Mixter — Unstable Chromium Sesquioxide. 295 



Art. XIX. — Unstable Chromium Sesqitioxide, and Correc- 

 tions of Previous Work on the Heat Effect of Chromium 

 and Aluminum, Sesquioxides in Fusions with Sodium 

 Peroxide ; by W. G. Mixter. 



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



In a former paper- the heat effect of 1 gram of amorphous 

 chromium sesquioxide reacting with sodium peroxide is given 

 as 867 and 878 cal. The writer regrets errors in the calcula- 

 tions. The corrected figures are 712 and 722 cal. A new 

 determination, Experiment 1, p. 297, gives 726 cal. The 

 average is 720 cal. For 1 gram molecule of chromium 

 sesquioxide reacting with sodium peroxide the result is 109*4 

 Cal. The sesquioxide used in all the above determinations 

 was made by heating the hydroxide over a blast lamp. Essen- 

 tially the same valnef was found for the crystalline oxide. 

 As the values are alike, the ignited oxide, which was apparently 

 amorphous, may in reality be crystalline, for the heat of forma- 

 tion of a crystalline compound is commonly higher than an 

 amorphous one. Professor Hastings, however, found in a very 

 careful microscopic examination no appearance of crystals in 

 oxide made by heating the hydroxide. Whether or not snch 

 oxide is made up of ultra microscopic crystals, it is to be 

 regarded as the same polymer as the crystalline form, since, as 

 shown later, both are condensation products of the unstable 

 form of chromium sesquioxide. 



As Moissan^: states, chromium sesquioxide which has not 

 been calcined oxidizes below a red heat in air and oxygen 

 while the calcined oxide does not. It has long been known 

 that chromium hydroxide glows when heated, that is, it sud- 

 denly becomes hotter than the surrounding medium. Endell 

 and Rieke§ have studied the glowing of some hydroxides and 

 have found when the temperature is raised 80° a minute that 

 " Chromoxydgel, heiss, gefallt, zeigt eine bei 500° einsetzenge 

 und sich bis 610° hinziehende Warmetonung und Verglimmen 

 — Der Vorgang der Warmeabgabe is irreversibel u. entsprich 

 einer gewissen Kornervergrosserung." There is, therefore, a 

 stable and an unstable chromium sesquioxide. The two forms 

 differ in heat of formation, as will be shown later. 



The chromium hydroxide used in the work was from Kahl- 

 baum and had been in the laboratory some time. It was free 



* This Journal, xxvi, 125, 1908. 

 f Ibid. 



{Ann. Chim. Phys. (5), xxi, 199. 



§ Centralblatt f. Min. u. Geol., 1914, 246, Berlin, quotation from abstract 

 in Chem. Zentralblatt, 1914, I, 1991. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIX, No. 231.— March, 1915. 

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