Classical reactor design theory, incorporating the use of the axial dispersion model and assuming flotation to be a first order process, is shown to be adequate in predicting the performance of a large column using a rate constant determined in a small column as long as due consideration is given to any difference in bubble sizes in the two cells. If the bubble sizes in the two columns are not the same it is proposed that the proper value of the rate constant to be used for the large column is found by using the relationship k infinity d(b)(-1.5). The vessel dispersion number, D/uL, is accurately predicted using published relationships. The small column rate constant should preferably be determined under conditions in which the froth zone recovery is 100%; A froth zone recovery in the large column of25% was found to be applicable for the present scale-up calculation procedure.