digestion of a precipitate
Picture leaving a fresh precipitate to rest in its warm mother liquor like dough proving on a counter. Given time and gentle heat, the tiny first-formed crystals quietly reorganize into fewer, larger, sturdier ones. That patient resting is digestion.
Digestion (also called aging) is allowing a precipitate to stand in contact with the solution from which it formed, usually warm, so that small unstable crystals dissolve and redeposit onto larger ones. The total amount of solid barely changes, but its texture improves dramatically.
It matters because the resulting crystals are bigger, purer, and far easier to filter and wash. Digestion also lets trapped impurities escape as crystals partly dissolve and reform, making it one of the most effective ways to clean up a precipitate before weighing.
After barium sulfate first forms as a fine cloud, the beaker is kept warm on a hotplate for an hour; by then the solid has aged into coarse, granular crystals that filter quickly and rinse clean.
Warm standing lets small crystals dissolve and feed bigger ones.
Digestion works because small crystals are slightly more soluble than large ones, so material steadily migrates from small to large — a process known as Ostwald ripening.