ZIMMERN 497 ZINC the University of Gottingen he studied under and was befriended by Haller, and eventually was appointed public physi- cian to his native town. He became fa- mous in his profession, and published several works on miscellaneous subjects, with one on "Experiences in Medicine," which procured him the appointment of physician for Hanover to George III. The loss of his wife and other domestic calamities brought on an attack of hypo- chondria, from which a second mar- riage relieved him, and as a result of his recovery he produced his once celebrated treatise on "Solitude" (1784), by which out of his own country he is alone re- membered. In 1786 he attended Fred- erick the Great in his last illness, about whom he published two works, one of them "Conversations with the King," which involved him in painful contro- versy. Latterly he became deranged, and died in Hanover, Oct. 7, 1795. His "Autobiography" was issued in 1791. ZIMMERN, HELEN (tsim'mern), a German-English story writer; born in Hamburg. March 25, 1846. From child- hood she lived in England. She was author of: "Stories in Precious Stones" (1873); "Told by the Way" (1874); "Half-Hours with French Novelists" (1881) ; "Stories from Foreign Novel- ists" (2d ed. 1885). She wrote also "Schopenhauer, His Life and Philos- ophy" (1876) ; "G. E. Lessing, His Life and Works" (1878) ; "The Hansa Towns" (1889). ZINC, a bluish-white lustrous metal, having a crystalline lamellar structure, moderate hardness, a somewhat low melting-point. To obtain it pure, com- mercial zinc, or spelter, as it is termed, is dissolved in pure dilute sulphuric acid; a cement of sulphuretted hydro- gen is then passed through it, and it is filtered from any precipitate formed. The solution is then boiled to expel any sulphuretted hydrogen that may remain in it, and the zinc is precipitated in the form of carbonate by pure carbonate of soda. The carbonate is then ignited to form it into oxide of zinc, which is dis- tilled in a porcelain retort, with charcoal prepared from loaf-sugar. Zinc is brittle at ordinary temperatures, but is possessed of considerable malleability and ductility at a temperature of be- tween 200" and 300°, and may be wrought and rolled with ease. A little above this is becomes brittle again, and may be pulverized in a mortar. It fuses at 773° and at a bright red heat it may be volatilized. If its vapor is exposed to the air, it burns with great spkndpr, becomine converted into oxide, which is deposited in loose flocculi. At the ordinary temperature it is not acted on by the air, but when exposed to moist air or oxygen, it becomes covered with a tenacious gray coating of hydrated oxide, which impedes the further oxida- tion of the metal beneath. In this re- spect zinc rust differs from iron rust, which seems to accelerate the oxidation of the adjacer.t metal. By the conjoint action of oxygen and carbonic acid, zinc roofing becomes converted into a mixed oxide and carbonate. When melted in the air, the oxide is formed much more rapidly. The metal is readily dissolved by the mineral and vegetable acids. Boiling solutions of potash also act on zinc, hydrogen being liberated, and oxide of zinc remaining dissolved in the alkaline solution. The diflficultly oxidiz- able nature of zinc, its cheapness, the ease with which it is extracted from its ores, and the ready way in which it may be worked, are bringing it daily more and more into use. Neither the vapor nor its oxide is poisonous. It is of the greatest use in the labora- tory for the precipitation of certain metals and for the formation of hydro- gen. For voltaic purposes it is indis- pensable, and its principal alloy, brass, is too well known to need description. It forms alloys with iron and several other metals. The so-called galvanic iron is iron covered with a protective coating of zinc. It also enters the com- position of German silver. The origin of the term zinc is lost in obscurity; it was first employed by Basil Valentine, but the great Paracelsus was the first to associate the word with a metal pos- sessing the characters of zinc. It hardly seems probable that zinc was known to the ancients. An obscure passage in Strabo seems to show that a certain stone was found to drop false silver when melted, but there is little to show- that this false silver was zinc. It is possible, however, that its alloys were known to the later Romans, for numer- ous coins have been found containing copper and zinc nearly in the proper proportions to form brass. It was not till the beginning of the 18th century that zinc was commercially extracted from its ores in Europe. Before this, however, it was imported by the Portu- guese and others from the East Indies and China, under the name of tutenag and spelter. It seems first to have been made in England by Mr. Champion, of Bristol, about the year 1743. Long be- fore zinc was known as a metal, brass was made in large quantities by heating metallic copper imbedded in a mixture of calcined calamine and carbonaceous mat-
