The basic equations that describe the thermal diffusion column, including the forgotten effect, were solved numerically. When the density of the liquid in the column varies with concentration, the effect is important in transient batch operation of columns, increasingly so as the wall spacing decreases, but it has no influence at the steady state. Experimental work corroborated the theoretical results.

According to the theory, the instances of concentration reversal reported in the literature cannot be the result of the forgotten effect; the fluids involved could not have had the necessary properties. Attempted duplications of these instances in careful experiments yielded normal behavior. However, theoretical and experimental work on a column with a deliberately nonconstant wall spacing indicated that concentration reversals could occur in the complete absence of any forgotten effect contribution.