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).
Berzelius was an early worker in this field; he was succeeded by Bunsen, and Deville and Debray, who worked out the separation of rhodium; and at a later date by P. T.
The temperature was determined by a platinum-rhodium and platinum thermo-j unction in contact with the metal.
Platinum itself he discovered how to work on a practical scale, and he is said to have made a fortune from the secret, which, however, he disclosed in a posthumous paper (1829); and he was the first to detect the metals palladium (1804)(1804) and rhodium (1805) in crude platinum.
Gold, platinum, iridium and rhodium only are proof against the action of this powerful oxidizer.
Aqua Regia, a mixture of nitric and hydrochloric acids, converts all metals (even gold, the "king of metals," whence the name) into chlorides, except only rhodium, iridium and ruthenium, which, when pure, are not attacked.
Debray in the case of rhodium, iridium and ruthenium, which evolve heat when they are dissolved in zinc. When the solution of the rhodium-zinc alloy is treated with hydrochloric acid, a residue is left which undergoes a change with explosive violence if it be heated in vacuo to 400°.
- Gold alloyed with 4th or 1th of rhodium is, according to Wollaston,very ductile,infusible and of the colour of gold.