Polar aprotic solvent. See

The blue color of 83 has been observed in numerous experiments. For example, a brilliant blue color occurs if a potassium thiocyanate melt is heated to temperatures above 300 °C [132] or if eutectic melts of LiCl-KCl (containing some sulfide) are in contact with elemental sulfur [132, 133], if aqueous sodium tetrasulfide is heated to temperatures above 100 °C [134], if alkali polysulfides are dissolved in boiling ethanol or in polar aprotic solvents (see above), or if borate glasses are doped with elemental sulfur [132]. In most of these cases mixtures of much 83 and little 82 will have been present demonstrating the ubiquitous nature of these radicals [12]. 

Notably (a) The Chemistry of Non-aqueous Solvents (ed. J. J. Lagowski), Academic Press, New York and London, 1966-1970 (b) Non-aqueous Solvent Systems (ed. T. C. Waddington), Academic Press, New York and London, 1965. Neither of these compilations deals with the alcohols or with the so-called polar aprotic solvents. See also Chemistry in Non-aqueous Ionizing Solvents (ed. G. Jander, H. Spandau, and C. C. Addison), Vieweg-Interscience, Braunschweig and London, 1963-1971. 

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