Arsenic was used in ant poisons, insecticides such as Paris Green, weed killers, paint, fly paper, certain wall papers and ceramics. When added to molten lead, arsenic improves the spherical shape of shot. Arsenic compounds are still used as a wood preservative, e.g. copper chromium arsenate. Arsenic is also used in making special types of glass, such as arsenic trisulfide glass. This material has the lowest thermal change in refractive index of any infrared optical material in use today. Lenses or windows made from As₂S₃ glass do not show optical distortion when subjected to the intense IR radiation from YAG or CO-lasers. Indium arsenide is used to produce infrared devices and lasers. Arsine gas, AsH₃ is an important dopant gas in the microchip industry. The gas is added in tiny amounts so that a few arsenic atoms become incorporated into the microchip and it is those which determine the degree of semiconductivity. Gallium arsenide is used in light-emitting diodes (LEDs) and solar cells.

'Dr Fowler’s solution’ was concocted in 1780 by the eponymous doctor. It was essentially a solution of potassium arsenite (K₃AsO₃) plus lavender water, this being added to prevent accidents. A few drops of the medicine were added to a glass of water or taken with wine. In the nineteenth century it was regarded as a popular cure-all, a general tonic and an aphrodisiac. Donovan's solution (AsI₃) was another arsenic-containing medicine. Misguided as these uses may have been, arsenic really did find a role in medicine in 1909 when Paul Ehrlich discovered a chemical that was capable of curing syphilis. He had undertaken a systematic study of arsenic compounds guided by the belief that he might discover one that was toxic to the syphilis spirochaete yet not toxic enough to harm the patient. On his 606^th attempt he finally discovered the one he was looking for (arsphenamine). It quickly became the first-choice treatment for this disease, and was named Salvarsan ("salvation by arsenic"). Eventually it was superseded by penicillin. Other arsenic-containing compounds are still used to this day in the treatment of african trypanosomiasis sleeping sickness (see melarsoprol). Acetarsone suppositories and arsiquinoforme, an antimalaria drug, are outdated. Several modern Chinese medicines include arsenic sulfide as an ingredient. More recently, arsenic trioxide (As₂0₃), as the drug trisenox, was approved for use by the FDA for treating promyelocytic leukaemia.

An arsenic derivative, named lewisite, was used in World War I as a chemical weapon. It acted to disable soldiers by forming blisters on exposed skin and damaging the lungs if the vapour was inhaled. Lewisite is a liquid which boils at 170°C but it is volatile enough to provide a deadly vapour. The compound’s chemical name is dichloro(2-chlorovinyl)arsine. Its common name refers to the American chemist, Lewis, who developed it. The antidote for lewisite is British anti-lewisite (BAL), which is injected and forms a chemical compound with the agent, thereby removing it from the body. BAL (also known as 2,3-dimercaptopropan-1-ol) is still used to treat people who have been poisoned by arsenic, mercury and other heavy metals. The two sulfhydryl (SH) groups in this molecule attach themselves strongly to the arsenic so that they can wrench it from the proteins and enzymes to which it has become attached. In this way arsenic can be eliminated.