Disintegration of Metals at High Temperatures. 287 



dissociation) which would prevent a correct result from being 

 obtained are : — 



1. Change of barometer and temperature. 



2. Presence of unsaturated water-vapour in the apparatus, 



pressure unknown. 



3. Absorption or evolution of gas by the wire. 



4. Oxidation of parts of the leads not made of platinum. 



5. Large volume of apparatus rendering diminution of 



pressure inappreciable. 

 C). Evolution or absorption of gas by the glass. 

 7. Absorption and adsorption of gas by deposit, whether 



deposit be oxide, metal, or mixture *. 



(1) was corrected with great care, (2) overcome by drying, 

 (3) by heating the wire for 30 to 40 hours in the same gas 

 before the initial weighing, (4) by making the leads entirely 

 of thick platinum rods, and (5) by using an apparatus of 

 small volume. Still the amount of oxygen taken up was 

 always too small even for the formation of the oxide Pt 2 0, 

 (6) seemed negligible, but it was decided to overcome it by 

 having the vessel water-cooled as shown in fio*. 5 : on this 



-w-r 



being done the weight of oxygen lost was increased. With 

 air in the apparatus, the weight of oxygen lost sometimes 

 approximated very closely to that required for Pt 2 : it was 

 never equal to it, and it never exceeded it. The following 

 figures give the results of two very careful experiments made 

 in air on platinum :— 



Beginning of End of Expt. 



Expt. (42 hrs.). 



Barometer 754*4 mm. 754"8 mm. 



Temperature 18°*2 C. 18°*2C. 



Position of mercury in apparatus ... 9000 mm. 9000 mm. 



Position of mercury in reservoir ... 6400 mm. 588*0 mm. 



Weight of wire 175*80mgrns. 164*9 mgms. 



Volume of apparatus ' 20*40 cc. 



Loss of weight of oxygen 0*3884 mgm. 



Weight of platinum corresponding 



toPt 2 G 9*477 mgms. 



Actual loss of weight of platinum ... 10*90 mgms. 



Beginning of Expt. End of Expt. 



Barometer 764*7 mm. 764*3 mm. 



Temperature 17°*1 C. 17°*8 C. 



Position of mercury in apparatus ... 8550 mm. 855*0 mm. 



Position of mercury in reservoir ... 639*2 mm. 621*6 mm. 



Weight of wire 158*60 mgms. 151*20 mgms. 



Volume of apparatus 36*53 cc. 



Loss of weight of oxj'gen 0*261 mgm. 



Weight of Pt corresponding to Pt 2 0. 6*638 mgms. 



Actual loss of weight of platinum ... 7*40 mgms. 



* The conditions are further complicated by the formation of solid 

 .•solutions of the gas in the oxides, and of the oxides in one another. See 

 Wohler, Zeit. far Elektrochemie, 1909. 



