A new method for the determination of the solubility of disperse dyes

The solubility of sparingly soluble compounds, particularly when they are present in the finely dispersed state, is difficult to measure, especially at elevated temperature and pressure. To date there have been no simple methods of determination. A quick and very simple method is now presented, termed ‘solubility titration’, based on the idea that if the substance under test is added gradually in small amounts to a solvent or dilute solution, its extinction or light scattering in the u.v/visible region must change abruptly the moment the solubility is exceeded. Such is actually the case, and the solubility is found from the extinction or from the light scattered, at the point indicated by the intersection of two curves. This method was developed specifically to determine the water solubility of commercial disperse dyes under dyeing conditions, i.e. at 130d?C and elevated pressure (about 400 kPa). Tests gave precise, highly reproducible values.