Ö&9 



-^ Atomic weigths of t'leriients 



gators using the previoiislv descrihcMl iiietlKxls. By ploltiiig tlic 

 following data, weil-detiiied jterindio cnrves are obtained. 



From the curve it is seen tliat the alkali metals lie on tiie top 

 most points, whilst Zn.Cd and Hg lie on a straigiit line on the descending 

 |ioi'tion of the curve. l',As,81», ;vn<i Hi occupv similar positions in the 

 minima. 



Teinix'rntitri' coefpcii'nt of I'lectric fumlHctlviiii of t'lt'inenf.^. 



The recipi'ocal of the resistance of a conductor is called its con- 

 ductivity. Thus if S is the conductivity of a wire, Ohm's law is 

 expressed hv C' = SE. In tiie same way the specific conductivity 

 is tlie reciprocal of the specilic resistance and is connected with the 

 conductivity by tlie relation S ^ lus//, wiiero / is the length and .•>■ 

 the cross section; the conductivity is directly proportional to the 

 cross section and inversely proportional to the length. 



In the case of pure metals tlie specitic conductivity always decreases 

 with increase of temperature. Dkw.^k and Fi.emincj have shown that 

 at absolute zero the resistance of all pure metals approximates to 

 zero. As a result it has been found that if Rt is the resistance of 

 a platinum wire at the temperature P C on the air thermometer 

 and R„ is the resistance at a temperatuie of (V C, then the connection 

 between these quantities can be expressed by an equation of the form 

 Rt/R^ = 1 + «< 4- ^t\ 



In the expression tt and (i are constants which vary \ery slightly 

 from one specimen of wire to another. The value of these constants 



