356 Mixter — Determination of the Heat of Dissociation 



The results of the combustion of ethylene, omitting experi- 

 ment 14, are 



Experiment 13 344,800 

 " 15 343,400 



" 16 345,700 



An average of 344,600 calories at constant volume and 

 345,800 at constant pressure. Although the results agree well 

 they may be slightly in excess owing to a possible oxidation 

 of the bomb. There was, however, no rust where the steel 

 was exposed and the fine powder washed out of the bomb after 

 an explosion was mostly gold and was nearly free from iron. 

 Thomson* obtained for the combustion of ethylene 333,350 c 

 and Berthellotf 341,100° at constant pressure. In deriving the 

 heat of formation we have the difficulty already mentioned 

 regarding the choice of the numbers to be taken for the heats 

 of combustion of the constituents of ethylene. According to 

 Thomsen (loc. cit.) it is — 2710 c , and using Berthellot's figures 

 we have — 7800 c for the formation of ethylene from hydrogen 

 and amorphous carbon. If, however, we deduct 341*100 (B) 

 from 330*600, the heat of the combustion of the constituents 

 of ethylene adopted by Thomsen, we have — 10,500 c . The 

 writer's direct determinations of the heat of dissociation of 

 ethylene vary too widely to have much significance, but they 

 indicate that ethylene may be more endothermic than has been 

 assumed. 



Methane. 



The methane was made in the usual way by heating a mix- 

 ture of sodium acetate and soda-lime, and also of the acetate 

 and barium hydroxide, and the two products were united. 

 The gas was purified by passing it slowly through fuming sul- 

 phuric acid and then allowing it to stand over water containing 

 ferrous hydroxide. A combustion of the gas gave 0*677 gram 

 of C0 2 and 0*572 gram of water, corresponding to 93*8 vol- 

 umes of methane and 6*2 volumes of hydrogen. The gas was 

 fairly free from nitrogen. 



Experiment 17. — The bomb contained 1*18 gram of methane, 

 4*765 grams of acetylene and 0*061 gram of hydrogen and 

 nitrogen. Jacket, 1*4° ; room, 0°. The gas left after explod- 

 ing gave no carbon dioxide when burned. 



Minutes. Temperature, 



1*034 Water and water equivalent of 



3 1*034 calorimeter, 3252 grams. 



6 1*034 



9 3*589 Temperature interval, 



12 3*578 3*578— 1*034 + 0*023 = 2*567° 



* Therraochemische Untersuchungen. iv, 65. f Ann. Ch. Phys. [6], xxx, 557. 



