Mixter — Heat of Formation of Titanium Dioxide. 397 



rnent 1. The fusion of 2 when treated with hot water left 

 lead oxide and but little dioxide, while in 3, where less sodium 

 peroxide was used, considerable lead dioxide remained. These 

 facts indicate that the lead dioxide which separates on the 

 hydrolysis of sodium plumbate is reduced to oxide by sodium 

 peroxide in the presence of water. The following results 

 support this view : a mixture of the two oxides was placed in 

 cold water and the whole was heated. The solution contained 

 lead, but gave no chlorine after adding hydrochloric acid and 

 warming. A fusion of equal parts of lead and sodium per- 

 oxide left, after exhausting with water, lead dioxide, while when 

 two parts sodium peroxide were taken the insoluble residue 

 was brownish yellow and contained but little lead dioxide. 



The heat of hydrolysis of sodium plumbate is derived as fol- 

 lows : 



Na 2 O.Pb0 2 + Aq = 2(Na.O.H.Aq) + Pb0 2 - Na 2 .O.Pb0 2 - H 2 .0 

 15,500 c = 223,600 — 139,700 —68,400 



Since the Pb0 2 is in the solid state before and after the 

 hydrolysis of the plumbate, it makes no difference in the ther- 

 mal result if it first combines with water and is finally dehy- 

 drated. The hydrolysis as given above is only complete in a 

 large volume of water, since sodium plumbate is soluble as 

 such in a concentrated solution of sodium hydroxide. 



Zirconium Dioxide. 



Two experiments were made with mixtures of zirconium 

 dioxide, sodium peroxide, and sulphur. The fusions were not 

 good, and the residues remaining after treatment with hot 

 water set free chlorine from hydrochloric acid, indicating the 

 presence of a peroxide. The results were 251 c and 268 c for 1 

 gram of zirconium dioxide, mean 258 c and for 1227 grams 

 31,700 c . If the dioxide was all oxidized to trioxide 19,400° are 

 to be added, giving 51,100 c . The only interpretation to be given 

 to the result is that the heat of Zr0 2 or Zr0 3 +Na 2 is small. 



Ceric Oxide. 



But one experiment was made with ceric oxide with the 

 result of 94. 6 C for 1 gram and 16,300 c for 172 grams. The fusion 

 was placed in cold water and after gas ceased to come off the 

 solution was decanted. When the insoluble residue was treated 

 with hot water much gas was evolved — an indication of the 

 j)resence of a peroxide of cerium. If 2Ce0 2 is oxidized by 

 sodium peroxide to Ce 2 5 9,700 c are to be added for the heat of 

 the oxygen taken from sodium peroxide. The thermal result 

 does not indicate combination of sodium oxide with an oxide 

 of cerium. 



Am. Jour Sci.— Fourth Series, Vol. XXVII, No. 161.— May, 1909. 

 27 



