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ARSENIC. A brittle metal of a bluish white colour, possessing very little lustre. By exposure to the atmosphere it becomes nearly black, and slightly pulverulent. It is very fusible, and is frequently employed to assist the fusion of other metals. At 856° Fahr. it is volatilized in white fumes, which constitute the arsenious acid, or white arsenic. It is from this substance that the metal of commerce is obtained, and is imported in large quantities from Saxony, the cobalt works of which supply Europe with arsenic. The ores of cobalt contain, with many other impuntics, much arsenic. This is dissipated by torrefying them when reduced to powder in a furnaoe with a long horizontal flue. The arsenious acid becomes condensed in this, and is removed by condemned criminals, the employment being very dangerous, and even fatal to life, on account of the impossibility of preventing particles of this powerful Raison from entering the mouth or nostrils. When first volatilised, it is contaminated with sulphur, &c., from which it is separated by mixing with impure potash, and subliming again in close vessels. It then constitutes the white arsenic of the shops. The metal is obtained from this by incorporating it with carbonaceous matter, and heating in a vessel provided with a receiver, to condense the arsenic which rises in vapour. The ores of arsenic are numerous and abundant, and it is a component of an endless variety of minerals. The process of roasting the ores of copper, iron, &a. is unhealthy, chiefly on account of the quantity of arsenic liberated. The minerals called realgar and orpiment (sulphurets of antimony) possess much beauty. Arsenic combines with oxygen in two pro portions, the first of which, the arsenious acid consists of arsenic 76 + oxygen 24. The second arsenic, acid of arsenic, 76 + oxygen 40. Both these compounds possess the characteristics of acid bodies; they redden vegetable blues, and combine with many salifiable bases, forming neutral salt. The first of these deserves particular attention, as it is the fatal poison so frequently employed in the destruction of human life by the suicide or the assassin. It is nearly inso luble in cold water, and is, therefore, generally taken in the state of turbid mixture. It adheres with singular obstinacy to the coats of the stomach and intestines, and produces speedy corrosion and inflammation. The symptoms of the poison are generally manifested within a quarter of an hour after it has been swallowed: these are sickness, pain at the stomach, thirst, burning heat in the mouth and fences, fainting., cold sweats, debility, and at last cramp, and contrac tions of the limbs. Most, and frequently all, of these symptoms are displayed by the sufferer before death. The only medicines likely to be effectual, are sulphuretted hydrogen water, and copious draughts of bland mucilaginous liquids. Carbonate of magnesia and opium have been on more than one occasion found highly beneficial. In cases of suspected poisoning by this mineral, the contents of the stomach, or the ejected matter, should be carefully saved and digested in distilled water.

This must be filtered through 11011111/1 paper, and, if highly coloured with beer, coffee, or other description of food, a small quantity of newly prepared pure animal charcoal, in powder, must be mixed with it until the colouring matter is destroyed. A second filtration produces a limpid and transparent fluid, suscep tible to the action of tests, which must now be applied. To one portion in a test-tube, add a small quantity of transparent lime-water ; in a short time, if arsenic is present, the fluids will become turbid and opaque. To another portion, add a few drops of liquid ammonia, and a solution of sulphate ofcopper ; this will produce a bright green precipitate, which is the pigment called Scheele's green. Pass a current of sulphuretted hydrogen gas through another portion, which will convert the arsenic into a eulphuret of a lemon yellow colour. To another portion add a few drops of ammoniated nitrate of silver, which will throw down a golden yellow precipitate, the arsenite of silver. If all these tests produce the effects here described, the corroboration will leave no room to doubt that aresenio was present ; but it is advisable, and especially where human life depends on the testimony, to place the matter beyond the possibility of doubt, by reducing the arsenic to the metallic state. This is effected by taking any of the before-named precipitates, and, when carefully dried, mixing it with about an equal quantity of black flux (finely divided charcoal and potash). A few grains of this must be carefully placed at the bottom of a test-tube, so that none shall adhere to the side. The flame of a spirit lamp must now be directed by a blow-pipe against the matter in the tube, and, in a short time, the arsenic will be sublimed, and coat the interior of the glass with the reduced metal of a shining grey colour ; or any of the precipitates may, when dry, be placed on a piece of ignited charcoal, when the arsenic will be volatilized, forming a dense white clouc and emitting a powerful odour, like that of garlic, which is peculiar to this metal. Arsenic is a metal easily combustible, and, in some cases, burns with singular intensity. If a small quantity is mixed in a mortar with chlorate of potash, a violent explosion takes place. When thrown into chlorine gas, it takes fire spontaneously if finely divided. The spec. gray. of arsenic is 5.763. A sulphuret of arsenic, called orpiment, is extensively used in dyeing. It is prepared by digesting arsenious acid in muriatic acid, and precipitating by sul phuret of ammonia. It is of a bright yellow colour, and produces a permanent dye. Arsenic is used for various purposes in the arts (see ALLOY) ; it promotes the fusion of other metals, and occasions many that are very refractory to melt at low temperatures. It is employed in the manufacture of lead shot, which it renders more brittle, and more easy to granulate.