To better understand the batch production of 5-nitrosalicylic acid by means of the nitration of salicylic acid through the mixture nitric acid/acetic acid, the solubility of the two main mononitro derivatives of salicylic acid is investigated. For this purpose, the behavior of the two mononitro compounds in the ternary system organic/acetic acid/nitric acid is separately studied at different temperatures (288 to 303) K and nitric acid concentrations [(0 to 2) mol center dot L-1 for 5-nitrosalicylic acid, (0 to 1) mol center dot L-1 for 3-nitrosalicylic acid]. The solubility of these compounds increases with a rise in temperature, whereas only the solubility of 5-nitrosalicylic acid is dependent upon the nitric acid concentration. The mutual effect of each organic acid on the solubility of the other is also investigated. The observed dependencies are explained through simple thermodynamic relationships.