Thallium: Pyrites Flue Dust to Thallous Chloride and Sulphate, Deposited on Zinc (Roscoe 1913)

Thallium hides in the dust of works that burn pyrites for sulphuric acid. Water pulls it out, salt or hydrochloric acid throws it down as thallous chloride, and after cleaning as the sulphate it plates out on zinc. Result: bluish-white thallium, soft enough to mark with a fingernail (sp. gr. 11.8, melts at 303 °C). Thallium and its salts are highly poisonous. Source: Roscoe and Schorlemmer, A Treatise on Chemistry vol. 2 (1913), pp. 759-760. Unknown: the flue dust; no blueprint collects it yet. Picture drawn by Youblob.