Stanley Isaac Levy

“ The rare earths constitute the most striking example of the association of chemical substances with others which are closely allied to themselves, and from which they are separable only with extreme difficulty. They form a group to themselves, sharply demarcated from the other elements, and it is my belief that by following the study of them to the utmost limits, we may arrive at the explanation of what the chemical elements really are and how they originated, and discover the reasons for their properties and mutual relations. ”

“ He found that the helium ratio, i.e. the volume of helium per gram of uranous oxide, UO2, varies with the amount of thoria present; but where the latter is absent the variations are much less marked. If helium were produced in a mineral from uranium alone, and none escaped, it is obvious that the helium ratio would depend only on the age of the mineral. For minerals of about the same age, and containing no thorium, the helium ratio would be roughly constant, if no disturbing factor required consideration. ”

“ The Manufacture of Mantles from Artificial Silk. —Whilst the fabrics made by the various processes outlined above are more expensive than the cotton and ramie formerly exclusively used in the mantle industry, they have the advantage, in addition to the fact that they produce better and more lasting mantles, that they do not need the laborious and troublesome process of washing which is so essential in the case of the vegetable fibres. From the nature of the methods used in its manufacture, artificial silk can contain no mineral residue; hence the fabric is immediately ready for impregnation. ”

“ We shall be set free from the need for experiment, knowing a priori what the result of each and every experiment must be; and our knowledge then will as much transcend our present scientific systems as the knowledge of the skilled mathematician of the present day exceeds that of primitive man, counting upon his fingers. The great problem of the nature and genesis of the elements is approaching solution, and when the consummation is reached it will undoubtedly be found that the study of the rare earths has been an important factor in bringing it about. ”

“ The oxalates of the rare earth elements are of the greatest importance, on account of the fact that they are not only insoluble in water, but are also very sparingly soluble in dilute mineral acids, and in excess of oxalic acid. They can be completely precipitated even from strongly acid solutions by addition of sufficient excess of oxalic acid, or alkali oxalate, and thus afford a means of easily and completely separating the rare earth group from the commoner elements. ”

“ The compounds of tetravalent titanium are much more stable than the compounds in which the element has a lower valency, and are very readily formed from them. The dioxide is amphoteric in character, and acts as a weak acid as well as a weak base; the salts it forms with acids as well as those it forms with bases are very easily hydrolysed, with separation of the hydrated oxide. Titanium salts, therefore, can only be held in solution by a considerable excess of acid. ”

“ The nature of the mineral used for the extraction will, as a rule, afford useful information. It is known that in some minerals the cerium group, in others the yttrium group, predominates more or less completely; certain minerals, also, are known to be rich in elements of one or another subgroup. An approximate knowledge of the relative [148] proportions of the cerium, terbium, and yttrium groups will be afforded by a rough double sulphate separation; thorium, zirconium, and scandium come down with the cerium earths. ”

“ Sixteen elements (excluding thorium and zirconium) are at the present time recognised as belonging to the rare earth group. With one or two exceptions, these show the closest resemblance to one another, both in chemical behaviour and in the properties of their compounds, so that the difficulties of separating and purifying them are very great. They may be said to form a series, in which the properties vary continuously but gradually from member to member, so that no sharp differences are anywhere perceptible. ”

“ If an organic substance be used to form a paste with metallic zirconium, the final process of heating results in the formation of the carbide; the same compound is also obtained by another process protected by Sander (loc. cit.) in which the hydride of zirconium, prepared by the reduction of the oxide by means of powdered magnesium in an atmosphere of hydrogen, is mixed with a cellulose solution, and the liquid treated as in the manufacture of artificial silk, the threads obtained being then heated to remove all organic matter as far as possible. ”

“ After the relatively simple separation from foreign elements has been accomplished, the enormously greater difficulty of separating the elements from one another has to be encountered. So great is this difficulty, by reason of the fact that, with the sole exception of cerium, the elements show no variation in property sufficient to allow of the use of ordinary analytical methods, that even at the present day it is extremely doubtful if all the elements in the yttrium group are known to us. ”

“ By far the most important property of the oxide, from the technical point of view, is the ease with which it resists high temperatures. The natural oxide can be freed, to a very large extent, from the iron oxide which it encloses, by the prolonged action of hydrochloric acid; experiments were carried out on the material so obtained by Simonis, [604] who showed that by prolonged heating at a high temperature, the remaining impurities, chiefly ferric oxide and silica, could be volatilised, leaving the zirconia unchanged. ”

“ In arc lamps in which pencils containing titanium compounds are used, the anode is generally made of copper, and is placed below the cathode, the reverse being the case where carbon electrodes are employed. The copper is inactive, and contributes nothing to the light; if the anode be of suitable dimensions, it wears away very slowly, whereas the cathode, containing the titanium compound, is rapidly consumed. In lamps in which carbon electrodes are used, the light is emitted chiefly from the extremities of the electrodes, the path of the arc being comparatively non-luminous ”

“ The group relations are borne out by the isomorphism of many related salts. The hydroxide and oxide show polymeric modifications, and the former has the usual tendency of compounds of this group to form colloidal solutions, a tendency which extends to the element itself. The metal resembles titanium in the eagerness with which it combines with other elements, especially with oxygen, nitrogen, and carbon, whilst the chloride closely resembles titanium tetrachloride in general properties, and in the ease with which it forms addition and condensation products with other substances. ”

“ The sulphate, Sc2 (SO4) 3, is obtained anhydrous by evaporating the excess of acid from a solution of the oxide in the concentrated acid, care being taken to avoid too high a temperature. The compound dissolves very easily in water, and slowly hydrates itself with evolution of heat; no crystals can be obtained from the solution until it has been concentrated to the consistency of a syrup, when on cooling it slowly deposits the hexahydrate. This effloresces in a dry atmosphere, forming the pentahydrate, which appears to be the most stable hydrate at ordinary temperatures. ”

“ The preparation of alloys of titanium with almost all the commoner metals is protected by patent, but few of these are of technical importance. Small quantities of titanium are said to improve very considerably the properties of copper and its alloys, the brasses, bronzes, etc., especially in castings. The addition is usually made in the form of an appropriate titanium alloy, prepared by reduction of the mixed oxides with carbon in an electric furnace, or treatment of the mixed oxides, together with the alloying metal, with aluminium under similar conditions. ”

“ The extraction of pure thorium compounds from monazite is a process of very great technical difficulty. The percentage of thoria is small, whereas that of the ceria oxides is high. The mineral is almost always decomposed by heating with concentrated sulphuric acid, and when the resulting pasty mass is taken up with water, a large amount of free sulphuric acid must be present in order to hold the rare earth phosphates in solution. [276] For the separation of thoria from ceria and yttria compounds in acid solution no processes were known until quite recently. ”

“ Such minerals may often contain titanium, zirconium, or thorium, and, for convenience, the term may be taken to include the commoner zirconium and thorium minerals, but not the commoner titanium minerals.
A second point of even greater interest is that the rare earth minerals are as a general rule strongly radio-active; further, it only occasionally happens that any mineral in which the rare earths do not form an important constituent has more than the feeblest activity; the exceptions being, of course, those uranium minerals which do not contain rare earths. ”

“ Soon after the introduction of gas as an illuminating agent it was realised that the luminosity of the flame is dependent on the presence of solid particles, which by the heat of combustion of the gas are raised to a temperature at which they emit radiations of wave-lengths corresponding to the ‘luminous rays’ of the spectrum. ”