of the Radium Emanation. 727 



A number o£ experiments have been made at still lower 

 pressures, but the results of these will be reserved for a later 

 paper. The vapour-pressure curve of the emanation is 

 similar in general respects to that of carbon dioxide although, 

 as we have seen, the boiling-point of the emanation is some- 

 what higher. 



An unexpected effect was observed in these experiments 

 which is still under examination. It was found that when 

 the pressure was kept constant, the emanation did not all 

 condense when once the condensation had started, but a con- 

 siderable raising of the pressure was necessary to produce 

 complete condensation. I do not think this effect could be 

 ascribed to slowness of diffusion of the emanation in the 

 capillary tube. It appeared as if the emanation were not 

 homogeneous and that some of the emanation condensed 

 at a lower temperature than the remainder. An investi- 

 gation* in conjunction with Mr. Tuomikoski has lent support 

 to this point of view. It has been found that, on condensation 

 of the emanation, the uncondensed part which is pumped off 

 has on the average a slower rate of decay than the part 

 condensed. A more complete determination of the vapour- 

 pressure curve of the emanation is withheld until this point 

 has been more completely examined. 



Experiments with Liquefied Emanation. 

 If the emanation in the capillary tube at about atmospheric 

 pressure is plunged suddenly in a refrigerant well below the 

 temperature of initial condensation, the emanation is condensed 

 locally at several parts of the tube, probably at points where 

 the glass is thinnest. The liquid emanation causes an intense 

 greenish coloured phosphorescence on the walls of the tube. 

 If the liquid emanation is concentrated in the bottom of the 

 capillary, apart from the local phosphorescence of the glass, 

 it appears practically colourless when viewed by a micro- 

 scope by transmitted light. A very different effect is 

 observed when the emanation is condensed in liquid air at 

 the bottom of the capillary. A few seconds after the 

 beginning of condensation, the emanation shows a reddish 

 tinge and rapidly becomes orange-coloured. It is difficult to 

 be certain whether the emanation under these conditions is in 

 the liquid or solid state. The term u liquid emanation " will 

 be used for convenience in describing the effects observed. 

 If kept in liquid air, the condensed emanation viewed under 

 its own light in a microscope retains its colour unchanged 



* A preliminary account of this work was communicated to Manch. 

 Lit. and Phil. Soc. March 23, 1909 



