PLATINUM. SEUBERT. 119 



we have here, in the potassium compounds, a distinct indi- 

 cation of minute differences of deportment working in 

 opposite directions. 



The ammonium bromo-platinate comes out practically 

 exactly on the atomic ratio, while the potassium salt gives 

 an analytical excess " high * J or positive, corresponding to 

 about 0.2 on the atomic weight of platinum. 



It will be noticed that the chloro-salt of potassium was 

 " low " to about the same extent. 



Thus, combining such salts, differing only by one ele- 

 ment, we notice a compensation of the minute errors or 

 deviations. 



We need not re-state that it would be mathematically 

 absurd to calculate the atomie weight from these data taking 

 them to be absolutely exact, and then to wonder and ponder 

 how the chloro-salt will give a higher value for the atomic 

 weight of platinum, than the bromo-salt, or how the ammo- 

 nium compound can give a different atomic weight from the 

 potassium compound. 



The fact that the sign or direction of the analytical excess 

 oscillates with the metal (Ka, Am) or the intermediate (Br, 

 Cl), while the numerical amount of this analytical excess 

 remain practically the same, shows that we here simply are 

 at the very limit of precision of this kind of chemical work. 



As now the amount of this analytical excess corresponds 

 to at most two-tenths on the atomic weight of platinum, it 

 is palpable, that the totality of these experimental determi- 

 nations demonstrate the atomic weight of platinum to be 

 195 exacth r , which the individual determinations or series of 

 determinations hit squarely or deviate from in either direc- 

 tion to an extent not exceeding 0.2. 



The most excellent chemical work done by Seubert in 

 iSSi, permits us to say that the true atomic weight of plati- 

 num does not differ from the standard value 195 by any 

 fraction within the limits of precision attained, which is 

 about 0.2. 



All deviations from 195 actually noted, are within this 

 limit, and about equally frequent, according to the elements, 

 positive and intermediate, present in the platinum salt used. 



