EXPLOSION OF ETHANE AND OXYGEN. 155 



At we should therefore have for the difference between the 

 heats of combustion at constant pressure and at constant 

 volume 



+ 0-54 X J = + 0-27. 



At 15 to this figure must be added + 0'03, which raises the 

 correction to + 0*30. The heat of combustion of carbonic oxide 

 at constant pressure and at 15 will therefore be + 68*3 Cal. 

 Take again the combustion of ethane 



C 2 H 6 + 7 = 2C0 2 + 3H 2 



ff = l + 3J = 4J 

 N' = 2 (assuming water liquid) 



N - N' = 2. 



The difference between the two heats of combustion is ex- 

 pressed at 15 by + 1425 Cal. 



The correction relative to condensation should in principle be 

 reduced by a small quantity on account of the appreciable 

 tension of water vapour at 15, but this quantity may be 

 neglected, owing to its smallness, in the present calculation. 



11. We should, on the contrary, bear in mind that the 

 correction due to the formation of water vapour is very appreci- 

 able in the calculation of the heat of combustion at constant 

 volume, as well as at constant pressure, seeing that it represents 

 the formation of gaseous water, which liberates less heat than 

 the formation of liquid water. It has been verified in all these 

 experiments from the internal capacity of the bomb, and con- 

 formably to Kegnault's tables for the tension of water vapour 

 and the vaporisation heat of water, at the temperature of the 

 calorimeter. 



12. More than three hundred explosions have been effected in 

 these instruments. No accident has occurred in the instruments 

 themselves, in spite of the magnitude of the sudden pressures 

 developed during the explosions. These pressures are estimated 

 at fifty atmospheres in certain cases where previously com- 

 pressed gaseous mixtures have been operated upon. 



13. We have, however, twice observed the spontaneous 

 explosion of the gaseous mixtures while they were being shaken 

 in closed and very dry glass vessels, with mercury. This very 

 serious and singular accident appears due to internal electric 

 sparks, produced by the friction of the mercury on the glass of 

 the flasks, these being held in the hand and realising conditions 

 of condensation similar to those of a Ley den jar. 



14. We shall now expound the data of a determination, with 

 the object of showing the method followed in the experiments, 

 verifications and calculations. 



Ethane. The gas was prepared by the electrolysis of 

 potassium acetate. It was freed from carbonic acid by potash, 

 from ethylene by bromine, and from carbonic oxide by a pro- 



