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Atomistry » Iridium » Physical Properties » Atomic Weight | ||
Atomistry » Iridium » Physical Properties » Atomic Weight » |
Atomic Weight of IridiumApproximate Value of Atomic Weight of Iridium
That the atomic weight of iridium is of the order of 193, and not a multiple or submultiple of this amount, may be gathered from several lines of argument. The more important of these may be briefly summarised as follows:
Exact Atomic Weight of Iridium
The first determination of the atomic weight of iridium is due to Berzelius. His single analysis of potassium chlor-iridate leads to the very high value Ir = 196.7.
This value was not supplanted until Seubert's analyses of ammonium and potassium chloriridate were published in 1878. The salts were ignited in a stream of hydrogen, and the residual metal weighed; in the case of the potassium salt, of course, the metal was obtained mixed with potassium chloride, which was dissolved out, recovered by evaporation, and weighed. The results were as follow: (NH4)2IrCl6: Ir:: 100.000: 43.732; whence Ir = 193.38 K2IrCl6: Ir:: 100.000: 39.880; whence Ir = 192.99 K2IrCl6: 2KCl:: 100.000: 30.820; whence Ir = 192.88 K2IrCl6: 4Cl:: 100.000: 29.291; whence Ir = 193.26 In 1890, Joly determined the percentages of potassium chloride and iridium in the salt IrCl3.3KCl.3H2O, and the percentage of iridium in the salt IrCl3.3NH4Cl: Ir: 3KCl:: 100.000: 115.848; whence Ir = 193.07 (NH4)3IrCl6: Ir:: 100.000: 42.003; whence Ir = 193.27 Determinations of the percentage of iridium in ammonium chlor-iridate were made by Hoyermann in 1911: (NH4)2IrCl6: Ir:: 100.000: 43.630 whence Ir = 192.59 and by Holzmann in 1912: (NH4)2IrCl6: Ir:: 100.000: 43.734 whence Ir = 193.40 The preceding results fall considerably short of the modern standard of atomic weight work, and further determinations of the atomic weight of iridium are desirable. Archibald, in 1909, announced that he had determined the value Ir = 192.90 from analyses of potassium iridi-chloride, but no details of the work have yet been published. The International Committee's Table for 1918 gives Ir = 193.1. |
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