III.—CHEMISTRY OF AIR.
CARBONIC DI-OXIDE FROM THE LUNGS PASSED INTO LIME WATER (CAO₂H₂).
Experiment.—Dissolve some quicklime (CaO₂H₂) in water. Let it settle and pour off the clean part. Blow your breath into this. What follows, and why?
A quaint old book called “The Tin Trumpet” remarks that “three bad mothers have borne three good daughters.” Long-Suffering begat Patience, Astrology gave birth to Astronomy, and Chemistry is the daughter of Alchemy. The facts of science have taken the place of the fancies of the early investigators. Men used to be attacked, when they entered ravines and caverns, by supernatural beings, as they supposed, who choked, and sometimes killed them. In 1754 Joseph Black showed that these fatal results were due alone to the presence of an invisible gas, which he called “fixed air,” as he found it locked up in limestone. “Geist,” the name invented by Van Helmont to represent this strange power, signified ghost or spirit, so that the “ghosts” of the seventeenth century are the gases of the nineteenth. The word gas is derived from geist.
In studying the history of science we often wonder at the near approach which men made to truths which remained undiscovered for a long time after. One finds, all along, intimations of approaching disclosures which resemble those peculiarities in animals and plants that the geologist notes in the lower strata of the rocks, as prophesying the development of future species. The astrologer failed in his attempt to read human destiny, but he led men forward to the time when, in the stars, they should read the “thoughts of God.” The alchemist did not succeed in distilling the “elixir of life,” but he prepared the way for chemists to make those useful discoveries which have greatly promoted the safety and comfort of men and extended the period of human life. Some of the most important investigations in which science is now engaged concern the character and contents of that all-pervading aërial ocean which surrounds our earth to the height of from fifty to five hundred miles. Pure air is one of the great essentials of health and life. How to secure it is a difficult but beneficent inquiry which the spectroscope, microscope and chemical analysis may yet answer.
NITRIC ACID DISSOLVING COPPER.
Experiment.—Place copper in nitric acid. Also try iron and zinc successively.
COMPOSITION OF AIR.
Air is a mixture, and not a compound. This distinction, as before intimated, is one of great importance. A cup of coffee is a good illustration of the former; there we have united water, coffee, cream, and sugar, but no new substance is thereby produced, and each of these ingredients may be removed without affecting the others. Gunpowder is a mixture, being composed of sulphur, nitre, and charcoal—a most admirable mixture it is, too, for every particle of it contains these three substances, as may be shown; the sulphur may be removed by heat, and the nitre by washing, leaving the carbon alone; the microscope also would reveal in each grain these three substances. That the air is a mixture can be proven in two ways. First, water will absorb each of its two principal ingredients, and, secondly, they do not exist in air in that definite ratio which always characterizes chemical combination. The principal materials in air are oxygen, nitrogen, carbonic di-oxide, watery vapor, ammonia, and very minute portions of many other materials. Professor Steele says, that if the entire atmosphere were compressed to the density of that immediately surrounding the earth, it would extend above it only about five miles. Now, if the substances entering into its composition were to be arranged in the order of their specific gravity, watery vapor would form a sheet about the earth five inches deep, carbonic di-oxide another just above it, thirteen feet in depth, then a layer of oxygen one mile thick, and nitrogen another layer above that, four miles in thickness.
In short, four-fifths of the air is nitrogen, about one-fifth is oxygen, four ten-thousandths is carbonic acid, and water exists in variable quantities. It will be readily seen that the chemical and physical changes constantly going on in the surface of the earth must be throwing off other materials into the atmosphere. For example, the spectroscope has shown that common salt exists almost everywhere in the air. This arises from the fact that the ocean surrounds all lands, and its yeasty waves are broken into foam which is caught up by the winds and borne over the whole earth. One of the most remarkable facts connected with this subject is the wonderful uniformity of this mixture. Upon the whole, the amount of each ingredient is nearly the same. Some slight variations, such as the following, are observable: More CO₂ is found near cities than in the country, and there is more of the same over the land than over the sea. That the substances which enter into the composition of air do not arrange themselves according to weight, is due to a most interesting law called
THE DIFFUSION OF GASES.
PHOSPHORUS BURNING IN AIR.
Experiment.—Prepare nitrogen as described elsewhere in this article.
By this we mean that gases tend to intermingle, the lighter even descending, and the heavier ascending, until they occupy the same space. This can be shown in the following manner: Fill one bottle with hydrogen, and another with carbonic acid gas, fit into each a cork, perforated so as to admit a tube, connect the two by inserting a tube, placing the bottle of hydrogen above with the top downward; although the carbonic acid is twenty-two times heavier than the hydrogen, in an hour or two it will rise into the bottle above, as can be proved by pouring into it some lime water, which will immediately become milky, showing that the carbonic acid has united with the lime, forming calcium carbonate. That the hydrogen has passed down into the other bottle may be demonstrated by first absorbing such portions of the carbonic acid as still remain by pouring in cream of lime, when there will be found still in the bottle a substance (hydrogen) which will burn with a faint yellowish light. Another pleasing experiment may be performed in the following manner: Take an unglazed porcelain cup, fit to it a brass cap, perforated so as to admit tightly a long glass tube, insert one end of the tube into some colored water contained in a goblet, the inverted cup being supported above on the other end of the tube; now hold over the cup a jar filled with hydrogen; bubbles will soon be seen escaping through the water from the lower end of the tube, showing that the hydrogen has entered and mingled with the air; remove the jar, and the liquid will rise in the tube, proving that the gas has escaped from the cup. This diffusive force in the atmosphere prevents the accumulation of noxious gases by distributing them throughout the whole mass. The constant agitation of the air in gales and storms facilitates this operation, and it is only in certain confined places like caves, such as the Grotto del Cane,[1] mines, and wells, that we find apparent exception.
SILVER COIN DISSOLVING IN NITRIC ACID.
Experiment.—Place a five-cent piece in some nitric acid for two or three hours. Drop into a portion of the liquid a little salt; you show the presence of the silver. Drop into another portion some aqua ammonia; the blue color reports the presence of the copper.
Lieutenant Maury has said that the atmosphere makes the whole world akin. The breezes that blow over our land may in turn visit every other, carrying bane or blessing. Alas! we fear, to-day, that the feverish breath which poisons the air of Italy may spread its pestilence to our shores. One lesson we learn from this is, that the misery or prosperity of any one portion of the earth may affect every other; and that which benefits a part, contributes in this way a blessing to the whole.
NITROGEN.
In our first article of this series somewhat extended reference was made to oxygen, and we shall therefore not dwell upon that element at this time.
Nitrogen, which constitutes by measure 79.04, and by weight 76.8 of the air, is remarkable for the absence of positive qualities. It is a colorless, tasteless, odorless gas, will not burn, nor support life or combustion. Its chief office is that of a diluter. Without it we should live too fast; even as it is we live too fast! With oxygen alone to breathe, ours would be a short and fevered existence. All flames and fires would be kindled into furious combustion, stoves themselves would burn, and the very “elements melt with fervent heat.”
MERCURY DISSOLVING IN NITRIC ACID.
We can prepare air artificially, by mixing one part of O with four parts of N, thoroughly shaking them together. Nitrogen can easily be obtained in the following manner: Make a small cavity in a piece of cork; line this by sifting into it a little plaster or crayon dust. Place the cork on some water in a deep plate. Insert now in the cavity a piece of dry phosphorus (always handle phosphorus with care), touch the P with a heated wire, and quickly place over it an inverted jar. White fumes will instantly rise, which are phosphoric anhydride, P₂O₅. These will be quickly absorbed by the water, and the water will rise and fill one-fifth of the jar. It will be necessary to add water as that in the plate rises. The remaining four-fifths of the jar will be occupied by nitrogen.
The following is an instructive experiment: Take two jars of equal size (one open at both ends), one of which is fitted with a stopper; fill one with O and the other with N. Place a smooth glass plate under each before removing the pneumatic trough, and holding the plates closely over the top, invert one jar on the other—plate to plate—the jar of O being below. Now carefully remove the plates, and also the stopper from the jar of N, and quickly insert a lighted taper with a long snuff. As it descends through the N it will be extinguished, but as it enters the O it will be rekindled. This may be repeated many times by raising and lowering the taper. N does not seem to be strongly attached to anything; that is, it has but slight affinity for the substances with which it combines. Strange enough, from this sluggishness results a marvelous activity. Being held with such little force it is liable at any time to be liberated in the form of a gas, and the decomposition of the whole compound of which it formed a part will take place. Hence, instability is the most marked characteristic of N. It reminds one of some loafer, without steady occupation or aims, restless, vacillating, but always a factor in every turbulence or outbreak.
BISMUTH DISSOLVING IN NITRIC ACID.
Gunpowder, gun-cotton, nitro-glycerine, and dynamite all contain N, and their explosive character depends largely upon its presence. Nitrogen and chlorine form a compound, which explodes with such terrific violence that its manufacture should never be attempted by students.
Nitrogen iodide is another of these dangerous combinations. It can be made in very small quantities, however, in the form of a black powder, which may be handled with impunity while it is damp. The touch of a feather, or a zephyr, will sometimes explode it when dry. It is almost impossible to keep it; the jar of a foot-fall or slamming of a door is often sufficient to liberate the unstable nitrogen, and the substance disappears with a loud report. The tremendous rending force of dynamite is well known. A small charge in a torpedo will sink a ship. The Greely Relief Expedition used it to open their way through the arctic ice fields. Its atoms rush apart with such frightful velocity that if a pound of it be exploded upon a naked bowlder, of many tons weight, the rock is shivered into fragments.
COMPOUNDS OF N AND O.
At every breath we take into the lungs a mixture of N and O. The operation is not only harmless, but essential to life. When, however, N and O are compounded, the resulting substances are very different. Nitrous oxide (N₂O) forms the well known laughing gas, which breathed, produces for a time a species of intoxication, and if its inhalation is continued, results in insensibility. Nitric oxide (NO) when first formed consists of suffocating red fumes, while nitric acid (HNO₃) is a very corrosive liquid which will cauterize flesh, and acts with great energy upon most of the metals. It is sometimes termed aqua fortis, and is much used in etching upon copper. The surface of the metal plate is covered with varnish or wax, upon which the design is then traced by a sharp pointed instrument. The acid is then applied and remains until, in the judgment of the artist, the impression is deep enough. Any one can easily etch his name, in this way, on a knife blade, or make a stencil plate from a thin strip of brass or copper. Silver, copper, mercury, lead, zinc, iron, bismuth can all be dissolved by nitric acid.
The five compounds of N and O admirably illustrate the laws of atomic combination. Their symbols are as follows: Nitrogen monoxide, N₂O; nitric oxide, NO; nitrogen trioxide, N₂O₃; nitrogen peroxide, NO₂; nitrogen pentoxide, N₂O₅. A careful examination of the weights of these substances, which may be made by consulting some good chemical manual, will show that there is an exact ratio of combination, their proportional weights being respectively as 1¾ to 1, 1¾ to 2, 1¾ to 3, 1¾ to 4, 1¾ to 5. Since atoms can not be divided they must combine atom for atom, or in multiples. This principle has been more fully stated in the form of six
LAWS OF COMBINATION.
The first law of weights says that the elements of a given compound always unite in the same proportions, by weight. The second law is, that if two or more substances unite to form several compounds, their highest combining proportions will always be multiples of their lowest combining weights. The third law announces that the combining weight of a compound is the sum of the combining proportions of its constituents. The volumetric laws are as follows: 1, If two or more elements unite to form a compound, their proportion by volume will always be the same; 2, if they unite to form a variety of compounds, these proportions will always be multiples of the lowest combining volumes. 3. The third law is most curious of all; that the combining volume of a gaseous compound is always 2. For example, if two elements represented by x and y unite in proportion of one volume of x to one of y, there would be formed two volumes of the compound. If there should be two volumes of x and one of y there would be two volumes of the compound, and if they should unite three volumes of x and one of y, again there would be but two volumes of the product. Just why two should be such a favorite number is difficult to explain. No one can carefully study these interesting laws without perceiving the necessity for a rare intelligence in arranging all materials with such mathematical exactness.
How absurd to ascribe to atoms the power to count, to weigh, to measure, to arrange themselves in orderly combinations which surpass the most skilful marshaling of battalions on a great battle field. It would be to make gods of atoms.
AN ALLEGORY—THE FOUR KINGS.
AMMONIA GAS AND CHLOROHYDRIC GAS MEETING IN THE AIR AND FORMING AMMONIC CHLORIDE.
Experiment.—Place some ammonia in one glass and chlorohydric acid in the other. Ammonia gas (NH₃) and chlorohydric gas (HCl) will meet in the air and form ammonic chloride (NH₄Cl).
Once upon a time, as the story goes, the King of the Acids, whose name is Sulphuric, arrogantly walked forth to view his wide domain. He was sour and fierce. Many conquests had made him boastful, until he thought himself the mightiest of the earth. Soon he came to where the King of the Metals, whose name is Gold, sat in royal state, his countenance shining with wonderful beauty. The haughty monarch of the Acids was angered as he approached, to see that his rival did not recognize him, nor acknowledge his power. “I am mightier than thou!” he said, but King Gold smiled in silent derision. Thereupon the former fiercely attacked him, but was easily repulsed. The savage aggressor, insane with rage, went away muttering, “I have two sons who can slay thee!” He instantly commanded Nitric Acid and Hydrochloric at once to unite in an attack upon his opponent. Their father gave them a banner on which was inscribed “Aqua Regia,” which might be translated “King Slayer.” It was indeed too true a symbol. Alas! before their combined onslaught the royal metal yielded. The old king now grew more arrogant than ever, and boastfully announced that his sway knew no limits. One day he discovered, in his walk, one of a smooth and gentle countenance, yet with an expression indicating that if aroused he might make biting and caustic replies. It was Potassa, King of the Alkalies. From hot words, they soon passed to blows, until in the wild struggle both were slain. Horrible to contemplate, they ate each other! The spot on which they perished can still be pointed out. This story is a warning to vaulting ambition, and a tragedy surpassed in pathos only by the mournful story of the Kilkenny cats![2]
CARBONIC ANHYDRIDE, CO₂.
This substance is also called carbonic di-oxide and carbonic acid gas. It is the dreaded “choke-damp” of the miner. It Is produced when carbon unites with O, whether by the decay of vegetation, combustion of vegetable matter, or the oxidation of the blood. It is so heavy that it may be poured or dipped out from vessel to vessel, like water. It extinguishes flame, and is largely employed for that purpose in contrivances like the Babcock Fire Extinguisher,[3] and the more recent Fire Grenade.[4] Taken into the stomach in the form of soda water it is refreshing and beneficial, but its inhalation is always injurious, and will produce death if breathed in considerable quantity, by causing asphyxia.[5] A practical problem of great importance is that of ventilation, as this material is constantly being thrown off from the lungs, of both animals and men. In the days of ample fire-places, our homes, if they had less heat had purer air. The railroad car, in point of comfort, is a marvelous improvement over the ancient stage coach, but the latter was better in the matter of ventilation. The sleepiness of congregations should be attributed as much to the foul air as to the dull preaching. Can not some of our writers on homiletics prepare us a stirring chapter on the relation of carbonic acid to eloquence?
Homes, school houses, and all public buildings should be supplied in some way with a gentle and universal circulation of air. Fierce draughts should by all means be avoided. Ventilation is now generally best secured by the construction of flues in the wall, which have openings in the lower and upper portion of the room. The world yet waits to bless the inventor of a simple and effective system of ventilation which is of universal application.
OTHER ATMOSPHERES.
As has been suggested, there must be in the air a variable quantity of other substances beside those named as forming its mass. Ammonia gas (NH₃) is present, and it is from this material that most of the nitrogen found in plants is obtained. Water readily absorbs it and conveys it to the roots. Other elements require only additional heat to volatilize them. Almost all of the elements of nature have been liquefied; carbonic acid has been solidified, forming a beautiful white solid, intensely cold. It is generally accepted as a truth that all substances could be solidified by the sufficient removal of heat, and it would of course follow that they could all be vaporized by applying heat enough. In earlier geologic times many of the materials forming our earth must have existed as vapor in the heated atmosphere, and the time will come when our globe will have no atmosphere, no seas, lakes, nor rivers. It will float in space, cold and desolate like the moon.
The opposite of this condition can be seen to-day in many of the heavenly bodies. The spectroscope reveals in the sun’s atmosphere gold, iron, copper, zinc, and many other substances. Vast disturbances are constantly heaving and tossing these materials, which are intensely heated. The cyclonic movements are so violent and extensive that the wildest hurricanes of our earth would seem as zephyrs in comparison.
Hydrogen flames have flared out one hundred thousand miles from its surface. It has been suggested that the mighty fires in the sun may be fed by millions of meteoric bodies which are tossed into its raging heats by the power of gravity. Nothing could withstand such terrible combustion. Lockyer says that if all of the sun’s heat were concentrated upon a mass of ice as large as the earth it would melt it in two minutes, and convert it into vapor in fifteen.
Science has accomplished few things more wonderful than that of crossing over the vast spaces of the universe, and revealing to us the chemical composition of the celestial atmospheres.
End of Required Reading for December.