Enrico Clerici (15 October 1862 â 26 August 1938) was an Italian mineralogist and geologist. From 1903 on, he worked at the University of Rome. He published in 1907 the composition of a solution with a density of 4.25 g/cm<sup>3</sup> at 20ðC, to determine the density of minerals. The Clerici solution is a mixture of thallium formate (Tl(CHO<sub>2</sub>)) and thallium malonate (Tl(C<sub>3</sub>H<sub>3</sub>O<sub>4</sub>)) in water.