Definition of "foaming"

Athelstan Arundel walked home all the way, foaming and raging. No omnibus, cab, or conveyance ever built could contain a young man in such a rage. His mother lived at Pembridge Square, which is four good measured miles from Lincoln's Inn.

1892, Walter Besant, “Prologue: Who is Edmund Gray?”, in The Ivory Gate […], New York, N.Y.: Harper & Brothers, […], page 16

After three foamings, a steady state is reached.

1946, Stanford University. Dept. of Chemistry, Contributions, volume 17, page 1599