimate constitution of matter. All experimental
inquiry points towards a similar conclusion. It is true we have no
direct evidence of any elementary atom actually undergoing a change
of state; but when we regard the variations produced by electrical
influence, the changes of state which arise from the power of heat, and
the physical alterations produced by light, it will be difficult to
come to any other conclusion than that the particles of matter known
to us as ultimate are capable of change, and consequently must be far
removed from positively simple bodies, since the real elementary atom,
possessing fixed properties, cannot be supposed capable of undergoing
any transmutation. Allotropism could not occur in any absolutely simple
body.
It will now be evident that in all chemical phenomena we have the
combined exercise of the great physical forces, and evidences of some
powers which are, as yet, shrouded in the mystery of our ignorance. The
formation of minerals within the clefts of the rocks, the decomposition
of metallic lodes, the germination of seeds, the growth of the plant,
the development of its fruit and its ultimate decay, the secret
processes of animal life, assimilation, digestion, and respiration, and
all the changes of external form, which take place around us, are the
result of the exercise of that principle which we call chemical.
By chemical action plants take from the atmosphere the elements of
their growth; these they yield to animals, and from these they are
again returned to the air. The viewless atmosphere is gradually formed
into an organized being, the lordly tree upon whose branches the fowls
of the air have their homes, and the human animal, exalted by being
charged with a spiritual soul: yet the tree and the man alike are
gradually resolved again into thin air. The changes of the mineral
world are of an analogous character; but we cannot trace them so
clearly in all their phenomena.
The planet on which we live began its course charged with a fixed
quantity of physical force, and this has remained constant to the
present moment, and will do so to the end of time. By influences
external to this earth the balance of these forces is continually
disturbed; and in the effort to restore the equilibrium, we have the
production of all the varied forms of matter, and the manifestation of
each particular physical principle or power. As motion and attraction,
balanced against each other, maintain the earth in her elliptical
orbit, so the opposition of forces determines the existence of the
amorphous rock, the light-refracting crystal, the fixed and flowering
plant, and the locomotive animal.
An eternal round of chemical action is displayed in nature. Life and
death are but two phases of its influences. Growth and decay are
equally the result of its power.
FOOTNOTES:
[212] Dr. Priestley appears to have been the first to observe the
peculiar property of the diffusion of gases. Dr. Dalton, however,
first drew attention to the important bearing of this fact on natural
phenomena, and he published his views on _The Miscibility of Gases_ in
the Manchester Memoirs, vol. v. The following extract from his memoir
_On the Constitution of the Atmosphere_ will exhibit its bearings:--
It may be worth while to contrast this view of the constitution of the
atmosphere with the only other one, as far as I know, that has been
entertained.
According to one view, | According to the other view,
|
1. The volumes of each gas | 1. The volume of each gas
found at the surface of the | found at the surface of
earth are proportional to | the earth, _multiplied by
the whole weights of the | its specific gravity_, is
respective atmospheres. | proportional to the whole
| weight of the respective
| atmospheres.
|
Azote 79 | Azote 76·6
Oxygen 21 | Oxygen 23·4
Aqueous vapour 1·33 | Aqueous vapour 0·83
Carbonic acid 1·0 | Carbonic acid 0·15
------- | ------
101·43 | 100·88
|
2. The altitude of each | 2. The altitude of each
atmosphere differs from that | atmosphere is the same, and
of every other, and the | the proportion of each in the
proportions of each in the | compound atmosphere, is the
compound atmosphere gradually | same at all elevations.
vary in the ascent. |
|
3. When two atmospheres are | 3. When two atmospheres
mixed, they take their places | are mixed, they continue
according to their specific | so without the heavier
gravity, not in separate | manifesting any disposition to
strata, but intermixedly. | separate and descend from the
There is, however, a separate | lighter.
stratum of the specifically |
lighter atmosphere at the |
summit over the other. |
[213] The discussion of this question, commenced by Arago in his
_Eloge_, was continued by Lord Brougham in his _Lives of Watt and
Cavendish_, and by Mr. Vernon Harcourt, in his address as President
of the British Association, and more recently in his _Letter to Lord
Brougham_. Watt’s _Letters_ on the subject have been since published
under the superintendence of Mr. Muirhead.
[214] See several papers _On Ozone_, by Professor Schönbein, in the
Philosophical Magazine, and in the Reports of the British Association.
Consult a paper by the Author: _Athenæum_, September, 1849.
[215] Memoire _sur l’Ozone_; Bàle 1849. Poggendorff’s _Annalen_,
lxxvii., p. 592. Ibid, lxxviii. p. 162.
[216] _Chemical Gazette_, 1849.
[217] Iodide of silver has been found at Albarradon, near Mazapil, in
Mexico. Iodide of mercury, of a fine lemon-yellow colour, has been
discovered in the sandstone of Casas, Viegas, Mexico. Algers; Phillips’
_Mineralogy_.
[218] GENTELE’S Reports of the Stockholm Academy.
[219] Stahl, taking up the obscure notions of Becher and Van Helmont,
supposed the phenomena of combustion to be due to phlogiston. He
imagined that by combination with phlogiston, a body was rendered
combustible, and that its disengagement occasioned combustion, and
after its evolution there remained either an acid or an earth: thus
sulphur was, by this theory, supposed to be composed of phlogiston and
sulphuric acid, and lead of the calx of lead and phlogiston, &c.
[220] Being called upon by the Solicitor for the Admiralty to examine
into the causes of the fire which destroyed the _Imogene_ and
_Talavera_, in Devonport Arsenal, I discovered a bin under the roofing
which covered these ships, in which there had been accumulating for a
long period all the refuse of the wheelwrights’ and painters’ shop; and
it was quite evident that spontaneous combustion had taken place in the
mass of oiled oakum, sawdust, anti-attrition, and old sail-cloth, there
allowed to accumulate.
[221] _Researches on Flame_: Sir H. Davy’s Collected Works.
[222] See note, _ante_, _On the Chemical Theory of Respiration_.
[223] At the request of the British Association, a committee undertook
the investigation of this subject. Experiments were carried on by Dr.
Daubeny, in the Botanic Gardens at Oxford, and by the Author, at his
residence, Stockwell. Dr. Daubeny, in his report made at the meeting
of the British Association at Birmingham, appears disposed to consider
ten per cent. of carbonic acid in excess as destructive to the growth
of ferns. I found, however, that, by gradually increasing the quantity,
the ferns would live in an atmosphere still more highly charged with
carbonic acid.
[224] See memoir _On the Pilchard_, by Mr. Couch, in the Reports of the
Royal Cornwall Polytechnic Society.
[225] “This scale, in which the humidity of the air is expressed,
is the simple natural scale in which air at its maximum of humidity
(_i.e._, when it is saturated with vapour) is reckoned as = 100, and
air absolutely deprived of moisture as = 0; the intermediate degrees
are given by the fraction 100 × actual tension of vapour ÷ tension
required for the saturation of the air at its existing temperature.
Thus, if the air at any temperature whatsoever contains vapour of half
the tension, which it would contain if saturated, the degree is 50; if
three-fourths, then 75; and so forth. Air of a higher temperature is
capable of containing a greater quantity of vapour than air of less
temperature; but it is the proportion of what it does contain, to what
it would contain if saturated, which constitutes the measure of its
dryness or humidity. The capacity of the air to contain moisture being
determined by its temperature, it was to be expected that an intimate
connection and dependence would be found to exist between the annual
and diurnal variations of the vapour and of the temperature.”--Sabine,
_On the Meteorology of Toronto_; Reports of the British Association,
vol. xiii. p. 47. _The Temperature Tables_: by Prof. W. H. Dove;
Reports for 1847 should be consulted.
[226] Sir David Brewster’s _Optics_, and Memoirs in the Philosophical
Transactions. Sir John Herschel’s Treatise on _Light_, Encyclopædia
Metropolitana.
[227] _On the Colour of Steam under certain circumstances_: by
Professor Forbes; Philosophical Magazine, vol. xiv. p. 121, vol. xv.
p. 25. In the first paper the following remarks occur:--“I cannot
doubt that the colour of watery vapour under certain circumstances
is the principal or only cause of the red colour observed in clouds.
The very fact that that colour chiefly appears in the presence of
clouds is a sufficient refutation of the only explanation of the
phenomena of sunset and sunrise, having the least plausibility, given
by optical writers. If the red light of the horizontal sky were simply
complementary to the blue of a pure atmosphere, the sun ought to set
red in the clearest weather, and then most of all; but experience shows
that a lurid sunrise or sunset is _always_ accompanied by clouds or
diffused vapours, and in a great majority of cases occurs when the
changing state of previously transparent and colourless vapour may be
inferred from the succeeding rain. In like manner, terrestrial lights
seen at a distance grow red and dim when the atmosphere is filled
with vapour soon to be precipitated. Analogy applied to the preceding
observations would certainly conduct to a solution of such appearances;
for I have remarked that the existence of vapour of high tension is
by no means essential to the production of colour, though of course
a proportionally greater thickness of the medium must be employed to
produce a similar effect when the elasticity is small.”
[228] _On the Law of Diffusion of Gases_: by Thomas Graham, M.A.,
F.R.S., &c.; Edinburgh Philosophical Transactions, 1832. _Sur l’Action
Capillaire des Fissures, &c._: by Döbereiner; Annales de Chimie, xxiv.
332.
[229] _Electro-chemical Researches on the Decompositions of the Earths,
with observations on the Metals obtained from the Alkaline Earths,
and on the Amalgam procured from Ammonia_: by Sir Humphry Davy;
Philosophical Transactions, 1808, and collected works, vol. v. p. 102.
[230] _Elements of Chemical Philosophy_: by Sir H. Davy.