Cerium

“ The rare metals cerium, lauthanum, and didymium have been lately investigated by Drs. Hillebrand and Norton, in Bunsen's laboratory. Cerium looks like iron, having both its color and lustre, but is heavier, and has the hardness of calcite. It tarnishes slowly in dry air and rapidly in moist air. It ignites so readily that pieces scratched off inflame, and its wire burns more brilliantly than magnesium wire. Lauthanum is a little harder, but also a little lighter. It tarnishes more easily and inflames less easily than cerium. Didymium resembles lauthanum. ”

“ Cerium compounds have also been proposed for use in arc-lamp electrodes; it is claimed that they give a very [320] intense light, one patent [583] adding that the presence of cerium peroxide and a little fluorspar causes the arc to burn evenly and quietly. In another, the use of a mixture of tungstates or molybdates of the alkaline earths, with fluorides of the rare earth elements is protected; [584] the use of pyrophoric alloys, either entirely, or for the core of the electrode, has also been suggested. ”

“ It is a bluish-green powder, which on exposure rapidly combines with the oxygen of the air. By the addition of caustic soda to cerous salts, a white precipitate of cerous hydroxide is formed. Cerium dioxide, CeO2, is produced when cerium carbonate, nitrate, sulphate or oxalate is heated in air. It is a white or pale yellow compound, which becomes reddish on heating. Its specific gravity is 6.739, and its specific heat 0.0877. It is not reduced to the metallic condition on heating with carbon. Concentrated sulphuric acid dissolves this oxide, forming a yellowish solution and ozone. ”

“ The Cerous Compounds
The salts of trivalent cerium are very similar to those of the other rare earth elements, and a detailed description of them is therefore unnecessary. The sesquioxide, Ce2O3, cannot be obtained by ignition of the oxalate, nitrate, or other similar salt, since these decompose at high temperatures with formation of the dioxide, CeO2. It has been prepared by the reduction of the dioxide with calcium; [200] it has a great affinity for oxygen, and readily absorbs the gas when exposed to moist air. ”

“ From the crude oxide so obtained (which contains lanthanum and didymium oxides) the cerium may be separated by conversion into its double sulphate on the addition of potassium sulphate, the sulphates of the cerium group being insoluble in a saturated solution of potassium sulphate. The sulphate is subsequently boiled with water, when a basic sulphate is precipitated. For the preparation of pure cerium compounds see Auer v. ”

“ The yttrium elements can be separated from the cerium metals, and the latter from one another, by taking advantage of the differences of solubility shown by the potassium double carbonates. If a concentrated solution of the salts in potassium carbonate solution be fractionally diluted with water, the cerium elements separate in the order: lanthanum, praseodymium, cerium, neodymium, and samarium; the more soluble yttrium compounds remain in the solution. Thorium forms double alkali carbonates which are very readily soluble in excess of alkali carbonate ”

“ The uncertainty is more pronounced among the yttrium elements than among the cerium elements; owing to the opportunities for investigation furnished by the commercial treatment of monazite, the chemistry of the cerium group may be regarded as complete.
In the following table the elements are arranged in order of increasing atomic weight, and it can be seen at once how closely the division into groups follows this order:
In their chemical relations, the rare earth elements may be placed between the metals of the alkaline earths, and the trivalent metals iron, aluminium, and chromium. ”

“ Cerium salts have been proposed for tanning, and in the preparation of enamels; cerium sodium sulphate is used in the catalytic oxidation of aniline to aniline black. The oxalate has a very slight use in medicine. The oxidising power of ceric salts is of some use in photography; ceric sulphate in acid solution is also said to be an efficient oxidising agent for aromatic hydrocarbons. On account of the [314] deep colour of the higher oxide of praseodymium, didymium salts find a limited application for marking textiles.
Compounds of the yttrium group have at present no technical importance. ”

“ These solutions are obtained by precipitating a dilute solution of a salt of cerium mixed with gold, by means of a lye of potash or soda. The green precipitate obtained is then dissolved in warm dilute acetic acid. The acetate of soda then gives a violet-red precipitate containing all the gold in the liquor and a little basic acetate of cerium. ”

“ Zirconium is always, with the doubtful exception of its peroxy-compounds and the lower oxides, tetravalent. Cerium, as already described, can form two series of compounds, in which it is respectively tri- and tetravalent; thorium, like zirconium, is always tetravalent.
Titanium, Ti = 48·1
Though generally classed among the rare elements, titanium is probably at least as widely distributed in nature as most of the common metals. It occurs as the dioxide in small quantities in all the common silicate rocks and minerals, and in traces in the animal and vegetable kingdoms ”

“ In their most stable state of oxidation, the rare earth elements are generally trivalent. In the case of cerium, the dioxide, CeO2, is more stable than the sesquioxide Ce2O3, but the ceric salts are unstable, and are very readily reduced to cerous compounds, corresponding to the oxide Ce2O3. Higher oxides are known with certainty among the other elements only in the cases of praseodymium and terbium, but these do not give rise to salts. ”

“ In photography, ceric sulphate has been employed for some time for the purpose of ‘reducing,’ i.e. removing silver from over-developed negatives. [572] It is said to act very evenly and rapidly, the small quantity of free sulphuric acid required to hold the salt in solution having no bad effect. More recently, cerium salts have been proposed for use in colour photography. [573] An emulsion is obtained by adding salts of iron, uranium, or cerium to a colloidal solution of albumen in ammonia, borax solution, or sodium carbonate solution ”

“ The solution of sulphates is precipitated with free oxalic acid, which forms salts insoluble in water and dilute acids with all the cerite and gadolinite oxides. The oxides themselves are obtained by igniting the oxalates. When ignited in the air the cerium passes from its ordinary oxide Ce2O3 into the higher oxide CeO2, which is so feeble a base that its salts are decomposed by water, and it is insoluble in dilute nitric acid. Therefore it is always possible to remove all the cerium oxide by repeated ignitions and solutions in sulphuric acid. ”

“ They are thrown down as gelatinous precipitates on addition of potassium or sodium silicofluoride to boiling, neutral solutions of rare earth salts. In presence of mineral acids, however, they are not thrown down in the cold; on boiling, the cerium metals are precipitated as fluorides, by hydrolysis of the silicofluorides—the yttrium elements, with the exception of scandium, being held in solution by the mineral acid. ”

“ The double ceric nitrates [219] are a large and very important class of compounds; they are the most stable of the ceric salts. With nitrates of the monovalent metals, ceric nitrate [164] forms double nitrates of the type R2Ce (NO3) 6; these are deep red hygroscopic substances, crystallising in the monoclinic system, readily soluble in water and alcohol, but dissolving only sparingly in nitric acid. The ammonium salt is important for the separation of cerium. ”

“ Yttrium, it′ri-um, n. a rare metal obtained as a blackish-gray powder, and contained in a few minerals in which there are usually also present compounds of one or more other rare metals, such as cerium, didymium, erbium, and lanthanum.—n. Ytt′ria, its oxide, a yellowish-white powder.—adjs. Ytt′ric; Yttrif′erous; Ytt′rious.—ns. Ytt′ro-cē′rite, a violet mineral found embedded in quartz, a fluoride of yttrium, cerium, and calcium ”

“ I made some commercial inquiries, and there seemed even then much truth in Gordon-Nasmyth’s estimate of the value of the stuff. It was before the days of Capern’s discovery of the value of canadium and his use of it in the Capern filament, but the cerium and thorium alone were worth the money he extracted for the gas-mantles then in vogue. There were, however, doubts. Indeed, there were numerous doubts. What were the limits of the gas-mantle trade? How much thorium, not to speak of cerium, could they take at a maximum. ”

“ Brauner [196] dissolves the oxides in nitric acid, and after removal of excess of acid, boils with a large volume of water—basic ceric nitrate is thrown down, the other elements remaining in solution as nitrates. The precipitate is redissolved, and the process repeated until the cerium is found spectroscopically to be free from didymium. The hydrolysis of the ceric salt may be effected more quickly and completely by the addition of ammonium sulphate or magnesium acetate. ”

“ The thorium nitrate obtained after purification by the sulphate method, or by the less generally employed acetate method, is usually considered sufficiently pure for technical purposes. Even now, however, it may contain traces of sulphate, of iron, of alkalies, and of cerium metals. If absolute purity is desired, the salt may be dissolved, and freed from all impurities, except the cerium compounds, by precipitation with ammonium oxalate and thorough washing; the oxalate may then be dissolved in chromic acid, and potassium chromate solution added drop by drop ”

“ One of the most significant developments of modern chemistry is seen in the efforts which are constantly being made to turn the so-called rare elements to useful account; and when they are found to be technically valuable it is generally observed that hitherto unknown sources of supply are soon available. Cerium salts have been found to be useful in the colouring of glass and porcelain, as mordants in dyeing, in photography, and in medicine. Zirconium has been used in incandescent electric lighting, and thallium has been employed in the manufacture of highly refractive optical glass. ”

“ Analyses of material from different localities exhibit wide variations in chemical composition. In addition to uranium oxides, there are thorium, cerium (and lanthanum) , yttrium and lead oxides, each varying in amount from a trace up to 10%. Calcium, iron, magnesium, manganese, silica, water, &c., are also present in small amounts. ”

“ The thorium nitrate is made up with distilled water to a solution of 25-35 per cent. strength, and the calculated quantity of a standard solution of cerium nitrate is added. It is usual to add to the mixture a small quantity of another nitrate, which on ignition will leave an oxide of which the function is to strengthen the skeleton of ash. Beryllium, zirconium, magnesium, or aluminium nitrate is usually employed, in quantity calculated to leave an amount of oxide constituting about 0·5 per cent. ”

“ Slight impurities in the earths or the gas will speedily spoil the light. The best results are obtained from a mixture of 99 parts thoria and 1 part ceria. It is the ceria that gives the light, yet a little more of it will lower the luminosity.
The non-chemical reader is apt to be confused by the strange names and their varied terminations, but he need not be when he learns that the new metals are given names ending in -um, such as sodium, cerium, thorium, and that their oxides (compounds with oxygen, the earths) are given the termination -a, like soda, ceria, thoria. ”

“ The ease with which misch-metal and its alloys with iron and other elements throw off glowing particles when struck is due to the low ignition temperature of cerium, and the energy with which it combines with oxygen. When such alloys are scratched, small fragments are struck off, which are raised to the ignition temperature by the heat of friction. ”

“ The second class contains the yttrium and cerium metals, with zirconium and thorium; the technical importance of these elements is due chiefly to the use of their oxides in illumination, to a small extent in Nernst lamps, and to a much greater extent in the so-called Incandescent Lighting. The manufacture of incandescent mantles [487] is a large and ever-extending industry, intimately bound up with the older process of coal-distillation, with its innumerable ramifications ”

“ Yet among the elements the sea’s plants and animals concentrate are the very materials with which we are apt to be most concerned: Strontium, cesium, cerium, ruthenium, cobalt, iodine, phosphorus, zinc, manganese, iron, chromium, and others. Radioisotopes [6] of all these elements occur as by-products of human nuclear activities. Many concentrating organisms are microscopic in size and are frequently impossible to raise in captivity. It is apparent that we are faced with a research program of considerable challenge and proportion. ”

“ The chief mineral species are monazite, a phosphate of the cerium metals, containing thorium (this mineral supplies the ceria and thoria employed in making incandescent gas mantles) ; cerite, a hydrated silicate of calcium and the cerium metals; gadolinite, a silicate of beryllium, iron, and the yttrium metals; samarksite, a niobate and tantalate ofboth the cerium and yttrium metals, with uranium, iron, calcium, etc.; and keilhauite, a titanosilicate of yttrium, iron, calcium and aluminium; other species are fergusonite, orthite, aeschynite, euxenite and thorianite. ”

“ Then the multiplication of the species of matter with which Lockyer's results menace us, is at first sight startling. They may lead, we are told, to eventual unification, but the prospect appears remote. Their only obvious outcome is the disruption into several constituents of each terrestrial "element." The components of iron alone should be counted by the dozen. And there are other metals, such as cerium, which, giving a still more complex spectrum, would doubtless be still more numerously resolved. ”