SILICON.

Silicon may well be considered important on account of its _quantity_ in the earth, if on no other. In an earlier chapter it has been shown that oxygen exists in our globe—including its atmosphere and its oceans—in an amount equal to about one-half of the weight of the whole. Now silicon exists in a quantity equal to about one-fourth of this entire weight. In the earth however, neither of these substances exists in the uncombined form. These facts seem to involve as a necessary consequence that they exist in the earth, to a large extent, combined with each other; indeed this is found to be the case. The principal earthy matter of our planet is the compound of silicon and oxygen, existing either alone in the form of sand, quartz crystal and similar minerals, or else in combination with other well-known abundant earth materials, such as oxides of calcium, magnesium and aluminum. It has already been stated that carbon is the characteristic element of animal and vegetable matters; so silicon is the characteristic element of mineral matters. Thus granite and similar archaic rocks contain approximately twenty-five per cent of silicon.

In nature, silicon performs its important office as a constituent of rock material, with a fitness that is referable largely to the high degree of stability possessed by most of its compounds. The permanence of the materials of the earth’s surface under the influence of heat, and water, and frost, and similar agencies is an illustration of this principle.

_Silicic oxide_ (SiO2), occurs on our globe in many different forms of which diatomaceous earth and rock crystal may be mentioned.

Diatomaceous earth is a powdery material found in abundant deposits in many parts of the world. Its characteristic structure, when examined under the microscope, reveals its nature; then it is seen to be made up of the shells of minute vegetable organisms called diatoms. These assume a great many beautiful forms, and some of them are checkered all over with markings of such extreme fineness that they have been used as test objects for trying the resolving power of the objectives of microscopes. This kind of earth is employed, as has already been stated, in the preparation of dynamite.

microscope.]

Quartz sometimes occurs in colorless transparent masses of great beauty and clearness called rock crystal. The amethyst is the same substance slightly colored by compounds of the metal manganese, while quartz exists of a variety of other shades, in some of which it is prized as a gem. Quartz generally assumes forms of a hexagonal tendency: they are often hexagonal prisms terminated by hexagonal pyramids.

Quartz and the finer and purer varieties of sand are used largely in the manufacture of glass. The silicic oxide here displays what may be expressed as its acid tendencies; for in the manufacture of glass it is fused with sodic carbonate, and then the silicic oxide displaces the carbon dioxide from the sodic carbonate; as a result there is formed what must be regarded as a true salt, or a mixture of salts, that in the simplest kind of glass may be termed _sodic silicate_.

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_Closing Words._ The course laid out in the preface is now terminated with silicon, as there planned. From scientific considerations, this is a natural ending; it seems to be appropriate on another account also. After the reader has been carried, in thought, among the various gaseous elements, that make up atmosphere and oceans, it seems suitable that we should say farewell to him upon the discussion of that element that may be called the characteristic material of our solid earth.

INDEX.

Abel, F. A., 182 Acid, Boric, 157 ——— Nitric, 35, 168 ——— Sulphuric, 35, 37, 152 ——— Chlorohydric, 33, 190 ——— Phosphoric, 192 Affinity, Chemical, 44, 46-52 Alizarine, 226 Alkali Trade, 94, 106 Allotropism, 190 Amethyst, 229 Ammonia, 166, 174, 225 Anhydride, 151 Anhydrite, 146 Anthracene, 226 Antimony, Sulphide of, 148 Apatite, 188, 189 Arsenic, Sulphide of, 148 Atom, 41, 42 Atomic Theory, 52 Atmosphere, 170

Bacon, Roger, 178 Balard, 100 Balloons, 74 Barilla, 107 Benzole, 227 Berthollet, 94 Berzelius, 24 Beverages, effervescing, 219 Binary Compounds, 32 Biot, 80 Black, Joseph, 61, 63, 76 Bleaching-Powder, 93 Blende, 146 Blowpipe, Compound, 129 Bone-Ash, 187 Borax, 157 Boron, 157 Boussingault, 217 Brandt, 187 Bromine, 100

Carbon, 197 ——— Dioxide, 173, 216 ——— Monoxide, 215 Cavendish, Henry, 60 Charcoal, 197 Chemistry, Scope of, 7, 9 Chlorine, 85 Cinnabar, 146 Coal, 201 Coal-tar, 226 Coke, 226 Compounds, 32 ——— Number of, 8, 9 ——— Organic, 221 Copper, Sulphate of, 51 Cotton, 181 Courtois, 108 Current, Galvanic, 64

Daguerre, 103 Dalton, John, 52, 56 Davy, Humphry, 60, 86, 108 De Rozier, 78 Diamond, 203 Diatoms, 185, 228 Diffusion, 69 Döbereiner, 70 Dynamite, 183, 185

Earth’s Crust, Composition of, 15 Elements, Chemical, 9, 12, 14, 28 ——— Names and Symbols of, 19, 23 Equivalence, 48, 72 Ethylene, 227 Explosives, 177

Fertilizers, 188 Fluorine, 112 Fireworks, 180 Fulminates, 181

Galena, 146 Gas, 63 —— Illuminating, 221 Gas-Carbon, 226 Gay-Lussac, 80 Glaisher and Coxwell, 81 Glass, 229 Glycerine, 184 Granite, 228 Graphite, 201 Gun-Cotton, 181 Gunpowder, 177

Haüy, 15 Heat, unit of, 71 Hydrogen, 58

Iodine, 105 Iron, Sulphide of, 146

Janssen, 83

Kelp, 107

Lamp-Black, 200 Larderel, 160 Lavoisier, 19, 21, 118 Lead, 34 ——— Sulphide of, 146, 148 Leblanc Process, 94 Liebig, 101 Light, Calcium, 131 ——— Electric, 211, 226 Limestone, 209 Lithium, 30

Marble, 209 Mass, 39 Matches, 192 Mayow, 121, 163 Metals, 28, 29 ——— Names of, 16, 20 Mercury, 30 ——— Sulphide of, 146 Moisture in the Air, 173 Molecule, 40 Montgolfier, 74 Murdoch, 222

Nobel, 185 Nitrogen, 162 Nitroglycerine, 184 Nomenclature, Chemical, 19, 20, 32, 33, 37 Non-metal, 30

Oxide, Ferroso-ferric, 66 Oxygen, 117 ——— Abundance of in the earth, 14, 16

Palladium, 70 Pelletier, 89 Petroleum, 209 Photography, 93 Phosphorus, 187 Phosphorus Necrosis, 189 Phosphuretted Hydrogen, 191 Potassic Chlorate, 123 Priestley, Joseph, 64, 118, 163 Puymaurin, 115 Pyrites, 146

Quartz, 228

Roe, 89 References, Reading, 10, 17, 24, 27, 31, 38, 45, 56, 73, 84, 98, 111, 116, 133, 156, 161, 186, 196, 214 Rutherford, 163

Scheele, 85, 114, 118, 162, 187 Silicon, 228 ——— Abundance of, 16 Sodium, 67 Sugar, 41 Sulphur, 142 ——— Dioxide, 33, 149 ——— Trioxide, 33, 151 Sulphuretted Hydrogen, 147

Ternary Compounds, 34

Van Helmont, 63 Varech, 107 Vitriol, Oil of, 152

Water, 127, 134 Weight, Atomic, 17

Zinc, 68 —— Sulphide of, 146, 149