624 PROFESSOR DITTMAR AND MR JOHN M'ARTHUR ON 



was dried only at 100°. Found per Cl 2 parts of fixed chlorine : — M = 592 '56 ; 

 platinum = 201-95; loose chlorine — 40224 X CI. Hence, assuming Pt = 195-5, 

 and that the surplus platinum (201-95 — 195-50 = 6*45) is present as PtX 6 H 2 ; 

 we have, for the composition of M parts — 



Platinum, 201-95 



2RC1, by calculation, 243-79 



4-0224x01, 142-61 



Hydroxyl, 299 



Hydrogen, 0-07 



Other water, 1-15 



592-56 



Experiment VII. 



This experiment was carried out pretty much in the same way as Experi- 

 ment VI. in the potassium series, and its object, like that of the latter, was to 

 ascertain the composition of the unwashed chloroplatinate precipitate. 20 c.c. 

 of the rubidium solution were weighed out, and poured into a tared bottle of 

 120 c c.'s capacity; a known (predetermined) weight of platinum solution was 

 then added, the bottle filled up to near the shoulder with water (total volume 

 = 200 c.c. about), the whole mixed, and allowed to stand over night. Platinum 

 used = 0-969 grm.; P = 195-2. 



After determination of the exact weight of the whole, as much as possible 

 of the clear liquor was sucked off into a tared Erlenmeyer flask, weighed, and 

 analysed by reduction with hydrogen. To be able to determine the loose 

 chlorine of the precipitate, the chloroplatinic acid solution was analysed 

 immediately before the experiment, by reducing a known weight with hydrogen, 

 weighing the platinum, and determining the chlorine in the filtrate ; the small 

 quantity of fixed chlorine in that solution being determined by itself, and 

 allowed for. The uncertainty in the titre of the rubidium solution of course 

 affected this experiment as well as it did the (unpublished) synthetical data of 

 Experiments I. to VI.; yet this uncertainty is not sufficient to invalidate the 

 principal result, which was that (for every Cl 2 parts of fixed chlorine) the 

 platinum amounted to 205-48 parts, ± say one unit ; but even 204-5 would be 

 a very high result. The loose chlorine amounted to 4-151 x CI; a large excess 

 over 4. 



Experiment VIII. 



From the above experiments we concluded that our " chloroplatinates of 

 rubidium" were not even normally constituted alkyl-chloroplatinates, i.e., 

 mixtures of the composition PtCl 6 li 2 ; but included hydrogen instead of part 



