CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 583 



did at the time ; any other value which one could reasonably substitute would 

 lead to, essentially, the same conclusion) — 



PtC1 4w5Hc!} + M82Ha 



To check our work, we added up the several instalments of platinum, &c. 

 found in " C," " E," and " D," and contrasted them with the quantities found 

 in the original chloroplatinate. We had for 





Platinum. 



Fixed Chlorine. 



Loose Chlorine. 



«C" + "E" + "D," 



2-4965 



0-90419 



1-79265 grms. 



Original precipitate, 



2-4961 



0-90038 



1-79623 „ 



Considering the complexity of the operations involved in obtaining the 

 upper set of numbers, the agreement is very satisfactory. From our 

 analysis of chloroplatinates V. and Ya., and of their derivatives, we see that in 

 both cases the original chloroplatinate, by being recrystallised, lost chlorine 

 and platinum, with formation of free hydrochloric and chloroplatinic acids, 

 which passed into solution, and the most plausible explanation of the result is 

 to assume that the original chloroplatinates were mixtures of the constitution 



PtCl 6 K 2 +<Pt(OH) H 2 or Pt0 3 H,). 



and that part of the hydrochloric acid formed in the substitution of oxygen or 

 hydroxyl for PtCl 4 -chlorine served to dissolve away the ^Pt0 3 H 2 of oxyplatinate 

 of hydrogen as chloroplatinic acid. 



Now, in the original chloroplatinate of Experiment V. the weight of 

 platinum " Pt " per 2KC1 parts was (by synthesis) = 19667 ; while in the twice 

 recrystallised salt the corresponding quantity was = 195-54. 



In the case of chloroplatinate Va. we had "Pt" = 19658, and for its 

 derivatives — 



Salts "C." and "E." 



"Pt." = 195-48 194-93 



The analysis " E " was carried out on a relatively small scale. The mean 

 of the other two values is 195 51; and, supposing our theory to be correct, 

 the true atomic weight of platinum should be either equal to or less than 195*51. 

 Now the degree of completeness with which the surplus platinum is eliminated 

 by recrystallisation should be the higher the purer the chloroplatinate started 

 with, and of all our chloroplatinates those produced in Experiments VIII. and 

 IX. by means of a large excess of chloroplatinic acid apparently come nearest 

 to the ideal substance ; hence we thought the best thing we could do would be 

 to prepare a large supply of such chloroplatinate, to analyse it, and then to 

 see what value would come out for the weight of platinum per 2KC1 parts, 

 after recrystallisation from water and hydrochloric acid respectively, which 

 latter solvent we hoped would eliminate the surplus platinum more completely, 



