296 Mixter — Unstable Chromium Sesquioxide. 



from chloride and sulphate, but held a very little ammonia 

 and considerable carbon dioxide. Iowitschitsch* found that 

 chromium hydroxide absorbs the latter from the air. All 

 attempts to dehydrate chromium hydroxide below temperatures 

 at which it would glow or change to the stable oxide failed to 

 expel all of the water or carbon dioxide. One portion of 

 chromium hydroxide was heated for a day at 320° while the 

 vapor and gas were pumped off. The product contained 92 

 per cent of Cr 2 3 . After heating at common pressure to about 

 420° for three hours in a current of hydrogen to prevent oxida- 

 tion, it had 94*1 per cent. This product is designated as A. 

 Another portion of chromium hydroxide which was heated in 

 hydrogen for a day at about 420° (the temperature may have 

 been higher at times) still retained 3*4 per cent of water and 

 carbon dioxide. This preparation (B) was a dark olive green. 

 Both A and B glowed when heated in a closed tube, but the 

 glow did not extend through the mass when the end of it only 

 was heated unless the whole was moderately hot. B at a 

 temperature below that required to make it glow became red 

 hot when a rapid current of oxygen was passed into the tube 

 containing it. The heat of the oxidation was sufficient to 

 change the unstable olive green substance to the stable green 

 oxide, the higher oxide first formed giving up oxygen. 

 Another portion of chromium hydroxide was heated two days 

 as just described and gave a product (C) like B. It lost 3*4 

 per cent on ignition. Part of C was next heated another day 

 to approximately 400° in hydrogen. The temperature of the 

 electric furnace used may have been somewhat higher at night. 

 The olive green oxide was changed to bright green. It did not 

 oxidize or glow on heating and lost 1*3 per cent on intense igni- 

 tion. One gram of it gave w T hen fused with sodium peroxide 

 687° cal. This is approximately the heat effect of ignited Cr 2 3 . 

 Apparently long heating of the unstable oxide at a temperature 

 below that at which it glows changes it to the stable oxide. The 

 following experiments confirm this supposition. A portion of 

 C was placed in a bulb with a capillary neck and gradually 

 heated in an air bath to above 500° in a glass vessel. No glow- 

 ing was observed and the oxide became bright green. It was 

 also found that C did not glow when dropped into a platinum 

 crucible below a faint red heat but oxidized and became black. 

 Preparation A was used for experiment 2, Table I, B for 3 

 and 4, and C for 5.f All contained water and carbon dioxide, 



*C. E. clviii, 872, Chem. Zentralblatt, 1914, I, 1635. 



f The lampblack used in the experiments was nearly free from ash. It 

 was heated for three hours to about 1100°. Each portion used in a calori- 

 metric experiment was heated to a faint red and left to cool in a desiccator. 

 Determinations of the heat effect of the lampblack in fusions with sodium 

 peroxide gave 10638, 10636 and 10635 ; mean 10636 cal. for 1 gram of lamp- 

 black. The oxidation of the lampblack was complete. 



