Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/73

Rh M E T M E T 63 guidance, to rely on the very numerous analyses which have been made of slags actually produced (by the rule of thumb) in successful metallurgical operations. For some of such slags also Plattner has determined the fusing points. He found for (1) Freiberg lead sla&amp;lt;: 9RO, 3alO, 8Si0 2 ; oxygen-ratio, 3:4; melting-point at 1317 C? (2) Freiberg crude slag, 15RO, 3alO, 18Si0 2 ; oxygen-ratio, 1:1 melting-point at 1331&quot; C. ; (3) Freiberg black-copper slag, 24FeO A1 2 3, 15Si0 2 ; oxygen-ratio, 9:10; melting-point at 1338 C. (4) High-furnace slag, GCaO, 3alO, 9810.,; oxygen-ratio, 1:1 melting-point at 1431&quot; C. 1 Metallurgic Assaying. To assay an ore originally meant to execute a set of tentative experiments on a small scale in order to find out the proper mode of working it practically. But nowadays the term is always used in the sense of an analysis carried out to determine the money-value of an ore. For this purpose, in many cases it is sufficient to determine the percentages of the metals for which the ore is meant to be worked. But sometimes nothing short of a complete analysis will do. This holds more especially of ores of iron. As this metal is cheap, the value of an ore containing it depends as much on the nature and relative quantities of the im purities as on the percentage of metal. The proved absenceof sulphur and phosphorus may be worth more than an additional 5 per cent, of iron, which latter again would perhaps not compensate for the proved presence of a large percentage of uncombined silica. An assay to be of any value must start with a fair sample of the object of sale. The fulfilment of this condition in all cases is difficult. The general method is, from say a given ship load of ore, to take out (say) half a ton of ore from a large number of different places and to crush this large sample into small fragments of uniform size, which are well shovelled up together. From different parts of this ore-heap a sample of the second order amounting to, say, 20 lb is then drawn, and rendered more homogeneous by finer powder ing and mixing. From this sample of the second (or perhaps from one of the third) order quantities of 1 or 2 lb are bottled up for assaying. At the same time the moisture of the ore is determined, on a large scale, by some conventional method, such as the drying of 1 or 2 tb in an open basin at 100 C., and weighing of the residue as dry ore. This is done at the sampling place by the firms concerned. The assayer further pounds up and mixes his sample, and then pro ceeds to determine the percentages of moisture and metal in his own way. He has always the choice between two methods, the dry and the wet. For the majority of gold or silver ores, and for cobalt and nickel ores almost as a rule, certain dry-process tests are preferred as the most exact analytically. In almost all other cases it may be said that the wet method is susceptible of the higher degree of pre cision, yet even in some of these cases the old dry-process tests are preferred to the present day. For instance, all copper ores in the British Isles are sold by the result of the Swansea assay, a kind of imitation of the process of sulphureous copper-ore smelting; and this, singularly, is adhered to even in the case of such cupriferous materials as are worked by the wet way, although the Swansea assay is well known to lose about 1 per cent, of the copper present. A copper-smelter therefore had better buy 5 per cent, than 10 per cent, copper-pyrites cinders, because in the first case he pays only for four-fifths, while in the latter he must pay for nine-tenths of the copper present. To compensate for this anomaly, empirical methods have been contrived for calculating prices. ( W. D. ) METALS. The earliest evidence of a knowledge and use of metals is found in the prehistoric implements of the so-called Bronze and Iron ages. In the earliest periods of written history, however, we meet with a number of metals in addition to these two. The Old Testament mentions six metals gold, silver, copper, iron, tin, and lead. The Greeks, in addition to these and to bronze, came also to know mercury ; and the same set of metals, without additions, forms the list of the Arabian chemists of the 8th and of the Western chemists of the 13th cen tury. During the 15th century Basilius Valentinus dis covered antimony ; he also speaks of zinc and bismuth, but their individuality w r as established only at a later period. About 1730-40 the Swede Brand discovered arsenic and cobalt (the former is not reckoned a metal by modern chemists), while the Englishman Ward recognized the individuality of platinum. Nickel was discovered in 1774 by Cronstedt, manganese in 1774 by Scheele. The brothers D Elhujart, in 1783, prepared tungsten; Hjelm, in 1782, isolated molybdenum from molybdic oxide, where 1 For further information on slags, see Berthier, Traite des essais par la voie seche ; Winkler, Erfahrunyssatze iiber die Bildung der Schlacken, Freiberg, 1827 ; Plattner, Vorlesungen uber allgemeine Jfuttenkunde, i. 28 sq.; Percy, Metallurgy. its existence had been conjecturally asserted by Bergmann in 1781. Uranium, as a new element, was discovered by Klaproth in 1789 ; but his metallic &quot; uranium,&quot; after having been accepted as a metal by all chemists until 1841, was then recognized as an oxide by Peligot, who subsequently isolated the true metal. Tellurium was discovered by M tiller von Reichenbach in 1782 (again by Klaproth in 1798); titanium, by Klaproth in 1795 ; chromium, by Vauquelin in 1797 ; tantalum, by Hatchett in 1801, and by Ekeberg in 1802. Palladium, rhodium, iridium, and osmium (which four metals always accompany platinum in its ores) were discovered, the first two by Wollaston in 1803, the other two by a number of chemists ; but their peculiarity was established chiefly by Smithson Tennant. After Davy, in 1807 and 1808, had recognized the alkalies and alkaline earths as metallic oxides, the existence of metals in all basic earths became a foregone conclusion, which was verified sooner or later in all cases. But the discovery of aluminium by Wohler in 1828, and that of magnesium by Bussy in 1829, claim special mention. Cadmium, a by no means rare heavy metal, was discovered only in 1818, by Stromeyer. Of the large number of discoveries of rare metals which have been made in more recent times only a few can be mentioned, as marking new departures in research or offer ing other special points of interest. In 1861 Bunsen and Kirchhoff, by means of the method of spectrum analysis, which they had worked out shortly before, discovered two new alkali-metals which they called caesium and rubidium. By means of the same method Crookes, in 1861, discovered thallium; Reich and Richter, in 1863, indium ; and Lecoq de Boisbaudran, in 1875, gallium. The existence of the last-named metal had been maintained, theoretically, by Mendelejeff, as early as 1871. The existence of vanadium was proved in 1830 by Sefstrb m ; but what he, and sub sequently Berzelius, looked upon as the element was, in 1867, proved to be really an oxide by Roscoe, who also succeeded in isolating the true metal. The development of earlier notions on the constitution of metals and their genetic relation to one another forms the most interesting chapter in the history of chemistry (see ALCHEMY). What modern science has to say on the matter is easily stated : all metals properly so called (i.e., all metals not alloys) are elementary substances ; hence, chemically speaking, they are not &quot; constituted &quot; at all, and no two can be related to each other genetically in any way whatever. Our scientific instinct shrinks from embracing this proposition as final ; but in the meantime it must be accepted as correctly formulating our ignorance on the subject. All metallic elements agree in this that they form each at least one basic oxide, or, what comes to the same thing, one chloride, stable in opposition to liquid water. This at once suggests an obvious definition of metals as a class of substances, but the definition would be highly artificial and objectionable on principle, because when we speak of metals we think, not of their accidental chemical relations, but of a certain sum of mechanical and physical properties which unites them all into one natural family. What these properties are we shall now endeavour to explain. All metals, when exposed in an inert atmosphere to a sufficient temperature, assume the form of liquids, which all present the following characteristic properties. They are (at least practically) non-transparent ; they reflect light in a peculiar manner, producing what is called &quot; metallic lustre.&quot; When kept in non-metallic vessels they take the shape of a convex meniscus. These liquids, when exposed to higher temperatures, some sooner others later, pass into vapours. What these vapours are like is not known in many cases, since, as a rule, they can be produced only at