involved in the Formation of Complex Atoms. 733 



wrong. He concludes that it is impossible that the helium 

 found in vacuum-tubes is formed from hydrogen. However, 

 it is evident that it is the slow reaction velocity, rather than the 

 sign of the energy change, which prevents ordinary hydrogen 

 from going over into helium, and when the evidence offered 

 by stellar phenomena for the evolution of the elements is 

 considered, it does not seem unlikely that part at least of 

 the helium which appears in these tubes may be formed 

 from the hydrogen. It might equally well, of course, be 

 formed by the disintegration of the electrodes or the walls 

 of the tube, by reason of the intense energy used. 



While, as stated above, there are changes in mass in 

 chemical reactions, a simple calculation shows that they 

 are far too small to be detected. In the formation of one 

 mol. of water 68,000 calories, or 2*89 x 10 11 ergs of energy 

 are liberated. Then 



AM=-2-89xlO n /9xl0 20 



= -3-18xl0- 9 gm. 



Thus the energy involved in our ordinary chemical reactions 

 is extremely small in comparison with that involved in the 

 formation of the elements. 



Since in the radioactive changes from radium to lead 

 there is a certain amount of energy liberated, the atomic 

 weight of lead should differ from that of radium by more 

 than the weight of the helium atoms shot off. The heat 

 effect for the complete series from radium to lead is not 

 known, but the heat evolved in the decay of 1 gram of Ka 

 in equilibrium with its products to IlaO has been determined 

 as 132 cal. per hour. Calculations using this value will not, 

 of course, give the total change in mass which would result 

 in the change of I\a to Pb, but will give an idea of the 

 magnitudes involved. Since at any time the amount of heat 

 evolved by any one of the radioactive elements which are in 

 the equilibrium mixture has the same ratio to the total 

 amount as at another time, the entire heat effect may be 

 considered to decrease at the same rate as the activity of the 

 radium. That is, Q' at any time t is given by 



Q'=Qo«- M , 



where Q is the heat evolved initially. If the time is 

 expressed in hours, \ = 4\52 x 10~ 8 . The half-period for Ra 

 is 1-582 XlO 1 hrs. Q = 2i)8xl0 4 cal. The total heat Q 

 evolved in the complete disintegration of 1 mol. of Ea equals 



