Chapter XIV: 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.

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.

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.

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.

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.

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.

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.

[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.