Condensation of the Radioactive Emanations. 571 



calcium chloride and the bulb V filled with air mixed with the 

 radium emanation which was then allowed into the exhausted 

 spiral kept below the temperature of condensation. The 

 apparatus was then repeatedly exhausted by the pump, and 

 after each exhaustion a bulb-full of oxygen was sent into the 

 spiral, the temperature of the bath being allowed to rise 

 slowly during the exhaustion. The temperature at w r hich the 

 first trace of emanation escaped and the amounts at succeeding 

 temperatures were noted as before. The following table is an 

 example of the results obtained : — 



Divisions of Electrometer 

 Temperature. per second. 



-153° 



-151° 



-148°-5 -74 



-146°\ r > 5-3 



-143° 5-1 



-139° -7 



-135° -08 



The mean of several results gave —150° as the point at 

 which the emanation first began to volatilize, and this is in 

 good agreement with the result by the blowing method, that 

 is, —153°. The difference is in the expected direction, for 

 in the static method the mass of the gas employed is much 

 smaller, and any emanation that is volatilized by the rush of 

 heated gas in its passage through the spiral has time to be 

 recondensed. The temperature — 150° C. may therefore be 

 taken with considerable confidence as being the true point at 

 which the radium emanation first commences to volatilize. 

 On the other hand, the table shows a somewhat less sudden 

 volatilization than in the case of the blowing method, but 

 this is inherent to the static method employed. The glass 

 spiral connecting-tube between the pump and the copper 

 spiral had a greater volume than the latter itself, and at each 

 exhaustion some of the volatilized emanation is left in this 

 spiral. In the case of the thorium emanation this decays 

 practically to zero before the next observation is taken, but 

 in the case of the radium emanation it does not, and is added 

 to the amount removed at the next exhaustion. The tem- 

 perature of volatilization found in these experiments has 

 almost exactly the value given by Ramsay and Travels Eor 

 the boiling-point of nitric oxide under atmospheric pressure 

 149°'9 0. A bath of liquified nitric oxide was prepared, and 

 used in place of the ethylene in former experiments. Its 

 boiling-point rose steadily until about one-fifth had boiled off. 

 It then became constant at —151° C, as determined bv the 



