CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 595 



calculated that 100 grins, of the original chloride of sodium contained 21 

 mgs. of potassium calculated as K 2 0. This potassium was allowed for in the 

 test experiments. 



Two such experiments were made, and both are reported in the 

 " Challenger Memoir," along with some further details which are here omitted 

 for brevity's sake. We satisfy ourselves with quoting one of the two reports. 



Chloride of sodium used, .... 

 Potassium present, calculated as K 2 in mgs. 



by 



Chloride of potassium taken, .... 

 „ in the chloride of sodium, 



2 - 9 grms. 



Old Atomic New Atomic 



Weights.* Weights. + 



50-04 5012 



006 006 



5010 



5018 



Analysis. — Potassium found, calculated as K 2 in milligrammes. 



I. In the crude chloroplatinate by calculation, . 4790 48'35 



la. By calculation from the metallic Pt obtained 



therefrom, 



II. In the pure chloroplatinate, 



11a. Calculating from the metallic Pt obtained, 



III. In filtrate from crude chloroplatinate, 



IV. In filtrate from pure chloroplatinate, 



Sum of II., III., and IV., . 

 Excess over synthesis, . 

 Sum of Ha., III., and IV., 

 Excess over synthesis, . 

 From the numbers given under I. and the synthesis we 

 see that Fresenius' method, if used as it stands, would 

 have given a loss of potash amounting to 

 Or, per 100 of K 2 to be determined, to ... 



Note. — The chloroplatinates were weighed after being dried at 



drying at 105°, were only about 0001 more per unit weight of precipitate. 



For the analysis of salt mixtures poor in potassium Finkener's is the 

 only method that works at all ; for the analysis of potassiferous substances 

 generally, it of course only competes with other methods, but over any of 

 these it offers the great advantage of being in a high degree independent of the 

 nature of the foreign bases present. It must be admitted, however, that the 

 Finkener method, in the form in which it came out of the inventor's hands, owes 

 what there is in it of precision, to some extent, to compensation of errors. 

 Finkener's own test-analyses prove this : they gave very exact results, because 

 Finkener, in reducing his platinum- weights to potash, used the old atomic 



*K = 39; Cl = 35-5; Pt = 198. 



fK = 39-13; CI = 35-454; Pt = 194-8. 



47-62 



48-53 



47-06 



47-50 



46-62 



47-51 



2-64 



2-68 



0-85 



0-87 



5055 



51-05 



0-45 



0-87 



50-11 



51-06 



001 



0-88 



2-20 



1-83 



4-4 



3-7 



130°. 



The weights, after 



