History of Arsenic

Two yellow pigments were used by the ancient Egyptians; the one, a dull yellow, was a natural ochre or hydrated oxide of iron; the other was the bright yellow natural sulphide of arsenic. There is evidence that the latter was employed as early as the 18th Dynasty (1580 to 1350 b.c.) at Tell el Amarna and in the Theban necropolis. Arsenic is frequently found in ancient Egyptian copper and bronze, but the highest amounts recorded (2.3, 3.9 and 5.6 per cent.) are not higher than might have been present as natural impurities in the ores used.

The two naturally occurring sulphides were undoubtedly the first forms in which arsenic was known to the early Greeks, but it is doubtful whether two distinct substances were recognised by them. Aristotle, in the fourth century b.c., used the term sandarach; his pupil and successor, Theophrastus, referred to the same material as arrhenicum; and in the first century a.d., Dioscorides, a Greek herbalist, writing of arsenicon,5 said that as a remedy for coughs and asthma it " should be burned in combination with resin and the smoke inhaled through a tube." Pliny the Elder (first century a.d.) recommended its use for the same purpose " in the form of a fumigation with cedar dust," and such use probably accounts for the presence of the small quantity of realgar discovered recently in the Roman stratum of the floor in Wookey Hole, Somerset, there being no evidence in the district of its employment as a pigment.

Pliny identified sandarach with arsenicon or arsenicum, but he designated that which "resembleth burnished gold in colour," which he considered to be of the best quality, auripigmentum, of which term orpiment, the present name for the yellow sulphide, As₂S₃, is a contraction. Thus the name arsenic appears to be of Greek origin, its meaning being masculine or valiant, referring to the powerful activity of the sulphide, to which it applied. An Arabic origin of the word has been suggested, possibly from arsa naki, but there is doubt as to the authenticity of this term, and a closer relationship may be found in the Persian word for arsenic, zarnich or zirnuk. The more usual form of sandarach was reddish in colour and was undoubtedly the mineral, more or less pure, now known as realgar, As₂S₂, a name derived from the Arabic Rahj al ghar, " powder of the mine." The sandarach mines at Pompeiopolis, in Paphlagonia, in which criminal slaves were employed during the first century a.d., are described in the writings of Strabo. It is evident that white arsenic, in an impure form, must have been observed as a product of the combustion of the sulphides, but although certain medicinal properties were early recognised, no mention appears to have been made of its toxic nature. Nor does its identity as an individual substance appear to have been recognised before the eleventh century, when an Arabian chemist, Avicenna, described it as the product of sublimation of yellow or red arsenic; the thirteenth-century Latin translation of Geber's " Summa Perfectionis," supposedly written in Arabic in the eighth or ninth century, contains similar mention, but the origin of this work is not known. Roger Bacon showed that this arsenicum album could be obtained by heating orpiment with iron scale - evidently by oxidation of the liberated arsenic vapour. The substance soon became familiar to the mediaeval alchemists and arsenicum was thought to be of a nature akin to sulphur, and supposed to contain sulphurous earth, salt and a metal. As its poisonous qualities were recognised it became known under various names, such as Goblet-fiend, Bowl-sprite, and the German equivalents Scherben-kobold, Napchenkobold, also Cobaltum and Fly-poison, while the arsenicum album was known as Flowers of Arsenic, Huttenrauch (arsenical fume), Giftmehl (poison flour) and Rat-poison. Chaucer, however, referred to arsenicum as arsnek, which later was printed as arsnecke and arsenik; while Thynne in 1599 explained that " this Resalgar is that which by some is called Ratisbane, a kynde of poysone named Arsenieke."

According to Berthelot, a fragmentary writing attributed to Zosimus (fifth century a.d.) clearly indicates the preparation of metallic arsenic, but such a product does not appear to have been recognised until the thirteenth century, when Albertus Magnus obtained it by fusing arsenicum (i.e. orpiment) with twice its weight of soap. During the seventeenth and eighteenth centuries it was prepared by reduction of white arsenic by heating with oil or with potash and soap. That the product was not a true metal was soon recognised; Basil Valentine called it a "bastard metal" and Brandt a "semi-metal," and the latter, who early in the eighteenth century made the first discerning experiments on the chemical nature of the arsenical compounds, observed that white arsenic was the calx of metallic arsenic.

Scheele in 1775 discovered arseniuretted hydrogen and recognised arsenic acid as a chemical entity. The existence of the latter appears to have been suspected by Cavendish, according to his recorded experiments, as early as 1759, whilst the solid product resulting from the oxidation of arsenious oxide by heating with potassium nitrate was observed by the alchemists, Paracelsus describing it as arsenicum fixum and Libavius as butyrum arsenici; van Helmont called it a "fiery salt."

Berzelius in 1817 investigated the stoichiometrical relations of arsenic with other elements and examined the various compounds with sulphur. The physical properties of the element caused it to be classed with the metals, but its non-metallic chemical properties and its similarity in chemical behaviour to nitrogen and phosphorus were gradually recognised.