564 PROFESSOR DITTMAR AND MR JOBN MARTHUR ON 



drying at 110° C, weighed 217*9 mgs.; 193*5 mgs. of it, when reduced in 

 hydrogen (dry-way), yielded 77*8 mgs. of metal, or 87'61 mgs. per 217*9 mgs. of 

 precipitate. The filtrate from the " chloroplatinate " contained 2*4 mgs. of 

 " platinum," and 0*49 mg. of chloride of potassium (determined and weighed 

 as PtCl 6 K 2 ). Hence chloride of potassium in the precipitate = 6479 (weight of 

 KC1 used) —0-49 = 64'3 mgs. Platinum (1) by synthesis, = 88*0; (2) by analysis, 

 = 87*61 ; hence platinum per 2KC1 by (1) = 2042; by (2) = 203*3. These numbers 

 are certainly higher than the true atomic weight of platinum, but, considering 

 the small scale on which the analysis was made, and that all the impurities 

 of the 10 grms. of original metal were concentrated in that small remnant of 

 90*4 mgs. of metal, the original metal, we thought, could be accepted as 

 sufficiently pure. To prepare a standard solution, 49*5327 grms. of Matthey's 

 metal (sponge) were ignited in a porcelain crucible, which brought down the 

 weight to 49*5302 grms. These were dissolved in a Berlin basin, under 

 a funnel, in aqua regia, made from specially prepared acids, the nitric acid 

 expelled by repeated evaporation with hydrochloric acid, the ultimate residue 

 dissolved in water, diluted to 1 litre, and weighed. A small quantity of an 

 insoluble residue separated out on dissolving the chloroplatinic acid crystals 

 in water; it was filtered off, ignited, and weighed, and its weight, 3*4 mgs., 

 deducted from the original weight of platinum taken, as a correction. The 

 solution was preserved as containing very nearly 49 5 mgs. of metal per c.c, 

 and exactly 0*45930 grm. per 10 grammes of solution. 



The vast majority of our quantative syntheses and analyses were made 

 with this or some other standard solution derived from Matthey's metal. 

 Wherever St Petersburg metal was used, this is specially stated. 



Chloroplatinic acid, as prepared by means of the aqua regia process, is liable 

 to be contaminated with the nitroso-compound PtCl 6 (NO) 2 . After having made 

 a considerable number of syntheses and analyses of alkaline chloroplatinates, 

 we found that one of our solutions at least was thus contaminated. It is 

 difficult to see how a small admixture of the nitroso-body could affect a 

 synthesis of potassium or rubidium chloroplatinate, yet its presence is at 

 best no improvement; hence, after that discovery, we tried to make platinum 

 solution by means of hydrochloric acid and chlorine gas, i.e., the method 

 which Seubert used once (for his Darstellung III., p. 16 of his memoir), 

 to return to the old process. We soon saw how it came that Seubert tried 

 the process only once ; the solution of the metal takes place with an exas- 

 perating degree of sluggishness. 



In the following form, however, we found the method to work satis- 

 factorily. The platinum, preferably in the spongy form, is introduced into 

 a light-coloured glass-stoppered bottle of, say, 2 litres' capacity; a sufficiency 

 of fuming hydrochloric acid is poured on it, and the bottle filled with chlorine 



