423 
Fig. 1. 
gators using the previously described methods. By plotting the 
following data, well-defined periodic curves are obtained. 
From the curve it is seen that the alkali metals lie on the top 
most points, whilst Zn, Cd and Hg lie on a straight line on the descending 
portion of the curve. P,As,Sb, and Bi occupy similar positions in the 
minima. 
Temperature coëfficiënt of dectric conductivily of dements. 
The reciprocal 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 by C~SE. In the same way the specific conductivity 
is the reciprocal of the specific resistance and is connected with the 
conductivity by the relation S — ms/I, where l is the length and s 
the crosssection ; the conductivity is directly proportional to the 
cross section and inversely proportional to the length. 
In the case of pure metals the specific conductivity always deereases 
with increase of temperature. Dewar and Fleming have shown that 
at absolute zero the resistance of all pure metals approximates to 
zero. As a result it has been found that if R t is the resistance of 
a platinum wire at the temperature f C. on the air thermometer 
and R 0 is the resistanee at a temperature of 0° C., then the connection 
between these quantities can be expressed by an equation of the form 
Rt/R 0 = 1 
In the expression « and are constants which vary very slightly 
from one specimen of wire to another. The value of these constants 
