Equivalent weight is the weight of an element or compound which combines with or displaces the equivalent weight of any other element or compound; for an element, for an element it equals the relative atomic mass (atomic weight) divided by the valence. This presupposes the law of equivalent proportions, which states that the ratio of the weights of two elements A and B which combine with the same weight of an element C, is the same as the ratio of the weights of A and B which combine with each other, or a small integral multiple of it. Since an element may have more than one valence, and a compound may react in more than one way, they may have more than one equivalent weight. The normality of a solution is its concentration in gram-equivalent weights per liter; a solution whose normality is 1 is called normal.