(1) A chemical analysis of water in which the quantity of [[ion|ions]] in solution is determined for the common cations and anions (e.g., **Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, S0₄^{- -}, Cl^-, CO₃^{- -}, HCO₃^-**). The character of the solution can be described in terms of the ion concentrations in parts per million, milligrams per liter, or its reaction value. The unit of concentration, parts per million, is related to the weights of positive and negative ions in solution, and the combined weight of the positive ions does not balance the combined weight of the negative ions. The reaction value relates the weight of each ion to its valence and [[atomic weight|atomic (or radical) weight]]. For example, {{ :terms:p101f1.gif }} The reaction values of positive and negative ions are exactly equal when all ions have been considered. (2) An electrical [[resistivity]] analysis of water. Resistivity values of water solutions of interest, as determined by actual measurement of each sample in a [[conductivity]] or resistivity cell, are important in the analysis of [[resistivity logs|resistivity well logs]].