Poole — On the Detonating Action of a Particles. 



95 



tests varied in duration from five minutes to about twenty hours, but the decay of 

 the deposit rendered the period after the first two hours of negligible importance. 

 The number of a particles in each case is calculated from the initial activity of the 

 source, as measured by a 7-ray electroscope, the curve of decay of the active 

 deposit, and the geometrical conditions : — 



The potassium pierate was considerably darkened in colour by the exposure 

 to a rays. 



The total number of a particles involved in all these tests amounted to about 

 10^^ which would have caused about 30,000 detonations in iodide of nitrogen, so 

 that the chance of detonation for the other bodies tested is very small indeed 

 compared with that for the iodide, and probably zero. It must be remembered, 

 however, that unless the chance is absolutely non-existent, the danger remains, 

 as the fact that 10^^ a particles did not produce an explosion does not in itself 

 ensure Safety. This number of a particles would be emitted in about three weeks 

 in one ton of average rock, and so would be exceeded in a comparatively short time 

 in a large mass of explosive if the radioactivity of the latter were at all comparable 

 with that of ordinary materials. 



In conclusion, I wish to express my indebtedness to Professor Werner and 

 Mr. J. V. Collins, of Trinity College, Dublin, for their kindness in preparing the 

 majority of the specimens used. 



