Incredibly dense, reflective metal with a slightly yellow hue to it m.p. 2410 ºC; 4370 ºF b.p. 4130 ºC; 7466 ºF density 22.42 g/cc (17 ºC); 1399.63 pound/cubic foot (63 ºF)	memory peg
	1803 Smithson Tennant, England; parallel by Antoine François de Fourcroy and Nicolas Louis Vauquelin, and by Hippolyte Victor Collet-Descotils, France
	Ιρις (Iris) = Greek goddess of the rainbow

Smithson Tennant (1761-1815) discovered Iridium along with Osmium in the summer of 1803 in the black residue formed by the dissolution of native Platinum in aqua regia (see Osmium). As with his Osmium work Tennant heated the black powder, followed by fusion with caustic soda at red heat. The resulting cooled mass was then dissolved in water, and the black residue remaining was treated in "marine acid" (hydrochloric acid). The residue was again fused with caustic soda and extracted with HCl, giving dark red crystals, probably of Na₂[IrCl₆].nH₂O. On heating these an unknown element was obtained as a white powder which "appeared of a white colour, and was not capable of being melted, by any degree of heat I could apply." About the naming of the new element, he wrote:

In 1801 Joseph-Louis Proust (1754–1826) had studied the dissolution of crude platina in aqua regia and attributed the small amount of black residue remaining to "nothing else but graphite or plumbago", a claim dismissed by Tennant, as noted below. Antoine François de Fourcroy (1755–1809), working with Nicolas Louis Vauquelin (1763–1829), took over the research of this black residue.
On the .. September 1803 and 17 vendémiaire an 12 (= 10 October 1803) they read a paper to the Institut National in Paris, published in 1804, in which they described their study of this black solid. They fused it with potash, extracted the cooled melt with water (to give a solution which they believed contained chromium but which may also have contained rhodium – later to be isolated by Wollaston in 1804) and treated the residue with more aqua regia. Addition of ammonium chloride to the latter gave, depending on conditions, red or yellow crystals. They thought that the red crystals contained a compound of a new metal, in addition to compounds of titanium, chromium, iron and copper.
These crystals could well have been, or could have contained, iridium as (NH₄)₂[IrCl₆], but crucially they did not name their "new element" (note).

On the same day as their first memoir was read to the Institut in September 1803, Hippolyte Victor Collet-Descotils (1773–1815), who had been a student of Vauquelin, reported essentially similar results, and published a more concise paper in 1803. Like the cautious Fourcroy and Vauquelin he did not name the new metal which he believed to be present, but said that he would assign it a name after further research. (note).

The memoirs of Fourcroy and Vauquelin and of Collet-Descotils were known to Tennant when he read his paper on the 21 June 1804 (note):

Upon making some experiments, last summer [1803], on the black powder which remains after the solution of platina, I observered that it did not, as was generally believed, consist chiefly of plumbago, but contained some unknown metallic ingredients. Intending tot repeat my experiments with more attentions during the winter [1803/04], I mentioned the results of them to Sir Joseph Banks, together with my intention of communicating to the Royal Society my examination of this substance, as soon as it should appear in any degree satisfactory.
Two memoirs were afterward published in France, one of them by M. Descotils and the other by Messrs. Vauquelin and Fourcroy. M. Descotils chiefly directs his attention to the effects produced by this substance on the solution of platina. He remarks that a small portion of it is always taken up by nitromuriatic acid during its action on platina; and, principally from the observations he is thence enabled to make, he infers that it contains a new metal [= iridium, PvdK], which, among other properties, has that of giving a deep red colour to the precipitates of platina. M. Vauquelin attempted a more direct analysis of the substance, and obtained from it the same metal as that discovered by M. Descotils. But neither of these chemists have observed that it contains also another metal [= osmium, PvdK], different from any hitherto known.

According to some authors, Fourcroy and Vauquelin gave the new substance the name of Ptene, from Greek πτηνος (ptènos) = winged. This Ptene consisted of Osmium and Iridium. Griffith wrote about this name: "There are references in the literature to ptene or ptène (...) as a name for osmium; indeed, Tennant is said to have proposed this name for it, whereas Partington says that Fourcroy and Vauquelin proposed it. The author can find no trace of this ungainly name either in Tennant's paper or in those of the French authors." (the references are J.N. Friend, Man and the Chemical Elements, London: Griffin, 1951, p. 303, and J. R. Partington, A History of Chemistry, London: Macmillan, 1962, Vol. 3, p. 105).

• Griffith, W.P., Bicentenary of Four Platinum Group Metals, Part II: Osmium and Iridium – events surrounding their discoveries. In: Platinum Metals Review 48, 4 (October 2004): 182-189 (on-line).
• International Platinum Association, Iridium History (on-line).
• Platinum. Gmelins Handbuch der anorganische Chemie, 8. Aufl.; System-Nummer 68 (1951), Pt. A. pp. 12-13.
• Tennant, Smithson, "On two Metals, found in the black powder remaining after the solution of Platina." Philosophical Transactions of the Royal Society of London 95 (1805), 411-418.
• Weeks, Mary Elvira, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 414-418.
• Greek Mythology: IRIS Goddess of the Rainbow & Messenger of the Gods w/ Pictures (on-line) (The illustration to the right is from that page).