Page:EB1911 - Volume 28.djvu/1008

 variable in thickness. The most carefully executed part is on the south and south-east, where the wall is decorated by a row of granite monoliths beneath which runs a double line of chevron ornament. The interior has been much destroyed by the ravages of gold-seekers and amateur excavators. Enough, however, remains to show that the scheme was a combination of such a stone kraal as that at Nanatali with the plan of a fort like those found about Inyanga. The only unique feature is the occurrence of a large and a small conical tower at the southern end, which Bent and others considered to be representatives of the human phallus. Their form, however, is not sufficiently characteristic to warrant this identification, though it may be noted that the nearest approximation to phallic worship is found amongst the most typical of African peoples, viz. the Ewe-speaking natives of the West Coast. The floor of the enclosure is constituted as in the other Zimbabwe buildings by a thick bed of cement which extends even outside the main wall. This cement mass is heightened at many places so as to make platforms and supports for huts. Groups of these dwellings are enclosed by subsidiary stone walls so as to form distinct units within the larger precinct.

The “Acropolis” is in some ways more remarkable than the great kraal which has just been described. It is a hill rising 200 to 300 ft. above the valley, fortified with the minutest care and with extraordinary ingenuity. The principles of construction, the use of stone and cement are the same as in the “elliptical” kraal, there is no definite plan, the shape and arrangement of the enclosures being determined solely by the natural features of the ground. Between this and the “elliptical” kraal are the “Valley Ruins,” consisting of smaller buildings which may have been the dwellings of those traders who bartered the gold brought in from distant mines. Zimbabwe was probably the distributing centre for the gold traffic carried on in the middle ages between subjects of the Monomotapa and the Mahommedans of the coast.

Compare also the articles : Archaeology, and.

See D. Randall-MacIver, Mediaeval Rhodesia (London, 1906); ''Journal of Anthrop. Inst., vol. xxxv.; Geog. Journal (1906); Mauch’s report in Ausland (1872) is now only of bibliographical interest, while Bent’s Ruined Cities of Mashonaland'' (1892) and R. N. Hall’s Great Zimbabwe (1905) are chiefly valuable for their illustrations.

 ZIMMERMANN, JOHANN GEORG, (1728–1795), Swiss philosophical writer and physician, was born at Brugg, in the canton of Aargau, on the 8th of December 1728. He studied at Göttingen, where he took the degree of doctor of medicine; and he established his reputation by the dissertation, De irritabilitate (1751). After travelling in Holland and France, he practised as a physician in his native place, and here he wrote Über die Einsamkeit (1756, emended and enlarged, 1784–85) and Vom Nationalstolz (1758). These books made a great impression in Germany, and were translated into almost every European language. They are now only of historical interest. In Zimmermann’s character there was a strange combination of sentimentalism, melancholy and enthusiasm; and it was by the free and eccentric expression of these qualities that he excited the interest of his contemporaries. Another book by him, written at Brugg, Von der Erfahrung in der Arzneiwissenschaft (1764), also attracted much attention. In 1768 he settled at Hanover as private physician of George III. with the title of Hofrat. Catherine II. invited him to the court of St Petersburg, but this invitation he declined. He attended Frederick the Great during that monarch’s last illness, and afterwards issued various books about him, of which the chief were Über Friederich den Grossen und meine Unterredung mit ihm kurz vor seinem Tode (1788) and Fragmente über Friedrich den Grossen (1790). These writings display extraordinary

personal vanity, and convey a wholly false impression of Frederick’s character. Zimmermann died at Hanover on the 7th of October 1795.

See A. Rengger, Zimmermann’s Briefe an einige seiner Freunde in der Schweiz (1830); E. Bodemann, Johann Georg Zimmermann, sein Leben und bisher ungedruckte Briefe an ihn (Hann., 1878); and R. Ischer, Johann Georg Zimmermann’s Leben und Werke (Berne, 1893).

 ZINC, a metallic chemical element; its symbol is Zn, and atomic weight 65·37 (O＝16). Zinc as a component of brass ( ) had currency in metallurgy long before it became known as an individual metal. Aristotle refers to brass as the “metal of the Mosynoeci,” which is produced as a bright and light-coloured, not by addition of tin, but by fusing up with an earth. Pliny explicitly speaks of a mineral  or cadmia as serving for the conversion of copper into aurichalcum, and says further that the deposit (of zinc oxide) formed in the brass furnaces could be used instead of the mineral. The same process was used for centuries after Pliny, but its rationale was not understood. Stahl, as late as 1702, quoted the formation of brass as a case of the union of a metal with an earth into a metallic compound; but he subsequently adopted the view propounded by Kunckelin 1677, that “cadmia” is a metallic calx, and that it dyes the copper yellow by giving its metal up to it.

The word zinc (in the form zinken) was first used by Paracelsus, who regarded it as a bastard or semi-metal, but the word was subsequently used for both the metal and its ores. Moreover, zinc and bismuth were confused, and the word spiauter (the modern spelter) was indiscriminately given to both these metals. In 1597 Libavius described a “peculiar kind of tin” which was prepared in India, and of which a friend had given him a quantity. From his account it is quite clear that that metal was zinc, but he did not recognize it as the metal of calamine. It is not known to whom the discovery of isolated zinc is due; but we do know that the art of zinc-smelting was practised in England from about 1730. The first continental zinc-works were erected at Liege in 1807.

Occurrence.—Zinc does not occur free in nature, but in combination it is widely diffused. The chief ore is zinc blende, or sphalerite (see ), which generally contains, in addition to zinc sulphide, small amounts of the sulphides of iron, silver and cadmium. It may also be accompanied by pyrites, galena, arsenides and antimonides, quartz, calcite, dolomite, &c. It is widely distributed, and is particularly abundant in Germany (the Harz, Silesia), Austro-Hungary, Belgium, the United States and in England (Cumberland, Derbyshire, Cornwall, North Wales). Second in importance is the carbonate, (q.v.) or zinc spar, which at one time was the principal ore; it almost invariably contains the carbonates of cadmium, iron, manganese, magnesium and calcium, and may be contaminated with clay, oxides of iron, galena and calcite; “white calamine” owes its colour to much clay; “red calamine” to admixed iron and manganese oxides. Calamine chiefly occurs in Spain, Silesia and in the United States. Of less importance is the silicate, Zn2SiO4·H20, named electric calamine or hemimorphite; this occurs in quantity in Altenburg near Aix-la-Chapelle, Sardinia, Spain and the United States (New Jersey, Pennsylvania, Missouri, Wisconsin). Other zinc minerals are (q.v.), Zn2SiO4, hydrozincite or zinc bloom, ZnCO3·2Zn(OH)2,  (q.v.) or red zinc ore, ZnO, and franklinite, 3(Fe,Zn)O·(Fe, Mn)2O3.

Production.—Until about 1833 the supply of zinc was almost entirely obtained from Germany, but in this year Russia began to contribute about 2000 tons annually to the 6000 to 7000 derived from Germany. Belgium entered in 1837 with an output of about 2000 tons; England in 1855 with 3000; and the United States in 1873 with 6000 tons. The productions of Germany, Belgium and the United States have enormously and fairly regularly increased; the rise has been most rapid in the United