HYDEOGENISED PALLADIUM . 



3â9 



reached. Thereafter, in virtue of the escape of the hydrogen from the 

 palladium, the resistance ceases to increase ; and as the heating is 

 continued past 250° C. a very rapid diminution of resistance sets in, 

 until, as the temperature approaches 300° C. all the hydrogen is di'iven 

 out, so that the wire becomes pure palladium and behaves accordingly. 

 An unexpectedly simple relation was found to hold very ap- 

 proximately between the temperature coefficients for différent amounts 

 of charge. The relation may be expressed in two ways, thus : — the 

 resistance of a given wire in different states of charge increases by 

 approximately the same amount for a given rise of temperature ; or 

 the total increase of resistance of a palladium wire when charged to a 

 certain amount is the same at all temperatures below 150°. This 

 requires that the temperature coefficient is smaller for the higher 

 charges. Thus, if i?o is the resistance of pure palladium at 0° centi- 

 grade and a the temperature coefficient so that the resistance at t" is 



li, = iij(l + at) 



and if r,, be the resistance at 0° C. of the same wire with a given 

 charge of hydrogen, then its resistance at t° is 



r, = r, + R,at 



Hence the temperature-coefficient for a given specimen of Avire 

 charged with hydrogen is inversely as theresistance of the wire. In 

 the following table the first column gives the resistances of the same 

 wire at successive saturations ; the second' column contains the 

 corresponding temperature-coefficients ; and the third gives the 

 product, which in accordance with the above statement, should be the 

 same for all. 



