A settler-soaking apparatus for treating the effluent from an acid-catalyzed alkylation reaction is disclosed which comprises three interconnected vertically aligned chambers. The uppermost chamber possesses a hydrocarbon outlet means above an acid hydrocarbon inlet means and a downspout having an acid transfer means extending through and ending in the lower end of the middlemost chamber. The latter possesses a hydrocarbon outlet means at an elevated position with respect to the end of the acid transfer means in the downspout and a lower situated acid outlet means. The lowermost chamber possesses a multitude of spaced horizontal perforate trays and an acid hydrocarbon inlet means, which is in connection with the hydrocarbon outlet means of the uppermost chamber. The middle and lowermost chamber are in open communication via a chimney which extends upwardly into said middle chamber to provide a hydrocarbon outlet means at a point above the end of said downspout.