Alpha Rays from Polonium in Mercury Vapour. 299 



ionization-charnber, polonium, &c. was enclosed in a larger 

 electric furnace as indicated in the figure. Alternating 

 current was used in both the large and the small furnace. 

 The ends of the larger furnace were shielded as well as 

 possible by means of asbestos so as to prevent rapid loss 

 of heat. 



Determination of the Ionization Curve. 



By means of a tube similar to the one used but having an 

 opening at the top for the insertion of a thermometer, 

 determinations were made to ascertain ihe value of the 

 current that must be sent through the small electric furnace 

 surrounding B in order to keep B at a temperature very 

 slightly above that of the other part of the tube. By 

 keeping this slightly warmer, about one-fourth of a degree, 

 it was assured that there would be no condensation of the 

 mercury vapour upon the top of the polonium. In case any 

 should condense it would interfere seriously with the ex- 

 periment. 



The entire apparatus, as described above, was evacuated, 

 and then by means of an open air-manometer a basin of 

 mercury was raised till it rose to the top of one of the glass 

 tubes extending through D. The mercury was then allowed 

 to flow into the apparatus till it filled the tube to within one 

 centimetre of the top of the glass tubes through which the 

 wires leading to the electric furnaces were inserted. The 

 currents were then started in the two furnaces and increased 

 slowly till such values were reached as would raise the 

 temperature to 330 degrees centigrade. The vapour-pressure 

 of mercury at this temperature was 451 millimetres. The 

 alpha particles had a range of 7*30 centimetres in the 

 mercury vapour at the above temperature and pressure. 

 After the temperature had become steady, measurements 

 w 7 ere taken of the deflexions of the electrometer for the 

 various distances of the polonium from the ionization- 

 charnber. By plotting the deflexions of the electrometer in 

 scale-divisions per minute as ordinates, and the corresponding 

 distances of the polonium from the ionization-charnber as 

 abscissas, a curve similar to the dotted curve II. in fig. 2 

 (p. 300) was obtained. Several determinations of this curve 

 were made under similar conditions, and the dotted curve II. 

 in fig. 2 was plotted from the entire series of observations. 

 It is seen that the curve does not have nearly such great 

 differences in the values of the ionization at different points 

 along the curve as has been found in other gases and 

 vapours. 



