>10 PROFESSOR E RUTHERFORD ON Till- 



are several arrangements of the constituents of the atoms to form a system of some 

 slight stability. The two radioactive products resulting from the disintegration of a 

 single atom would probably be present in unequal proportions. A closer investigation 

 of the radioactive bodies will very probably lead to the separation of a numl>er of 

 radioactive products, present in a small proportion among the main products. 



29. Difference between Radioactive and Chemical Change. The successive 

 changes occurring in the radio-elements are distinguished in certain important 

 particulars from ordinary chemical change. We have seen that each active product, 

 left to itself, is transformed according to a definite law and at a definite rate. The 

 law of change is the same as for a monomolecular reaction in chemistry, and shows 

 that only one changing system is involved. The constant of change X is independent 

 of the degree of concentration of the product, and of the nature and presence of the 

 surrounding gas, and, in most cases, is not much affected by wide differences of 

 temperature. The work of CURIE and DANNE, however, shows that the constant X of 

 the product radium C (see section 21) is certainly altered by temperature. After 

 this substance has been subjected for a few minutes to a temperature of about 

 1100 C., its value of \ (when cooled to atmospheric temperature) is permanently 

 altered. The value of X at 1100 C. is about 1'4 times the normal value. Above 

 1100 C. the value of X decreases again, and at 1300 C. it is about I'l times the 

 normal. These results show that increase of temperature to a certain point increases 

 the rate of disintegration of radium C, but that on exposure to a still higher 

 temperature the rate of disintegration decreases again and becomes nearly equal to 

 the normal value. 



The two features which differentiate the radioactive changes from ordinary chemical 

 change are :-- 



( 1 ) The expulsion of charged particles with great velocity ; 



(2) The emission of an enormous amount of energy compared with the amount of 



matter involved. 



Except in the case of the radio-elements, no chemical change is known which is 

 accompanied by an expulsion with great velocity of a product of the change. In each 

 change that is accompanied by the expulsion of a rays, the amount of energy liberated, 

 weight for weight, is over 100,000 times greater than has previously been observed 

 in any chemical reaction. Dr. BARNES and the writer* showed that 75 per cent, of 

 the heat-emission of radium was due to the emanation and its further products. The 

 emanation from a gramme of radium gives out heat at the rate of 75 gramme-calories 

 per hour. The total amount of heat liberated during its life is 10,000 gramme-calories 

 approximately. Now from the work of RAMSAY and SODDY it is known that the 

 volume of the emanation extracted from 1 gramme of radium is not greater than 

 1 cub. millim. The energy emitted from 1 cub. centiin. of the radium emanation is 



* ' Phil. Mag.,' Ful.ruHiy, 1904. 



