Element Hydrogen, H, Non Metal

Hydrogen was known to the alchemists as a product of the interaction of acids and metals, and was called "inflammable air."

The suggestion first made by John Joachim Becher (1635-1682), that combustion is essential to chemical change, was further developed by Georg Ernst Stahl (1660-1734). Stahl's theory involved a number of assumptions, which admit of the following summary -

1. All combustible substances are compounds.
2. Burning eliminates from these substances a constituent common to them all, " phlogiston".
3. The degree of combustibility increases with the proportion of phlogiston present.
4. Substances like phosphorus, carbon, sulphur, and many organic bodies contain a large proportion of phlogiston.
5. Metals also contain phlogiston in varying proportions. They are to be regarded as compounds of this substance with the calx left after their combustion.
6. The reconversion of metallic calxes into the metal by heating with carbon, gases, and other substances - in modern parlance the reduction of the oxide - is the result of a combination of the phlogiston of the reagent with the calx.

The phlogiston theory remained unrefuted for about fifty years. In 1772 Rutherford discovered nitrogen, and in 1774 Priestley isolated oxygen ("dephlogisticated air"). Between the years 1772 and 1788 Lavoisier made numerous investigations into the nature of combustion, his results leading him to the conclusion that there is no essential difference between respiration, combustion, and calcination.

Hydrogen was discovered in 1766 by Henry Cavendish, an English chemist and physicist; he observed a gas produced by zinc-acid reaction, flammable in the air. Paracelsus, Boyle, Lemery and other scientists of 16 - 18 centuries prepared hydrogen by metal-acid reactions, observed the burning and explosions of inflammable gas. In 1783, Lavoisier, who was investigating the composition of water by its synthesis and analysis, gave the element the name of hydrogen or hydrogene, from the Greek words "hydor" (water) and "gennao" (give birth to).

In 1781 Cavendish and Watt proved water to be produced by the combustion of hydrogen. A repetition of their experiments in 1783 by Lavoisier and Laplace indicated that water contains 1 volume of oxygen and 1.91 volume of hydrogen. The interaction of red-hot iron and steam, with liberation of free hydrogen and production of a calx of iron, was also observed by Lavoisier.

The discovery of the compound nature of water by Cavendish and Watt, and the results obtained by Lavoisier and his coadjutors in their investigations of the quantitative composition of this substance, rendered the phlogiston theory untenable. It had played a useful part as the first step to placing the science of chemistry on a rational basis, and it is interesting to note that both Priestley and Cavendish remained phlogistians to the end.

The isotopes were discovered in 30-s of 20^th century. They play very important role in science and engineering. In the end of 1931 Urey, Murphy and Brickwedde analyzed the matter residue from the simple evaporation of liquid hydrogen and found very small amount of an isotope of hydrogen with an atomic mass of 2. It was called Deuterium, D, from the Greek word for "two". After four years another, heavier isotope of hydrogen ³H, was found by electrolysis of heavy water. It was called Tritium, from the Greek word for "third".

Hydrogen is the most abundant element in the universe (in great abundance in Sun, giant planets like Jupiter and Saturn, stars, interstellar medium, nebulae); Hydrogen makes up 63% of space matter, 36% makes Helium and 1% make other elements. Hydrogen is the third most plentiful element on Earth (after oxygen and silicon), it constitutes the basis of hydrosphere. Most of the Earth's hydrogen is in the form of chemical compounds (such as water, living creatures, oil, natural gas and minerals). It has also been observed in the upper layers of atmosphere.

Hydrogen comprises 3-4% of the cells dry matter. Its ability to form a vast array of compounds with carbon and, especially, with oxygen (water) has become one of the factors of origin of life on the Earth. It is involved in all biochemical and physiologic reactions.



The proportion of free hydrogen in the earth's atmosphere is very minute, a fact accounted for by the great affinity of the element for oxygen. There is much discrepancy between the analytical results of different investigators. Gautier found 0.02 per cent, by volume, but Rayleigh's value is only 0.003 per cent. Dewar detected only 0.001 per cent. Claude found less than 0.0001 per cent., and Ramsay gives an equally low value.

The decomposition of organic matter by specific organisms, and the exhalations of volcanoes, are the two main sources of atmospheric hydrogen. In the absence of air, certain anaerobic bacteria induce fermentation of cellulose and proteins, with production of free hydrogen, most of the hydrogen of the atmosphere having this origin. According to Bunsen, the volcanic gases of Iceland contain 25 per cent, of hydrogen, and Moissan found 22.3 per cent, in the gases evolved from Mont Pelee in Martinique during the eruption of 1902. Its presence in these gases is probably the result of the interaction of metals with water- vapour at a high temperature.

Hydrogen was also found by Gautier in many large rocks, and by Reichardt in the occluded gases of the coloured salt-deposits at Stassfurt. Pollacci has observed it in the gases given out by green plants.

Hinrichs has calculated that at a height of 100 kilometres the earth's atmosphere contains 95 per cent, of hydrogen, the high proportion being due to the low density of the gas, and to the fact that the lower the density of an atmospheric gas the less rapidly does the amount of it present diminish with increase in the height of the atmosphere.