AbstractThe results of density and viscosity measurements are given for ammonium nitrate and the salt mixtures ammonium nitrate—potassium chloride and ammonium nitrate‐ammonium dihydrogen phosphate. The latter system is complicated because of the formation of non‐ortho phosphates and the results obtained refer to the equilibrium mixture obtained after heating for 3 h at 180°c. After this treatment, about 40% of the phosphate was converted to non‐ortho forms.The density of ammonium nitrate is given by: for values of t between 170°c and 190°c. Similar relationships can be deduced for the solutions.The viscosity of ammonium nitrate, in centipoises, is given approximately by: for values of T between 443° and 453° k. Similar relationships hold for the nitrate—phosphate solutions.