OXYGEN.
Oxygen may justly claim a high degree of importance as a subject for
the study alike of the professional chemist and the casual reader. This
importance depends upon a variety of considerations. Among them are
the surpassing abundance of the substance itself, the great number of
compounds into which it enters, the activity of its chemical powers,
and finally, the interesting circumstances under which its distinct
recognition, or, as perhaps we may say, its discovery, was attained.
Its great abundance has been pointed out already in the declaration
that oxygen makes up, by weight, fully one-half of our terrestrial
globe—including earth, ocean and air. The air is about one-fifth oxygen
by weight; all water, wherever existing, is sixteen-eighteenths oxygen
by weight, while quartz, sand, and other similar widespread and most
commonly occurring mineral matters, are a little more than one-half
oxygen. Other solid matters than the rocks, such as most parts of the
material structures of animal and vegetable beings, contain oxygen as
an important constituent element. While thus we have scanned the great
multitude of substances spread immediately about us by the hand of
nature, and found oxygen in them all, it is none the less true that
oxygen is an important factor in artificial products—that is, those
resulting from man’s manufacturing operations.
Chemical Activity of Oxygen.
Again, oxygen plays a part of exceeding activity in some of the
grandest chemical processes of nature and of the arts.
For example, it is essential to the vital processes of all animals.
Wherever a living being inhales the breath of life, whether from the
fresh air of the mountain tops, or from the populous streets of the
swarming metropolis, or from the solitary deck of the bark that creeps
with the ocean’s currents; or wherever the humbler servants of man’s
table find their way through unexplored depths of the ocean and pluck
from its waves the modicum of life-giving gas dissolved within them;
there is this wonderful agent, which has no substitute, sustaining
by active processes truly chemical, that vitality of man or of beast
which gives to nature its forms of highest beauty and most admirable
intelligence.
Again, oxygen is the necessary agent in all ordinary combustions. So
wherever a faggot, glowing beneficently in a sparsely peopled forest,
helps to sustain man’s vital spark; or, where in a highly civilized
community, the fires on the altars of modern industry draw from the
flinty rocks the metals that serve to give employment to millions of
children of toil;—there oxygen is ever active, the true supporter of
the combustion of all those flames which in the past have served as
signs of life and civilized activity, and which are still the best
symbols of vitality and intelligence.
The Discovery of Oxygen.
The first discovery of oxygen is usually attributed to Dr. Joseph
Priestley, an English clergyman and student of natural science. He
lived in a time when men’s minds all over Europe were strongly drawn
toward the pursuit of chemical knowledge. In fact, at almost the same
moment that Priestley was enthusiastically conducting his experiments,
Scheele was also producing oxygen in his apothecary’s chamber in
Sweden. And the brilliant Lavoisier, prominent among the men of
distinction who thronged the gay capital of France, was also working
in the same direction; it was he, who said about oxygen in one of his
own chemical works: “Cet air que nous avons decouvert presque en même
temps, Dr. Priestley, M. Scheele et moi,” so that he is sometimes
declared by his enthusiastic countrymen to be entitled to the merit of
the earliest discovery of this most magnificent of elements.
[Illustration: JOSEPH Priestley,
Born near Leeds, England, March 13, 1733; died in Northumberland, Pa.,
February 6, 1804.]
Priestley’s life included ample materials for a romance. On the one
hand, the ingenious discoverer in physics and chemistry and the friend
of that Benjamin Franklin—who was then minister at the brilliant
court of France from a handful of colonies that appeared capable of
being plucked up by the roots, but were instead destined to grow to
an unrivalled empire—himself a figure in a romance; and, on the other
side, a preacher to a dissenting congregation; a victim of public odium
for his liberal opinions on religious and political subjects; his house
set on fire by a mob, his apparatus wrecked, his library cast to the
winds; finally, an emigrant with his wife and children to an almost
unknown village in Pennsylvania, whose little burial-ground still gives
his bones repose;—these are but brief suggestions of the trials of this
perturbed spirit, in his life “sadly driven about and tossed,” now
cherished as one of those who in the realm of thought has made no mean
contribution to the glory of the English name.
Dr. Priestley prepared oxygen from red precipitate of mercury, a
substance now designated by the name mercuric oxide and by the formula
HgO. Heating this substance in a receiver and by means of a burning
glass or lens, he observed that a peculiar kind of air was evolved. He
further discovered that this air had an unusually stimulating influence
upon burning bodies, and was well suited for the respiration of living
animals. Priestley’s prime experiment was performed on the first day of
August, 1774, a date which may be accepted as almost the birthday of
modern chemistry.
Like many other great discoverers, Priestley was, to a certain degree,
anticipated. Thus a certain John Mayow, an English physician, fully a
hundred years before the time of Priestley’s experiment, enunciated the
doctrine that the atmosphere contains an air, in a certain sense the
essential food of animal life and of flame. But these wonderful views
of Mayow, brought forward too early for the state of thought at his
time, lay dormant and unproductive for an entire century.
First Method of Preparing Oxygen.
Oxygen may be prepared in many ways, but only two need receive
attention here. The first method is Priestley’s. If the red oxide of
mercury is heated over a powerful gas flame and in a tube of not easily
fusible glass, the oxygen passes from the metal and may be carried
by any small conducting tube into a convenient receiver filled with
water and standing in the _pneumatic trough_. If the gas so collected
is tested by means of a candle, having only a spark on its wick, the
oxygen is readily recognized by the fact that the taper promptly bursts
into a full and brilliant flame. This method is of historical interest
chiefly, though it may well attract some attention from the simplicity
of the chemical change involved. Thus this change is represented by the
following equation:
=2HgO= _heated_ = =O₂= + =2Hg=
Two molecules of One molecule of Two atoms of
Mercuric oxide, Oxygen, Mercury,
432 32 400
parts by weight. parts by weight. parts by weight.
\______________/ \____________________________________/
| |
432 432
A word about the pneumatic trough is not out of place here, because
this useful contrivance was the invention of Priestley. The name may
be appropriately applied to almost any vessel of water in which may
stand the open mouth of a bell-glass suitable for containing gas. The
water serves at once to seal the mouth of the jar, and also to afford a
material through which the exit tube of an appliance may be dipped, and
through which also the gas from the tube may freely and conveniently
flow into the bell-glass. Before Priestley’s time gases had been
collected in bladders or varnished bags, but the new contrivance
furnished a much superior means of detecting small quantities of gas
and working with them.
Second Method of Preparing Oxygen.
The second method, and that oftenest pursued, employs a salt not known
in Priestley’s time. This salt is called potassic chlorate and is
represented by the formula KClO₃.
This substance, when heated, evolves a large amount of oxygen, but it
does so with almost explosive violence.
The chemical change is represented by the following equation:
=2KClO₃= _heated_ = =2KCl= + =3O₂=
Two molecules of Two molecules of Three molecules of
Potassic chlorate, Potassic chloride, Oxygen,
245 149 96
parts by weight. parts by weight. parts by weight.
\______________/ \________________________________________/
| |
245 245
On the other hand, if the potassic chlorate is mixed with about
one-third of its weight of the earthy mineral known as black oxide of
manganese, (but called by the chemist, manganese dioxide,) the mixture
when heated evolves oxygen more slowly and continuously than the
chlorate alone—and it does it at a lower temperature. Strangely enough
however, the manganese dioxide appears to take either no _chemical_
part in the operation or else only a very obscure one. Indeed, some
other oxides will serve the same purpose, while they likewise appear to
undergo no chemical change.
In this method, as in the other, the oxygen gas produced may be
collected in a bell-glass over the pneumatic trough, and afterwards its
nature may be demonstrated as before by means of the taper having a
spark upon it.
The Properties of Oxygen.
It has been the custom of chemists to say of oxygen that it is a
_permanent gas_. The force of this expression is found in the fact
that until recently all attempts to liquefy it were futile. But recent
experiments, with apparatus capable of subjecting it at once to more
intense cold and to greater pressure than were ever before employed,
seem to demonstrate that it will turn to a liquid when these conditions
are carried to a sufficient extreme.
That oxygen is colorless and odorless appears plain from the properties
of the atmospheric air throughout which this gas is thoroughly diffused
and intimately intermingled, although it constitutes but one-fifth of
it.
Chemical Properties of Oxygen.
[Illustration: FIG. 34.—The rays of sunlight concentrated, by a lens,
upon a diamond placed in oxygen gas, with a view of proving the
combustibility of the gem.]
Of the chemical powers of oxygen the most striking and important seems
to be its marked tendency to combine with other elementary substances.
In many cases this combination does not commence except when the
substances are heated. Thus the noble buildings of a city are every
day and every night continuously and harmlessly bathed within and
without by that same oxygen, that, in time of conflagration, is ready
chemically to combine with their elements and as a result to reduce
the metropolis to ashes. But such combination, once inaugurated, often
itself affords sufficient heat not only to make the process continue,
but also to generate that flame or fire which is the token of what
is ordinarily called combustion. In this view, oxygen is often
spoken of as a supporter of combustion. That this property, known to
be associated with the atmospheric air, does in fact reside in the
oxygen of it, is to some extent proved by the more rapid and brilliant
combustion of the candle in pure oxygen.
Another interesting experiment is performed when a piece of charcoal,
which may be supported on a wire, is burned a little so as to acquire
a spark, and then is dipped in oxygen gas. The single coal would soon
cease to burn in atmospheric air, but it burns readily and brilliantly
in pure oxygen.
Even the diamond, the most compact and imperishable form of carbon
known, may burn in pure oxygen gas just as the most humble piece of
coal does, and the relationship of the gem to the commonplace fuel is
proved by this experiment.
[Illustration: FIG. 35.—The burning of a spiral of iron wire in a jar
of oxygen gas.]
Still another experiment in the same direction may be conducted with
sulphur. For this purpose a fragment of sulphur set on fire may be
dipped in a jar of pure oxygen. The sulphur burns with vastly increased
rapidity and with a violet flame much more brilliant than that of
sulphur burning in air.
Again, some substances not ordinarily considered combustible will burn
in oxygen gas. Thus a bundle of iron wire, to which a little lighted
chip is attached, itself takes fire and burns brilliantly when dipped
into oxygen gas.
The Products of Combustions in Oxygen.
As a necessary result of the combustion of substances in oxygen there
are produced a multitude of compounds called oxides.
This is true of the candle, which consists mainly of carbon and
hydrogen. When the candle burns, these two substances change into
oxides. The carbon produces carbon dioxide, whose formula is CO₂, and
which is familiarly known as carbonic acid gas. This oxide, it is
true, is not easily recognized by the ordinary observer because it is
an invisible gas, but the chemist can prove that it is in fact the
product of this combustion. At the same time the hydrogen produces an
oxide whose formula is H₂O and which will be recognized as the chemical
expression for water. And so water is in fact produced, though in the
form of vapor, by the burning candle.
Charcoal is composed almost entirely of what the chemist calls carbon,
and when it burns it produces the oxide called carbon dioxide (CO₂).
This is the same invisible gas that has already been declared to be
produced when the carbon of the candle is burned, and in this case as
in the other it is easy for the chemist to prove its presence.
In case of carbon, the chemical change is represented by the following
equation:
=C= + =O₂= = =CO₂=
One atom of One molecule of One molecule of
Carbon, Oxygen, Carbon dioxide,
12 32 44
Parts by weight. Parts by weight. Parts by weight.
\______________/ \____________________________________/
| |
44 44
And likewise when iron is burned, there is formed an oxide whose
composition is expressed by the formula, Fe₃O₄; (to this substance the
chemical name ferroso-ferric oxide is applied).
So when sulphur is burned, sulphur dioxide is formed (SO₂).
In this case the chemical change is represented by the following
equation:
=S= + =O₂= = =SO₂=
One atom of One molecule of One molecule of
Sulphur, Oxygen, Sulphur dioxide,
32 32 64
Parts by weight. Parts by weight. Parts by weight.
\_____________________________________/ \______________/
| |
64 64
Compound of Oxygen with Hydrogen.
[Illustration: FIG. 36.—Hydrogen gas, generated by use of zinc and
sulphuric acid, is then passed through a drying tube containing calcic
chloride (CaCl₂). By the act of combustion the union of the dried gas
with oxygen of the air produces drops of water.]
It has already been shown that the hydrogen escaping from a suitable
tube may be lighted in the air. If the burning jet is introduced into
oxygen gas the same combustion proceeds, only with greater energy. In
either case there is produced a compound of hydrogen and oxygen. This
compound is represented by the formula H₂O, a formula representing no
other than the familiar substance water. At the moment of combustion
of hydrogen very great heat is generated. In fact, a pound of hydrogen,
upon burning in pure oxygen, yields about four times as much heat
as a pound of pure carbon does in burning under the same favorable
conditions. Indeed, the pound of hydrogen, when in combustion, yields
more heat than a pound of any other substance known. On account of this
heat the water resulting from the burning hydrogen at first floats off
in the air in the form of vapor; but if the hydrogen flame is brought
in contact with some cooling surface, the water formed condenses in
drops upon it and thus it may be readily recognized as in its ordinary
form.
A great multitude of experiments show that the composition of water is
as follows:
+---------------------------------------------------------------+
| WATER IS MADE UP BY THE UNION OF, |
+----------+-------------------+---------------------+----------+
| | PARTS BY WEIGHT, | PARTS BY BULK, | ATOMS. |
+----------+-------------------+---------------------+----------+
| HYDROGEN,| 2 | 2 | 2 |
| | | | |
| OXYGEN, | 16 | 1 | 1 |
+----------+-------------------+---------------------+----------+
The composition of water, as displayed in the foregoing table, has
been demonstrated by analysis, this word meaning “the process of
taking apart.” Thus by chemical influences a portion of water may be
subdivided into its constituents and their amounts determined. On
the other hand the composition of water has also been made out by
synthesis, this word meaning “the process of putting things together.”
In this latter case, by putting together what are believed to be the
proper proportional amounts of hydrogen and oxygen to form water, and
then upon using some suitable means for bringing these things into a
state of true chemical combination, it has been found that they do
combine in fact to form water and in the proportions already given in
the table.
The Compound Blowpipe.
The fact of the enormous heat developed when hydrogen burns, was
known long ago, and it gave rise to the invention of a contrivance
for utilizing it. This has taken the form of the apparatus called the
compound blowpipe, also the oxy-hydrogen blowpipe.
[Illustration: FIG. 37.—Apparatus for analysis of water by use of the
galvanic battery.]
[Illustration: FIG. 38.—Apparatus devised by Dumas for determining the
composition of water.]
This blowpipe, as usually constructed, has a single jet or tip—to
which there is conveyed by separate tubes, on the one hand oxygen,
on the other hand hydrogen. The gases, when lighted, give rise to
a flame of but little luminous power but of intense heating power.
Many difficultly fusible metals, such as iron for instance, melt like
wax before it, while others, like lead and zinc, boil and vaporize
beneath its fervent breath. It must not be looked upon however as a
mere chemical toy; it has some uses in the arts. Of these one of the
most prominent is its application to the melting and refining of the
ores and alloys of platinum, substances which no ordinary furnace can
liquefy.
For purposes of this sort, a special furnace or crucible must be
provided, and it must be constructed of some substance that is itself
practically infusible. Such a material is found in quicklime (calcic
oxide, CaO), for this substance does not melt under the influence of
any known contrivance for producing heat. Moreover it does not conduct
heat rapidly, and thus any heat applied to the metal within, is not
subject to serious loss by being conducted away through the walls
of the vessel. For melting platinum then a crucible constructed of
quicklime, and having a cover of the same material, is employed. A
stream of burning gases from a compound blowpipe is forced through an
aperture in the crucible cover in such a way as to fall on the metal to
be melted.
[Illustration: FIG. 39.—Flame of the oxy-hydrogen blowpipe directed
upon a crucible in a furnace of lime.]
The Calcium Light.
Another interesting application of this blowpipe is found in the lime
light, an appliance also known as the calcium light and sometimes as
the Drummond light. In this apparatus, whatever may be its particular
form, the stream of burning gases is directed upon a small block or
cylinder of lime. Of course the block becomes highly heated,—in fact it
assumes a white heat, without melting; and while at this temperature it
gives out a dazzling light. This light has been utilized by architects
and engineers for carrying on important constructions during the
darkness of night. It is also often used in some of the finer forms of
the magic lantern, as for example in the various stereopticons used in
illustrated lectures. So numerous are the uses of the calcium light in
large cities that it has become a regular industry there to furnish
the oxygen and hydrogen gases in separate iron cylinders or cans,
into which they are pumped under great pressure.[5] (It is true that
illuminating gas is sometimes substituted for hydrogen with decided
economy in cost, and yet without serious loss of illuminating power.)
When the cylinders are in use the stop-cocks are slightly opened, and
the gases are under sufficient pressure to flow to the top of the
blowpipe as freely as can be desired.
[Illustration: FIG. 40.—Drummond light, or calcium light. The flame of
the oxy-hydrogen blowpipe directed against a block of lime renders the
latter intensely luminous.]
[5] DANGEROUS EXPLOSIBILITY OF MIXTURES OF OXYGEN AND HYDROGEN.—At
this point a warning should not be omitted, for mixtures of oxygen and
hydrogen gas, whether produced purposely or by accident, are capable
of very dangerous explosions. Even a soap bubble, inflated with the
mixed gases, and then lighted with a torch, explodes with tremendous
violence and a loud report. This result is all the more wonderful when
the extreme thinness and weakness of the filmy confining envelope is
considered. Such explosions are in entire harmony with the various
statements already made. For when the two gases combine, the intense
heat then generated gives rise to a momentary but enormous expansion
of the vapor of water produced by the combustion. The greatly expanded
vapor immediately strikes the air a sharp and violent blow. In
another instant however the vapor suddenly cools and condenses to an
exceedingly minute drop of liquid water. Immediately upon this effect,
the air that was previously forced outward immediately falls into the
vacancy left, and now a second blow results. It is these two violent
shocks the one following the other in almost instantaneous succession,
that produce the report; and to the same causes must be referred
the terribly destructive results of the accidental explosion of
considerable quantities of the mixed gases. It is plain therefore that
all contrivances, destined to employ these gases in close proximity,
must be handled with great caution when ready for use.
Oxygen as Related to Combustions in General.
But oxygen is prominent in many other combustions besides that of
hydrogen. Of course the best known and most common are those in which
the ordinary forms of fuel are the things burned. Here generally the
principal constituent of the combustible material is carbon.
Oxygen as Related to Animal Respiration.
Oxygen performs also one of its most important offices in connection
with the process of animal respiration. In the fulfillment of this
mission no element is known that can in any way act as a substitute.
The gas, which is to serve as the breath of life for the humblest as
well as the most exalted individuals of the animal creation, must
possess a combination of qualities truly marvellous when residing in
a single substance. Even a brief description of the ways in which it
discharges this delicate and manifold duty ought to substantiate the
general proposition.
Oxygen is qualified to sustain respiration by virtue of the exceeding
abundance of the atmospheric air, an abundance such that it extends
above our heads a distance of forty thousand times the height of a man.
Nor are the denizens of the sea forgotten, for oxygen possesses such
capacity for dissolving in water that there exists, absorbed in the
liquid of the rivers and oceans, enough of this vital gas to furnish
breath for all the finny tribes.
Again, the oxygen, so violent in its combinations, is yet bland enough
to pass through all the delicate passages leading into the lungs
without exciting the throat to the slightest cough; to filter through
the fine membranes of the lungs without doing an injury; to saturate
the blood, and to flow to every tissue and cell of the body, and not
only do no harm but everywhere accomplish a reviving work. It performs
throughout the animal frame a well regulated but no inconsiderable
combustion. Indeed the body of a living creature may be properly
looked upon as a kind of furnace, taking in air whose oxygen shall
sustain the combustion of worn-out parts. Nay more, these as they burn
do in their very death make as a final contribution the gift of that
warmth and glow which maintains the animal temperature at the vital
point.
While carrying out the important functions just referred to, oxygen
produces several gaseous substances, each of which, as if under the
constant direction of an ever watchful barometer, maintains its proper
bulk and pressure, so as to do no injury to the most delicate capillary
of a vein or to the tender walls of the smallest chambered cell of the
lungs. With each breath exhaled from the system, the blood, and thence
the lungs, discharge the gaseous products of the combustion already
described; plainly they do it somewhat in the same manner as a chimney
does in its proper action, only the lungs do their work in a far more
perfect way.
The parallelism is not strained here, for the burning of the animal
tissue in the body gives rise principally to the production of the gas
called carbon dioxide and the vapor of water, just as when a faggot
burns in the chimney-place, the carbon and the hydrogen of the wood
oxidize into the self-same products, both of which are wafted up the
flue and out into the great ocean of atmosphere beyond.
READING REFERENCES.
Gases, Liquefaction of
=Cailletet=, M.—Annales de Chimie et de Physique.
5 Sér. xv, 132.
———— Chem. News. xxxvii, 11.
=Coleman=, J. J.—Chem. News. xxxix, 87.
=Pictet=, R.—Annales de Chimie et de Physique.
5 Sér. xiii, 145.
———— Chem. News. xxxvii, 1, 23, 83.
=Roscoe and Schorlemmer.=—Chemistry. New York. 1878.
ii, pt. II, 516.
=Schutzenberger=, P.—Traité de Chimie Générale. i, 25.
Priestley, Joseph
=Brougham=, H.—Lives of Men of Letters, etc. p. 402.
———— Amer. Chemist. iv, 362-441; v, 11-35, 43, 210.