Definition of "effervescing"

I took up the 'Christian Scientist' book and read half of it, then took a dipperful of drench and read the other half. The resulting experiences were full of interest and adventure. All through the rumblings and grindings and quakings and effervescings accompanying the evolution of the ache into the botts and the cold into the blind staggers I could note the generous struggle for mastery going on between the mash and the drench and the literature […]

1899, Mark Twain, “Christian Science and the Book of Mrs. Eddy”, in The Cosmopolitan, vol. 27 May-Oct