7 8 SCIENCE PROGRESS 



The results obtained are here briefly summarised. The 

 observation by Ramsay and Soddy, that the emanation obeyed 

 Boyle's Law, was confirmed by numerous sets of measurements. 

 The divergence of the results in different experiments is due to 

 the nature of the glass capillary employed. The emanation 

 forces a large part of the helium it produces into the walls 

 of the tube. After some time, the disintegration products — 

 radium D especially — appear to act as a shield. The helium 

 is no longer forced into the walls, and the total volume increases. 

 If the glass is unusually impermeable this expansion takes 

 place from the beginning of the experiment, thus showing that 

 the emanation produces more than its own volume of helium. 

 Ramsay and Soddy found from their spectrum measurements 

 that the ratio was about 3:1; the later measurements of the 

 actual volumes confirmed this figure. This agrees with the fact 

 that three a particles are produced by the time that radium D is 

 formed. 



The life of radium D is so long that at the end of a 

 month, by which time less than 1 per cent, of the emanation 

 remains, scarcely any of the after-products have been formed ; 

 while the lives of A, B, and C are of such short duration 

 that they disappear completely within a few hours of their 

 formation. After heating the measuring tubes to remove the 

 colour, an extremely small amount of a brown deposit, possess- 

 ing a submetallic lustre, has been observed ; in all probability 

 this is radium D. 



On account of the slight volatility of the emanation at — 185 

 (referred to previously) the experiments showed no very close 

 agreement. The mean of the three which were considered most 

 accurate gave the result that 877 milligrams of metallic radium 

 (in solution as bromide) gave rise in 3*86 days (the half-life 

 period of the emanation according to Sackur) to 0*310 cubic 

 millimetres of emanation. This is the volume occupied by 

 a small pin-head. Ramsay and Soddy's figure for the same 

 quantity of radium was 0*222 cubic millimetres. 



In addition Ramsay and Cameron observed a new change, 

 quite different from ordinary disintegrations ; it appeared to 

 explain the large decrease in volume observed by Ramsay and 

 Soddy in their first experiment. In the last four experiments, 

 in which the actual initial volumes varied from 0*058 to 0*397 

 cubic millimetres, the volume contracted in about one and a 



