396 Mixter — Heat of Formation of Titanium Dioxide. 



The fusion was yellow and it yielded to hot water a little 

 sodium plumbate. The insoluble yellowish brown powder left 

 by the water liberated chlorine from hydrochloric acid — a 

 proof of the presence of peroxide. 



The heat of Pb.O = 503 is Thomsen's. Tscheltzow* found 

 for PbO.O=12'l, hence Pb.20^62'4, which is used in the 

 following calculation : 



2NaX> + Pb = Na PbO + Na,0 + .... 63,500 



2Na 2 + 20 = 2Na„0 2 + 38,800° 



2Na 2 4- 20 + Pb = Na 2 Pb0 3 + 102,300 c 



Pb + 20 = Pb0 2 + 62,400° 



2Na 2 + Pb0 2 = Na 2 Pb0 3 + 39,900° 



As the fusion in the foregoing experiment yielded a mixture 

 of lead oxides, it seemed best to use lead dioxide in place of 

 the metal. For this purpose the dioxide w x as made by acting 

 on lead acetate with a hypochlorite and also by treating reel 

 lead with nitric acid, but the products were not pure enough 

 for the purpose. Accordingly dioxide was prepared by elec- 

 trolyzing a saturated solution of lead nitrate in dilute nitric 

 acid. It was washed, dried, pulverized, and washed again to 

 remove adhering nitrate. Finally the lead dioxide was heated 

 to 280° until the weight was constant, and as it still retained 

 water the temperature was raised until some red lead formed on 

 the bottom of the beaker containing it. The composition of 

 the product was as follows : Pb0 2 , 93'7 ; PbO, 6*0 ; H 2 0, 0*3 per 

 cent. The correction for lead oxide and water would be small 

 and was not made in the following experiments : 



Lead dioxide 



Sulphur 



Sodium peroxide . _ - . 



Water equivalent of system 

 Temperature interval 



Heat observed 1 3,733 



a 



a 





2 







3 







20. 





o-l 



•ams 20. 



<»' 



rams 



9- 







u 



1-5 





a 



25 







a 



15 





a 



4,018 







a 



4,090 





a 



3-418 



o 





2-658° 







13,733° 









10,871° 







— 10,542° 









-7,906° 







— 48° 









— 48° 







+ 151° 









+ 260° 







3,294° 



3,177° 





" " iron . 

 oxygen evolved . . 



For 1 gram of lead dioxide . . 165° 1 59° 



The mean is 162° for 1 gram of lead dioxide and for 238-9 

 grams it is 38,700°, which agrees well with the result of experi- 



*C. R., c, 1458. 



