a. Chem. [f. THALLI-UM + -OUS.] Abounding in thallium; spec. containing thallium in greater proportion, relatively to oxygen, than thallic componnds. Thallious oxide = Thallium monoxide, Tl2O.
1858. Watts, Dict. Chem., V. 749. Thallic salts are easily distinguished from thallious salts by their behaviour with alkalis. Ibid., 750 [see THALLIC]. Ibid. (1873), Fownes’ Chem. (ed. 11), 412. Thallious Iodide, Tl I, is formed by direct combination of its elements, or by double decomposition.
