W. G. Mixter — Polymerization of Oxides. 



Art. II. — The Heat of Formation and Polymerization of 

 some Oxides and \ Determination of the Heat of Combination 

 of Water by Fusion with Sodium Peroxide ; by W. G-. 

 Mixter. 



[Contribution from the Sheffield Chemical Laboratory of Yale University.] 



The heat of formation of an oxide may be determined directly 

 by combustion, or it may be derived from the heat of the reac- 

 tion of a metal and its oxide with water, or acids, or sodium 

 peroxide. The thermal result is usually for an oxide formed 

 at a high temperature and above that at which a given hydrox- 

 ide glows. In the article* on chromium and aluminum sesqui- 

 oxides it was shown that the heat of polymerization of the 

 former is not small. The present paper contains results ob- 

 tained with other oxides and also determinations of the heat 

 effect of combined water in fusions with sodium peroxide. 



The heat of combination of some oxides with water is found 

 by direct treatment with water, or the same result may be 

 obtained by dissolving the oxide and the corresponding hydrox- 

 ide in an acid. When an hydroxide or oxide becomes anhy- 

 drous at low temperatures the method of fusion with sodium 

 peroxide applies as shown later. The heat effect of the com- 

 bined water is the difference between the heat of fusions of 

 mixtures of sodium peroxide and the hydrous and anhydrous 

 compound, if the latter is not a polymer. This value subtracted 

 from the heat of the reaction of water and sodium oxide is the 

 heat of combination of the water with the anhydrous com- 

 pound. As is well known, some oxides retain water at temper- 

 atures below that at which they glow and polymerize. The 

 heat of combination of such water can only be estimated 

 approximately. 



The heat of the reaction between water and sodium peroxide 

 is derived from the heats of formation of the peroxide, water 

 and sodium hydroxide, thus 



(2Na + 20) + (2H + O) = 2(Na + O + H) + O = 15-5 Cal. 

 119-8 68-4 (Thomsen) 203-7 (Thomsen) 



and 19 # 4 Cal.f are required to separate the oxygen. Hence 



* This Journal, xxxix, 295, 1915. 



fDeForcrand found in 1898 (C. R., cxvii, 514), 2Na + 20= 119-8 and 

 Na 2 + O = 19-4. Recently (C. R., clviii, 991, 1914) he obtained 119-7 and 

 19'03 Cal. respectively. I have used the value 19'4 Cal. in previous work 

 and the results have accorded well with tbose obtained by combustion in 

 oxygen or other methods. This value is used in calculating the heat effect 

 of oxygen liberated in fusions with sodium peroxide. For each cubic centi- 

 meter of oxygen at 0° and 700 mm pressure 1-734 small calories are added to 

 the observed heat of an experiment. 



