Mixter — Unstable Chromium Sesquioxide. 299 



atomic weight of chromium while 52*0 is used in deriving the 

 following values : 



2Cr + 30 = Cr 2 3 (crystalline) + 267 Cal. 

 2Cr + 30 = Cr o 3 (stable, amor. ?) + 2G6. 

 2Cr +30 = Cr" 2 3 (unstable) + 243, approx. 



New determinations have been made of the heat effect of 

 alumina in fusions with sodium peroxide with higher results 

 than were obtained six years ago.* The difference, roughly 

 speaking, in the two sets of experiments is in the oxygen, 

 given off from the fusions. In the first experiments little or 

 none was observed, while in the recent work the heat equivalent 

 of oxygen set free is in some of the experiments over 100 cal. 

 per gram of alumina. It is probable that in the previous 

 work oxygen was also set free, for in only one of the live ex- 

 periments was the pressure in the bomb taken after a combus- 

 tion and in that the increase was small. Yery likely the bomb 

 had leaked under pressure. In the recent experiments the 

 bomb was connected with an inverted flask filled with water 

 into which the gas passed as evolved. Anhydrous alumina 

 was made by heating the hydroxide 15 minutes over the blast 

 lamp. Alumina containing 1*7 per cent water was made by 

 heating the hydroxide for 24 hours at approximately 500°. 

 The preparation lost 1*7 per cent over the blast lamp and the 

 loss is called water. The crystalline alumina was corundum. 

 The experimental data are in Table II. 



The average of the experiments 1 to 5 inclusive for amor- 

 phous alumina is 539 cal. and 55*1 Cal. for one grain molecule 

 combining with sodium oxide. This should be regarded as an 

 approximate value since the results from which it is derived 

 vary widely. As ortho- and m eta-alum in ates exit, it may be 

 that the products were not the same in the different combus- 

 tions. One determination with corundum gave 48 - Cal. The 

 average of experiments 7 and 8 is 594 cal. without correction 

 for 1*7 per cent of water. This value indicates that alumina 

 which has been nearly dehydrated at 500° polymerizes at 

 higher temperatures. 



*Loc. cit. 



