126 Mixter — Heat of Combination of Acidic Oxides. 



that it is necessary to allow for oxygen taken up or set free. 

 The correction of 1*2° for 1 milligram is based on the heat of 

 formation of sodium peroxide from the oxide which according 

 to deForcrand" is 19390 c . For oxygen liberated there is a 

 loss of heat which is to be added, and for oxygen absorbed the 

 gain is to be subtracted from the heat observed. The best way 

 to find the change in the oxygen content of the bomb is to 

 connect it after a combustion with a manometer. To avoid 

 excessive detail in the data given of the work only the heat 

 equivalent of the oxygen liberated or taken up is stated. 

 Most of the work was done with a bomb of 500 cc capacity 

 and in the work on chromium the oxygen correction was large. 

 To obviate the correction or make it insignificant a sterling 

 silver bomb of 100 cc capacity was made. It proved. to be 

 admirably adapted for calorimetric work with sodium peroxide. 

 The water equivalent of this bomb and calorimeter can was 

 109 c . The large bomb was used in the experiments in which 

 the water equivalent was over 3200 grams, and the small one 

 in those in which it was less than 3100 grams. When a 

 molten mass is in contact with the cold bomb it solidifies at 

 once and the combustion is not complete. Hence it is better 

 to put the peroxide mixture into a thin silver cup which is in 

 contact with the inner surface of the bomb at only a few 

 points. In order to make ignition certain the bomb was filled 

 with oxygen, as it was found that with air in it the burning 

 iron often failed to start the combustion. The carbon used is 

 the finely divided form made from acetylene and the heat 

 effect of its reaction with sodium peroxide is taken as 11100 c f 

 per gram of carbon. The carbon gives the temperature needed 

 to effect the combustion of other substances and also reduces 

 the peroxide to the sodium oxide required in the reaction with 

 an acidic oxide. The initial temperature of the experiments 

 was between 18° and 19°. 



Boric Oxide. 



The heat effect of the combination of boric oxide with 

 sodium oxide has been determined. The oxide used, in the 

 experiments, made by fusing boric acid in a platinum dish, 

 was pulverized and weighed in a stoppered bottle. It was 

 exposed to the air as short a time as possible on account of its 

 hygroscopic character. The reaction of boric oxide on an 

 excess of sodium peroxide yields the orthoborate thus : 



3Na 2 2 + B 2 3 = 2Na 3 B0 3 + 30 



No perborate results, as shown by the following experiment : 



* C. E., cxxvii, 574. f This Journal, xix, 434. 



