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Element Bromine, Br, Halogene

About Bromine

General. - Bromine is an element which closely resembles chlorine in all its relations. Discovered by Balard in 1826, it has since then been found to be, indeed, very widely distributed, but it is met with in much smaller amount than chlorine. Its compounds occur in small quantities in sea-water, and are contained, therefore, in the residues left on the artificial or natural evaporation of this. From the residues which are obtained by the latter process, and which, in Germany, chiefly occur near Stassfurt, bromine is obtained and sent into the market.

Bromine is a dark, brown-red liquid, transparent only in thin layers and having a density 3.1. It boils at 60°, and even at room temperature possesses a considerable vapour pressure. Bromine, therefore evaporates very quickly even under ordinary conditions; and as its vapour has a very unpleasant smell and a strong corrosive action on the mucous membrane, care must be observed in working with it. Bromine solidifies at - 7° to - 8° to a dark-coloured, crystalline mass.

The vapour of bromine is very heavy. If a small bulb filled with bromine be broken, or if, by means of a pipette, a drop of bromine be placed at the bottom of a large, empty bottle, it is seen that the brown-yellow vapour produced remains at the bottom and sways heavily when the bottle is moved. Only after standing undisturbed for a considerable time does the bromine vapour slowly ascend into the upper parts of the bottle, in accordance with the general law of the diffusion of gases, which states that equilibrium occurs only when the partial pressure of each gas or vapour present has become equal throughout the whole space.

If the same experiment be repeated in a bottle filled with hydrogen, diffusion takes place much more rapidly; and by performing two parallel experiments with air and with hydrogen side by side, the great difference in the height of the bromine will be perceived even after 5 to 10 minutes. This appears remarkable, since the difference of density as compared with hydrogen is much greater than that compared with air, and, therefore, the work to be performed against gravity is also greater. That, nevertheless, bromine vapour and hydrogen mix more quickly is due to the fact that diffusion proceeds more rapidly in hydrogen because, in this case, the mutual friction of the gases is less. The velocity of diffusion obeys, to some extent, though by no means exactly, the same law as the velocity of effusion, and is, in the case of hydrogen, about four times as great as in air.

From determinations of the density of bromine vapour, its molar weight has been found to be 160, or five times as great as that of oxygen. Bromine vapour is, therefore, 5.5 times as heavy as air. Since the combining weight has been found to be half as great (the exact figure being 79.96), the composition of bromine vapour is represented by the formula Br2. At very high temperatures, the molar weight becomes somewhat less. Since similar relations are found and have been more fully investigated in the case of iodine, we shall discuss this phenomenon at that point.

Bromine dissolves in water, forming a yellow to brown coloured liquid, which possesses the smell of bromine and can be used in place of pure bromine when only a small quantity of the substance is required. The solution, saturated at room temperature, contains about 3 per cent of bromine. If the water contains saline compounds of bromine in solution, more bromine is dissolved, readily decomposable compounds of bromine being formed which, in most of their relations, behave like free bromine. These relations, also, will be discussed more fully under iodine.

From the aqueous solution of bromine (bromine water) there separates out, on cooling, a solid hydrate which behaves quite similarly to chlorine hydrate.

Bromine History

Chronologically Bromine was first isolated by Carl (Karl) Jacob Lowig, the Heidelberg University student (and, later, Heidelberg professor and Robert Wilhelm Bunsen's successor in Breslau), working Laboratory of Medicine and Chemistry of Prof. Leopold Gmelin, at the University of Heidelberg. Gmelin realized that this intensely deep dark-red liquid with an unpleasant smell was an unknown substance and encouraged Lowig to produce more of it so they could study it in detail. However Lowig's work delayed too long. In the mean time, Balard who was working in a pharmacy school in Montpellier, studying the brown seaweed Fucus in 1826 published his paper describing the new element. Initially Balard suggested the name muride, from the Latin word "muria" for brine. But the French Academy of Science, in turn, presuming that this name could create a confusion with Acidum muriaticum, which was actually HCl, and its salts - muriates, proposed (Joseph-Louis Gay-Lussac) the name brome from the Greek word bromos meaning stench to indicate its strong irritating odor. This name had been accepted everywhere.

Bromine Occurrence

Bromine is never found in its elemental form naturally, but in compounds with other substances, known as bromides and which are used as the raw material to produce commercial brominated products.

Bromine crustal abundance is 1.6x10-4% by mass, the total quantity is estimated as 1015-1016 tons. Mostly Bromine occurred as bromide salts (NaBr, KBr, and Br2) in very diffuse amounts in magmatic rocks as a permanent satellite of chlorined salts with concentrations 0.03% Bromine in halite (rock salt NaCl), up to 0.3% Bromine in potassium salts, such as sylvite and carnallite. The most recoverable form of bromine is from soluble salts found in seawater, salt lakes, inland seas, and brine wells. Sea water contains bromine in about 65 part per million (ppm) but Br is found in much higher concentrations (2500 to 10000 ppm) in inland seas and brine wells. Bromine migrates in easily soluble forms, forming hard rocks such as bromyrite or bromargyrite is a natural mineral forms of silver bromide AgBr, embolite Ag (Cl, Br) and iodembolite Ag (Cl, Br, I). The minerals are formed in oxidizing zones of sulphide silver-bearing deposites in dry arid regions.

Br is abundant in nature as bromide salts or as organobromine compounds, which are produced by many types or marine organisms. There are 7x10-4% of bromine in terrestrial plants and 1x10-4% in animal organisms. Bromine is found in various secretion liquids, such as tears, saliva, perspiration, milk, bile). Healthy human organism contains from 0.11 to 2.00 mg% bromine. Radioactive 82Br helped to trace the limited Bromine absorption by thyroid, medulla and pituitary gland. Bromides injected into human or animals bodies strengthen inhibitory process in brain-cortex, normalize nervous system which has been harmed by inhibitory process overwork. Being kept in the thyroid bromine competes with iodine essentially influencing metabolism process.

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