Flotation scale-up has been a major difficulty and is becoming more so as the flotation machines continue to grow in size. It has been proposed by Gorain and his;coworkers that the flotation rate constant has a linear relationship with the bubble surface area flux. This paper discusses that claim using the data presented to validate that claim. It can be shown that the measurement and computation of superficial gas velocity, and partially also the bubble size may be biased in some conditions. This makes the bubble surface area flux behave such that the final outcome is in doubt. The validation does not address the different particle sizes at all. (C) 2000