2SS Mr. J. H. T. Roberts on the 



Platinum in Pure Oxygen. 



Beginning of Expt. End of Expt., 



Barometer 754*7 mtn. 761*5 mm. 



Temperature 14°*8 C. 15°'l cc. 



Position of mercury in apparatus ... 740'0 mm. 740*0 mm. 



Position of mercury in reservoir 5720 mm. 537'3 mm. 



Weight of wire 209'1 mgms. 199'1 origins. 



Volume of apparatus 27*41 cc. 



Loss of weight of oxygen 1*39 mgms. 



Weight of Pt corresponding to Pt0 2 . 8*478 mgms. 



Actual loss of weight of platinum ... 10*00 mgms. 



It is impossible, after the most careful experiments, to> 

 obtain an exact simple atomic relation with platinum : the 

 results obtained in air, and the fact that the weight of 

 oxygen taken up frequently approximated to, but never 

 exceeded, that required for the lower oxide Pt 2 0, might seem 

 to indicate the formation of this oxide in air and its partial 

 dissociation. Since in an atmosphere of oxygen the ratio of 

 platinum to oxygen approximates to that required for PtQ 2 , 

 it is possible that the oxide formed is in all cases Pt0 2 , and 

 that in air so much dissociation takes place that the ratio 

 approximates to that required for Pt 2 0. Since in air the 

 partial pressure of the oxygen is less, we should expect a 

 greater amount of decomposition of the oxide, as is easily 

 seen by applying the law of mass action to the equation 



Pt0 2 -^-^Pt-f-0 2> 

 whence we obtain 



P Pt o 2 = K(Pp t xPo 2 ). 



The dissociation will be compensated for to an unknown, but 

 probably small, extent by the adsorption of oxygen by the 

 dissociated platinum particles *. As mentioned above, this- 

 platinum will be the result of the dissociation of the oxide. 



Iridium in Pure Oxygen. 

 The effect with iridium is very striking ; the deposit upon 

 the glass is perceptible after two or three minutes. The 

 following experiment took about 30 minutes : — 



Beginning of Expt. End of Expt. 



Barometer 761*2 mm. 7620 mm. 



Temperature 13°\ r > C. 13°*3 C. 



Position of mercury in apparatus ... 7400 mm. 740*0 mm. 



Position of mercury in reservoir 549 9 mm. 454*5 mm. 



Weight of wire 431*00 mgms. 402*15 mgms. 



Volume of apparatus 2899 cc. ....... 



Loss of weight of oxygen 4*89 mgms. 



Weight of iridium corresponding to 



Ir0 2 29*51 mgms. 



Actual loss of weight of iridium 28*85 mgms. 



* It is worth noticing that if the deposit formed on the walls of the- 

 ■vessel consisted of platinum particles, the absorption of the oxygen 

 corresponding* to Pt0 2 would represent the enormous absorption by the 

 platinum of 2470 volumes. 



