Clerici solution

from Wikipedia, the free encyclopedia

The Clerici solution is a chemical solution of equal parts of thallium formate [Tl (CHO 2 )] and thallium malonate [Tl (C 3 H 3 O 4 )] in water . It is an easy flowing, odorless liquid, the color of which changes from yellowish to colorless with decreasing thallium salt concentration. With a density of 4.25 g / cm³ at 20 ° C, the saturated Clerici solution is one of the heaviest known aqueous solutions. It was discovered in 1907 by the Italian chemist Enrico Clerici and introduced in mineralogy and gemology in the 1930s as useful for separating minerals according to the traditional Archimedean principle . Its advantages include transparency and the easily controllable density in the range of 1 to 5 g / cm³. In addition, the ease with which the density can be measured is an advantage.

The density of the solution is so high that minerals such as spinel , corundum , diamond and most garnets float on top of the solution. When the saturated solution is heated from 20 to 90 ° C, the density can be increased from 4.25 to 5.0 g / cm³ due to the increased solubility of the thallium salts in water. The refractive index changes significantly, linearly and easily reproducibly with density; this makes it easy to measure the density using optical methods.

A special feature is that the color of the solution changes significantly even if it is slightly diluted with water: The concentrated solution at room temperature is amber-yellow with a density of 4.25 g / cm³ and becomes amber-yellow when diluted to a density of 4.0 g / cm³. cm³ similarly transparent as glass or water.

The generally applicable method for density measurement using this solution is as follows: The crystal grain of a mineral to be examined is placed in a small test vessel with the concentrated solution, the crystal grain floating on the surface. Then water is added drop by drop until the crystal grain goes under, because then the density of the liquid is identical to the density of the mineral. The now reached density of the liquid is either directly by weighing, or indirectly by its having the Abbe - refractometer determined measured refractive index.

The disadvantage of the solution is its high toxicity and corrosiveness .

Individual evidence

  1. ↑ E. Clerici: Preparazione di liquidi per la separazione dei minerali . In: Atti della Reale Accademia Nazionale dei Lincei: Memorie della Classe di Scienze Fisiche, Matematiche e Naturale . tape 16 , 1907, pp. 187 (Italian).
  2. ↑ a b c d R. H. Jahns: Clerici solution for the specific gravity determination of small mineral grains . In: American mineralogist . 24, 1939, p. 116.
  3. ↑ a b c Peter G. Read: Gemmology . Butterworth-Heinemann, 1999, ISBN 0-75064411-7 , pp. 63-64.
  4. ↑ a b B. A. Wills, T. Napier-Munn: Wills' mineral processing technology: an introduction to the practical aspects of ore treatment and mineral recovery . Butterworth-Heinemann, 2006, ISBN 0-75064450-8 , p. 247.
  5. ↑ A. Kusumegi: Total absorption Counter and Viewing Shield by The Use of Heavy Liquidst . In: Bull. Inst. Chem. Res., Kyoto Univ. . 60, No. 2, 1982, p. 234.