616 PROFESSOR DITTMAR AND MR JOHN M'ARTHUR ON 



platinum, and enough (by calculation) of standard sulphuric acid to displace 

 the chlorine of the chlorides. Mixture (#R 2 S0 4 + PtCl 6 K 2 ) " recrystallised," 

 platinum reduced out in the wet- way, and weighed. 



Analysis (2) — Solution Finkenerised exactly as in (1) ; but recrystallisation 

 omitted. From mixture «R 2 S0 4 + PtCl 6 K 2 , the sulphates extracted by sal- 

 ammoniac ; the residual chloroplatinate dissolved, the platinum reduced out, 

 and weighed. The KC1 contained in the filtrate beside NH 4 C1 recovered by 

 evaporation and ignition, and weighed ; then dissolved in water, wrought 

 with PtCl 6 H 2 (in Fresenius' way), and the chloroplatinate weighed. 



In Analysis (3), Tatlock's method was applied in all strictness, except 

 that the chloroplatinate received an extra washing with 6 drops of platinum 

 solution. 



Analysis (1) — Finkener's Method; Recrystallisation. 



A = 77-22 mgs. ; p = 102*2 ; p x 076084 = 77*76; 

 Error = + 0*54 mg., or 0*7 per cent of A. 



Analysis (2) — Finkener's Method ; Sal- Ammoniac Form. 



A = 162-44 mgs.; p = 217*4; px 076084 =165-41 ; 



Excess over A = 2 97 rngs.' Crude KC1 from filtrate (from p) = 166*9 ; 

 Excess over A = 4*5 mgs. Chloroplatinate from the crude chloride of 

 potassium = 527'6 mgs.; whence by ' multiplication with 030627 = 161'59 

 mgs. of chloride of potassium ; deficit against A = 0*85 mg., or 0*52 per cent. 

 Platinum out of the last chloroplatinate = p' = 212*0; p' x 0*7608 = 161*30, 

 which is less than A by 1*14 mgs.. or 0*70 per cent. 



Analysis (3) — Tatlock's Method. 



A = 65*44 mgs. ; C = 209*2; C x 0*30627 = 6407 T ; T-A = -1*37, or 

 2*1 per cent of A. Platinum from C = 84*0 = p. p x 0*7608 = 63*91 = T'. 

 T'— A = — 1*53 mgs., or 2*3 per cent, of A. 



Analysis (2) did not do justice to its method, through unobserved causes, 

 it is true. Yet the error in (1) or (2) did not rise beyond 0*7 per cent, of the 

 small quantity to be determined. The Tatlock method loses 2 per cent, of 

 the chloride of potassium to be determined; i.e., it would report 9*8 instead 

 of 10 per cent. We believe the line of the applicability of Tatlock's process 

 must be drawn at about the " 10 per cent." salt. 



Three Analyses of synthetically prepared Sea- Water Salts. 



(Average ocean- water salts contain 2*11 per cent, of potassium calculated 

 as KC1.) 



