THE TRANSFORMATION OF ELEMENTS 79 



half hours to 50 per cent, of the original, within the limit of 

 experimental error. In two experiments readings were taken 

 every few minutes ; the change in volume plotted against time 

 gave an exponential curve, in that respect resembling ordinary 

 radioactive changes. The volume change could be reversed by 

 heating, for at 8o° the gas expanded to within 10 per cent, of its 

 original volume. After the rapid contraction was completed, 

 a slow contraction began ; this was proportional to the decay 

 of radioactivity. 



The authors attempted to explain this phenomenon by the 

 supposition that the emanation at first was a monatomic gas, as 

 are the other gases which it resembles; after the initial change 

 was completed the gas had become diatomic (2 Em! = Em 2 ) with 

 consequent halving of volume. In this respect comparison may 

 be made with nitrogen peroxide ; at low temperatures its mole- 

 cule is represented by the formula N 2 4 , while heat converts it 

 into N0 2 molecules. It is not yet known if this change occupies 

 a measurable time. 



It is necessary to refer in some detail to the heating effect 

 of radioactive substances, radium and its emanation especially. 

 P. Curie and Laborde first noted that a radium salt kept itself 

 at a temperature several degrees higher than the surrounding 

 air. They measured the amount of heat in a calorimeter, and 

 calculated that one gram of pure radium chloride emits 100 gram- 

 calories of heat per hour. Precht in 1906, using an ice calorimeter, 

 calculated that one gram of anhydrous radium bromide emits 

 nearly 80 gram-calories per hour. Rutherford and Barnes have 

 shown that 75 per cent, of the heating effect is due to the 

 emanation and its products; the total heat evolved during the life 

 of a cubic centimetre of the gas is about seven million gram- 

 calories. When the same volume of electrolytic gas (hydrogen and 

 oxygen in the proportions to form water) is exploded, it evolves 

 3 calories ; hence during its disintegration the emanation emits 

 over two million times the amount of heat evolved by the 

 explosion of an equal amount of electrolytic gas ; the latter 

 reaction gives rise to more heat than any other known chemical 

 change. 



Ramsay has shown qualitatively in a very interesting 

 manner the production of heat from emanation. Two ther- 

 mometers were taken, one an ordinary instrument reading to 

 tenths of a degree; the bulb of the other was hollow; it was 



