In a gradient of magnetic field, magnetic dipoles of the air are attracted toward the region of intense field such that the air pressure is more in the regions of more intense field. The formed pressure gradient exerts a net force on a body placed in the air in this gradient of magnetic field toward the region of low pressure or the region having weaker field. This is like what takes place in sink-float separation. If so, we may construct an innovative instrument for separating oxygen from air.