In the following year he discovered rhodium; and at about the same time Smithson Tennant added two more to the list - iridium and osmium; the former was so named from the changing tints of its oxides (ipcs, rainbow), and the latter from the odour of its oxide (ovµA, smell).
Nitrogen oxides, recognized by their odour and brown-red colour, result from the decomposition of nitrates.
Chlorine, bromine, and iodine, each recognizable by its colour and odour, result from decomposable haloids; iodine forms also a black sublimate.
Cyanogen and hydrocyanic acid, recognizable by their odour, indicate decomposable cyanides.
Ammonia, recognizable by its odour and alkaline reaction, indicates ammoniacal salts or cyanides containing water.