O = The general mean of all, if 0 = 16, gives Pt 194.867. Hence, for all practical calculations, the value 195 may be safely employed. OSMIUM. The atomic weight of this metal has been determined by Berzelius and by Fremy. Berzelius* analyzed potassium osmichloride, igniting it in hydrogen like the corresponding platinum salt. 1.3165 grammes lost .3805 of chlorine, and the residue consisted of .401 grm. of potassium chloride, with .535 grm. of osmium. Calculating only from the ratio between the Os and the KCl, we have, Os = 198.494; or, if 0 = 16, Os = 198.951. Fremy's determination † is based upon the composition of osmium tetroxide. No details as to weighings or methods. are given; barely the final result is stated. This, if O 15.9633, is Os = 199.190. If 0 = 16, Os = 199.648. O = Berzelius' work is evidently entitled to preference, although neither determination is in any sense equal to the present requirements of chemical science. The values given are doubtless several units too high. IRIDIUM. The only early determination of the atomic weight of iridium was made by Berzelius, who analyzed potassium iridichloride by the same method employed with the platinum and the osmium salts. The result found from a single Compt. Rend., 19, 468. Journ. für Prakt. Chem., 33, 410. 1844. 1828. analysis was not far from Ir = 196.7. This is now known to be too high. I have not, therefore, thought it worth while to recalculate Berzelius' figures, but give his estimation as it is stated in Roscoe and Schorlemmer's "Treatise on Chemistry." In 1878 the matter was taken up by Seubert,* who had at his disposal 150 grammes of pure iridium. From this he prepared the iridichlorides of ammonium and potassium, (NH), IrCl, and K,IrCl, which salts were made the basis of his determinations. The potassium salt was dried by gentle heating in a stream of dry chlorine. Upon ignition of the ammonium salt in hydrogen, metallie iridium was left behind in white coherent laminæ. The percentages of metal found in seven estimations were as follows: 43.742 43.725 43.745 43.739 43.726 43.739 43.705 Mean, 43.732, .0035 The potassium salt was also analyzed by decomposition in hydrogen with special precautions. In the residue the iridium and the potassium chloride were separated after the usual method, and both were estimated. Eight analyses gave the following results, expressed in percentages: K39, N = 14, Ag = = 108, and Cl = 35.5, give nearly The general mean of all, if 0 = 16, gives Pt 194.867. Hence, for all practical calculations, the value 195 may be safely employed. The atomic weight of this metal has been determined by Berzelius and by Fremy. Berzelius* analyzed potassium osmichloride, igniting it in hydrogen like the corresponding platinum salt. 1.3165 grammes lost .3805 of chlorine, and the residue consisted of .401 grm. of potassium chloride, with .535 grm. of osmium. Calculating only from the ratio between the Os and the KCl, we have, Os 198.494; or, if 0 16, Os = 198.951. = = Fremy's determination † is based upon the composition of osmium tetroxide. No details as to weighings or methods. are given; barely the final result is stated. This, if O= 15.9633, is Os = 199.190. If O 16, Os 199.648. Berzelius' work is evidently entitled to preference, although neither determination is in any sense equal to the present requirements of chemical science. The values given are doubtless several units too high. IRIDIUM. The only early determination of the atomic weight of iridium was made by Berzelius, who analyzed potassium iridichloride by the same method employed with the platinum and the osmium salts. The result found from a single *Poggend. Annal., 13, 530. + Compt. Rend., 19, 468. 1828. Journ. für Prakt. Chem., 33, 410. 1844. 1828. IRIDIUM. = 255 196.7. This is now known analysis was not far from Ir to be too high. I have not, therefore, thought it worth while to recalculate Berzelius' figures, but give his estimation as it is stated in Roscoe and Schorlemmer's "Treatise on Chemistry." In 1878 the matter was taken up by Seubert,* who had at his disposal 150 grammes of pure iridium. From this he prepared the iridichlorides of ammonium and potassium, (NH4), IrCl, and K,IrCl, which salts were made the basis of his determinations. The potassium salt was dried by gentle heating in a stream of dry chlorine. Upon ignition of the ammonium salt in hydrogen, metallic iridium was left behind in white coherent laminæ. The percentages of metal found in seven estimations were as follows: 43.742 43.725 43.745 43.739 43.726 43.739 43.705 Mean, 43.732, .0035 The potassium salt was also analyzed by decomposition in hydrogen with special precautions. In the residue the iridium and the potassium chloride were separated after the usual method, and both were estimated. Eight analyses gave the following results, expressed in percentages: Cl1 29.290 39.890 30.842 29.277 39.868 39.876 30.835 29.289 39.877 30.825 29.287 39.879 30.811 29.310 39.882 30.814 29.285 39.883 30.792 29.288 29.291, .0024 * Ber. d. Deutsch. Chem. Gesell., 11, 1767. From these data several values for the atomic weight of iridium may be calculated: In the potassium salt, instead of calculating from the percentages directly, we may reckon upon the ratios between Ir and Cl, and between Ir and 2KC1: Again, we may combine this mean with the value derived from the ammonium iridichloride, and so estimate the relative importance of the latter: We may assume, then, from all the facts before us, that if 16, the atomic weight of iridium varies from the even number 193 only within the limits of experimental error. = PALLADIUM. The atomic weight of palladium has been studied by Berzelius and by Quintus Icilius. In an early paper Berzelius* found that 100 parts of the metal united with 28.15 of sulphur. Hence Pd = 113.63, a result which is unquestionably far too high. * Poggend. Annal., 8, 177. 1826. |