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Published online by Cambridge University Press: 06 July 2012
The analytical methods referred to in our heading are infected with numerous sources of error, amongst which until lately the uncertainty of our knowledge of the combining constant “Pt” played a prominent part. This uncertainty, it is true, has been removed to a great extent by Seubert's investigation “Ueber das Atomgewicht des Platins,” Liebig's Annalen (for 1881), vol. ccvii. p. 1 et seqq. The value 194·8 for Pt, which he ultimately adopted, falls in well with his analyses of the chloroplatinates of potassium and ammonium, and there can be no doubt that his chloroplatinates were close approximations to the ideal substances. Hence his atomic weight 194·8 must be admitted to be nearer the truth than the value 198 of Andrews, which, until lately, was so generally employed by chemists in the calculation of their analyses. But it does not follow that in, for instance, the determination of chloride of potassium “as metallic platinum,” the factor 2KCl : Pt = 0·7657, calculated from Seubert's Pt, gives a more correct result than even the factor 0·75252, which follows from K = 39 : Cl = 35·5, and Pt = 198.
page 561 note * Let us state at once that in this memoir all atomic weights are referred to O = 16. For the atomic weights of potassium, ammonium, and chlorine we adopt Stas' numbers, as calculated by Lothar Meyer and Seubert; K = 39·136; NH4 = 18·056; Cl = 35·455.
page 562 note * “Challenger Reports,” Physics and Chemistry, vol. i., published by order of Her Majesty's Stationery Office, &c. Adam and Charles Black (and others).
page 562 note † A good deal of black iridium remained.
page 563 note * Specially made from pure (Trommsdorff's) carbonate-crystals, in a nickel basin.
page 566 note * The silver solution and a volumetric deci-normal solution of sulphocyanate.
page 568 note * Sometimes a film of platinum adheres firmly to the sides of the flask. This is easily recovered by dissolving it in aqua regia, evaporating to dryness in a porcelain crucible, and igniting the residue.
page 576 note * Meaning a solution containing so many centigrammes of metallic platinum per c.c.
page 578 note * The water determination in Experiment III. forms an exception, in this sense, that the substance was heated in a current of nitrogen, and the products filtered through a stopper of copper gauze (instead of metallic silver).
page 579 note * No doubt some COCl2 had been produced from the CO and AgCl, and not all been decomposed by the silver spiral, although we operated at the highest temperature permissible in a Bohemian glass tube.
page 580 note * We mean the bulk of the original precipitate; i.e., that part of it which did not pass on the filter, and which, as stated on page 570, amounted to 9·6244 grms. after drying at 130°C.
page 581 note * And a small slip in a calculation; the correctly calculated value is 196·64.
page 582 note * The AgCl in the titrations had a tinge of pink indicating platinum.
page 582 note † Including the 0·87 mg. from the distillate.
page 582 note ‡ Instead of 194·93, as found for “E.”
page 584 note * This second experiment was earned out for us by Mr James Robson.
page 585 note * Made each out of two lipless test-tubes sliding over one another.
page 588 note * “P” stands for weight of platinum used as chloroplatinic acid, per 2KCl parts.
page 589 note * Per 1 grm. chloride of potassium as calculated from the platinum, assuming Pt to correspond to 2KCl.
page 592 note * “Ether alcohol,” in connection with Finkener's method, always means 1 volume of anhydrous ether and 2 volumes of absolute alcohol.
page 593 note * For details, see “Challenger Memoirs,” Physics and Chemistry, vol. i. (appendix), p. 233Google Scholaret seqq.
page 593 note † 
page 594 note * We subsequently came to prefer the perchlorate for obvious reasons.
page 595 note * K = 39; Cl = 35·5; Pt = 198.
page 595 note † K = 39·13; Cl = 35·454; Pt = 194·8.
page 597 note * We adopted this word for designating the operation described.
page 598 note * Meaning a solution containing 5 centigrms. of platinum metal per c.c. The phrases “5 per cent.,” “10 per cent.,” &c, platinum solution must be read in this sense.
page 599 note * Determined by a blank carried out on a large scale.
page 601 note * Finkener does not say it is; but for a time it was our method.
page 602 note * For mode of preparation, see “Challenger Memoir,” p. 16.
page 603 note * See last line of this page.
page 603 note † The designations of the following sets of experiments do not in general indicate the order in which they were carried out.
page 603 note ‡ Meaning a mixture containing 95 parts of chloride of potassium in 100 of total anhydrous salts.
page 604 note * In only one case, No. (4), did the filtrate contain a trace of platinum. It was recovered by H2S, the PtS2 made into Pt, and its weight (0·4 mg.) added on.
page 607 note * As communicated by him to a Committee of the British Association, and published by them in a Report presented to the Meeting at Glasgow, in 1876.
page 608 note * We used to be under this erroneous impression ourselves until some three years ago, when we analysed a carefully prepared platinum solution (which had been specially freed from extra hydrochloric acid) for chlorine and platinum. It contained very nearly 6 × Cl for 1 × Pt, which, by the way, is in accordance with an old analysis of “chloride of platinum,” quoted in Gmelins's handbook as having been made by Vauquelin.
page 610 note * These factors were calculated from results for “M” in the first series of potassium experiments. We did not consider it necessary to recalculate the analyses with our present factors.
page 611 note * Those of (4) were lost by a disaster in the laboratory.
page 614 note * From the one analysis of this set in which Tatlock's directions were strictly obeyed.
page 621 note * A weighed portion of the filtrate from the platinum evaporated to dryness, and made neutral, as above explained, and weighed. Actual weight = ·2213 grm. for the fraction analysed. The salt was analysed, and found to contain 29·09 per cent, of chlorine, i.e., almost exactly as much as the original chloride of rubidium.
page 631 note * This experiment was carried out for us by Mr James Robson.