gradate

gradate (third-person singular simple present gradates, present participle gradating, simple past and past participle gradated)

1. (transitive, intransitive) To change imperceptibly from one gradation of tone etc. to another.
2. (transitive) To arrange in order of grades.
3. (transitive, chemistry) To bring to a certain strength or grade of concentration.

   to gradate a saline solution

• at grade, at-grade