Clerici solution

Clerici solution is a solution of equal parts of thallium formate (Tl(CHO₂)) and thallium malonate (Tl(C₃H₃O₄)) in water. It is a freely flowing, odorless liquid which changes from yellowish to colorless upon decreasing the concentration of the thallium salts. At a density of 4.25 g/cm at 20 °C, the saturated Clerici solution is one of the heaviest aqueous solutions known. The solution was invented in 1907 by the Italian chemist Enrico Clerici (1862–1938) and introduced to mineralogy and gemology in 1930s as a valuable liquid, which allowed separating minerals by density with a traditional flotation method. Its advantages include transparency and variable and easily controllable density in the range 1–5 g/cm.