Part 11

This gas, so named from two Greek words signifying the maker of acid, was discovered by Dr. Priestly in 1774. He obtained it by heating the red oxide of mercury in a glass retort, when the gas escaped in considerable quantities. In the ensuing year Scheele obtained it by a variety of methods, and a few years afterwards Lavoisier discovered that it was contained in atmospheric air, where it exists in the proportion of about one-fifth, the remaining four fifths being almost entirely nitrogen.

Oxygen gas may be obtained for the purpose of experiment, by heating to redness the black oxide of manganese in an iron bottle, to the mouth of which a flexible tube is attached to convey away the gas as fast as it is liberated from the manganese. The first portions should be allowed to escape, being mixed with the air in the tubes and bottle, and the remainder may be collected in a gasometer, or in glass jars inverted over water.

Another method to obtain the gas, and one to be used only in the absence of other ingredients, is to mix in a retort some of this same oxide of manganese with about half its weight of strong sulphuric acid, and apply heat to the retort, when the gas will come over in considerable quantities; the first portions must be allowed to escape as before. If the gas is required very pure, a small quantity of the salt called chlorate of potassa, may be heated in a retort, and oxygen gas will be evolved, and may be collected as before. If you have an iron bottle, the first mode is by far the cheapest, as the heat of a bright fire is sufficient for the operation, and a large quantity of gas is obtained in a short time from a very inexpensive material. The most rapid and convenient process of all is to heat a mixture of two parts chlorate of potash, and one of powdered black oxide of manganese, in a common clean oil flask, to which a cork and bent tube has been adapted. Care must be taken not to mistake sulphide of antimony for black oxide of manganese, as very serious accidents have arisen from this cause.

Oxygen is largely distributed over our globe, both in its uncombined state, and in union with other substances. Besides forming one-fifth of the atmosphere, it forms eight-ninths by weight of all the water in the ocean, rivers, and springs on the face of the whole earth. It also, in combination with various metals, forms the various earths and minerals of which the crust of the earth consists, so that it is the most abundant and widely distributed substance in nature, and in combination with other elements, forms nearly half the weight of the solid earth.

In its uncombined state it is a colorless gas, somewhat heavier than atmospheric air, without taste or smell. It is a powerful supporter of combustion, and is absolutely necessary for the support of animal life, which cannot exist for any time without a free supply of this gas, which is constantly consumed in the act of breathing and is replaced by an equivalent portion of carbonic acid gas. The want of oxygen is partly the cause of the oppression felt in crowded rooms, where the air cannot be renewed so fast as is required for the number of persons who are constantly consuming the oxygen; and if an animal be confined under a glass jar inverted over water, it will presently die, just for the same reason that burning tapers are extinguished under similar circumstances.

If a jet of this gas be thrown upon a piece of charcoal, sulphur, or almost any combustible body in a state of ignition, it will make it burn with great vividness and rapidity.

FOOTNOTE:

Some boiling water should be added to the mass left in the retort directly the gas has ceased to come away, or it will adhere to the glass so firmly, that the retort will certainly be spoilt.

Experiment.

But by far the most intense heat, and most brilliant light, may be produced by introducing a piece of phosphorus into a jar of oxygen. The phosphorus may be placed in a small copper cup, with a long handle of thick wire passing through a hole in a cork that fits the jar. The phosphorus must first be ignited; and, as soon as it is introduced into the oxygen, it gives out a light so brilliant that no eye can bear it, and the whole jar appears filled with an intensely luminous atmosphere. It is well to dilute the oxygen with about one-fourth part of common air to moderate the intense heat which is nearly certain to break the jar if pure oxygen is used.

Experiment.

If a piece of charcoal, which is pure carbon or nearly so, be ignited, and introduced into a jar containing oxygen or common atmospheric air, the product will be carbonic gas only, of which we shall speak presently. As most combustible bodies contain both carbon and hydrogen, the result of their combination is carbonic acid and water. This is the case with the gas used for illumination; and in order to prevent the water so produced from spoiling goods in shops, various plans have been devised for carrying off the water when in the state of steam. This is generally accomplished by suspending over the burners glass bells, communicating with tubes opening into the chimney, or passing outside the house.

To show that oxygen, or some equivalent, is necessary for the support of combustion, fix two or three pieces of wax-taper on flat pieces of cork, and set them floating on water in a soup-plate, light them, and invert over them a glass jar; as they burn, the heat produced may perhaps at first expand the air so as to force a small quantity out of the jar, but the water will soon rise in the jar, and continue to do so until the tapers expire, when you will find that a considerable portion of the air has disappeared, and what remains will no longer support flame; that is, the oxygen has been converted partly into water, and partly into carbonic acid gas, by uniting with the carbon and hydrogen, of which the taper consists, and the remaining air is principally nitrogen, with some carbonic acid; the presence of the latter may be proved by decanting some of the remaining air into a bottle, and then shaking some lime-water with it, which will absorb the carbonic acid and form chalk, rendering the water quite turbid.

Nitrogen.

This gas is, as its name implies, the producer of niter, or at least forms a portion of the nitric acid contained in niter. It is rather lighter than atmospheric air, colorless, transparent, incapable of supporting animal life, on which account it is sometimes called azote--an objectionable name, as it is not a poison like many other gases, but destroys life only in the absence of oxygen. This gas extinguishes all burning bodies plunged into it, and does not itself burn. It exists largely in nature, for four-fifths of the atmosphere consists of nitrogen gas. It is also an important constituent of animal bodies, and is found in the vegetable world.

Nitrogen may be most easily obtained for experiment by setting fire to some phosphorus contained in a porcelain or metallic cup, placed under a gas jar full of air, and resting on the shelf of the pneumatic trough, or in a soup-plate filled with water.

Nitrogen combines in five different proportions with oxygen producing five distinct chemical compounds, named respectively nitrous oxide, nitric oxide, nitric tri-oxide, nitric tetroxide, nitric pent-oxide, which last, united with water, forms nitric acid, now called hydric nitrate, as nitrous acid is termed hydric nitrite.

Nitrous oxide gas is generally known by the name of “laughing gas,” from the jolly sensations experienced on inhaling it. It may be procured by distilling in a glass retort a salt called nitrate of ammonia, which yields the gas in considerable quantities, and it should be kept standing in jars over water for some hours before it is used. It should be transferred into a silk air-tight bag, furnished with a stop-cock and mouth-piece, from which the gas may be breathed; a little practice is required to do this easily, and more resolution to desist when the gas begins to produce its effects, as it appears to fascinate the experimenter, and actual force is often necessary to remove the bag from the mouth. The effects produced vary according to the temperament of the person inhaling it; they are, however, always of a highly pleasurable nature, muscular action being generally greatly exalted, compelling the individual to race round the apartment and execute leaps and pirouettes perfectly astounding. Some persons shout and sing, and I have seen one expend his superfluous animation in twisting his features into such ludicrous grimaces as would be the envy of the candidates at a grinning match, and beat them all out of the field.

This gas is heavier than air, and supports combustion nearly as energetically as oxygen, as may be shown by introducing a piece of ignited phosphorus into a jar of this gas. It will not, however, support the life of small animals, such as mice, which introduced into it die very quickly.

The next compound of nitrogen with oxygen, when one proportion of nitrogen unites with two of oxygen, is termed nitric oxide gas. It may be easily procured by heating in a retort some copper turnings in dilute nitric acid. It is colorless and transparent, and has the property of combining with oxygen to form other compounds.

Experiment.

Into a jar of this gas standing over water pass some oxygen gas. The jar will be filled with red fumes, which will be rapidly absorbed by the water. If atmospheric air be used instead of oxygen, there will remain in the jar the nitrogen of the air amounting to four-fifths of the air employed.

This gas is destructive to animal life, in consequence of its property of uniting with the oxygen in the lungs, and producing the highly corrosive nitrous acid gas. It will, however, support the combustion of a few substances, phosphorus for instance, provided it is sufficiently heated before being plunged into the gas.

We pass over the third and fourth compounds of nitrogen with oxygen, as they are not calculated for amusing experiments. Nitric acid is easily prepared on the small scale, by gradually heating equal parts by weight of nitric and sulphuric acid in a retort to which a receiver has been adapted. The receiver, which may be a clean oil flask, should be kept cool with wetted blotting paper.

Nitrogen combines with chlorine and iodine, forming detonating compounds, the former being so extremely dangerous that it will be better to pass it by.

The compound with iodine, called iodide of nitrogen, may very easily be made by pouring a strong solution of ammonia (a compound of nitrogen and hydrogen) upon some iodine in a vial, shaking them well together, and after letting them stand for a few hours, pouring off the fluid; the black powder remaining in the vial is the explosive compound, the iodide of nitrogen. When dry, it is very apt to detonate spontaneously; it should therefore be shaken out of the vial while wet, and spread in very small quantities on separate pieces of blotting paper, which should be kept apart from each other. When thoroughly dry, the slightest touch with the point of a feather, shaking the paper on which it rests, or even opening too rapidly the door of a closet where it has been put to dry, will cause it to explode, producing a quantity of violet-colored fumes. The explosion is somewhat violent, producing a sharp cracking noise; and the greatest care should be taken in experimenting with it.

Atmospheric Air.

As has been already mentioned, nitrogen is the principal constituent of the air of the atmosphere which surrounds our globe, extending to a height of about forty-five miles above it, and playing a most important part in the economy of nature, inorganic as well as organic.