Element Silver (Argentum), Ag, Transition Metal

On account of its remarkable properties and of its occurrence in the metallic state, silver, or Argentum is one of the longest known metals. It is also a typical example of a "noble" metal, i.e. one which does not undergo oxidation in the air either in the cold or in the heat; under the most varied conditions, it completely retains its metallic character, even externally. This resistibility, together with its fine lustre, its plasticity, and comparatively scarce occurrence, have assured for silver its use for costly articles and for coinage. On account of the property possessed by many silver compounds of undergoing chemical change when exposed to light, this metal has found a very extensive technical application in photography. Further, the sparing solubility of many silver compounds, especially the halogen derivatives, has conditioned the use of silver as a reagent in the laboratory, and has made it indispensable for such purposes.

In its chemical behaviour silver exhibits various relationships. A bond of union with the alkali metals is formed by its elementary ion; some silver compounds are also isomorphous with the corresponding sodium compounds. The sparing solubility of its halogen compounds allies it to the cuprous, mercurous, and the thallous compounds; the last-named metal forms the connecting link between silver and the alkali metals.

Silver is a metal of a fine white colour, which melts at 945°, and in the air behaves indifferently towards the oxygen and water vapour. It is attacked, however, by sulphuretted hydrogen, being converted into silver sulphide; many organic sulphur compounds, and the soluble metallic sulphides, act similarly. Even at a comparatively high temperature oxygen under ordinary pressure does not act on silver - if, however, the pressure is increased, the pressure of decomposition of silver oxide is soon exceeded, and the latter is formed from silver and oxygen.

Besides the white silver in coherent condition, there are other forms of this metal. Thus, when silver is precipitated in the metallic state from solutions by means of reducing agents, it can assume a great variety of colours according to circumstances. It appears that the yellow and brown forms of silver, more especially, which separate out under the action of light on mixtures of silver salts and organic substances (which have a reducing action) are amorphous; they are more quickly attacked than the grey and black forms of silver, and also change into these under the influence of catalysers.

Metallic silver also has the property of passing into the colloidal condition. This colloidal silver is obtained by reducing silver in alkaline liquids, and also when an electric arc is produced between silver electrodes under water; by the latter means, the silver is first volatilised and then suddenly precipitated in the surrounding water, whereby it passes into the less stable form of colloidal silver. These solutions are of a brown or red colour; the forms of colloidal silver obtained by chemical means dry up to masses with a metallic lustre, the colour of which can be altered by slight influences, so that it passes through all shades of yellow, red, violet, and green. Notwithstanding their metallic lustre, these masses do not behave like metallic silver, since they do not conduct the electric current. They are unstable, and are converted by many catalytic influences into ordinary white or grey silver.

Silver is not attacked by dilute acids except nitric acid, which readily dissolves it with evolution of nitric oxide and formation of silver nitrate. It dissolves to the sulphate, also, in concentrated boiling sulphuric acid, whereby sulphur dioxide escapes. It is very resistant to basic substances; crucibles and dishes of silver are used in the laboratory in working with caustic potash and soda, as this, metal is not attacked to any considerable extent even on fusing these substances.

In the pure state silver is a white tenacious metal, which can be readily drawn into wire, and made into very thin sheets by rolling or hammering. For use it is alloyed with 10 per cent of copper in order to make it harder. It conducts heat and electricity very well, and occupies, in this respect, the first place among the metals.

The combining weight of silver is an important magnitude, since on account of the excellent properties of its halogen compounds for analysis, many other combining weights have been determined by means of these. The following method has been used in order to establish the combining weight of silver with respect to oxygen.

Silver, or Argentum is known by the mankind since Pre-History, and its discovery is estimated happened to shortly after that of copper and gold, even though silver is also found in native form. Archaeological evidence suggests that Egyptians had been using silver for at least since predynastic period (5000 - 3400 B.C.). However before the middle of 2^nd millennium B.C. silver was rarity and was more valuable than gold. Ancient Egyptian silver is believed to be obtained from Syria. Earliest silver articles from Egypt and other Western Asian countries contained from 1 to 38% gold and are considered to be smelted from natural alloys. Perhaps such alloys had been called "white gold".

Chikashige has observed the presence of silver, in association with other metals, in specimens of Chinese money dating from 722 to 481 b.c.; and also in a Corean mirror of the tenth century a.d.

Silver is a rare element, its abundance in the Earth's crust thousands times less than that of copper. Estimated crustal abundance is less than 1 ppm. In Central Europe silver abundance is significantly higher than average, especially in Ore Mountains, the Harz, mountains of Bohemia and Saxony.

In the period of discovery, conquest and settlement in Americas, as great number of native solver had been found in Peru, Chili, Mexico and Bolivia. For instance, plate-shape silver nugget from Chili a weighed 1420 kg. Argentina is the only country which had been named after known chemical element. The last native silver nuggets were found in Ontario, Canada in 20^th century. One of the most well-known of them, the Silver Pavement was 30 meters long and 18 meters high going deep into the Earth. A 20 tons ingot was smelted from it.

Native silver is very rare; this element is found mainly as a constituent part of minerals, which are known over 50. Silver is associated with tellurium, selenium, sulphur, and halogens. The most important of minerals is argentite Ag₂S. Much more silver is spread up in complex polymetallic ores, which contain copper, lead and zinc.

Silver is found in nature both in the free state and in combination. Its principal ores are argentite, Ag₂S; dyscrasite, Ag₂Sb to Ag₆Sb; hessite, Ag₂Te; horn-silver, AgCl; stephanite, 5Ag₂S,Sb₂S₃; pyrargyrite, 3Ag₂S,Sb₂S₃; proustite, 3Ag₂S,As₂S₃; stromeyerite, Ag₂S,Cu₂S; polybasite, 9(Ag₂S,Cu₂S),Sb₂S₃,As₂S₃; fahlore, a complex sulphide of silver, arsenic, and antimony; the bromide and iodide; and amalgams of varying composition. It is also associated with native sulphides, such as galena, chalcopyrite, and zincblende. Sea-water contains about 0.001 mg. per litre.

Silver is a permanent constituent part of living organisms. In sea plants its abundance reaches 0.025 mg per 100 g of dry matter in terrestrial ones 0.006 mg; in sea animals 0.3-1.1, in mg, in terrestrial animals trace of element, 10^-2-10^-4 mg. Silver is accumulated in animals organisms in some glands, eye pigment layer and erythrocytes. Silver creates complexes with proteins, blood globulins, and haemoglobin. Blocking sulfhydryl group's silver prevents creations of active zones and inhibits various processes, for instance, deactivates myosin adenozintriphosphate activity. When parenterally injected, silver is bound mostly by blood globulins.