Kohli, Nitin, and R.P. Singh. “3-Nitroso-4-Hydroxy-5,6-Benzocoumarin (NHBC) As a Reagent for the Spectrophotometric Determination of copper(II) in Alloys”. CHIMIA, vol. 28, no. 11, Nov. 1974, p. 661, https://doi.org/10.2533/chimia.1974.661.