The rotary chamber technique is capable of observing small levitated bubbles in liquid for various research purposes. The present paper focuses on diffusion of a small spherical bubble into undersaturated water. The decaying bubble size is recorded in time by image processing. The results are plotted as Sherwood versus Reynolds number where the Schmidt number is of order 300. Similarity is found for each of four gases in water. The boundary layer prediction Sh $ \propto \sqrt {{\rm{Re}}} $ is confirmed in general. A physically accountable model provides a good representation of results.