The usefulness of 6-nitro BIPS as a photochromic tracer in org. liqs. was investigated. The photochromic effect of this dye permits the soln. to be decolored conveniently after each tracer expt. so that the same liq. may be used in a closed loop for a large no. of runs, which is essential for large-scale expts. The photochromic behavior of the dye and the stability of its colorless form was studied in a range of solvents. Of all liqs. tested, a no. of alcs. including MeOH, EtOH, and their mixts., with glycerol proved to be fully compatible with the desired photochromic features. 6-Nitro BIPS was used to study the axial dispersion of EtOH-glycerol mixts. of a wide range of viscosities in a 0.3-m-diam. packed column. Tracer concns. were monitored colorimetrically at various locations in the packing. The absorbance measurements of the liq. took place in several small flow-through cells inserted into the packing, which were optically connected to a light source and to photomultipliers by fiber optics. [on SciFinder (R)]