Acid–base reaction models as theories that complement each other. For example the current Lewis model has the broadest definition of what an acid and base are, with the Bronsted-Lowry theory being a subset of what acids and bases are, and the Arrhenius theory being the most restrictive. The first scientific concept of acids and bases was provided by Lavoisier in around 1776. Since Lavoisier's knowledge of strong acids was mainly restricted to oxoacids, such as (nitric acid) and (sulfuric acid), which tend to contain central atoms in high oxidation states surrounded by oxygen, and since he was not aware of the true
Simultaneously extracted metals and Acid-volatile sulfide be determined. In initial versions of the SEM-AVS approach, six metals were measured: nickel, zinc, cadmium, copper, lead, and mercury. More current methods call for the measurement of silver in addition to these metals. In applying the SEM-AVS approach, two concentrations are determined: the total concentrations of all toxic heavy metals of interest, represented as [SEM], and the acid-volatile sulfide concentration, represented as [AVS]. From these concentrations, the [SEM]/[AVS] ratio can be obtained, summarizing the results in a single value. Based on the extremely low K values for heavy metal sulfides, if [SEM]/[AVS] is less than 1 ([SEM < [AVS]),