The Schlieren technique with double optical path was established.With the new technique

the natural convection of CO2 absorption into and desorption from chlorobenzene in a quiescent cell was visualized from horizontal and vertical directions simultaneously.During the absorption process

the convection does not appear

and only dark stripes appear from the vertical direction.In the desorption process

evident convection emerges in both horizontal and vertical directions.At the beginning of the desorption process

the stratification appears in the vertical direction

and it is destroyed with the convection becoming more and more intense.The characteristic velocity of the horizontal convection is larger than that of normal one

then the convection appears in the horizontal direction.The convection structure tends to move to the center of the cell because of the heat effect from the mass transfer.The results show that the dual-path Schlieren technique can be used to observe tridimensional convections easily and simultaneously

based on which the mass transfer can be studied more deeply.