Defined for ionic species B by λ = | z B | F u B where z B is the charge number of the ionic species B, F is the Faraday constant, and u B is the electric mobility of species B. In most current practice z B is taken as unity, i.e. ionic conductivity is taken as that of species such as Na⁺, Ca²⁺/2, La³⁺/3 etc. To avoid ambiguity the species considered should be clearly stated, e.g. as λ Ca 2+ / 2.