BY PROF. J. T. EDWARDS, D.D.
Director of the Chautauqua School of Experimental Science.

CHEMISTRY OF EARTH.

John B. Gough declares that a few kind words spoken to him, in a crisis of his life, saved him from ruin. He afterward carefully educated the orphan daughters of the gentleman who uttered those words.

“Why,” you say, “it was a little thing.” “Yes, little for him, but a big thing for me.”

The importance of many things depends upon the point of observation. To a hypothetical astronomer on a distant star, this world would be too minute for observation. In that shining pathway of the heavens, called the “milky way,” there have been discovered eighteen millions of stars, each hundreds of times larger than our earth; yet our atom in immensity is, just now, of marvelous interest to us. Indeed, it must be of interest to the highest intelligences, for such are the harmonies of God’s universe that the minutest planet is in many of its forces and laws representative of the whole. So that our world is, in a sense, both a microcosm and a cosmo.

Let us briefly consider some characteristics of the earth, from the standpoint of the chemist.

All substances have been divided into two great classes, the inorganic and organic. The latter contains two subdivisions—the vegetable and animal world. Nature thus comprises three great sub-kingdoms, the mineral, vegetable and animal.

A mineral is an inorganic body (that is, one in which no parts are formed for special purposes), possessed of a definite chemical composition, and usually of a regular geometric form. It may seem at first glance that the last part of this definition is not correct, but there is reason to believe that all mineral substances may, under favorable circumstances, assume crystalline forms. Water and air are minerals. Other liquids and gases are included in the term, but as we have had already something to say of these latter substances, we shall, for the purposes of this article, use the word earth in the popular sense; namely, inorganic matter, which at ordinary temperature is solid. All materials are classified into

ELEMENTS AND COMPOUNDS.

By an element is meant a substance which has never been resolved into parts, and conversely, one that can not be produced by the union of two or more substances. There is some difference of opinion as to their number. It is usually given as sixty-four. There are a great many compounds. Nature seems to delight in surprising us by the simplicity of the means employed in producing marvelous results. As the mind of Milton combined the twenty-six letters of our alphabet to form “Paradise Lost,” so the Infinite arranged and re-arranged the elements to form the sublime poem of creation. Fifty-one of the elements are metals, and thirteen metalloids; gold is a familiar example of the former, and sulphur of the latter. A few, like hydrogen and oxygen, are gases; two are liquids; quicksilver and bromine: the greater number exist as solids. But few of them are found native, i. e., chemically uncombined with other substances. In the fierce heat of former ages they were mixed as in a mighty crucible, and few escaped the power of affinities thus engendered. Gold and copper are sometimes found pure, but even they, more frequently than otherwise, exist fused with other substances.

Compounds are of three classes—acids, bases and salts. Sand is a specimen of the first, lime of the second, and clay of the third. Fixedness is a characteristic of mineral compounds, yet they are by no means incapable of change; certain influences come in to promote it, of which the following are the most important—heat, solution, friction and percussion.

Two gases, oxygen and hydrogen, may remain side by side for years uncombined, but a single spark will cause them to rush together with terrific energy.

If the contents of the blue and white papers in a Seidlitz powder are mixed, no chemical action follows, but if dissolved separately in glasses of water, and then poured together, a violent effervescence takes place. If a small amount of potassium chlorate and a little piece of sulphur be put together in a mortar, and then pressed by the pestle, sharp detonations follow. Dynamite, which is nitro-glycerine mixed with infusorial earth, sugar or sawdust, is quite harmless when free from acid, unless struck. The above instances illustrate the various influences that stimulate chemical combination. Almost all the crust of the earth is formed of three substances—quartz, lime, and alumina. Wherever we stand on the round globe, it is safe to say that one or all of these are beneath our feet.

QUARTZ.

This mineral comprises about one half the earth’s crust. Its symbol is SiO2, being a compound of silicon and oxygen, in the proportions indicated. It is very hard, easily scratching glass, of which it forms an important constituent, is acted upon by only one acid—hydrofluoric; this attacks it eagerly, as may be shown by the following interesting experiment: Take a little lead saucer, or in the absence of this, spread lead foil carefully over the inside of an ordinary saucer, and in this place some powdered fluor spar. This mineral is quite abundant in nature, and is always to be obtained, in the form of a powder, from dealers in chemicals. Have a pane of glass covered by a thin film of wax. Now trace upon this surface with a sharp point, anything you may desire, verse or picture. Pour into the saucer containing the fluor spar, sufficient sulphuric acid to make a paste. Place over this the plate of glass, with the waxed side down, and let it remain for twenty-four hours. Remove the wax by heating, and on the glass you will find a perfect etching, the HF having removed the silica.

The same effect may be produced in a few moments by applying to the bottom of the saucer a moderate heat. Care should be taken not to inhale the fumes, as they are highly corrosive.

Quartz can be melted at a high temperature, and may be dissolved in certain hot solutions. It is still a question in dispute, whether the numerous quartz veins found in rocks were introduced there in melted form or in solution. Probably, sometimes in one state and sometimes in the other. Any visitor to a glass manufactory can see how easily glass in a melted state is manipulated; and travelers often bring from the geysers[1] fine specimens of silica called geyserite, derived from the material held in solution in the hot water, and deposited on the edge of the “basin.”

Quartz may be classified under two varieties—the common and the rare. Sand, pebbles, many conglomerates, all sandstone rocks come under the former head. The old red sandstone described by Hugh Miller,[2] in which fossil fish are so abundant, and the new red sandstone of the Connecticut valley, famous for its bird or reptile tracks, brought to light through the labors of Dr. Hitchcock,[3] were formed of sand cemented together under pressure by the peroxide of iron. There are many beautiful varieties of the rarer forms of quartz. Not a few of these were known to the ancients, as may be seen by reading the twenty-first chapter of Revelations, where a number are mentioned in the description of the heavenly city. “The wall of it was of jasper, and the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald; the fifth, a sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.”

All of these excepting the sapphire, which is crystallized alumina, are either pure or mixed varieties of quartz, colored with some metallic oxide. One of the most beautiful forms of these precious stones is the agate, especially that kind called the onyx, which consists of a succession of opaque and transparent layers. When carved into gems, this is called the cameo. A wonderful carved cameo was in the Tiffany exhibit at the Centennial Exposition, valued at four thousand dollars. The several layers were so cut as to represent a man looking through the bars of his prison.

LIME.

Another very plentiful substance in the earth is lime. It is chiefly found in the form of three salts, the carbonate, sulphate and phosphate (CaCO3) (CaSO4) (Ca3(PO4)2), respectively. The first is familiarly known as limestone. When crystallized, it appears as marble. The shades of marble are due to the tinting of metallic oxides, and sometimes to the presence of fossils. The most beautiful marble is obtained from Carrara, Italy, which has long been famous for furnishing the material used for statues. It is pure white. Pure black marble is found in some ancient Roman sculptures. Sienna marble is yellow. Italy furnishes one kind that is red. Verd-antique is a mixture of green serpentine and white limestone, while our beautiful Tennessee marble, used so profusely in the new Capitol at Washington, is a blended red and white.

Common limestone is almost entirely the product of minute animals[4] which lived in early geologic times. Ages before the Romans drove piles into the Thames, or the first hut was erected on the banks of the Seine, these little creatures laid the foundations which underlie London and Paris. They built the rocky barriers which gave to England the name Albion, derived from the white cliffs along her shore. It is a suggestive crumb of comfort for little folk, that the great tasks in the building of our earth have been performed by the smallest creatures.

The wide distribution of limestone is shown from the fact that it is found to be an ingredient in almost all waters. It is readily dissolved, as is seen in the numerous caves which are found in limestone regions.

When limestone is heated, the carbonic anhydride[5] is expelled, leaving quicklime. All are familiar with the manifold uses of this material. United with sand, it forms a silicate of lime, called mortar, which becomes harder with age. In the old stone mill[6] at Newport, R. I., which is of unknown antiquity, the mortar in some places actually protrudes beyond the stones, showing it to be more durable than the rock itself. The catacombs of Rome were excavated in a very soft kind of limestone, called calcareous tufa.

Sulphate of lime, also known as gypsum and plaster of Paris, is widely distributed. One beautiful variety is called satin spar, and another alabaster.

Great quantities of sulphate of lime are quarried for use in the arts and for agricultural purposes. Dr. Franklin was one of the first to discover its value in connection with crops, and is said to have sown it with grain on a side hill, so that when the wheat sprang up, observers were surprised to see written in gigantic green letters, “Effects of Gypsum!” I suspect he got the hint from Dr. Beattie, who sowed seeds so that their flowers formed the name of his son, to prove to the boy the existence of a God, from evidences of design in nature.

ALUMINA—Al2O3.

This material is found both alone and in combination with silica. It forms an important ingredient in alum. Crystallized, it furnishes some of our most rare and beautiful gems, the color of which depends upon the metal combined with them.

The ruby is red, the emerald green, the topaz yellow, the sapphire blue.

Slate rocks consist largely of this material, and clay is a compound of alumina with siliceous anhydride. Among the first earthy substances utilized by man was clay. We find remains of pottery even as far back as the stone age[7]. The ingenuity of man seems to have been displayed constantly and successfully in the ceramic[8] art, the art of making pottery. Note the accounts given by Prescott, in his “Conquest of Peru and Mexico,” and the Cesnola collection of Cypriote remains[9] exhibited in the Metropolitan Museum in New York City.

History is repeating itself by renewing the ancient enthusiasm for decoration of china and earthen ware. Bricks made from clay are found to rival granite in durability, and surpass it in resistance to heat, as was proven in the great fires of Boston and Chicago. It will be observed from the symbol of alumina that it is largely composed of the metal aluminum. If this could be readily liberated from the oxygen with which it is combined, the world would be immensely enriched.

Every clay bank or clayey soil contains it in great quantities. Next to oxygen and silicon, it is the most abundant element in the earth. Note its valuable properties. It is but two and one-half times heavier than water, as bright and non-oxidizable as silver, malleable, ductile, tenacious, and can be welded and cast. Who will lay the world under obligation by doing with alumina what has been done with iron ores, cheaply liberate the oxygen?

In this brief enumeration of earth materials, we have intentionally omitted the forms of carbon. They constitute no insignificant portion of the earth’s crust, but belong to the class of organic substances. We introduce, however, an illustration showing one of the shapes in which is cut the diamond—that most costly of all forms of matter,—crystallized carbon.

THE COMMON METALS.

First in importance is iron. The fact already mentioned that its oxide is the most common coloring matter in the mineral world will also indicate its wide dissemination.

Trap rock, gneiss, even granite, sands, clays and other rocks all borrow tints from this source. Iron is never found native except in meteors. It exists most abundantly in the form of three ores, the composition of which is as follows:

Black or magnetic oxide (Fe3O4), red oxide (Fe2O3), hydrated sesquioxide (Fe2O33H2O). From all of these the oxygen is removed in a blast furnace, by the use of some form of carbon. As thus prepared, it is called cast-iron. Two other varieties are employed in the arts, wrought iron and steel. The last differs from the first in having less carbon, and from the second in having more. The general properties of this material are too well known to require description here. A single property of this substance alone has marvelously affected the commerce of the world; that is, the power first discovered in magnetic iron ore, of attracting iron, and pointing northward. The first compass, it is said, consisted of a piece of this metal placed on a cork floating on water.

Copper seems to have been one of the few metals known to barbarous peoples. It is found pure, and in combination. Specimens obtained from the Lake Superior region, in mines worked by the mound builders,[10] have led some to believe that they possessed the art of hardening copper. Malachite is a carbonate of copper, of a beautiful mottled green color, and is made into elegant ornaments. Some magnificent specimens were in the Russian exhibit at the Philadelphia Exposition. It is found in great perfection in the Ural mountains.

Tin is obtained from its binoxide (SnO2). It was known to the ancients. Some historians claim that the Phoenicians procured it long before the time of Christ, from the mines of Cornwall, England. Until recently our country has seemed to be destitute of this valuable metal. Reports now indicate that Dakota is destined to supply this deficiency. It is a handsome metal, but little affected by oxygen, and capable of being rolled into thin sheets.

Zinc is found in two different ores: red oxide (ZnO) and zinc blende (ZnS), from which it can be separated by smelting, in much the same manner as we obtain iron.

Lead constitutes the fifth of the common metals which are preËminently useful. It is found in the sulphide of lead (PbS), the sulphide being expelled by roasting the ore. It forms numerous compounds, some of which are of great value. For example, lead carbonate (PbCO3), the white lead which furnishes the most valuable ingredient of all paints.

NOBLE METALS.

These are so called because they retain their brilliancy and are not easily affected by other substances. Three of them are specially important: gold, silver and platinum. Gold is mentioned in the second chapter of Genesis: “and the gold of that land is good.” Although constituting an inconsiderable part of the earth, it is much more widely distributed than many suppose, but often exists in such small quantities that its production is not profitable.

Australia and California are the gold lands. It is found principally in three situations: in sands which have been washed from the mountains, in little pockets in the rocks, and in veins of quartz. From the first it is separated by simply washing away the lighter materials, from the last situation it is procured by quarrying the rock, crushing it with stamping machines, then washing with water to remove the pulverized quartz, and gathering up the powdered gold with quicksilver. The mercury is removed by vaporizing. Gold is nineteen times heavier than water, extremely ductile, and the most malleable of all substances. Silver is abundant in the mountains of the west. It is usually found in the form of black sulphide (Ag2S) or horn-silver (AgCl). When unpolished it is perfectly white, and is called dead or frosted silver. All are familiar with the properties of this attractive metal. Just now its producers in Colorado seem to fear its displacement from its important position in the coinage of the country. In nitrate of silver (AgNO3) we have a material that perpetuates the faces of our friends, many a goodly landscape, and marvelous picture.

Platinum stands at the extreme limit of the elementary world in point of weight, being twenty-one and fifty-three hundredths times heavier than water. Russia has almost a monopoly of the production of this metal. It is about the value of gold, and to the chemist is of immense importance, on account of its high point of fusibility, which is over 4,000°. It is so ductile that it can be drawn out into wire so fine as to be invisible to the naked eye. This microscopic wire is used for centering the field of view in the finest telescopes.

EARTH’S CRUST AND CENTER.

Our earth is called “terra firma;” it is regarded as the very embodiment of stability, but every waving outline, every hill and mountain peak, not less than the rumbling of the earthquake, and the bursting forth of volcanic fires, indicate that it has been, and may again be, the scene of mighty disturbances. Indeed, upon reflection, one wonders that we can live on it at all. The temperature of the earth increases one degree for every fifty feet as we approach the center. At this rate, at the depth of fifty miles the heat would be sufficient, according to Humboldt,[11] to melt the hardest rocks. Fifty miles is one one-hundred and sixtieth of the earth’s diameter. It thus appears that if we should have a globe three feet in diameter full of molten liquid, surrounded by a covering of infusible material one eighth of an inch in thickness, that film of solid matter would represent the earth’s crust. Think of it!

A “LEAD TREE.”

Ex.—Place in a glass a dilute solution of acetate of lead; suspend in it a strip of zinc. Some of the lead will be precipitated in crystals upon the zinc. This is caused by the zinc taking a portion of the acetic acid, and thus forming a new compound called zinc acetate, thereby liberating some of the lead.