Mixter — Heat of Combination of Acidic Oxides. 133 



Chro m hi m Sesq u ioxide. 



Amorphous chromium sesquioxide was prepared by heating 

 an hydroxide. The crystalline oxide was made according to 

 Ditte's* method of melting together equal parts of pure potas- 

 sium dichromate and sodium chloride until the evolution of 

 oxygen ceased. After cooling, the soluble portion of the prod- 

 uct was dissolved in water and the crystalline powder obtained,, 

 washed, digested with hydrochloric acid and washed again. 

 The crystals were so small that some passed through filter 

 paper. Under the microscope they appeared unmixed with 

 any amorphous substance. Tested by the spectroscope the 

 preparation proved to be free from sodium and potassium. 

 The following results show the heat of the reaction between 

 chromium sesquioxide and sodium peroxide : 



Experiments. 



12 3 



Chromium sesquioxide 4-236 3*831 7'436 



" " unburned 0-062 0-018 0'805 



" burned.. 4-174 3-813 6'631 



Carbon ... 0-516 0-456 0-4015 



" not burned 0*007 0*006 0-151 



" burned.. ._ 0'509 0*450 0*2505 



Sodium peroxide 17* 15* 21* 



Water equivalent of system ... 2828* 2902* 2936* 



Temperature interval 3-047° 2-703° 2*922° 



6*o76 grams 

 0-097 

 6-479 

 0*425 

 0-012 

 0*413 

 20* 

 3077* 

 3*038° 



Heat observed ' 862 3 C 



" of oxidation of carbon —5650 



" " " of iron for ignition —16 

 " due to oxygen absorbed or 



evolved _. —69 



2888 



For one gram of chromium sesqui- ) 



oxide, reacting with sodium r 692 

 peroxide ) 



7844 c 



-4995 



— 10 



-70 



2769 



7579 c 



■2780 



— 62 



+ 14 



5751 



867 



9348° 

 •4584° 



— 48 c 



— 30° 

 5686° 



878° 



Crystalline sesquioxide was used in experiments 1 and 2. 

 The results are 692° and 726° and a mean of 709° for the heat 

 of the reaction of 1 gram of crystalline chromium sesquioxide 

 with sodium peroxide. For a gram molecule it is 108000°. 



The experiments 3 and 4 were with amorphous sesquioxide. 

 The results are 867° and 878° and the mean is 872° for the 

 heat of the reaction of 1 gram of amorphous chromium sesqui- 

 oxide with sodium peroxide. For a gram molecule it is 132000°. 

 * C. R.,cxxxiv, 336. 



Am. Jour. Sci.— Fourth Series, Vol. XXVI, No. 152.— August, 1908. 

 10 



