168 



THE SIGNS OF LIFE 



From which it is evident that where the resistance of the object 

 examined is great as compared with the resistance of the galvano- 

 meter and electrodes (20,000 ohms in this instance), we may regard 

 alterations of deflection as indicating alterations of conductance. 

 Whereas, if the resistance of the object be relatively small, we must 

 calculate the conductance after subtracting from the total resistance 

 in circuit the resistance of the galvanometer and electrodes. 



For many purposes e.g., for comparing the resistance (or con- 

 ductance) of various objects it will evidently be necessary to reduce 

 our results to a common denomination, i.e., to the resistance (or 

 conductance) of a cube of i centimetre. Thus, e.g., a stem 10 cm. 

 long with a sectional area of 10 square millimetres, having a 

 resistance of say 200,000 ohms ( = a conductance of 57) has a 



resistivity = - and a conductivity = 5 x 10 x 10. The reduction 



to the cube of i cm. is in conformity with the practice of modern 

 physical chemistry. The conductivity of I megohm, or i y, = i.io~ 15 

 C.G.S. unit, that of i ohm, or ioy being i.io~ !) . 



Electrolytes in general are increased in conductivity by rise of 

 temperature, the co-efficient of increase being approximately 2 per 

 cent, per degree. 



