Arsenic As

Discovery

Arsenic compounds were known in antiquity. Yellow orpiment and red realgar served as pigments and medicines and appear in Greek and Roman writings. The medieval scholar Albertus Magnus is often credited with isolating the element around the thirteenth century, though who first prepared it is not certain.

Arsenic trioxide is tasteless and odourless, which made it a notorious poison from the Middle Ages into the nineteenth century. In 1836 the British chemist James Marsh devised a test sensitive enough to reveal tiny traces of arsenic in tissues, a milestone in forensic toxicology.

In 1910 Paul Ehrlich introduced Salvarsan, an arsenic compound that treated syphilis. It is regarded as the first modern synthetic drug designed to attack a specific pathogen, and it opened the era of chemotherapy.

Origin of the name

The English name traces back through Latin arsenicum to Greek arsenikon, which is usually linked to a Persian word, zarnikh, for the yellow mineral orpiment. The symbol As comes from the Latin form.

Main uses

• Semiconductors: gallium arsenide and indium gallium arsenide are used in radio-frequency chips, laser diodes and infrared devices, and arsenic is a common n-type dopant in silicon.
• Alloys: small additions harden lead, historically for battery grids and shot.
• Medicine: arsenic trioxide is a standard treatment for acute promyelocytic leukaemia (APL).
• Wood preservation: chromated copper arsenate (CCA) protected timber for decades, but many countries now restrict it for residential use.

Isotopes

Arsenic has only one stable isotope, arsenic-75, so natural arsenic is monoisotopic and its atomic weight is known very precisely. Several radioactive isotopes can be made artificially, but they have few everyday applications beyond research tracers.

In everyday life

Arsenic leaches naturally from rocks into groundwater. Contamination of tube wells in Bangladesh and West Bengal has exposed tens of millions of people and is often described as one of the largest mass poisonings in history. The World Health Organization recommends a guideline of 10 micrograms per litre in drinking water.

Rice takes up arsenic from flooded paddies more than most crops, so rice products contain small amounts; rinsing rice and cooking it in plenty of water can lower the level somewhat. Most arsenic in seafood and seaweed is in organic forms of much lower toxicity.

In the nineteenth century, arsenic-based green pigments such as Scheele's green and Paris green coloured wallpaper, fabrics and even confectionery, and they are blamed for many cases of illness.