Inorganic Chemistry

INORGANIC CHEMISTRY Inorganic Chemistry, which is concerned with the prepara tion and properties of the elements and non-carbon compounds, was primarily developed through the investigation of minerals, and was in consequence termed mineral chemistry, whereas or ganic chemistry resulted from the study of plant and animal products. Though it was well recognized that organic substances were amenable to the same general chemical laws as mineral sub stances, it was not found possible, prior to 1828, to prepare organic substances from the elements synthetically, and it was supposed that a fundamental difference existed between organic and inorganic substances. In 1828, F. Wi hler's synthesis of urea imparted a great impetus to the study of organic substances, and within a few years it was found convenient to separate chemical science into the domain of the carbon compounds, organic chemis try, and that of the elements and non-carbon compounds, inor ganic chemistry. It is usual and convenient, however, to include in inorganic chemistry the oxides and nitride of carbon and their simpler derivatives, such as metallic carbonyls, carbonates and cyanides.

Early Discoveries.

The earliest discoveries in inorganic chem istry were made in the metallurgical and medical arts and in the domestic economy of the ancients. Gold, silver, copper, tin, iron and lead, some of the simpler alloys, metallic salts and mineral products, and the rudiments of metallurgical, glass-mak ing, enamelling, painting, dyeing, alchemical and medical arts were known to the ancient Chaldeans, Hindus, Chinese, Egyptians and Greeks, many centuries before the Christian era. By about the middle of the 17th century, the alchemists were acquainted with most of the common metals, their alloys and salts, a few acids, alkalis, medicinal minerals, and non-metallic elements. In 1733 G. Brandt of Sweden isolated cobalt, and in 175o A. F. Cronstedt prepared metallic nickel. These discoveries were fol lowed by Henry Cavendish's recognition of elementary hydrogen in 1766, the isolation of nitrogen by Daniel Rutherford in 1772, manganese by J. G. Gahn in 1774, oxygen by Joseph Priestley and chlorine by K. Scheele in 1774, and molybdenum by P. J. Helm in 1782. Cavendish in 1784 made the far-reaching discovery that water is composed of two volumes of hydrogen to one of oxygen, and in the following year he succeeded in synthesizing nitric acid by passing electric sparks through moist air. His further discovery, that minute residue of the air would not combine with oxygen, was ignored for over a century, until Lord Rayleigh and Sir William Ramsay in 1895 proved that the inert residue consists of a mixture of the noble gases, argon, krypton, neon and xenon.

The mineral pitchblende, in which M. H. Klaproth detected uranium in 1789, is of great historical importance, for W. F. Hillebrand exactly a century later obtained from it a gas which he supposed was wholly nitrogen, but which Ramsay in 1894 proved was a mixture with about 12% of the noble gas, helium, first detected spectroscopically in the sun by E. Frankland and Sir J. N. Lockyer in 1868. Henri Becquerel's detection in 1894 of the emission of radiation by uranium salts from pitchblende, led to the epoch-making discovery in 1898 of the radioactive com pounds of polonium and radium by Marie and Pierre Curie, and of the heaviest noble gas, radon, by Ernst Dorn in 1900 (see RADIOACTIVITY) .

Zirconium was detected by Klaproth in 1788, and titanium by McGregor in 1791. Don Fausto d'Elhuyar isolated tungsten in though the existence of tungstic acid had been proved by Scheele 20 years earlier. In 1794 J. Gadolin discovered the "rare earth" yttria, the chief constituent of the mineral later called gadolinite found in Ytterby in Sweden. The "rare earth" group of closely allied elements has been the subject of intensive chemi cal research for over a century. Cerium was detected simul taneously and independently by Klaproth, J. J. Berzelius and W. Hisinger in 1803. C. G. Mosander detected lanthanum in "didymia" in 1841 and terbium and erbium in 1843. "Ytterbia" was detected by J. C. G. de Marignac in 1878, scandium by Lars F. Nilson in 1879, samarium in the same year by Paul E. Lecoq de Boisbaudran and also holmium and thulium by P. T. Cleve. Mosander's "didymia" was resolved in 1885 into praseodymia and neodymia by Carl Auer von Welsbach, and G. Urbain resolved Marignac's "ytterbia" into ytterbia and lutecia in 1907. In 1886 Lecoq de Boisbaudran detected dysprosium and, with Marignac, gadolinium. The radioactive element actinium, the heaviest of the "rare earth" series, was detected by A. Debierne in 1899. The gap in atomic number between neodymium (6o) and samarium (62) was filled in 1926 by the discovery of illinium by X-ray spectroscopy by J. A. Harris, L. F. Yntema and B. S. Hopkins, thus completing the series of "rare earth" elements. These eighteen elements are all proper to group III. of the periodic classification (q.v.), scandium to period 4, yttrium to period 5, the 15 elements from lanthanum to lutecium to period 6 and actinium to period 7.

Platinum was probably known to the natives of Mexico and South America many centuries before its recognition by Scalinger in 1558 and William Brownrigg's description of it to the Royal Society in 1750. W. H. Wollaston discovered palladium in 1803 and rhodium in 1804. In the following year Smithson Tennant discovered iridium and osmium. The lightest of the "platinum metals" was not discovered till 1826, when Osann claimed to have isolated three new elements in native platinum alloys from Ruthenia in Russia. C. E. Claus was able to confirm the existence of only one of these new elements, which he called ruthenium.

Beryllium and chromium were detected by L. N. Vauquelin in 1797, and in the following year Klaproth isolated tellurium. Its congener, selenium, was not discovered till 1817, when Ber zelius detected it as a red deposit in Swedish sulphuric acid chambers. In similar seleniferous deposits in German sulphuric acid works, Sir William Crookes in 1861 discovered thallium, the heaviest metal of the aluminium family.

The beginning of the 19th century witnessed the discovery of the most powerful method for the analysis of compounds into their elements, that of electrolysis. By this means Sir Humphry Davy was enabled to decompose the supposed elements, soda and potash, and isolated the metals sodium and potassium in 1808. Shortly afterwards he obtained magnesium, calcium, strontium and barium from magnesia, lime, strontia and baryta respectively. The discovery of boron by J. L. Gay Lussac and Davy in 1809 led Berzelius to investigate the supposed element, silex or silica, which he proved in 1810 to be the oxide of a new non-metallic element, silicon. The element was obtained by the reduction of fused silica with carbon and iron, and was finally obtained pure in 1823 after Berzelius had discovered the general method of reduction by heating potassium double fluorides with potassium. Using the new method he isolated zirconium in 1824, titanium shortly afterwards and thorium in 1828. A similar but more ac cessible method was introduced by Wohler in 1827, beryllium and aluminium being isolated by heating their chlorides with potassium.

In 1812 B. Courtois isolated the element iodine from the ashes of marine plants. The analogy of iodine to chlorine was quickly recognized, and in 1815 Gay Lussac isolated cyanogen, a compound which in combination behaves very similarly to the halogen elements, chlorine and iodine. Bromine, intermediate in atomic weight and properties between chlorine and iodine, was discovered by A. J. Balard in 1826. The lightest of the halogen family of elements, fluorine, though well recognized as an element, resisted numerous attempts to isolate it until 1886, when Henri Moissan obtained the elementary gas by the electrolysis of a solution of potassium hydrogen fluoride in hydrofluoric acid in a platinum vessel.

The lightest of the alkali metals, lithium, was discovered by Arfedson in 1817, but the two heaviest, rubidium and caesium, were not detected till 1861 and 1860, respectively, when Robert W. Bunsen and G. R. Kirchhoff applied spectrum analysis to the detection of elements, a new method discovered by them in This method has been of immense service in chemistry, and has led to the discovery of thallium by Crookes, indium by F. Reich and H. T. Richter in 1863, and gallium by Lecoq de Boisbaudran in 1875, all members of the aluminium family. The spectroscopic method has also played an important part in the characterization of the "rare earths," and has proved of fundamental importance in ascertaining the composition of the sun and stars. Its ex tension to X-ray spectra has in recent years led to great advances in physical knowledge of the structure of atoms.

Vanadium was discovered by Del Rio in 1801, and the allied element, niobium (columbium), by C. Hatchett in the same year. Tantalum, the next heavier member of this family, was discovered by A. G. Ekeberg two years later, but Wollaston in 1809 pro nounced niobium and tantalum to be identical. These elements were not separately distinguished until 1844, when H. Rose showed that the mineral columbite contained two distinct ele ments, the lighter of which he named niobium and the heavier tantalum. Nevertheless, confusion continued to exist between these elements till Marignac proved in 1866 that Rose's niobium was in fact Hatchett's columbium. The separation of these ele ments is one of the most difficult problems of analytical chemistry, most methods being based on slight differences in solubility or hydrolizability of their double fluorides. The radioactive element, protoactinium, is the heaviest of the vanadium family, and was discovered by Otto Hahn and Lise Meitner in 1918. The atomic weight of protoactinium is uncertain and its atomic number is known only by inference from the radioactive disintegration series.