We present experiments on a bubble train in a 23-cm-diameter fluidized bed of a Geldart B powder. The bubbles are injected via a single capillary inserted in the bed. We use our double X-ray tomographic scanner to measure the solids distribution in two parallel cross sections of the bed. We report data for four different heights of the measuring planes above the capillary outlet. The velocity of individual bubbles is found from the time of flight from the lower to the upper plane. We have done separate calibration experiments for the velocity. In this article, we present data for the size and velocity of individual bubbles. From the bubble velocity, we could obtain the vertical dimension of the bubbles. This makes it possible to measure the volume of each bubble. The results show that our scanner is capable of measuring properties of bubbles with a size of 2.5 cm and above. (C) 2010 American Institute of Chemical Engineers AIChE J. 57: 2684-2690, 2011