When we talk about Arsenicum in homoeopathic circles we actually mean Arsenicum album, which is arsenicum oxide or As2O3.
Arsenicum metallicum is not very well known, Clarke gives a brief description, but it was assumed to be quite similar to Arsenicum album. Now that we know the influence of the oxygen component we are better able to make the subtle distinctions between the two.
Arsenicum album, Natrium and Kali arsenicosum are also mentioned.
The name has been derived from the Greek word ‘arsenikos’ which means ‘male’. It was discovered in 1250. It’s use through the ages has mainly been as a poison, like rat poison or nerve gas. It isn’t really a metal but it has a few metallic properties. It readily evaporates in air.