without, but from within. I have, however, ventured to offer the introduction of this lecture in its present form, because any facts which lead us to reflect on the unity of plan in nature, will aid the recognition of the complexity of atomic motion in metals upon which it is needful to insist. The foregoing remarks have special significance in relation to the influence exerted by the rarer metals on the ordinary ones. With the exception of the action of carbon upon iron, probably nothing is more remarkable than the action of the rare metals on those which are more common; but their peculiar influence often involves, as we shall see, the presence of carbon in the alloy. Which, then, are the rarer metals, and how may they be isolated? The chemist differs somewhat from the metallurgist as to the application of the word "rare." The chemist thinks of the "rarity" of a compound of a metal; the metallurgist, rather of the difficulty of isolating the metal from the state of combination in which it occurs in nature. The chemist in speaking of the reactions of salts of the rarer metals, in view of the wide distribution of limestone and pyrolusite, would hardly think of either calcium or manganese as being among the rarer metals. The metallurgist would consider pure calcium or pure manganese to be very rare. I have only recently seen comparatively pure specimens of the latter. The metals which, for the purposes of this lecture, may be included among the rarer metals are: (1) Those of the platinum group, which occur in nature in the metallic state; and (2) certain metals which in nature are usually found as oxides or in an oxidized form of some kind, and these are chromium, manganese, vanadium, tungsten, titanium, zirconium, uranium, and molybdenum (which occurs, however, as sulphide). Incidental reference will be made to nickel and cobalt. Of the rare metals of the platinum group I propose to say but little. We are indebted for a magnificent display of them in the library of my friends, Messrs. George and Edward Matthey, and to Mr. Sellon, all members of a great firm of metallurgists. You should specially look at the splendid mass of palladium, extracted from native gold of the value of £2,500,000, at the melted and rolled iridium, and at the masses of osmium and rhodium. No other nation in the world could show such specimens as these, and we are justly proud of them. These metals are so interesting and precious in themselves, that I hope you will not think I am taking a sordid view of them by saying that the contents of the case exhibited in the library are certainly not worth less than £10,000. As regards the rarer metals which are associated with oxygen, the problem is to remove the oxygen, and this is usually effected either by affording the oxygen an opportunity for uniting with another metal, or by reducing the oxide of the rare metal by carbon, aided by the tearing effect of an electric current. In this crucible there is an intimate mixture, in atomic proportions, of oxide of chromium and finely divided metallic aluminum. The thermo junction (A, fig. 1, Pl. XXIII) of the pyrometer which formed the subject of my last Friday evening lecture here is placed within the crucible B, and the spot of light C, from the galvanometer D, with which the junction is connected, indicates on the screen that the temperature is rising. You will observe that as soon as the point marked 1,010° is reached energetic action takes place; the temperature suddenly rising above the melting point of platinum, melts the thermo junction, and the spot of light swings violently; but if the crucible be broken open you will see that a mass of metallic chromium has been liberated. The use of alkaline metals in separating oxygen from other metals is well known. I can not enter into its history here, beyond saying that if I were to do so, frequent references to the honored names of Berzelius, Wöhler, and Winkler would be demanded.1 Mr. Vautin has recently shown that granulated aluminum may readily be prepared, and that it renders great service when employed as a reducing agent. He has lent me many specimens of rarer metals which have been reduced to the metallic state by the aid of this finelygranulated aluminum; and I am indebted to his assistant, Mr. Picard, who was lately one of my own students at the Royal School of Mines, for aid in the preparation of certain other specimens which have been isolated in my laboratory at the mint. The experiment you have just seen enables me to justify a statement I made respecting the discriminating action which certain metals appear to exert. The relation of aluminum to other metals is very singular. When, for instance, a small quantity of aluminum is present in cast iron, it protects the silicon, manganese, and carbon from oxidation.2 The presence of silicon in aluminum greatly adds to the brilliancy with which aluminum itself oxidizes and burns. It is also asserted that aluminum, even in small quantity, exerts a powerful protective action against the oxidation of the silver-zinc alloy, which is the result of the desilverization of lead by zinc. Moreover, heat aluminum in mass to redness in air, where oxygen may be had freely, and a film of oxide which is formed will protect the mass from further oxidation. On the other hand, if finely divided aluminum finds itself in the presence of an oxide of a rare metal, at an elevated temperature, it at once acts with energy and promptitude, and releases the rare metal from the bondage of oxidation. I trust, therefore, you will consider my claim that a metal may possess moral attri butes has been justified. Aluminum, moreover, retains the oxygen it 1 An interesting paper, by H. F. Keller, on the reduction of oxides of metals by other metals, will be found in the Journal of the American Chemical Society, December, 1894, page 833. 2 Bull. Soc. Chim. Paris, Vol. XI, 1894, page 377. 3 Ditte, Legons sur les Métaux, Part II, 1891, page 206. has acquired with great fidelity, and will only part with it again by electrolytic action, or at very high temperatures under the influence of the electric arc in the presence of carbon. [A suitable mixture of red lead and aluminum was placed in a small crucible heated in a wind furnace, and in two minutes an explosion announced the termination of the experiment. The crucible was shattered to fragments.] The aluminum loudly protests, as it were, against being intrusted with such an easy task, as the heat engendered by its oxidation had not to be used in melting a difficultly fusible metal like chromium, the melting point of which is higher than that of platinum. It is admitted that a metal will abstract oxygen from another metal if the reaction is more exothermic than that by which the oxide to be decomposed was originally formed. The heat of formation of alumina. is 391 calories, that of oxide of lead is 51 calories; so that it might be expected that metallic aluminum, at an elevated temperature, would readily reduce oxide of lead to the metallic state. The last experiment, however, proved that the reduction of oxide of lead by aluminum is effected with explosive violence, the temperature engendered by the reduction being sufficiently high to volatilize the lead. Experiments of my own show that the explosion takes place with much disruptive power when aluminum reacts on oxide of lead in vacuo, and that if coarsely ground, fused litharge be substituted for red lead, the action is only accompanied by a rushing sound. The result is, therefore, much influenced by the rapidity with which the reaction can be transmitted throughout the mass. It is this kind of experiment which makes us turn with such vivid interest to the teaching of the school of St. Claire Deville, the members of which have ren. dered such splendid services to physics and metallurgy. They do not advocate the employment of the mechanism of molecules and atoms in dealing with chemical problems, but would simply accumulate evidence as to the physical circumstances under which chemical combination and dissociation take place, viewing these as belonging to the same class of phenomena as solidification, fusion, condensation, and evaporation. They do not even insist upon the view that matter is minutely granular, but in all cases of change of state make calculations on the basis of work done, viewing changed "internal energy" as a quantity which should reappear when the system returns to the initial state. A verse of some historical interest may appeal to them. It occurs in an old poem to which I have already referred as being connected with the "Roman de la Rose," and it expresses nature's protest against those who attempt to imitate her works by the use of mechanical methods. The argument" runs thus: 66 Comme Nature se complaint, |