732 Prof. Harkins and Mr. Wilson on Energy Relations 



necessary to the formation of the elements out of hydrogen, 

 is not known. 



Using the equation given above, the energy involved in 

 the formation of one mol. of helium from four of hydrogen 

 is found to be 



AE = 9xl0 20 (4-00-4-0312) 



= -2'808xl0 19 ergs 



= - 6-708 xlO 11 calories 



This enormous amount of energy of formation of helium is 

 well in accord with our knowledge of its stability. 



From Table I. it is seen that oxygen is considered as 

 being made up of 4He. The energy change in its formation 

 is four times that of He if it is considered that it is formed 

 from hydrogen directly. It is evident that there would be 

 some energy change when oxygen is formed, whether from 

 hydrogen or from helium ; but according to the above con- 

 sideration there would be no final change in energy content 

 if it were formed from 4He. However, an error of O'OOl 

 in the atomic weight determination would cause an error of 

 9*0 x 10 17 ergs in the energy calculation. As the atomic 

 weights are known nowhere nearly so accurately, it may 

 well be that oxygen is formed from helium with a con- 

 siderable energy change. On the other hand, it may be 

 possible that oxygen does not contain helium nuclei as such, 

 although there are 16 hydrogen nuclei present. 



From these calculations it is clear why the radioactive 

 elements should be expected to break down into helium 

 instead of hydrogen. The stability of the helium is so much 

 greater than that of the system 4H ; u <?., the energy of the 

 helium is so much less than that of 4H, that if the atom 

 were about to break up, it would be much more unstable with 

 respect to a helium disintegration than with respect to the 

 hydrogen disintegration, 



In a recent paper on the " Analysis of Gases after the 

 Passage of Electric Discharge/' Egerton * considers the 

 energy change involved in the formation of lHe from 4H, 

 using the same method as used above. However, when he 

 substitutes the values for the weights involved, he inter- 

 changes the two terms, and obtains AE as a positive quantity. 

 That is, he considers that energy must be put into hydrogen 

 to form helium, with a decrease of mass, which is obviously 



* Proc. Roy. Soc. A. xci. p. 180 (1915). 



