132 Mixter — Heat of Combination of Acidic Oxides. 



12 3 



Heat observed 8916 c 12334 c 12274 c 



" oxidation of carbon.. — 2726 c — 4181 c — 4218 c 

 " " "iron in 



metal and for ignition — 94 c — 90 c — 92 c 



" due to oxygen absorbed — 288 e — 492 c — 4*7 2 C 



5808 c 757l c 7492 c 



For 1 gram of chromium burn- 

 ing with sodium peroxide., 3012 c 3055° 3044 c 



In the experiments 1, 2, and 3 a bomb of 500 cc capacity was 

 used. As the correction for oxygen absorbed was large, a 

 determination was made with the 100 cc bomb. The residue 

 insoluble in nitric acid was collected on a Gooch filter, dried 

 and its weight found. Next the carbon was burned off, and 

 finally the weight of unburned chromium was obtained. The 

 pressure in the bomb was 29 cm less after the combustion than 

 before. 



Experiment Jf.. 



Metal taken . 02-0520 grams 



" unburned -0015 " 



" burned 2*0505 " 



Chromium. .. 20361 " 



Iron . 0-0143 



Carbon taken. 0-3161 " 



" unburned 0-0017 " 



burned.. 0-3144 " 



a 



u 



Sodium peroxide . 15* 



Water equivalent of the system 2984- 



Temperature interval 3*282° 



Heat observed , 9793 c 



" of oxidation of carbon — 3489 c 



" " " " iron in metal — 23 c 



" " " " " for ignition.. -26 c 



" due to oxygen absorbed — 52 c 



6203° 



For 1 gram of chromium 3046 c 



Evidently the correction made for oxygen taken up in the 

 first three experiments w T as correct. The results are 301 2 C , 

 3055 c , 3011°, and 3046 c . In the first one the correction for 

 oxygen was not made w T ith the care that it was in the others, 

 and hence it is better not to include it in the final value. The 

 mean of the other figures is ,3048 c for the reaction of 1 gram 

 of crystalline chromium with sodium peroxide, and for 52*1 

 grams it is 158800 c . 



