130 Mirter — Heat of Combination of Acidic Oxides. 



Experiment 5. 



Aluminium oxide (amorphous) 4*237 grams 



" " in residue .. —0/195 " 



" " reacting 4*042 " 



Carbon ______ _____ 0*778 " 



Sodium peroxide 14* 



Water equivalent of system 2947* 



Temperature interval 3*484° 



Heat observed 10267° 



" of oxidation of carbon — 8635 c 



" " " " iron — 64 c 



1568 c 

 For 1 gram of amorphous alumina 388 c 



In the reaction, 2_NX0 2 + C — Na 2 C0 3 + _Na 2 0, 1 part of car- 

 bon produces 5 parts of sodium oxide. In the formation of 

 sodium metaluminate according to the equation, A^Og-f-jNTa^O 

 = 2_NaAlQ 2 , the ratio of the quantities of the oxides is 1 to 0*6, 

 while for the formation of the orthoaluminate three times as 

 much sodium oxide is required. The following table of results, 

 giving the calories evolved for one gram of alumina and the 

 ratio of the alumina to the sodium oxide, shows that sodium 

 orthoaluminate could not have been formed in experiments 3, 

 4 and 5, as there was not sufficient sodium oxide produced to 

 form it. It should be noted in this connection that too little 

 oxygen was set free in the combustions to indicate any material 

 difference in the quantity of sodium oxide formed. 



Na 2 



Calories for required to form. 



No. of 1 gram . Na 2 , * . , 



Exp. Al.Os C A1 2 3 formed NaAlO. Na 3 A10 3 



1 419 1-2 3*3 (amor.) 6* 2* 6* 



2 365 1*3 4*2 " 6*5 2*5 7*6 



3 283 0*8 3*3 (crys.) 4* 2* 6* 



4 310 0*8 3*2 " ' 4* 2* 6* 



5 388 0*8 4* (amor.) 4* 2*4 7*2 



It is evident that the chief product in the reactions is sodi- 

 um metaluminate, but possibly mixed with other aluminates. 

 Assuming that the reaction was essentially the same in all of 

 the combustions, we have for the heat of combination of 1 

 gram of amorphous alumina with sodium oxide a mean of ex- 

 periments 1, 2, and 5 of 390 c , and for a gram molecule 40,000 c . 

 For crystalline alumina it is 30,000 c . Hence the transformation 

 of the amorphous alumina into the crystalline form is accom- 

 panied with the heat effect of 10,000 c . 



