in such a way that concentration of PSS in differ- ent flasks ranged from 3.8 x 10-4 M to 3.04 X 10-4 M. where [l]() is the total concentration of dye in a sample solution and [I] and [I]e are the concentra- tions of dye in monomeric form determined (from the absorbance at 650 nm for TMPT and 657 nm for DEMPT) in the presence and absence of salts respectively. (a) Reversible polymerization TMPT exhibits in its visible spectrum peaks at 650 and 600 nm due to the a-(monomer) and 13- (dimer) forms respectively while the correspond- ing peaks for DEMPT appear at 657 and 595 nm respectively. As the concentration of PSS is grad- ually increased the intensity of the l3-peak gradu- ally diminishes and the peak completely disap- pears at [PSS] = 3.04 x 10- 3 M. The intensity of a-peak also decreases gradually. The stacking theory predicts that in the pres- sence of a large excess of polyanion the absorp- tion spectrum of the aggregated dye will revert to that of monomeric dye because of the redistribution of aggregated dye over the excessive binding sites of the polymer. The present metacliromasia of TMPT and DEMPT may be interpreted as being due to the dye cation occupying adjacent ionic sites on the polyanions and undergoing dye-dye interactions as in aggregates3-S. The a-peak rep- resents the unstacked dye molecules and l3-peak represents the stacked ones. The dye bound to PS is predominantly in dimeric for at relatively low [PSS]I[Dye] ratio whereas at [PSS]I[Dye] ratio of about 7 and above "dimeric" form is accompanied by an increase in monomeric form. This may be ascribed to the redistribution of dyes over the an- ionic sites on the freshly added PSS. Further TMPT owing to smaller size is bound to PSS more strongly than DEMPT. (b) Effect of alkali metal halides With the increase in electrolyte concentration (Li +, K + and Cs +) the metachromasia gradually decreases. The degree of destruction of metach- romasy (a) has been calculated for each electro- lyte using Eq. ( 1) Indian Journal of Chemistry Vo1.26A, October 1987, pp.862-864 Interaction of some Thiazine Dyes with Sodium Polystyrene Sulphonate in Presence of Alkali Metal Halides, Quaternary Ammonium Salts & Surfactants HIMANGSHU S BOSE Department of Chemistry, North Bengal University, Darjeeling 734 430 Received 4 September 1986; revised 15 December 1986; accepted 21 January 1987 The metachromasy 'of the dyes, viz. trimethylpropylthionine (TMPT) and diethylmethylpropylthionine (DEMPT) has been investigated in the presence of sodium polystyrene sulphonate. A colour change is noted when these dyes are bound to this anionic polyelectrolyte. The effect of alkali metal chlorides on the metachromatic behaviour of these dyes induced by PSS has also been investigated. The size of hydrated ion and hy- drophobicity of substituent are significant factors for inorgan- ic and organic salts. A peculiar phenomenon that the metach- romasy of the PSS- TMPT and PSS-DEMPT are enhanced on the addition of small amounts of cetyltrimethylammonium chloride is reported. In continuation of earlier works of the author on the metachromasy of thiazine dyes, such as trime- thylpropylthionine (TMPT) and diethylmethylpro- pylthionine (DEMPT)', and on metachromasy in the presence of electrolytes I and when sorbed on- to Na- and H-montmorillonites2, the present study has been undertaken to find the effect of difference in the stereochemistry of these dye molecules on dye-polyelectrolyte interactions. The dyes used have been described elsewhere. The exchange capacity of sodium polystyrene sul- fonate (PSS) (Fluka, Switzerland) was determined as usual. Stock solutions of the quaternary ammo- nium halides (Fluka, Switzerland) and of cetyltri- methylammonium chloride (CTACl) and decyltri- methylammonium chloride (DTACl) were stan- dardised by titrating against AgN03 solution using potassium chromate as indicator. Spectrophotometric measurements were carried out on a Shimadzu UV-240 (Japan) spectropho- tometer fitted with a quartz cell of 1 em path length. The concentrations of the polyanion was varied in the range of 3.8 x 10-4 M to 3.04 X 10-3 AI. Due to the very low solubility of PSS the scat- tering due to PSS was neglected. The mixed solu- tion was equilibrated for 10 min. The concentra- tion of the dyes used was 5 x 10- 5 M throughout the experiment. For the study of reversible polym- erization, to each volumetric flask PSS was added 862 [I] - [Ile a = [I]() - [I]e ... (1)