Hydrogen

Hydrogen, chemical element, symbol H, a colorless gas, without taste or smell, the lightest of all gases; it is 14.435 times lighter than air; 1 liter weighs 0.08987 g; specific weight in relation to air 0.06956; atomic weight 1.008; molecular weight 2.016; has no isotopes; atomic number 1; discovered by Paracelsus in the 16th century when dissolving iron in dilute sulfuric acid. At first it was called "inflammable air." The true nature of H as a new element was established by the works of Cavendish and Lavoisier, who also explained the nature of water. In nature, free H, unlike its compounds, is rarely found. In the air, near the earth's surface, it is contained in the amount of 0.01%; with increasing height this amount increases significantly. H is found in the atmosphere of the sun, is released during the decay and fermentation of many organic substances, and is found in the intestinal gases of animals. Of the compounds of H, the most common is water (11% H by weight); substances that make up the bodies of animals contain up to 80% H. In so-called organic substances, H is one of the most frequently occurring constituent parts, and therefore is listed among the so-called organogens. Hydrogen can be obtained from water: 1) by passing an electric current through water acidified with sulfuric acid; 2) by decomposing water with a metal; 3) by heating it to a high temperature (about 1,000°); 4) by passing superheated water vapor over superheated coal, whereby so-called water gas is formed, containing 50-60% H. In laboratories, H is obtained by the action of dilute sulfuric acid on zinc. H obtained by any of the above methods is contaminated with hydrogen sulfide, arsine, and others. To purify it, it is passed through a solution of potassium permanganate, mercuric chloride, and alkalis. H is the least dense of all gases, it easily diffuses, better than other gases it obeys the laws of Boyle-Mariotte and Gay-Lussac, and is very difficult to liquefy. Liquid H was first obtained by Pictet and Cailletet in 1877 by the combined action of cooling and strong pressure; at -259° H freezes into a solid white mass. In water, H dissolves little: 100 volumes at 0° and 760 mm dissolve 2.15 volumes of H. At ordinary temperature, the H element is not very active, it reacts only under changing conditions—when heated, compressed, under the action of light, and at the moment of release (in statu nascendi). H is combustible, flame temperature about 2,500°; in the atmosphere of H, most bodies do not burn. A mixture of 2 volumes of H and 1 volume of oxygen ignites with an explosion and is called explosive gas. H easily removes oxygen from compounds. Some metals can absorb H, for example, nickel, iron, platinum, and especially palladium (up to 900 volumes), as well as carbon. This phenomenon is called occlusion and is explained by the ability of metals to form with H easily dissociable compounds similar to alloys. At high temperature and high pressure, H displaces metals from salts. The H atom consists of a nucleus and one electron. In reactions, it either loses its electron and turns into a positive ion H+, for example, H+Cl^-, or it attaches another electron and gives a negative ion H^-; such an ion is present in compounds of H with metals—salt-like hydrides, for example, Na+H^-. The H+ ion determines an acidic medium: it is the essential ion for all acids (see Hydrogen ions). When atoms of many elements (nitrogen, carbon, silicon, etc., whose atomic weights are not multiples of 4) are decomposed by alpha rays, H and Helium are obtained. H and Helium represent the material from which atoms of other, heavier elements are built. According to the latest data, when H is acted upon by an electric current of 3,000-8,000 volts or by alpha rays, it is transformed into an active modification—hizon, which exists for 2-3 minutes; the hizon molecule consists of three atoms. Gaseous H is detected by spectral analysis and by reduction reactions; H+ is detected by indicators. H is used for reduction reactions, for example, for converting liquid fats into solid ones, for obtaining high temperature in soldering, welding and cutting metals, and for filling airships.