Bubble loading is a macroscopic measure which includes the micro sub-processes of true flotation. In this paper, new instrument for measuring the bubble loading in flotation column with the ability to generate the uniform size bubbles is introduced. This ability (generation of uniform size bubbles with mean diameter of 2 mm and standard deviation of 0.3 mm) make it possible to study the effect of bubble size on bubble loading. Laden bubbles sampling system consists of riser with diameter of 20 mm and height of 720 mm made of glass and collection chamber with diameter of 54 mm and height of 150 mm made of transparent Perspex installed directly on top of the riser. Applying the flotation column with low mixing (vessel dispersion number of 0.32 and axial mixing coefficient of 0.003 m(2)/s) and direct entry of bubbles from the riser to collection chamber caused the experiments to be reproducible by nearly 15 g (5% of total feed) of solid samples loaded by bubbles. Measured bubble loading was validated by comparing the recovery obtained based on bubble loading data and the recovery calculated from macroscopic mass flow rates of concentrate and feed. Results showed discrepancies less than 3%, confirming the reliability of bubble loading measurements by the developed instrument. (C) 2015 Published by Elsevier Ltd.