728 Professor Sir James Dewar [June 11, 



feeble or absent, as with some gases, the ionization can be demon- 

 strated. A long thin glass tube sealed at the end can be inserted 

 through a hole in the top plate of the cylinder and filled with liquid 

 air when necessary. Nitrous acid and nitric peroxide are condensed 

 upon it when placed in the phosphorescent stream. This is proved 

 by the well-known Starch Iodide of Potassium and Griess Reactions. 

 It is extremely difficult when using this large apparatus to prevent the 

 formation of some nitrous acid even if liquid oxygen is evaporated ; 

 and thus the proof that the phosphorescence is really due to ozone 

 alone and not to nitrous compounds is not perfectly conclusive. If a 

 current of carbon dioxide is substituted for air, the phosphorescence 

 is marked but much more feeble. Hydrogen gas alone gives no lu- 

 minosity, and if a trace of hydrogen is added to the phosphorescent 

 stream obtained by the evaporation of liquid oxygen or liquid air the 

 phosphorescence at once disappears. Thus 5 per cent, of hydrogen by 

 volume stops the glow in very pure oxygen, while 10 per cent, is re- 

 quired to arrest the light-stream in air. The rate at which the gas 

 passes through the discharge- tube makes a difference in the intensity 

 of the glow, but the presence of more or less moisture has little effect. 

 A little ether vapour or benzol behaves like hydrogen, arresting all 

 phosphorescence, and the luminosity does not reappear until all the 

 vapour has been carried away by the continually renewed pure gas 

 stream. All volatile organic bodies containing hydrogen stop or 

 diminish the phosphorescence. On the other hand, volatile organic 

 substances containing no hydrogen, such as carbon bisulphide, still 

 give phosphorescence, but pure cyanogen or tetrachloride of carbon 

 vapour give no luminosity. Pure carbon bisulphide and sulphur di- 

 oxide vapour alone give good phosphorescent streams at suitable 

 tensions. The glow with very pure oxygen is short but distinctly 

 more brilliant than that given by air. Nitrogen obtained from the 

 liquefied gas gives only a feeble and very diffuse glow. This gas 

 contains a few per cent, of dissolved oxygen, the presence of which 

 causes the glow, as pure nitrogen gives no visible luminosity with this 

 kind of electric discharge. 



Radium and its Emanation. 



What has all this to do with Radium ? It is now known that 

 bodies like ozone and nitric-oxide are produced from dissociated 

 molecules at very high temperatures under considerable absorption of 

 heat, and that such bodies are unstable. That may give us a clue to 

 the formation of radio-active bodies. In my Friday Evening 

 Address for the year 1888, I remarked : " Ozone is formed by the 

 action of a high temperature owing to the dissociation of the oxygen 

 molecules and their partial recombination into the more complex 

 molecules of ozone. We may conceive it not improbable that some 

 of the elementary bodies might be formed somewhat like the ozone, 



