Condensation of the Radioactive Emanations. 56i> 



The following table represents the results : — 



Temperature. Eesistance (ohms). Ratio. 



100° 0. -00947 135-1 



0° -00701 100 



-103°-5 -00437 62-3 



-169° -00262 37-4 



-192°-2 -00202 28-8 



In the last column the ratio of the resistance is given, the 

 value at 0° being taken as 100. In PL XIY. fig. 3 the results 

 are plotted with the resistance as ordinates and the temperature 

 as abscissse. It will be observed that the curve is very nearly 

 a straight line cutting the axis, if produced, at very nearly 

 the absolute zero. For the particular thermometer used, 

 therefore, the readings of the milli voltmeter may be taken 

 without appreciable error to be proportional to the absolute 

 temperature. The instruments employed were accurately 

 calibrated. The accuracy of the temperature determination 

 by this method depends only on the sensitiveness of the 

 millivoltmeter. At the temperature at which most of the 

 observations were made, one division of the scale corresponded 

 to about 4° C, and the readings could be made to 1/10 of a 

 division. The determinations were therefore accurate to 

 within o, 5, which was sufficient for the purpose. The great 

 advantage of the method is the ease and certainty with which 

 a continually changing temperature can be followed. 



Experiments for the Radium Emanation with a steady 

 current of Gas. 

 Experiments with the radium emanation are much simpler 

 than for that of thorium, since the activity does not decay 

 appreciably over the time required for a complete series of 

 observations, and much larger effects can be obtained. PI. XIY. 

 fig. 2 represents the general arrangement of the apparatus for 

 the determination of the volatilization temperature of the 

 radium emanation in a steady current of gas. The latter (either 

 hydrogen or oxygen) was conveniently obtained from a set o£ 

 eight voltameters, arranged in series across the 110 volt 

 circuit and capable of taking a current up to 3 amperes. 

 The latter, measured by a Weston ammeter, furnished a 

 measure of the number of c. c. of gas passing per second. 

 This enters the apparatus at A. The radium emanation mixed 

 with air is stored in the gas-holder B. The exit o\' the 

 copper spiral is connected with a testing-cylinder T of the 

 kind previously described, in which the ionization current 

 through the gas, due to the rays from the emanation. i> 

 measured by the electrometer E. D is a drying-tube. 



