THE nitric acid produced in the arc processes for the fixation of atmospheric nitrogen 1 usually has a concentration of 33 to 35 per cent. A dilute acid is also produced in its formation by the oxidation of ammonia, 2 while in the ordinary method of manufacture from Chili saltpetre a dilute acid (3 80 B~. or less) is obtained from the final towers Or tourilles of the condensing system. On account of the many uses for concentrated nitric acid, the problem of concentrating its dilute aqueous solutions is an important one and one which has received much attention. As is well known, dilute aqueous solutions of nitric acid can only be concentrated to about 68 per cent. HNO3 by distillation at atmospheric pressure, due to the formation of a mixture of maximum boiling point ; and by distillation with concentrated snlphuric acid aqueous solutions containing 68 per cent. nitric acid (mixture of maximum boiling point) can be concentrated to over 9 Β° per cent. a Attempts have been made to concentrate dilute nitric acid electrolytically, 4 but, as Molinari points out, ~ these have not yielded practical results.
When an aqueous solution of nitric acid is electrolyzed between platinum electrodes, the NO:cions and the H-ions migrate, respectively, to the anode and the cathode and are there discharged, the resulting NO~-radicals reacting with the water of the solution in accordance with the equation: 2NO3 ~-H20 = 2HNOa + O.