8 Prof. E. Rutherford on a Rulio -active 



with a greater velocity than 100 1 000 cm. per second for a 

 potential-gradient of one volt per cm. ; audit is probable that 

 the particles do not move at all in an electric field. By 

 blowing the emanation into an inductor, no evidence of any 

 charge in the emanation could be detected. We may therefore 

 conclude that the emanation is uncharged, and is not appreciably 

 affected by an electric field. 



Properties of the Emanation. 



The emanation passes through a plug of cotton- wool without 

 any loss of its radio-active powers. It is also unaffected by 

 bubbling through hot or cold water, weak or strong sulphuric 

 acid. In this respect it acts like an ordinary gas. An ion, 

 on the other hand, is not able to pass through a plug of 

 cotton-wool, or to bubble through water, without losing its 

 charge. 



The emanation is similar to uranium in its photographic 

 and electrical actions. It can ionize the gas in its neighbour- 

 hood, and can affect a photographic plate in the dark after 

 several days 5 exposure. Russell * has shown that the active 

 agent in producing photographic action in the case of metals, 

 paper, &c, is due to hydrogen peroxide. Hydrogen peroxide 

 apparently has the power of passing in some way through 

 considerable thicknesses of special substances, and in this 

 respect the emanation resembles it. Hydrogen peroxide, 

 however, does not ionize the gas in its neighbourhood. The 

 action of hydrogen peroxide on the photographic plate is purely 

 a chemical one ; but it is the radiation from the emanation, 

 and not the emanation itself, that produces ionizing and 

 photographic actions. 



The radio-active emanation passes through all metals if suffi- 

 ciently thin. In order to make certain that the emanation 

 passed through the material to be examined and did not 

 diffuse round the edges, the radio-active substance was placed 

 in a square groove of a thick lead plate. Two layers of paper 

 were pasted tightly over the opening to cut off the regular 

 radiation. The material to be tested was then firmly waxed 

 down on the lead plate. 



The following numbers illustrate the effect of different 

 metals. The rate of discharge, due to the emanation between 

 two parallel plates 4 cms. apart, was observed. 



* Proc. Koy. Soc. 1897. 



