Paul-Émile Lecoq de Boisbaudran, also called François Lecoq de Boisbaudran (18 April 1838 – 28 May 1912), was a self-taught French chemist known for his discoveries of the chemical elements gallium, samarium and dysprosium. He developed methods for separation and purification of the rare earth elements and was one of the pioneers of the science of spectroscopy. The Lecoq de Boisbaudran family was of considerable fortune until the revocation of the Edict of Nantes, after which much of their property was confiscated and sold. Paul Lecoq de Boisbaudran established a successful wine business in Cognac, benefiting from the hard work of the entire family including young Paul-Émile.
Anne Louise Lecoq de Boisbaudran was well educated and taught her son Paul-Émile history and foreign languages, including English. He obtained the syllabus of the École Polytechnique, and he studied the books assigned in its courses. In this way, he was self-taught as a scientist. As such, de Boisbaudran is an example of an autodidact. With the support of his family, he assembled a modest chemical laboratory on the second floor of their home on the Rue de Lusignan. In this laboratory, he repeated the experiments that he had studied in books. Through these experiments, he developed his theories of spectroscopy and made most of his discoveries, including the isolation of gallium. He developed ankylosis of the joints, and failing health hindered his work after 1895. He died in 1912, at the age of 74.
Research
Lecoq de Boisbaudran's early investigations focused on understanding the phenomenon of supersaturation, in which substances can exist in solution in higher concentrations than is possible under normal conditions. He showed that contact of supersaturated solutions with crystals of an isomorphous salt causes the substance to precipitate from the solution. He further showed that many anhydrous salts can be dissolved to create a supersaturated solution. These investigations were carried out from 1866 to 1869.
In 1874 Lecoq de Boisbaudran found that certain crystal faces dissolve more rapidly than other crystal faces. Specifically, he found that octahedral faces are less readily soluble than cubic faces in the case of ammonium alum crystals.
Boisbaudran developed new experimental apparatus and used these to carry out spectral analyses of various chemical elements.
To observe spark spectra in his experimental protocols, he typically placed a solution of a salt in a sealed glass tube, with a platinum wire in the solution as a negative pole, and another platinum wire above the surface of the liquid as a positive pole.
He named his new element "samarium" after the mineral samarskite from which it was isolated. The mineral itself was earlier named for a Russian mine official, Colonel Vassili Samarsky-Bykhovets.
Gallium
thumb|right| Gallium
A significant achievement of Lecoq de Boisbaudran was his discovery of the element gallium in 1875. Beginning in 1874, Lecoq de Boisbaudran investigated a sample of 52 kg of the mineral ore sphalerite obtained from the Pierrefitte mine in the Pyrenees. From it, he extracted several milligrams of gallium chloride. Using spectroscopic methods, he observed what appeared to be two previously unreported lines in the sample's spectrum, at wavelengths of 4170 and 4031 angstroms. He published an account of his investigations on the new element in Sur un nouveau metal, le gallium (1877).
De Boisbaudran calculated the atomic mass of gallium as 69.86, close to the currently accepted value of 69.723.
Dysprosium
thumb|right |Dysprosium
Lecoq de Boisbaudran experimented with the precipitation of rare earth compounds from water solution using potassium sulfate to induce precipitation. He then measured the spectra of solutions in which the liquid served as a positive pole. Lecoq de Boisbaudran noted a spectral band in the yellow-green portion of the spectrum, indicative of a new element. In 1886 he succeeded in isolating a purified sample of the source of the new spectral band. He named the element dysprosium, meaning "difficult to obtain" in the Greek language.
Periodic classification of elements
Lecoq de Boisbaudran contributed to the development of the periodic classification of elements. This contribution occurred when he proposed that the newly discovered element argon was a member of a new, previously unrecognized, chemical series of elements that came to be known as the noble gases.
Awards and honors
For his accomplishments, Lecoq de Boisbaudran was awarded the Cross of the Legion of Honour (1876),
the Bordin Prize from the French Academy of Sciencies (1872),
the Davy Medal (1879)
and the Prix Lacaze of 10,000 francs (1879).