| Jean Charles Galissard de Marignac | |
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Jean Charles Galissard de Marignac
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| Born | 24 April 1817 Geneva |
| Died | 15 April 1894 |
| Nationality | Swiss |
| Fields | Chemistry |
| Known for | Measurement of atomic weights Discovery of ytterbium Codiscovery of gadolinium |
Jean Charles Galissard de Marignac (24 April 1817 – 15 April 1894) was a Swiss chemist whose work with atomic weights suggested the possibility of isotopes and the packing fraction of nuclei and whose study of the rare earth elements led to his discovery of ytterbium in 1878 and codiscovery of gadolinium in 1880.
Born in Geneva, he was twenty-one years old when he began to attend the Ecole Polytechnique in Paris, and from 1837 to 1839 studied at the Ecole des Mines. Then, after a short time in Liebig's laboratory at Gießen, and in the Sèvres porcelain factory, he became in 1841 professor of chemistry in the academy of Geneva. In 1845 he was appointed professor of mineralogy also, and held both chairs till 1878, when ill-health obliged him to resign. He died at Geneva.
Marignac's name is well known for the careful and exact determinations of atomic weights which he carried out for fifty-seven of the elements. In undertaking this work he had, like J. S. Stas, the purpose of testing Prout's hypothesis, but he remained more disposed than the Belgian chemist to consider the possibility that it may have some degree of validity. Throughout his life he paid great attention to the rare earths and the problem of separating and distinguishing them; in 1878 he extracted ytterbium from what was supposed to be pure erbia,[1] and two years later found gadolinium and samarium in the samarskite earths.
In 1858 he pointed out the isomorphism of the fluostannates and the fluosilicates, thus settling the then vexed question of the composition of silicic acid; and subsequently he studied the fluorides of zirconium, boron, tungsten, and other elements. He prepared silicotungstic acid, one of the first examples of the complex inorganic acids. Marignac discovered that niobium and tantalum could be separated by fractional crystallization separation of potassium heptafluorotantalate from potassium oxypentafluoroniobate monohydrate, a process which was used commercially until displaced by solvent extraction separation of the same fluorides starting in the 1950s.
In physical chemistry he carried out extensive research on the nature and process of solutions, investigating in particular the thermal effects produced by the dilution of saline solutions, the variation of the specific heat of saline solutions with temperature and concentration, and the phenomena of liquid diffusion.