Conductivities of Mixtures and of their Constituents. 291 



Without endeavouring to express the relative values of the 

 three formulas numerically, we may arrange the three in order 

 of merit for each mixture as follows : — 





Order of merit of calculated Values. 



Best. 



Middle. 



Worst. 



Water and Ethyl Alcohol 



f Conductivity. 

 \ Logarithm. 



1 Logarithm. 



Resistivity. 

 Logarithm. 

 Logarithm. 



Resistivity. 

 1 Resistivity. 



1 



Resistivity. 



Conductivity. 



Conductivity. 



Resistivity. 



Conductivity. 



Conductivity. 



f Conductivity. 

 \ Logarithm. 



J 

 Resistivity. 



Logarithm. 



Conductivity. 



Resistivity. 



Logarithm. 



Water and Ethyl Alcohol 

 (Lees) 



Water and Glycerine 



Water and Acetic Acid ... 

 Water and Methyl Alcohol . 

 Ethyl Alcohol and Gly- 



Ethyl Alcohol and Methyl 

 Alcohol 





1 Tin ar.d Bismuth (Wiede- 

 mann) 



i Logarithm. 



Resistivity. 

 Logarithm. 



Resistivity. 



Logarithm. 

 Resistivity. 



Conductivity. 



Conductivity. 

 Conductivity. 



Vaseline and Marble 



Lard and Zinc Sulphate ... 



From this it will be seen that the formula 



P1 + P2 



represents the observed results worst, and that of the other 

 two the formula 



Pi +P2 



is somewhat better than 



1 1 



k 



r+P*j, 



2h +P2 



The representation of the observed facts which even the 

 best of the three gives is, however, only rough. As a rule 

 the mean resistivity formula gives too low, t and the mean 

 logarithmic formula too high, values for the conductivity of 

 each mixture. Now the conductivity of a compound built 

 up of two materials, as in fig. 3, but with the same structure 



