596 PROFESSOR DITTMAR AND MR JOHN M'ARTHUR ON 



weight of platinum (Pt = 198); if he had used Seubert's value, which no doubt 

 comes nearer to the truth, his results would have been by about 2 per cent, of 

 their value higher (in calculating for K 2 0). 



We thought it worth while to try and ascertain the several errors involved 

 in the method, with the view of either evading them, or finding a formula for 

 their correction. 



There is, however, one other form of the platinum process which, although 

 of less general applicability, as far as it goes, would appear to be as inde- 

 pendent of the nature of the impurities in the substance analysed as Finkener's. 

 We refer to Mr Tatlock's method, which, with anything that falls within the 

 denomination of " potash salt " (pure or impure) is well known to give, to say 

 the least of it, fair results. 



We accordingly decided to test both these methods, as far as they compete 

 side by side with each other. Passing over a deal of pioneering work, which, 

 instructive as it was to ourselves, would probably not interest the majority of 

 our readers, we will begin with our experiments on Finkener's method, and in 

 the first instance detail certain experiments made for determining its value for 

 the determination of relatively minute quantities of potassium salts, diffused 

 throughout a substance consisting chiefly of sulphates and chlorides of sodium 

 and magnesium. Let us state at once that we always worked with mixtures of 

 this kind, because other acid-tests (than S0 4 or Cl 2 ) are of rare occurrence, and 

 other bases than MgO and Na 2 are easily removed by analytical processes. 

 From what we are going to say, every chemist will easily see to what extent 

 the method is more widely applicable, — as a matter of probability at least. 



Blank Experiments with Unmixed Sulphate of Soda. 



The sulphate was made from the chloride of sodium which had served for 

 the experiments detailed above, pages 594 and 595. It contained potassium 

 = 193 mgs. of chloride in 71'08 grms. 



Experiment I. — 1;5 grms. of the sulphate of soda (anhydrous) were dissolved 

 in 30 c.c. of water, the solution mixed with chloroplatinic acid, containing 50 

 mgs. of metallic platinum, and evaporated to a magma. To it, alcohol (1 vol.) 

 was added, and then {\ vol. of) ether, to dissolve out the chloroplatinic acid, 

 which was washed away as far as possible with ether-alcohol. The remaining 

 salt was almost, but not quite white. This was no more than we had expected, 

 having previously found that the mixture obtained in Finkener's process is 

 liable to contain an excess of platinum. To remove this admixture, the salt, 

 after removal of the ether and alcohol by drying at a gentle heat, was re- 

 dissolved in water, and " re-Finkenerised " without platinum; i.e., again evapo- 

 rated to a magma, and the latter washed with ether-alcohol. The platinum thus 



