Ceram

“ 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. ”

“ Cerium nitride is a lustrous, brass yellow to bronze coloured solid, stable in dry air, but at once attacked by moist air, with evolution of ammonia, and formation of the dioxide. When moistened in air with a few drops of water, the substance reacts violently, becoming heated to redness. Alkalies and acids decompose it, with formation of cerous compounds. ”

“ In the ordinary process of extraction of the thorium, these elements remain as the sparingly soluble double carbonates, whilst the thorium double carbonate is removed in solution. From the mixed salts which contain 50-60 per cent. of the cerium compound, the cerium nitrate required for the manufacture of mantles is prepared, but the amount so used is a small fraction of the whole, and large quantities of compounds of cerium and the allied elements are available as soon as profitable uses can be found. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ 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 ”

“ 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. ”

“ Thus the attraction between oxygen and silver is so slight that at a comparatively low temperature the oxide of silver is decomposed. In like manner, limestone, or carbonate of lime, is decomposed when subjected to the heat of a lime-kiln, carbonic acid being given off, while quick-lime remains behind. Now, in separating heterogeneous atoms against the powerful force of chemical affinity, work is done as truly as it is in separating molecules from one another against the force of cohesion, or in separating a stone from the earth against the force of gravity. ”

“ 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. ”

“ When the copper is no longer coated, but remains clean and bright when immersed in the fluid, all the silver has been deposited, and the glass now contains a solution of copper.
Nearly all the colors used in the arts are produced by metals and their combinations; indeed, one is named chromium, from a Greek word signifying color, on account of the beautiful tints obtained from its various combinations with oxygen and the other metals. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ In presence of a large excess of alkali carbonate, double carbonates are formed. The stability as well as the solubility of these compounds increases in passing from the cerium to [131] the yttrium group, i.e. as the electropositive character becomes weaker. The double carbonates of the cerium elements are sparingly soluble, and are decomposed by water, especially on warming; they may, however, be recrystallised from alkali carbonate solution. The sodium and ammonium double salts are less soluble than the potassium compounds. ”

“ The ceric salts are yellow to red in colour; their solutions are strongly acid, owing to the ease with which the salts hydrolyse, and on boiling deposit insoluble basic salts.
Beside the methods which have already been mentioned, ceric compounds may be prepared from cerous by oxidation [161] with sodium peroxide, bismuth tetroxide, ammonium persulphate, etc. In electrolysis of cerous salts, also, ceric compounds are obtained at the anode. ”

“ Alumina, in its various forms of clay, is used for brick and tile-making, and for pottery; hardened into the form of slate, it is much used for roofing and for making cisterns. Lime, in the form of carbonate, constitutes the best building stones, including marble, so valuable for ornamental carving and decoration, and when burnt, to separate the carbonic acid, forms lime itself, which is invaluable as a cement when mixed with sand ”

“ All the substances of which the ordinary metals form the basis, are not equally abundant in nature; a great proportion of the numerous mineral species which figure in our classifications, are mere varieties scattered up and down in the cavities of the great masses or lodes. The workable ores are few in number, being mostly sulphurets, some oxides, and carbonates. These occasionally form of themselves very large masses, but more frequently they are blended with lumps of quartz felspar, and carbonate of lime, which form the main body of the deposit; as happens always in proper lodes. ”

“ They are this other constituent, “cementite,” so named because it was first discovered in steel made by the “cementation” process. It is a very hard and brittle substance, hard enough to scratch glass. It is the chemical compound (Fe3C) , unvarying in composition as chemical compounds always are. It consists of just three atoms of iron (93.4% by weight) and one of carbon (6.6%) .
Pearlite, therefore, is a sort of mechanical mixture of two separate constituents, ferrite or pure iron, and this chemical compound, carbide of iron, which is called cementite. ”

“ Here I have a crucible containing some copper. Any substance in the group would do, even hydrogen if there was any way I could handle the gas. I place it in the machine—so. Now, if you could watch inside you would see it change; it is now rubidium, now silver, now caesium. Now it is a hitherto unknown element which I have named after myself, presium, now a second unknown element, cottium—ah! there we have gold. ”

“ Thus it will be seen that corundum is composed almost wholly of alumina,—one of the constituents of common clay, which, when colored by traces of metallic oxides, chrome, etc., produces a greater variety of precious stones of a high rank than any other mineral. ”

“ 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. ”

“ The heat of the furnace opens the pores of the iron, and sets free the carbon contained in the charcoal; and as the cement prevents it from escaping and uniting with the oxygen of the air, it enters the pores of the iron and impregnates it. The fire is now suffered to die out, and the metal is taken from the troughs. It is no longer iron, but steel. ”

“ 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. ”

“ 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. ”

“ The matters which enter into the composition of the fluxes and which cause the adherence of the metallic oxyds are quartz, feldspar, borax and boracic acid, nitre, the carbonates of potash and of soda, red lead and litharge, and oxyd of bismuth. At Sevres, they employ, for under-glaze painting, seven kinds of fluxes, which suffice for all the colors. The majority of these fluxes are composed of quartz, oxyd of red lead and of boracic acid, and to some is added a small quantity of carbonate of soda. ”

“ But when they have a mind to shew the utmost of their skill in giving their wares a fairer gloss than ordinary, they lead them then with lead calcined into powder, which they also sift fine and strew upon them as before, which not only gives them a higher gloss, but goes much further too in their work than the lead ore would have done. ”