CHEMISTRY OF WATER. H₂O.
FORMS OF WATER CRYSTALLIZED.
Do not be disturbed by these cabalistic symbols; they are simply the chemist’s name for water; a most expressive name, too, as we shall presently discover. Some names are misnomers. Abel Blackman may be both weak and a white man. Our letters can not mislead. They abbreviate, show the class of each substance, the elements that form it, and their proportions. Berzelius devised this mode of naming. (Who was Berzelius?)
On the table stands a glass of water. How beautiful it is! Even diamonds, costliest of gems, are valued in proportion as they possess its marvelous clearness, those of the “first water” being most highly prized. We are now to speak of some of the chemical properties of water; hereafter we shall consider the physical characteristics.
DISTINCTION BETWEEN ATOMS AND MOLECULES.
See! I have dipped my pencil into the goblet, and brought up a drop of water. What force binds together the pencil and the drop? What holds the drop to other drops? Why is not this ice instead of water? If I shake the pencil in what direction does the drop fall? If the drop were larger than the world, which way would the world go? What other force is there in it which, according to Faraday, is equal to that in a flash of lightning? Here are, then, five great forces in a drop of water, yet none of them changes its nature. It is still H₂O.
Let us place this drop of water in the upright tube of an atomizer. Apply air. See, the drop has broken into thousands of particles. Now, suppose we could take one of these and place it in a flask. Apply heat, and we should separate the little particle into thousands of particles of steam, but each of these, and any lesser division of these, would still be H₂O. The minutest division of the water possible would be called a molecule, yet it would still be water, and composed of two parts of hydrogen and one of oxygen. The old ocean itself contains the same. The Cracow beds of salt are made of chlorine and sodium, and the minutest dust from one of its crystals would be found to contain the same elements, and in the same proportion, both by weight and measure. Molecules, then, combined, make only masses of the same nature. But molecules are composed of atoms, and whenever atoms of two or more different substances are combined they always form something different from either of these. The force that unites them is called chemical affinity, or sometimes the chemical force. For example, tenacious iron unites with a gas and forms a brittle, red substance, rust. Chlorine is a poisonous gas, and sodium will burn on water, both deadly; united they give us salt; absolutely essential to life. Hydrogen is the best substance in the world to burn, and oxygen the best supporter of combustion. When united they form water, which is universally employed to extinguish fire. Blue vitriol is blue, as the name implies, yet it is composed of four elements, two of which, H and O, are colorless, copper, which is red, and sulphur, which is yellow. Sulphur has little or no odor, and hydrogen has none, but when united they form a gas which has the odor of spoiled eggs. White sugar is nothing but black charcoal and water. It will thus be seen that here is a source of new things in nature. Whatever chemical affinity touches is changed.
And so we have found another force in our drop of water taken from the goblet, more wonderful than any yet named, a mighty, transforming energy which has but one worthy rival in the work of creating new things, the vital principle, and even that must yield at last to this all conquering power. If our goblet was large, and held a pound of water, (about a pint,) we should find that to pull the molecules apart, that is, make it into steam, would require a force which would raise four tons to the height of one hundred feet. But more wonderful still, to separate the pound of water into two chemical constituents would require, according to Prof. Cooke, an energy which would raise 5,314,200 pounds one foot. Our pint of water would then occupy 1800 times its present volume.
Let us now give a striking and beautiful illustration of chemical affinity. We will throw into this tumbler a piece of potassium (symbol K) half as large as a pea. This interesting metal was discovered by Davy in 1807. Its affinity for O is very great. As soon as it falls upon the water it abstracts oxygen and forms potassium oxide (potash), while the hydrogen and a small amount of volatilized K escape and are burned with a brilliant violet flame, on account of the heat evolved by the energetic chemical action.
POTASSIUM BURNING BY COMBINING WITH THE OXYGEN OF WATER.
IMPORTANT DATES.
The composition of water was discovered about one hundred years ago. Cavendish found hydrogen in 1776, and Priestly discovered oxygen in 1774, August 1st, a date which some one says “may almost be accepted as the birthday of modern chemistry.”
Is it not remarkable that four of the brightest “red letter days” in the history of this science should be embraced within two decades, from 1754 to 1774? In 1754 Joseph Black discovered carbonic acid gas; in 1766 Dr. Cavendish found hydrogen; in 1772 Dr. Rutherford discovered nitrogen, and in 1774 Dr. Priestly found the King of the Elements, oxygen. Until then mankind were ignorant of the existence of a substance which composes in the aggregate one half the earth.
ANALYSIS OF WATER.
Returning to our glass, let us suppose that the bottom has been so perforated that two little strips of platinum wire can be inserted side by side, at the distance of half an inch from each other, and so as to leave the tumbler water-tight. Now attach the lower ends of these wires to wires connected with the poles of an ordinary galvanic battery. Small bubbles will be seen to rise immediately around the wires in the water. Fill two glass tubes (closed at one end) with water, and having placed a little piece of paper over the top, hold the finger on the paper, and quickly invert the tubes over the wires. The escaping gases will thus be secured. The electric current is counteracting the affinity of the two elements that form water, and they are collecting in the tubes. You will soon find that the H gathers more rapidly than the O, and upon measuring them there will be twice as much of the former as of the latter. Weigh them, and the O outweighs the former eight times. If, then, one atom of O weighs eight times as much as two atoms of H (H₂O is the symbol for water, remember,) then one atom of O weighs sixteen times as much as one atom of H; or, in other words, H is sixteen times lighter than O, and is the lightest substance known.
Place the O and H in a eudiometer over mercury, and send an electric spark through them; the gases will disappear, with a loud explosion, and there, resting on the quicksilver, will be seen the original drops of water which we decomposed. We have now shown the composition of water, both by analysis and synthesis.
HYDROGEN.
An atom of H is the chemist’s unit. This is a colorless, odorless, tasteless gas, fourteen times lighter than air. When burned it produces a more intense heat than any other substance. Iron burns in its flame like paper. When united with O, and a piece of lime is inserted in the flame, the latter becomes exceedingly brilliant, forming the Drummond light, which has been seen at the distance of one hundred miles in the daytime. So diffusive is H that if a sheet of paper or gold-leaf be placed over an escaping jet of the gas, it will pass directly through the paper, and may be lighted on the upper side. H is easily prepared, and many interesting experiments may be performed with it, some of which it may be well to mention. Take up on a pointed wire or needle or with tweezers, a piece of the metal sodium, quickly insert it under a tube filled with water and invert in a glass of water; the sodium will at once take the O and leave the H to displace the water in the tube. Remove the tube, still holding it with opening downward; apply lighted match and a slight explosion will follow. What two properties of H have you shown by your experiment?
COLLECTING HYDROGEN EVOLVED FROM WATER BY SODIUM.
Take a bottle holding one or two pints, fit a cork to it, through which pass a glass or metallic tube, the end of which is drawn out so as to leave a small aperture at the top. Place in the bottle a few pieces of zinc, and some sulphuric acid, diluted with water, in the proportions of one part of acid to six of water, then insert the cork. You will immediately see bubbles of H rising. The explanation of this is as follows: The zinc takes O from the water, thus liberating H; the O forms an oxide on the surface of the metal, which would prevent further action, did not the acid dissolve the oxide, thus leaving a fresh surface to take the O, and continue liberating H until the metal disappears. After the H has been forming for two or three minutes, hold over the tube an inverted tumbler for a moment, remove the tumbler and then apply a match to the contents of tumbler. When the bottle has become filled with H you can light the gas at the top of the tube, and thus have a steady flame. Be careful not to attempt to ignite the gas until all of the air has been forced out of the bottle, as air mixed with H produces an explosive mixture. In the intense heat of the faint flame you can melt metals or glass. By placing a larger glass tube, open at both ends, over the flame, you may be able to produce the celebrated acoustic tones, varying in pitch and intensity with the size and length of the tube used. A hydrogen gun can easily be made by taking a tin tube five or six inches long (closed at one end), from one half inch to an inch in diameter; make a small aperture near the closed end; then invert the tube for a moment over the escaping H, keeping the small hole closed with the finger, place a cork in the open end, and apply a match to the hole. The cork will be forced out with a loud explosion. What compound is always produced when H is burned? Let us see. Invert a cold, dry tumbler over a burning jet, and you will always observe moisture gathering on its surface. Another pretty experiment may be performed with H by inserting the stem of a common clay pipe in a piece of rubber tubing, slip the other end of the tubing over the gas jet, prepare some strong soap suds, and with a little care you can blow beautiful soap bubbles with your pipe, which, by a skillful movement may be detached, and they will rise in the air like miniature balloons; by placing a burning match under them they will explode. Strike a bell in a large jar filled with H, and it has a squeaky sound. Our whole art and science of music would be changed if H should be mixed with the air to any great extent.
Nicely balance a flask or jar containing air; fill the same flask with H, and the beam will at once be seen to rise.
Let us find the antipodes of weight. Iridium, hammered to increase its density, is twenty-three times heavier than water; water is about eight hundred times heavier than air, and air is fourteen times heavier than H: 23×800×14=257,600; that is, one quart of Ir would balance 257,600 quarts of H.
OXYGEN.
There are four kings among chemical substances: Oxygen, king of all the elements; gold, king of the metals; oil of vitriol, king of the acids, and potash, king of the bases.
PREPARATION OF OXYGEN FROM MERCURIC OXIDE—MATERIALS USED BY DR. PRIESTLY.
This term of distinction is given to oxygen because of its marvellous activity and range of powers; it unites with all elements save one, fluorine. Its grasping disposition is often resisted by man; he keeps it from destroying his house by painting it; from gnawing at the quivering nerves of his teeth by filling them; from devouring his fruits by canning them; and Monsieur Goffart has now taught us to save green food for our cattle, from its ravages by excluding O from our silos. In spite of its destroying power we can not live without it. The light and warmth in our homes are produced by its rapid union with fuel. Every moment we breathe we are absorbing it into our bodies, where it unites with waste matter, producing heat and energy, and removing that which would clog and poison the system. There is nothing in nature more beautiful than the plan by which the animal and vegetable kingdoms mutually sustain each other by the interchange of O. Look at this little aquarium; here are two or three shiners, some goldfish, and a few water plants. In this little world we may see exactly what goes on in the great world. That goldfish is inhaling O, which is conveyed into the capillaries, unites there with the carbon, forming CO₂, which is exhaled, seized upon by the plant, and in the wonderful laboratory of its cells, the C is separated from the poisonous gas, and retained, while the O is thrown off, again to be used by the fish. Upon the nice adjustment of the plants to the animals, and vice versa, depends the life of both. While upon this subject we might note another interesting evidence of beneficent design in the provision made for both fish and plants.
Water absorbs gases with great readiness—some of them it takes more readily than others; for example, a pint of water will absorb seven hundred pints of ammonia gas. It will take but its own volume of carbonic anhydride under one pressure of the atmosphere.
The descending rain drops absorb these two gases and convey them to the rootlets of the plant, for food. More wonderful still, the Almighty has arranged that water should remove O from the air more readily than it does nitrogen; consequently the rain carries down the O to the fish in river, lake and ocean, adding its life-giving principle to the air, which is always contained in water. It is a pretty sight to watch the breathing of a fish as he sends the rapid currents of water through his gills in the act of aërating the blood, which, as it passes through, gives them a crimson color.
It may easily be proved that plants throw off O, by submerging any vigorous growing plant in a jar of water; in a short time little bubbles will be seen clinging to the leaves; now fill a bottle with water, invert, and touch the little globules gently, when they will detach themselves and pass up into the bottle, displacing the water, and may afterward be used in experimentation. Perhaps some of you, while drinking at the brook, have noted these bubbles of O on the leaves of the graceful water plants below. This is the only place in nature where you can see O free, and indeed you do not see it here, for O is a colorless, tasteless, odorless substance; what you do see is the thin sphere of water which contains it.
O is held by many substances so tenaciously that we can not liberate it; this gives us “terra firma.” Sand, and many rocks consist of O and silicon, but the greatest heat and heaviest blows can not separate them. There are materials, however, which readily yield their O. Dr. Priestly first found it by heating with a burning glass a compound known now as red oxide of mercury. The O went off, leaving the shining quicksilver.
You may repeat this historic experiment by placing the material in a test tube and heating it over an alcohol lamp.
Another substance used for this purpose is black oxide of manganese (MnO₂), but that which is now generally employed is a white salt, kept by every druggist, and usually called chlorate of potash (HClO₃).
PREPARATION OF OXYGEN FROM A MIXTURE OF POTASSIC CHLORATE (CHLORATE OF POTASH) AND MANGANESE DI-OXIDE.
Place a small amount of this, mixed with an equal quantity of the manganese, in a test tube, or flask, and heat over a flame. The O will be liberated, and may be bottled for use. A strange thing about this operation is that the MnO₂ yields none of the O, but comes out of the flask just as it went in. Such action, by mere presence, is called catalysis. We can not explain it, but have some such phenomena in social life, perhaps, when two people with an affinity for each other are having a delightful, confidential chat, and a third person joins the group, immediately producing silence—a plain case of catalysis! Having secured several jars of O we are now ready to test some of its interesting properties. Extinguish a candle and suddenly plunge it into a jar of O. It is relighted. A better way is to make a taper of waxed thread. This will keep the live coal better, and may be relighted many times. Attach to a wire a piece of charcoal bark. Ignite and place in another jar. Beautiful scintillations fill the jar, star like in form. Take a watch spring, heat one end and bend. Split a match and attach to the spring, light and place in the jar. It burns with great brilliancy.
Whittle out a little cup of chalk, or crayon, and place phosphorus in it. Touch the P with a hot wire and lower the cup, with a wire, into a jar of O. A beautiful combustion follows. In like manner sulphur may be burned, and produces a bright blue light.
A TAPER OR CANDLE BURNING IN OXYGEN.
A little ingenuity will supply all apparatus needed for these and other experiments with H and O. For example, a common pail with a wooden shelf in it two or three inches from the top makes an excellent pneumatic trough for transferring or gathering gases, and if the shelf can not be procured, two or three bricks in the pail will serve the purpose.
Before dismissing our glass of water we must remark that no matter where it may be found, in the depths of the sea or on the mountain; as a dew drop, or sparkling as spray; in lake Nyanza, or lake Chautauqua, the chemical constituents of water are just the same. Almighty care and wisdom weighs the atoms, even as “he weighs the mountains in scales and the hills in a balance.” The apparent character of water, as to color, form, hardness, saltness, and so on, is often varied by mixing with it other substances, but the changes produced are not chemical, and belong more properly to the domain of physics.
Note.—The illustrations in this article are from “The Young Chemist” of Prof. John Howard Appleton. We can heartily recommend to the members of the C. L. S. C., all of Prof. Appleton’s admirable works on Chemistry.