The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers - Unknown

Caution.—In diluting H₂SO₄ add the acid to the water; for the evolution of heat from the process will cause the water to boil, and reversing this process will cause the liquid to boil over and possibly result disastrously.

(19) Impurity in H₂SO₄.—Commercial sulphuric acid contains PbSO₄ as an impurity. This gives it the colored appearance, plumbic sulphate being soluble in strong sulphuric acid.

(20) H₂S.—Sulphuretted hydrogen is somewhat soluble in water, slightly poisonous, and is a reducing agent.

(21) Carbonic Acid.—H₂CO₃ does not exist as an acid. We infer its existence from the presence of its salts. Na₂CO₃ + 2HCl = 2NaCl + H₂CO₃, but the H₂CO₃ is so unstable that it breaks up at once into H₂O and CO₂.

(22) Test for a Carbonate.—To test for a carbonate, treat the substance with an acid; CO₂ is formed; pour the gas into a solution of lime-water, and a white insoluble precipitate is formed, CaCO₃.

TABLE OF ALL THE KNOWN CHEMICAL ELEMENTS

The Chemical Elements are the simplest known constituents of all compound substances. Chemists regard them as elements or elementary substances only when they have been proved to be not compound. The elements are somewhat arbitrarily divided into metals and non-metals, the former constituting by far the larger class. Several elements occupy positions on the border line. Below is a list of the elements at present known with certainty, and of their atomic weights as fixed by the various kinds of evidence obtained by very numerous, and in many cases varied, experiments. The values are all referred to oxygen as standard with atomic weight 16, and are those adopted, for 1910, by the International Commission on Atomic Weights. The standard O = 16 has been pretty generally adopted by chemists as, upon the whole, more satisfactory than H = 1.

Abbreviations.—At. wt., atomic weight; S. G., specific gravity; M. P., melting point; B. P., boiling point; C. T., critical temperature.

Name and Important Data	Occurrence, Preparation and Properties	Compounds and Chief Uses
Aluminum. Symbol Al. At. wt. 27.1. Valence III. S. G. 2.7. M. P. 658°. B. P. 1800°.	Occ.—cryolite AlF₃, 3NaF; bauxite, impure Al(OH)₃; in feldspars, micas and clay; emery, ruby, sapphire (Al₂O₃). Prep.—com’l, by electrolysis of Al₂O₃, from bauxite, dissolved in cryolite, water-power usually furnishing the electrical energy. Prop.—silver-white, ductile, malleable at 120°, tensile strength (wrought) 16 tons per sq. in. A better conductor of electricity, weight for weight, than copper. Molten metal not mobile enough to make castings. It turns badly in the lathe. Acted upon by dil. hydrochloric acid, slowly by sulphuric, but not by nitric or the acids occurring in foods. Soluble in alkaline hydroxides. The tarnishing action of moist air soon comes to an end as the tarnish acts as an adherent protective coating.	Used for cooking utensils, boat-building, military accouterments and small articles requiring lightness and strength; for electric leads. The powdered metal is used as a body for paint; and its mixture with ferric oxide, called thermite, is used for producing very high temperatures (up to 3700°C.) for welding rails, etc. Many metals are reduced from their oxides by means of Al, hence its use in casting steel. Aluminum bronze (10% Al), rolled, has tensile strength of 40 tons per sq. in. Its sulphate forms alums, e.g., KAl(SO₄)₂, 12H₂O, common alum.
Antimony. Symbol Sb. At. wt. 120.2. Valence III. and V. S. G. 6.6. M. P. 630.7°. B. P. 1440°.	Occ.—free, and as stibnite (Sb₂S₃). Prep.—roasting stibnite gives Sb₂O₄, which is then reduced by heating with carbon. Prop.—white, brittle, crystalline metal. Its alloys expand on solidification, and therefore give very sharp castings, e.g., for type. It does not tarnish, but may be burned in air, and unites directly with the halogens.	The metal is a constituent of the alloy type metal, Britannia metal and Babbitt metal (used for bearings). Its oxide (Sb₂O₃) is both basic and acidic. The trichloride, butter of antimony (SbCl₃), is easily hydrolyzed. Tartar emetic (SbOKC₄H₄O₆) is used in medicine and in dyeing.
Argon. Symbol A. At. wt. 39.86. Valence nil. Density 39.9 (oxygen = 32). B. P. -186°. M. P. -190°.	Present in the air 0.94% by volume. To isolate, air is freed from CO₂ by soda-lime, water by P₂O₅, oxygen by red-hot copper, nitrogen by magnesium and calcium. From the residual mixture argon is obtained by fractional distillation.	Forms no compounds, hence its name—does no work. Is a monatomic gas and is identified by its characteristic spectrum seen by examining the light emitted when the gas is placed in a vacuum tube at low pressure and sparked. More soluble in water than nitrogen, 100 vols. water dissolving 4 vols. argon under ordinary conditions.
Arsenic. Symbol As. At. wt. 74.96 Valence III. and V. S. G. 5.7. B. P. 616° (sublimes). M. P. about 800° (under pressure).	Occ.—free, as arsenical pyrites (FeSAs), as orpiment (As₂S₃) and as realgar (As₂S₂). Prep.—by heating arsenical pyrites, FeSAs—FeS + As. Prop.—a steel-gray, dully-metallic and crystalline element classed as a metalloid because intermediate between metals and non-metals. Its vapor has a density corresponding to As₄ at 644°, and to As₂ at 1700°. It burns in air and unites directly with the halogens, sulphur and with many metals.	Used for hardening lead for shot. All its compounds are poisonous. White arsenic (As₂O₃) is partly basic, forming a chloride and partly acidic, forming arsenites. Scheele’s green (CuHAsO₃) is a pigment dangerous in wallpapers. Traces of arsenic are detected by Marsh’s test in which the intensely poisonous arsine (AsH₃) is formed.
Barium. Symbol Ba. At. wt. 137.37. Valence II. S. G. 3.8. M. P. 850°.	Occ.—as barytes or heavy-spar (BaSO₄), and as witherite (BaCO₃). Prep.—by electrolysis of the fused chloride. Prop.—a silver-white, lustrous, malleable metal harder than lead. Like calcium, it acts slowly on water to give barium hydroxide and hydrogen. The vapors of its compounds impart a green color to the Bunsen flame.	The peroxide (BaO₂) is used in the manufacture of oxygen and of hydrogen peroxide. The nitrate and chlorate in pyrotechny to give green fires. The sulphate as the body for a permanent white paint and for filling glazed paper. All soluble compounds are poisonous.
Bismuth. Symbol Bi. At. wt. 208.0 Valence III. (and V.). S. G. 9.8. M. P. 270.9°. B. P. 1420°.	Occ.—free and as trioxide (Bi₂O₃) and trisulphide (Bi₂S₃). Prep.—the ore is roasted and then heated with charcoal and metallic iron (to remove traces of sulphur.) Prop.—an exceedingly brittle, crystalline shining metal, white with a tinge of pink. Bismuth expands on solidification. It does not tarnish, but can be burnt in air. Dissolves in oxygen acids.	Used for making fusible alloys, e.g. Wood’s metal, M. P. 60.5°, which are used in plugs of fire sprinklers and boiler safety valves, and for taking casts. The oxynitrate is used in medicine and as a cosmetic.
Boron. Symbol B. At. wt. 11.0. Valence III. S. G. (amorph.) 2.4; (cryst.) 2.5. B. P. 3500° (sublimes).	Occ.—as boric acid (H₃BO₃), borax (Na₂B₄O₇, 10H₂O), colemanite (Ca₂B₆O₁₁, 5H₂O). Prep.—amorphous boron by reducing B₂O₃ with Mg. Impure cryst. boron by reducing B₂O₂ with excess of Al. Prop.—amorphous boron is a greenish-black powder that burns in air at 700°, forming B₂O₃ and also BN. It is oxidized, by hot conc. sulphuric or nitric acids, to boric acid.	The compounds are analogous to those of silicon. Borax is used as a flux, and, in solution, as a mild alkali on account of its hydrolysis. Boric acid is used as a weak antiseptic and preservative.
Bromine.[884] Symbol Br. At. wt. 79.22 Valence I. S. G. 3.1 B. P. 59°. M. P. -7.3°.	Occ.—in seawater as alkali bromide, and in the upper layers of salt deposits as sodium and magnesium bromide. Prep.—by treatment of the brines with sulphuric acid and manganese dioxide, or else with chlorine. Prop.—a dark red liquid, smelling like chlorine, whose vapor irritates eyes, throat and nose. Dissolves in thirty parts of water (bromine water). Combines directly with most other elements, but less vigorously than chlorine.	Potassium bromide is used in medicine, silver bromide in photography. Bromine is used in course of the preparation of organic dyes.
Cadmium. Symbol Cd. At. wt. 112.40. Valence II. S. G. 8.6. M. P. 320.9°. B. P. 766°.	Occ.—in association with the zinc ores, as carbonate and sulphide. Prep.—in the distillation of impure zinc, the cadmium comes over in the first portions. Prop.—a silver-white metal, more ductile and malleable than zinc. It burns in air, and is attacked by dilute acids.	All the compounds are poisonous, and little ionized. The sulphide (CdS) is the basis of “cadmium yellow.” The iodide is used in medicine.
Caesium. Symbol Cs. At. wt. 132.81. Valence I. S. G. 1.9. M. P. 26.3°. B. P. 670°.	Occ.—in certain micas, and in the ashes of certain plants. Prep.—by heating the hydroxide (CsOH) with magnesium. Prop.—a white, silvery metal resembling potassium. It is one of the most active of metals, and decomposes water violently.	The compounds are characterized by giving, especially, two bright lines in the blue of the spectrum (caesius sky-blue).
Calcium. Symbol Ca. At. wt. 40.07. Valence II. S. G. 1.55. M. P. 803°.	Occ.—as carbonate (Iceland spar, calcite, aragonite, marble, chalk, limestone), sulphate (gypsum), phosphate (apatite), fluoride (fluor spar), and as complex silicates in great variety (feldspars, pyroxenes, amphiboles, etc.). Prep.—by electrolysis of the fused chloride. Prop.—a white crystalline metal, harder than lead, that can be cut, drawn, rolled and turned. It attacks water, and burns in the air at a red heat forming the oxide (CaO) and the nitride (Ca₃N₂). It unites with hydrogen to CaH₂, whose action on water is a source of hydrogen for balloons.	Calcium oxide (quicklime) is used for mortar and to remove hair from hides. The hydroxide [Ca(OH)₂] mixed with sand forms mortar; its solution is limewater. Plaster of paris, a less hydrated sulphate, takes up water on setting to form CaSO₄, 2H₂O. The phosphates are fertilizers. Bleaching powder is CaClOCl and calcium carbide is CaC₂. Common glass contains silicates of calcium and sodium.
Carbon. Symbol C. At. wt. 12.005. Valence IV. S. G. diamond 3.5: graphite 2.3: amorphous 1.9 M. P.—not realized; estimated at 4400°.	Occ.—as diamond and graphite, in the free state; in combination with hydrogen as petroleum, with oxygen as carbon dioxide in the air, with these and other elements as coal, and in plant and animal tissues; and as many carbonates. Prep.—by dry distillation of wood or coal, yielding charcoal and coke respectively. Prop.—diamond is crystalline and the hardest of minerals, the dark-colored “bort” being used for cutting and grinding. Graphite has a black metallic luster, is crystalline and may be scratched by the finger-nail. Charcoal is amorphous, and possesses the power of absorbing gases and also coloring matters. All three forms burn in oxygen to produce carbon dioxide.	The carbon compounds form the subject of “Organic Chemistry.” Carbon dioxide results from the burning of coal, coke, wood, oil or illuminating gas; from fermentation and decay, which are slow burnings; and is exhaled in the breath. Carbon monoxide, arising from recently-stoked fires, is an exceedingly poisonous gas.
Cerium. Symbol Ce. At. wt. 140.25. Valence III., IV. (and VI.). S. G. 6.8; M. P. 623°.	Occ.—as silicate in cerite, along with Nd, Pr and La; also in monazite sand. Prep.—by electrolysis of the fused chloride. Prop.—a metal with the color and luster of iron, like tin in hardness, and very ductile and malleable. Burns in air more easily and brightly than magnesium.	Welsbach incandescent gas mantles contain one per cent of cerium dioxide, CeO₂.
Chlorine. Symbol Cl. At. wt. 35.46. Valence I. (and VII.). S. G. (liquid) 1.3. M. P. -101°. B. P. -33.6°. C. T. +146°.	Occ.—in seawater as chlorides of the alkalis and alkaline earths, and as like compounds in salt deposits. Prep.—by electrolysis of alkali chloride, fused or in solution; or by the action of manganese dioxide on hydrochloric acid. Prop.—a greenish-yellow gas of characteristic odor, with a violent action on the respiratory tract. Unites directly with all elements save oxygen, nitrogen and the argon family. Displaces bromine and iodine from bromides and iodides, and substitutes hydrogen in organic compounds.	The gas is used in extracting gold and in preparing bleaching and disinfecting agents. In presence of water it bleaches many coloring matters. Forms chlorides (as NaCl, HCl, CaCl₂), hypochlorides [as solution of Ca(OCl)₂], chlorates (as KClO₃, used for matches and in pyrotechny), and perchlorates (as KClO₄).
Chromium. Symbol Cr. At. wt. 52.0. Valence II., III. and VI. S. G. 6.6. M. P. 1515°. B. P. 2200°.	Occ.—as chromite [Fe(CrO₂)₂]. Prep.—by reducing Cr₂O₃ with aluminum filings. Prop.—a steel-gray, lustrous, brittle and very hard metal. At high temperatures it burns in air to green Cr₂O₃. It is attacked by dilute sulphuric or hydrochloric acid, but not by nitric acid.	The alloy ferrochromium is used in steel-making. Chrome green, the pigment, is Cr₂O₃. Chrome yellow is PbCrO₄. Bichromates (as K₂Cr₂O₇) are used in photo-processes, tanning and dyeing and as oxidizing agents, e.g., in batteries.
Cobalt. Symbol Co. At. wt. 58.97. Valence II. and III. S. G. 8.6. M. P. 1490°.	Occ.—as smaltite (CoAs₂) and cobaltite (CoAsS). Prep.—by igniting the oxide in hydrogen. Prop.—a white, magnetic, malleable metal, less tenacious than iron. By exposure it turns pinkish. It is less active chemically than iron.	Its intensely blue silicates are used in coloring porcelain and constitute the pigment smalt.
Columbium (Niobium) Symbol Cb. At. wt. 93.5. Valence I., II., IV. and V. S. G. 12.7. M. P. 1950°.	Occ.—in the mineral columbite. Prep.—by reduction of CbO₂ by paraffin. Prop.—a light-gray, malleable and ductile metal, as hard as wrought iron, which is not affected by acids, even by aqua regia.	The hydride (CbH) burns in air. The compounds occur with those of tantalum, which they closely resemble.
Copper.[885] Symbol Cu. At. wt. 63.57. Valence I. and II. S. G. 8.9. M. P. 1083°. B. P. 2310°.	Occ.—free, as cuprite (Cu₂O), copper glance (Cu₂S), chalcopyrite (Cu₂S, Fe₂S₃), malachite [CuCO₃, Cu(OH)₃]. Prep.—after removal of iron and sulphur, the oxide is reduced by heating with carbon. It is refined electrolytically. Prop.—a red, lustrous, very ductile and malleable metal of tensile strength fourteen tons per square inch, second only to silver in electrical conductivity. In ordinary air it gradually becomes coated with basic carbonate. In absence of air, nitric acid alone among the dilute acids attacks it, but in presence of air even the acids found in foodstuffs can dissolve it.	The metal is used for coins, electroplating, electric leads, roofing, cooking vessels and for making alloys, such as brass, bell and gun metals, German silver and the bronzes. The soluble compounds are poisonous, and are therefore used as germicides in agriculture. Blue vitriol is CuSO₄ 5H₂O; the basic acetate is verdigris.
Dysprosium. Symbol Dy. At. wt. 162.5. Valence III.	Occ.—in monazite, gadolinite, etc. Prep.—not yet isolated. Prop.—the oxide dysprosia, along with three other rare earths, constitutes erbia.	The salts are green or yellow in color and show characteristic absorption bands.
Erbium. Symbol Er. At. wt. 167.7. Valence III. S. G. 4.8.	Occ.—same as for dysprosium. Prep.—not yet isolated pure. Prop.—crude erbia has been separated into erbia, holmia, thulia, and dysprosia.	The salts are rose-colored, and show characteristic absorption spectra.
Europium. Symbol Eu. At. wt. 152.0. Valence III.	Occ.—in monazite and other rare minerals. Prep.—not yet isolated. Prop.—this element so closely resembles samarium that the analytical separation of the two is difficult.	The salts are pinkish and show a faint absorption spectrum.
Fluorine. Symbol F. At. wt. 19.0. Valence I. S. G. (liquid) 1.11 at -187°. M. P. -223°. B. P. -187°.	Occ.—as cryolite (AlF₃, 3NaF), fluor spar (CaF₂) and very widely elsewhere in small quantities. Prep.—by electrolysis of dry hydrogen fluoride at -23°. Prop.—a pale yellowish-green gas that unites with every element excepting oxygen and the argon family. It rapidly displaces oxygen from water or chlorine from hydrogen chloride.	Hydrogen fluoride is used for etching glass and in silicate analysis. Silver fluoride is soluble and calcium fluoride insoluble, in contrast with the other halides of these metals.
Gadolinium. Symbol Gd. At. wt. 157.3. Valence III.	Occ.—in gadolinite and samarskite. Prep.—not yet isolated. Prop.—This element closely resembles terbium in its compounds.	The salts are colorless and show no absorption bands.
Gallium. Symbol Ga. At. wt. 69.9. Valence III. S. G. 5.9. M. P. 30.1°.	Occ.—in zinc blende and in bauxite. Prep.—by electrolysis of a suitable solution of its salts. Prop.—a bluish-white, tough metal that may be cut with a knife. Like aluminum, it is soluble in hydrochloric acid and in caustic alkali, but not in nitric acid.	It forms two chlorides (GaCl₃ and GaCl₂) which yield spark spectra very characteristic of gallium.
Germanium. Symbol Ge. At. wt. 72.5. Valence II. and IV. S. G. 5.5. M. P. 958°.	Occ.—in the rare mineral argyrodite. Prep.—by the reduction of the dioxide (GeO₂) by carbon. Prop.—a grayish-white, brittle, lustrous metal, insoluble in hydrochloric acid. It combines directly with the halogens.	The close relation of this element to carbon and silicon is shown in the compound germanium chloroform (GeHCl₃).
Glucinum (or Beryllium). Symbol Gl. At. wt. 9.1. Valence II. S. G. 1.7. M. P. below 960°.	Occ.—in beryl [Al₂Gl₂(SiO₃)₆]. Prep.—by electrolysis of the fused double fluoride, GlF₂, 2KF. Prop.—a hard, white metal that tarnishes when heated in air, and is soluble in dilute acids when powdered.	Its hydroxide [Gl(OH)₂] is feebly acidic as well as basic, thus resembling the hydroxide of zinc. Emerald is beryl colored green by chromium.
Gold. Symbol Au. At. wt. 197.2. Valence I. and III. S. G. 19.32. M. P. 1062.4°.	Occ.—chiefly free, but also as telluride; many specimens of iron are auriferous. Prep.—from gold-bearing sands by washing away the lighter material, and dissolving the gold from the residue by mercury, which is subsequently separated from the gold by distillation. Quartz ores are pulverized in stamping mills, and the powder is then carried by water over amalgamated copper plates on which the gold collects. Prop.—a soft, bright-yellow metal, easily scratched by the knife, an excellent conductor of heat and of electricity. The most ductile and the most malleable of all the metals. Chemically, gold is rather inert, and is not attacked by the oxygen of the air, by hydrogen sulphide, nor, indeed, by any single one of the common acids. It is attacked by fused alkalis, yielding aurates, and by aqua regia, yielding chlorauric acid (HAuCl₄).	Pure gold is called 24-carat gold. American, French and German gold coins are 21.6 carat, while British sovereigns are 22 carat, the balance in all these cases being copper. Jewelry is made in 18, 14, 9, etc., carat gold, the addition of copper increasing the hardness and rigidity. Sodium chloraurate (NaAuCl₄) is used for “toning” in photography, while potassium auricyanide [KAu(CN)₄] is used in electro-gilding.
Helium. Symbol He. At. wt. 4.00. Valence 0. S. G. (liquid at B.P.) 0.122. M. P. -272°. B. P. -268.7°.	Occ.—in air to the extent of one to two volumes per million; also occluded in certain minerals. Prep.—neon and helium are boiled off crude argon, and the neon solidified by cooling. Prop.—the lightest gas after hydrogen, transparent, odorless and colorless, very inert, forming no compounds with other elements.	It is one of the decomposition products of certain other (radio-active) elements.
Holmium.[886] Symbol Ho. At. wt. 163.5. Valence III.	...	...
Hydrogen. Symbol H. At. wt. 1.008. Valence I. S. G. (liquid at B.P.) 0.07. M. P. -259°. B. P. -252.5°.	Occ.—in air to the extent of one volume per 20,000 volumes air; combined, in water (11.19% by weight) natural gas, petroleum and all animal and vegetable bodies. Prep.—by treating zinc with hydrochloric or sulphuric acid; by electrolysis of water. Prop.—the lightest gas, transparent, odorless and colorless, soluble in water (2 volumes in 100 volumes water under everyday conditions), in platinum, in palladium (502 volumes in 1 of Pd). Burns in air and in chlorine, and unites with many of the other elements.	Its two oxides are water (H₂O) and hydrogen peroxide (H₂O₂), the latter of which is used in solution as a bleaching agent. Every acid contains hydrogen as an essential constituent. Its compounds with carbon and other elements number over 100,000. Hydrogen gas is used for the oxyhydrogen flame and for filling balloons.
Indium. Symbol In. At. wt. 114.8. Valence III. and I. S. G. 7.3. M. P. 155°.	Occ.—in zinc blende (ZnS). Prep.—electrolytically from solutions of its salts. Prop.—a white metal, malleable and softer than lead.	Its compounds color the nonluminous gas flame blue and show a characteristic blue line in the spectrum.
Iodine. Symbol I. At. wt. 126.92. Valence I., V. and VII. S. G. 4.94. M. P. 114°. B. P. 184°.	Occ.—in the ocean, in certain seaweeds, and in Chili saltpeter, always in the combined state. Prep.—from iodides by displacement of their iodine by chlorine. Prop.—a dark gray, brittle solid with a metallic luster. Its vapor is violet, as are its solutions in chloroform and in carbon bisulphide. It requires over 5,000 parts of water for its solution. Combines directly with many elements, but is much less active than chlorine and bromine.	Its tincture is used in medicine as a counterirritant. Potassium iodide (KI) and iodoform (CHI₃) likewise find application in medicine. The alkyl iodides (e.g., C₂H₅I) are much used in synthetic organic chemistry.
Iridium. Symbol Ir. At. wt. 193.1. Valence III. and IV. S. G. 22.4. M. P. 2300°.	Occ.—along with platinum. Prep.—by a complex series of operations from platinum ores. Prop.—a white metal, brittle when cold, and very hard. It is attacked by fused alkalies, but not by aqua regia.	It is used for pointing gold pens. Its alloy with nine parts of platinum is used for standard meter bars on account of its inalterability.
Iron. Symbol Fe. At. wt. 55.85. Valence II. and III. S. G. 7.86; pig 7.03 to 7.73. M. P. 1515°. B. P. 2450°. wrought 1100°- 1500°. steel 1375°. gray pig 1275°. white pig 1075°.	Occ.—as magnetic oxide (Fe₂O₄), hematite (Fe₂O₃), limonite (2Fe₂O₃, 3H₂O), siderite (Fe₂CO₃), which are important ores; iron pyrites (FeS₂); in rocks as complex silicates, and in plants and animals. Prep.—pig iron is prepared in the blast furnace by reduction of the ore by means of carbon monoxide in presence of a suitable flux. From pig iron, wrought iron is obtained by puddling, and steel by the Bessemer, Siemens-Martin or other process. Prop.—a white, malleable, ductile, magnetic metal, unchanged in dry air or air-free water, but rusting in moist air. Easily attacked by dilute acids, but not by fused alkalies. Cast iron contains 2 to 5% of carbon and other impurities, and is hard and brittle. Wrought iron contains less than 0.2% of carbon, and is softer and tougher, with a tensile strength of 22 to 25 tons per square inch. Steel contains from 0.2 to 1.5% of carbon, is permanently magnetic, may be tempered, and possesses tensile strength up to 100 tons per square inch.	The metal is used as a structural material, for rails, machinery, tools, etc. Jeweler’s rouge and Venetian red consist of the oxide (Fe₂O₃). Rust is chiefly the hydrated oxide (FeO, OH). Hammer scale and loadstone have the composition Fe₃O₄. Ferric chloride (FeCl₃), ferrous iodide (FeI₂) and other iron compounds are used in medicine. Green vitriol (FeSO₄, 7H₂O) is used in making ink, and in dyeing. Potassium ferrocyanide [K₄Fe(CN)₆] is used for making Prussian blue, potassium cyanide, etc.
Krypton. Symbol Kr. At. wt. 82.92. Valence 0. S. G. (Liquid at B. P.) 2.2. M. P. -169°. B. P. -152°.	Occ.—in minute quantity in the air. Prep.—from crude argon by fractional distillation. Prop.—an inert, colorless, odorless gas, resembling, but denser than, argon.	It forms no compounds, and is identified by its characteristic spectrum.
Lanthanum. Symbol La. At. wt. 139.0. Valence III. and V. S. G. 6.15. M. P. 810°.	Occ.—as lanthanite [La₂(CO₃)₃, 8H₂O]. Prep.—by electrolysis of fused LaCl₃. Prop.—an iron-gray metal tarnishing in air to steel-blue; malleable and ductile. Attacked slowly even by cold water.	When heated in air it forms oxide (La₂O₃) and nitride (LaN).
Lead. Symbol Pb. At. wt. 207.20. Valence II., IV. S. G. 11.4. M. P. 327.2°. B. P. 1525°.	Occ.—as galena (PbS), and in silver ores. Prep.—by calcination of partially roasted galena. Purification is effected by Parkes process. Prop.—a soft, gray metal, malleable, but of low tensile strength. In presence of air, water acts on lead to produce the hydroxide, which being slightly soluble, may cause lead poisoning, if present in water supplies. When heated in air it is oxidized to litharge (PbO), and, under suitable conditions, to minimum (Pb₃O₄)	The metal is used for water pipes, roofs and gutters and storage batteries. For shot it is alloyed with 0.4% of arsenic. Typemetal contains 20% of antimony. Babbitt metal, for bearings, contains over 70% of lead. Solder and pewter are alloys of lead and tin. The basic carbonate [Pb(OH)₂, 2PbCO₃], “white lead,” is the basis of most oil paints.
Lithium. Symbol Li. At. wt. 6.94. Valence I. S. G. 0.53. M. P. 186°. B. P. above 1400°.	Occ.—as a mixed fluoride with aluminium in amblygonite. Prep.—by electrolysis of the fused chloride. Prop.—a silver-white metal, softer than lead, that tarnishes quickly in air, and is easily acted upon by water. When heated, it unites vigorously with nitrogen.	The carbonate [Li₂(CO₃)] is used in medicine as a solvent for uric acid, lithium urate being soluble. The lithium salts give a carmine flame coloration.
Lutecium.[887] Symbol Lu. At. wt. 175.0.	Occ.—in euxenite. Prep.—it has not been isolated.	Its compounds resemble those of ytterbium.
Magnesium. Symbol Mg. At. wt. 24.32. Valence II. S. G. 1.75. M. P. 650°. B. P. 1120°.	Occ.—as magnesite (MgCO₂), dolomite (MgCO₃, CaCO₃), carnallite (MgCl₂, KCl, 6H₂O) and in very many complex silicates. Prep.—by electrolysis of dried, fused carnallite. Prop.—a silver-white metal, ductile when hot. It tarnishes in air, and acts slowly upon water, rapidly on steam. Burns in air to the oxide MgO, emitting a very bright light used in photography. It unites directly with nitrogen.	The sulphate (MgSO₄, 7H₂O) is known as epsom salts and is used in medicine, as are the oxide (magnesia), the carbonates and citrate. Magnalium is a light, hard alloy with aluminum.
Manganese. Symbol Mn. At. wt. 54.93. Valence II., III., IV., VI. and VII. S. G. 7.3. M. P. 1120°. B. P. 1900°.	Occ.—as pyrolusite (MnO₂), beaunite (Mn₂O₃), hausmannite (Mn₃O₄) and manganese spar (MnCO₃). Prep.—by heating Mn₃O₄ with aluminum filings. Prop.—a steel-gray, hard, brittle metal with a pinkish tinge. It rusts in moist air and is attacked by dilute acids.	Ferromanganese and spiegeleisen are alloys with iron, used in steel making. With copper it forms the hard, tough manganese bronzes, with tensile strength up to 30 tons per square inch. Impure sodium permanganate (NaMnO₄) is used in disinfecting as Condy’s fluid.
Mercury. Symbol Hg. At. wt. 200.6. Valence I. and II. S. G. 13.6. M. P. -39.5°. B. P. 356.95°.	Occ.—free and as cinnabar (HgS). Prep.—by roasting cinnabar HgS + O₂—Hg + SO₂. Prop.—a silver-white, mobile liquid with a vapor pressure at 0° of 0.0002 mm. It tarnishes but slowly in air and is attacked only by dilute nitric among the dilute acids. The vapor is monatomic.	It is used for filling thermometers and barometers. Its alloys are called amalgams, some of which are used in dentistry. Calomel (HgCl) is administered internally in medicine; corrosive sublimate (HgCl₂) forms a solution with very powerful germicidal properties.
Molybdenum. Symbol Mo. At. wt. 96.0. Valence III., IV., V. and VI. S. G. 10.0. M. P. 2450°.	Occ.—as molybdenite (MoS₂) and wulfenite (PbMoO₄). Prep.—by reducing the oxides with aluminum powder. Prop.—a white metal, as malleable as iron, that will not scratch glass. Insoluble in hydrochloric or dilute sulphuric acid.	The ferromolybdenum alloys are used in the manufacture of special steels.
Neodymium. Symbol Nd. At. wt. 144.3. Valence III. and IV. S. G. 7.0. M. P. 840°.	Occ.—with cerium and lanthanum. Prep.—by electrolysis of the fused chloride. Prop.—a yellowish metal, tarnishing in air.	The salts are rose-violet in color, and their solutions show characteristic absorption spectra.
Neon. Symbol Ne. At. wt. 20.2. Valence 0. B. P. ca. -243°.	Occ.—in minute quantity in the atmosphere. Prep.—neon and helium are boiled out of crude argon, and the neon separated from helium by cooling with liquid hydrogen. Prop.—a colorless, transparent, odorless, inert gas, resembling argon.	It forms no compounds, and is recognized by its characteristic spectrum.
Nickel. Symbol Ni. At. wt. 58.68. Valence II. and III. S. G. 8.8. M. P. ca. 1452°. B. P. ca. 2600°.	Occ.—as nicollite (NiAs) and nickel glance (NiAsS). Prep.—by igniting the oxalate in hydrogen. Prop.—a white, very hard, lustrous metal, malleable, ductile and tenacious. It rusts but slowly in air, and is attacked easily by only nitric acid.	The metal furnishes a protective coating when plated on iron. German silver is an alloy of nickel, copper and zinc. Nickel steel is used for armor plates. Manganin, containing nickel, copper and manganese, is used for electrical resistances.
Nitrogen. Symbol N. At. wt. 14.01. Valence III. and V. S. G. (liquid at B. P.) 0.81. M. P. -214°. B. P. -194°.	Occ.—free nitrogen forms about four-fifths of air by volume. As Bengal saltpeter (KNO₃), Chili saltpeter (NaNO₃); and as an essential constituent of vegetable and animal protoplasm. Prep.—by heating ammonium nitrite, by oxidation of ammonia, etc. Prop.—a colorless, odorless, transparent gas, rather inactive chemically. At ordinary temperature and pressure, 100 volumes of water dissolve 1.5 volumes of nitrogen. It unites directly with strongly heated boron, lithium, calcium and magnesium.	Nitrous oxide (N₂O), or laughing gas, is used by dentists. Nitric acid (HNO₃) has many applications in technical chemistry. Ammonia (NH₃) is a very soluble gas. Ammonium sulphate [(NH₄)₂SO₄] and Chili saltpeter are used as nitrogenous manures. Nitrogen is a constituent of the aniline dyes, the proteins and many other important classes of organic substances.
Osmium. Symbol Os. At. wt. 190.9. Valence II., III., IV., VI. and VIII. S. G. 22.477. M. P. 2500°.	Occ.—along with platinum. Prep.—by reducing OsO₄. Prop.—a gray metal, harder than glass, the heaviest of known bodies.	Its alloy with iridium is used in tipping gold pens. Osmium tetroxide (OsO₄) is used as a microscopic stain for fat.
Oxygen. Symbol O. At. wt. 16.00. Valence II. S. G. (liquid at B. P.) 1.13. M. P. -218.4°. B. P. -182.5°.	Occ.—free oxygen forms about one-fifth of air by volume. Water contains 88.88% of oxygen. The rocks of the earth’s crust contain about 45% in combination, chiefly as silicates. Prep.—in the laboratory by heating potassium chlorate (KClO₃). Commercially, from the air. Prop.—a colorless, odorless, tasteless, transparent gas, slightly heavier than air. At ordinary temperature and pressure, 100 volumes of water dissolve 3 volumes of oxygen. It is very active chemically, combining directly with all but a few of the other elements to form oxides. Sulphur, phosphorus, etc., burn much more vigorously in oxygen than in air. Liquid oxygen is magnetic.	The gas is sold compressed in mild steel cylinders, and is used for the oxyhydrogen blowpipe and in medicine, besides for chemical purposes. It is necessary to support animal respiration and to sustain ordinary combustion. It enters as a constituent into all oxides, most salts and many organic compounds.
Palladium.[888] Symbol Pd. At. wt 106.7. Valence II. and IV. S. G. 11.9. M. P. 1549°.	Occ.—along with platinum, and with gold in Brazil. Prep.—by a complex series of processes from platinum ores. Prop.—a silvery, malleable and ductile metal, related to platinum, unlike which, however, it is attacked by nitric acid. Under suitable conditions it can take up over 900 volumes of hydrogen.	Since it does not tarnish, it is used for coating silver goods, and by dentists as a substitute for gold.
Phosphorus. Symbol P. At. wt. 31.04. Valence III. and V. S. G. white, 1.82. red, 2.25. M. P. white, 44°. B. P. 289°.	Occ.—as phosphates, such as apatite [CaF(PO₄)₃]; in bones, teeth, brain and seeds of plants. Prep.—by reduction of calcium phosphate by carbon in the electric furnace in presence of a suitable flux. Prop.—phosphorus exists in two allotropic modifications: white phosphorus is waxy in consistency, soluble in carbon bisulphide, evil smelling and poisonous; red phosphorus is a solid, insoluble in carbon bisulphide, odorless and not poisonous. White phosphorus has a low ignition temperature, hence its former use in matches.	Red phosphorus is used in the manufacture of matches, as also is the compound P₄S₃. In the form of superphosphate of lime [CaH₂(PO₄)₂] phosphorus is an important artificial manure. The chlorides (PCl₃ and PCl₅) are much used in organic chemistry.
Platinum. Symbol Pt. At. wt. 195.2. Valence II. and IV. S. G. 21.48. M. P. 1753°.	Occ.—free, alloyed with the platinum metals, as nuggets in alluvial sands in the Urals, California, etc. Prep.—it is freed from the metals with which it is alloyed by a complex series of processes. Prop.—a silvery, tenacious, ductile and malleable metal, unaltered in moist air and unattacked by any single common acid. Aqua regia, fused alkalies, alkali nitrates and cyanides attack it, however. Platinum “sponge” and “black” are finely divided forms.	On account of its resistance to acids, platinum is much used for chemical vessels. Since platinum has a coefficient of expansion very close to that of glass, platinum wires can be fused through glass without danger of breakage on cooling. The salts are used in photography.
Potassium. Symbol K. At. wt. 39.10. Valence I. S. G. 0.86. M. P. 62.5°. B. P. 762°.	Occ.—as sylvite (KCl), carnallite (KCl, MgCl₂, 6H₂O); in plant and animal ashes, and in many complex silicates. Prep.—by reduction or by electrolysis of fused potassium hydroxide (KOH). Prop.—a silver-white, lustrous metal, as soft as wax, tarnishing instantly in moist air. Chemically it is a very active metal, decomposing water in the cold and uniting violently with the halogens, sulphur and oxygen.	An alloy with sodium is used in filling high-temperature thermometers. Bengal saltpeter is the nitrate and is used in pyrotechny, for gunpowder and as a preservative. The iodide (KI) is used in medicine. The chlorate, like the nitrate, is used as a source of oxygen in pyrotechny and for match heads. Caustic potash (KOH) has many chemical applications. The cyanide (KCN) is used in gold extraction.
Praseodymium. Symbol Pr. At. wt. 140.9. Valence III. and IV. S. G. 6.47. M. P. 940°.	Occ.—with cerium and lanthanum. Prep.—by electrolysis of the fused chloride. Prop.—a yellowish metal, remaining untarnished in air.	The salts are leek-green in color, and their solutions have characteristic absorption spectra.
Radium. Symbol Ra. At. wt. 226.0. Valence II. M. P. 700°.	Occ.—in minute quantity in pitchblende and other uranium minerals. Prep.—the metal has recently been isolated; the bromide is separated from the barium bromide prepared from pitchblende by fractional crystallization. Prop.—in all of its compounds, the metal has the power of emitting certain radiations. These can pass through matter that is opaque to light, render air a conductor, affect a photographic plate and cause a zinc-sulphide screen to fluoresce visibly.	The rays from radium compounds (such as RaBr₂, RaCl₂, RaCO₃) act destructively on living tissues and on bacteria. One gram of radium in any of its compounds gives off about 100 calories of heat per hour.
Rhodium. Symbol Rh. At. wt. 102.9. Valence II., III. and IV. S. G. 12.1. M. P. 1970°.	Occ.—in the ores of platinum. Prep.—by a complex series of processes from platinum ores. Prop.—a silvery, malleable and ductile metal, not tarnishing in air and not attacked by aqua regia.	The red chloride (RhCl₃) is formed by the action of chlorine upon the metal.
Rubidium. Symbol Rb. At. wt. 85.45. Valence I., III. and V. S. G. 1.53. M. P. 38.5°. B. P. 69.8°.	Occ.—the salts are associated with salts of potassium. Prep.—similar to that of potassium. Prop.—a silver-white metal resembling potassium, like which it attacks water vigorously.	The compounds show characteristic flame-spectra, and were recognized as those of a new element spectroscopically by Bunsen.
Ruthenium. Symbol Ru. At. wt. 101.7. Valence III., IV., VI., VII. and VIII. S. G. 12.1. M. P. above 1950°.	Occ.—in the ores of platinum. Prep.—by a complex series of processes from platinum ores. Prop.—a hard, white, brittle metal, oxidized when heated in air, scarcely attacked by aqua regia.	The following oxides are known: Ru₂O₃, RuO₂, RuO₄, as well as salts corresponding to RuO₃ and Ru₂O₇.
Samarium.[889] Symbol Sa. At. wt. 150.4. Valence II. and III. S. G. ca. 7.7. M. P. 1300 to 1400°.	Occ.—in the mineral samarskite. Prep.—by electrolysis of the chloride. Prop.—a whitish-gray metal, tarnishing in air.	The salts are topaz-yellow in color, and are similar to those of lanthanum.
Scandium. Symbol Sc. At. wt. 44.1. Valence III.	Occ.—in the minerals euxenite and gadolinite. Prep.—the metal has not been isolated. Prop.—the existence of this element, whose oxide was discovered in 1879, was predicted by Mendeléeff in 1869.	The chloride (ScCl₃) shows a characteristic spark spectrum.
Selenium. Symbol Se. At. wt. 79.2. Valence II., IV. and VI. S. G. amorphous 4.26. monoclinic 4.47 hexagonal 4.8. M. P. amorphous 50°. monoclinic 170 to 180°. hexagonal 217°. B. P. 688°.	Occ.—free in some specimens of sulphur, and in combination with lead, iron and other metals, as in pyrites. Prep.—(amorphous) by reducing selenious acid (H₂SiO₃) by sulphur dioxide. Prop.—three varieties are known: (1) red amorphous, soluble in carbon bisulphide, from which it is deposited as (2) red translucent monoclinic crystals, soluble in carbon bisulphide, (3) blue-gray metallic selenium, insoluble in carbon bisulphide. This last form conducts electricity many times better when exposed to light, and the better the brighter the light.	Selenium cells are used as indicators of intensity of illumination. The compounds strongly resemble those of sulphur. Hydrogen selenide is an evil-smelling inflammable gas. Selenic acid (H₂SeO₄) is a more powerful oxidizer than sulphuric acid and dissolves gold.
Silicon. Symbol Si. At. wt. 28.3. Valence IV. S. G. amorphous 2.3. crystalline 2.34. M. P. 1458°. B. P. ca. 3500°.	Occ.—silicon dioxide (SiO₂) occurs as flint, quartz, quartz sand, etc. The igneous rocks are composed largely of silicates, and this element constitutes over 25% of the earth’s crust. Prep.—by reducing sand with coke in the electric furnace. Prop.—amorphous silicon is a brown powder that burns when heated in air. Crystalline silicon forms black needles. It is less active than the amorphous variety and is attacked only slowly by a mixture of hydrofluoric and nitric acids. It unites with fluorine, however, at ordinary temperatures.	The “pigs” of silicon made at Niagara are used in steel-making. The ornamental varieties of quartz find uses as gemstones, as do several natural silicates. Silicon carbide, “carborundum” (SiC), is used as an abrasive. Sodium silicate solution is “water glass,” used to protect sandstone and to preserve eggs. Common glass is a mixture of sodium and calcium silicates.
Silver. Symbol Ag. At. wt. 107.88. Valence I. S. G. 10.53. M. P. 960°. B. P. 1955°.	Occ.—native, as sulphide (Ag₂S) often associated with galena; chloride (AgCl), etc. Prep.—from lead by the Pattison or Parkes process; from the ores by the Mexican and other processes. Prop.—a white, highly lustrous, tough, very ductile and malleable metal, the best conductor of heat and electricity known. Liquid silver dissolves oxygen. It is unaffected by the oxygen of moist air, and its tarnishing is due to the action of hydrogen sulphide. It dissolves in dilute nitric and in concentrated hot sulphuric acid.	It is employed for articles of use and of ornament and for coinage. U. S. sterling silver contains 90% silver and 10% copper. Lunar caustic is silver nitrate. This salt and the halides of silver are extensively used in photography. For electroplating, a bath of potassium argenticyanide [KAg(CN)₂] is used.
Sodium. Symbol Na. At. wt. 23.00. Valence I. S. G. 0.97. M. P. 965°. B. P. 883°.	Occ.—in the sea as chloride (NaCl); in salt deposits as chloride, borate, nitrate; in many complex silicates in rocks. Prep.—by electrolysis of fused sodium hydroxide (NaOH). Prop.—a silver-white metal, as soft as wax, that may be welded at ordinary temperature. Like potassium it is very active, uniting directly with many other elements, and attacking water vigorously in the cold.	The metal is used in the manufacture of several chemicals. Sodium chloride (NaCl) is a necessity of life to most animals; and is used in the manufacture of hydrochloric acid, chlorine and sodium compounds. Sodium carbonate (NaCO₃, 10H₂O) or washing soda, and sodium hydroxide (NaOH) are used for cleaning, and in the manufacture of soap and chemicals. Baking soda is sodium bicarbonate (NaHCO₃). The sulphate (Na₂SO₄, 10H₂O) is known as Glauber’s salt; the thiosulphate, by photographers, as “hypo.”
Strontium. Symbol Sr. At. wt. 87.63. Valence II. S. G. 2.55. M. P. ca. 800°.	Occ.—as strontianite (SrCO₃) and celestine (SrSO₄). Prep.—by electrolysis of the fused chloride. Prop.—a white metal, softer than calcium and harder than sodium, tarnishing to a yellow tint. Like calcium it is active enough to attack water vigorously in the cold.	The nitrate and chlorate are used in pyrotechny for red fire. All volatile compounds color the Bunsen flame red.
Sulphur. Symbol S. At. wt. 32.06. Valence II., IV. and VI. S. G. rhombic 2.06. monoclinic 1.96. M. P. rhombic 112.4°. monoclinic 119°. B. P. 444.9°.	Occ.—native, in combination with most metals as sulphides, and with some metals as sulphates. Prep.—by melting the free sulphur away from the rocky matrix, and subsequent purification by distillation. Prop.—natural sulphur is rhombic in crystalline form, yellow, brittle, of vitreous luster, and a poor conductor of heat and electricity. This and the monoclinic variety are soluble in carbon bisulphide, while amorphous sulphur is not. When heated, sulphur unites directly with most of the other elements.	Sulphur is used to prepare sulphur dioxide (SO₂), which is used in making sulphuric acid and sulphites, and for bleaching; also for vulcanizing rubber and in the manufacture of black gunpowder, fireworks and matches. Sulphuric acid (H₂SO₄) is to chemical industry what iron is to engineering.
Tantalum.[890] Symbol Ta. At. wt. 181.5. Valence II., IV. and V. S. G. 16.6. M. P. bet. 2250° and 2300°.	Occ.—in tantalite and many other rare minerals. Prep.—by the action of sodium on sodium tantalofluoride (Na₂TaF₇). Prop.—a hard, silver-white metal, ductile and malleable when hot, of very high tensile strength. The hot metal can absorb 740 volumes of hydrogen. It is not attacked by aqua regia.	The metal is used for filaments for electric lamps, which possess twice the efficiency of the carbon filament lamp.
Tellurium. Symbol Te. At. wt. 127.5. Valence II., IV. and VI. S. G. cryst. 6.2. M. P. cryst. 455°. B. P. 1400°.	Occ.—free and as tellurides. Prep.—by reducing tellurious acid (H₂TeO₃) by means of sulphur dioxide. Prop.—the crystalline variety is white, has metallic luster, and conducts heat and electricity. The precipitated variety is black and of lower density. The element is related to sulphur but is more metallic in character.	The compounds find few applications. Telluric acid (H₆TeO₆) has basic as well as acid characters, in keeping with the position of the element between metals and nonmetals.
Terbium. Symbol Tb. At. wt. 159.2. Valence III.	Occ.—in gadolinite, samarskite, and other rare minerals. Prep.—the metal has not been prepared.	The salts show no absorption spectrum.
Thallium. Symbol Tl. At. wt. 204.0. Valence I., and II. S. G. 11.8. M. P. 303. B. P. 1515°.	Occ.—in crookesite, and in small quantities in many samples of iron pyrites. Prep.—it is precipitated by zinc from a solution obtained by suitable treatment of the flue dust from sulphuric acid works. Prop.—a bluish-white, lead-like metal, rather soft, malleable, but of low tensile strength. It decomposes water rapidly at red heat, and dissolves in dilute acids.	It forms two sets of salts, the thallous (e.g., TlCl) and the thallic (e.g., TlCl₃). All the compounds show a characteristic green line in the spectrum.
Thorium. Symbol Th. At. wt. 232.4. Valence IV. S. G. 11.0. M. P. above 1700°.	Occ.—in monazite sand. Prep.—by reducing potassium thorium chloride with sodium, or by electrolysis of the chloride in a mixture of fused potassium and sodium chlorides.	The nitrate [Th(NO₃)₄, 6H₂O] is used in making Welsbach incandescent mantles, which consist of 99% of ThO₂. All the compounds are radio-active.
Thullium. Symbol Tm. At. wt. 168.5. Valence III. M. P. 1700°.	Occ.—in gadolinite and other yttrium minerals. Prop.—a metal with the color of nickel, that can be burnt in air. Hydrochloric acid attacks it but slowly.	The salts are of a pale bluish color which is destroyed very easily by minute quantities of erbium.
Tin. Symbol Sn. At. wt. 118.7. Valence II. and IV. S. G. white 7.3. gray 5.7. M. P. 231.8°. B. P. 2275°.	Occ.—as cassiterite (SnO₂). Prep.—after roasting, the ore is reduced by heating with carbon. Prop.—a silver-white, rather soft, very malleable and ductile metal, practically unchanged in air. When heated, it may be burned in air. Dilute nitric acid is the only dilute acid that attacks it rapidly. When kept long at temperatures below zero Centigrade, ordinary tin changes to a brittle, gray, powdery modification. This form is the stable one below 20°.	Large quantities of tin are used in the tinning of iron for tinplate. It is a constituent of the alloys Britannia metal, pewter, solder, bronze, etc. Tin forms two sets of salts, stannous (e.g., SnCl₂) and stannic (e.g., SnCl₄). “Pink salt” [(NH₄)₂SnCl₆] is used in dye. “Mosaic gold” is SnS₂.
Titanium. Symbol Ti. At. wt. 48.1. Valence II., III. and IV. S. G. 4.5. M. P. below 1850°.	Occ.—as rutile (TiO₂) and in titanic iron ore (FeTiO₃). Prep.—by reducing the chloride (TiCl₄) by means of sodium. Prop.—a hard, brittle metal, resembling polished steel in appearance, that may be forged at a low red heat. It dissolves in dilute sulphuric acid, and decomposes steam at 800°. It unites easily with nitrogen.	The element is very widely disseminated, though in small quantity. It is contained in the ashes of all plants.
Tungsten. Symbol W. At. wt. 184.0. Valence II., IV., V. and VI. S. G. 19.3. M. P. 3177°. B. P. ca. 3700°.	Occ.—as wolfram (FeWO₄) and as scheelite (CaWO₄). Prep.—by reducing tungstic acid (H₂WO₄) by carbon at a high temperature. Prop.—a hard, brittle, gray metal, attacked by chlorine only at 250°, although it can be caused to burn in air. It is slowly acted upon by dilute acids and even by water.	The metal is used for the filaments of incandescent electric lamps, giving an efficiency of 1.3 watts per candle power. Tungsten steel has 5% W. Sodium tungstates are used as mordants in dyeing.
Uranium. Symbol U. At. wt. 238.2. Valence III., IV., V. and VIII. S. G. 18.7. M. P. ca. 1500°.	Occ.—as pitchblende, which contains U₃O₈. Prep.—by reducing the oxides with aluminum. Prop.—a white, lustrous metal, tarnishing in air and attacking water slowly in the cold. It combines directly with many of the other elements.	All the compounds of uranium are radioactive in proportion to their uranium content. Glass to which uranium compounds have been added shows a greenish-yellow fluorescence.
Vanadium. Symbol V. At. wt. 51.0. Valence II., III., IV. and V. S. G. 5.7. M. P. ca. 1715°.	Occ.—in a few rather rare minerals. Prep.—by reduction of the dichloride (VCl₂) in hydrogen. Prop.—a silver-white, lustrous metal, harder than quartz. It does not tarnish nor attack water at ordinary temperatures, but can be burnt in oxygen.	Vanadium added to steel in even small quantity (0.2%) increases the tenacity and elastic limit without reducing the ductility.
Xenon.[891] Symbol Xe. At. wt. 130.2. Valence 0. B. P. -109°. S. G. (liquid at B. P.) 3.82.	Occ.—in minute quantity in the air, less than one volume in 100 million. Prep.—by fractionation of liquid argon. Prop.—a transparent, colorless and odorless gas, very inert like its congener argon. It is the densest of the argon family.	It forms no compounds.
Ytterbium (Neoytterbium). Symbol Yb. At. wt. 173.5. Valence III.	Occ.—in gadolinite, euxenite and other rare minerals. Prep.—the metal has not been isolated.	The compounds show a characteristic spark spectrum.
Yttrium. Symbol Y. At. wt. 88.9. Valence III. S. G. 3.8.	Occ.—in gadolinite, euxenite and other rare minerals. Prep.—by electrolysis of sodium yttrium chloride. Prop.—a gray, lustrous metal.	The chloride yields a characteristic, though complex, spectrum.
Zinc. Symbol Zn. At. wt. 65.37. Valence II. S. G. 6.9 to 7.2. M. P. 419.3°. B. P. 906°.	Occ.—as zinc blende (ZnS), calamine (ZaCO₂), zincite (ZnO), etc. Prep.—after roasting, the ore is reduced by coal, the metal distilling off. Prop.—a bluish-white, lustrous, brittle metal, that is malleable and ductile at 120°. It tarnishes in moist air, attacking water slowly in the cold and rapidly when heated in steam. It dissolves in dilute acids and in sodium hydroxide solution.	Sheet zinc is used for roofs and gutters. Iron is galvanized by dipping it in molten zinc, and so protected from rusting. Zinc is used for galvanic batteries and, alloyed with copper, to make brass. The salts are used in medicine; the chloride and sulphate antiseptic solutions.
Zirconium. Symbol Zr. At. wt. 90.6. Valence IV. S. G. 6.4.	Occ.—as zircon (ZrSiO₄). Prep.—by reducing the oxide (ZrO₂) with carbon in the electric furnace. Prop.—a hard, gray metal, remaining bright in air and only slowly oxidized at a white heat. It is dissolved by aqua regia and by caustic potash solution.	The oxide is contained in some incandescent gas mantles.