Mixter — Heat of Combination of Acidic Oxides. 127 



A mixture of 1*314 gram of boric oxide and 5 grams of sodium 

 peroxide was heated in an ignition tube. The loss in oxygen 

 was 0*950 gram ; calculated - 901 gram. Were perborate 

 only formed no oxygen would have been liberated, and if 

 metaborate was the product only one-third as much oxygen 

 would have been set free. 







Experiments. 











1 



2 



3 





Boric oxide 





1-269 



1-858 



1-8862 



grams 



Carbon . 





0-661 



1-080 



1-0384 



u 



Sodium peroxide. . 





15- 



20- 



20- 



« 



Water equivalent 



"of 











system 





3435- 



3465- 



3431- 



a 



Temperature interv 



aL 



2-679° 



4-280° 



4-149° 





Heat observed 





9202 c 



14830 c 



14235° 





Heat of oxidation 



"of 











carbon 



_ 



-7337° 



— 11988 c 



— 11526° 





Heat of oxidation 



of 











iron for ignition . 







-80 c 



— 64 c 



— 80 c 





Heat absorbed by oxy- 











gen given off 





+ 96° 



-f 60 c 



+ 131 c 







1881 c 



2838 c 



2760° 





For 1 grara of B 2 3 











uniting with sodium 











oxide . 





1482 c 



1522 c 



1463 c 





The three results are respectively 1482°, 1522°, and 1463°. 

 The average is 1489 for 1 gram and 104200° for a gram mole- 

 cule of boric oxide reacting with sodium oxide to form sodium 

 orthoborate. 



Note on Boron. — The only thermal data on boron are those 

 of Troost and Hautefeuille* and Bertlielot,f who determined 

 the heat of formation of boron trichloride and tribromide and 

 the reaction of these halides with water, and from the results 

 they calculated the heat of formation of the trioxide. Since 

 they give no analysis of the boron used, the purity of it is 

 doubtful. Moreover, Moissan;); has shown that boron prepared 

 by reducing the oxide with sodium or magnesium is not pure. 

 He removed the magnesium which the impure boron contained 

 by fusion with boric oxide, taking precautions to prevent forma- 

 tion of nitride. It may be added that while at work on boron 

 it was learned that another investigator, whose results are not 

 published, considers that none of the methods described in the 

 literature yield pure boron. Some of the observations of the 

 writer in regard to the burning of boron are interesting and 



*Ann. Ch. Phy. (5), ix, 74. fAnn. Ch. Play. (5), xv, 215. 



% Ann. Ch. Phy. (7), vi, 296. 



