Nickel.—This metal is found chiefly in the Hartz Mountains. It was formerly called by the Germans “Kupfer nickel,” or false copper, “nickel” being a term of detraction. It was first discovered about a century and a half ago by Cronstedt. It has a greyish-white colour, and is slightly magnetic, i.e. it is attracted by the magnet in the same way as iron and steel, but it loses this property if heated to about 600° Fahr. Its specific gravity varies between 8·40 and 8·50, according to the amount of compression it has received, and it is rather brittle; it may, however, be drawn into wire, and rolled flat, or into sheets. It is considerably harder and less ductile than any of the other metals employed in jeweller’s and silversmith’s work. In hardness it nearly approaches iron, and on this account, when polished, a characteristic brightness is produced. The malleability of nickel is less than that of iron, standing tenth in the list of useful metals; and in ductility it also occupies the tenth position. Nickel is very infusible, and does not so easily oxidize or tarnish at ordinary temperatures as copper does. Several countries have tried to employ it in the manufacture of small coin for the currency, but its use has now been almost abandoned.
Nickel alloys are much used in the arts for manufacturing purposes, under the name of “German silver,” there being large demand for this metal, as it forms the hard white alloy much used in making “electro-plate,” and on which silver is afterwards deposited. It also is used in common silver alloys, in order to keep up the whiteness of the latter element, the addition of too large a proportion of copper maintaining the tint of the latter metal, in too strong a degree to be altogether employed by the silver-worker. Nickel is sometimes specially employed, in combination with other metals, to replace or imitate silver in the manufacture of commercial wares, while with copper, zinc, tin, &c., it forms very useful alloys, producing great hardness.
Zinc.—This metal in its pure state is sometimes called spelter. At the present day it is not much used for alloying silver; but, as it is commonly employed in the preparation of silver-solder, it is necessary that the amateur and the student should know, as well as the practical mechanic, the distinctive characteristics of it, together with the qualities it imparts to others when in combination with them. As a metallic substance it was unknown until a long time subsequent to the discovery of the principal metals; and only since the commencement of the present century has its uses been thoroughly known and appreciated in the industrial world. In its pure state, zinc is a bluish-white metal, hard and highly crystalline; but, when raised to a heat of between 250° and 300° Fahr., it is malleable, and may safely be rolled and hammered: it is in this way that the zinc of commerce is produced.
Zinc may be annealed by placing it for a time in boiling water. Its specific gravity varies between 6·8 and 7·2, according to the previous kind of mechanical treatment it has received. At 773° Fahr. it melts, and is quickly oxidized by exposure to a current of air, emitting white vapours, which rise into the air, and are not unlike cotton-flakes; oxide of zinc is thus formed by the burning away of the zinc. Spelter or zinc is employed by jewellers in the manufacture of bright gold alloys, as it gives liveliness of colour to their wares not to be equalled by any other metal. (For the proportions and treatment of this composition see “The Goldsmith’s Handbook.”) It may be alloyed with most of the metals we have named; its uses in roofing, gutters, spouting, and chimney-pots being all well known. All the acids very readily attack it in the gold, and even when largely diluted; it speedily tarnishes, and becomes covered with a white oxide which protects the metal from atmospheric influences. In point of malleability zinc stands eighth among the metals, seventh in ductility, and as regards tenacity about seventh also. In chemistry it is represented by the symbol Zn. Its value when in a state of purity, commercially speaking, is about 4d. per. lb.
Tin.—This appears to have been one of the oldest known metals, and was employed in the Egyptian arts by the ancients, in combination with copper. Its colour is white, with a shining lustre almost as brilliant as that of silver, but it tarnishes much more quickly than alloys of the latter metal. With the exception of aluminum and zinc, it is the lightest of all the metals, its density being between 7·0 and 7·3, whether cast, hammered, or rolled. It is found in abundance in Cornwall, where it was also obtained at a very early period by the Phœnicians; and it is reported in Soame’s “Latin Church,” p. 30, that it was through the medium of the trade in tin that Christianity was first introduced into this country. Tin is not of a fixed nature like gold or silver, but melts in a moderate fire long before it becomes red hot, or about 442° Fahr. It is rapidly oxidized when kept for a long time in a fire having a free access to the air; and it is dissolved by hydrochloric, sulphuric, and nitric acids, the latter acting on it most powerfully. Tin should not be alloyed with gold or silver, as with either of these it easily enters into combination by fusion, rendering them extremely brittle, especially in the case of silver, which becomes by the least mixture of it so brittle that it is totally unfit for the work of the silversmith. However, for solder, for filing into dust, it may be advantageously employed to promote a quicker fusion; but even for this it should be avoided where it is possible to do so. The vapours of tin are also permanently injurious in the melting of gold, silver, and their alloys, as they render them very unworkable, and the operator being often at a loss to understand the cause of his misfortune; therefore, in melting silver alloys, it is advisable to avoid as much as possible the introduction of little bits of scrap tin into the furnace. If such a thing should happen, however, make the fire once or twice stronger in order that the tin may all be destroyed before the crucible containing the silver alloy is put in.
Fig. 15. Jupiter. Egyptian mark for Tin.