Why is the Peruvian steel so called?

Because it is an alloy of steel with certain portions of other metals from Peru. It is, technically speaking, sadder, not so easy to work as other steel, and yet much harder and tougher than any other.

CUTLERY.

Why is steel used for making cutting instruments? Because it combines the fusibility of cast with the malleability of bar iron, and when heated and suddenly cooled, becomes very hard.

The rapidity with which razors, knives, &c. are produced from the raw material, is truly astonishing. Thus in the workshops at Sheffield, we may in a few minutes see dinner knives made from the steel bar and all the process of hammering it into form, welding the tang of the handle to the steel of the blade, hardening the metal by cooling it in water and tempering it by de-carbonizing it in the fire.

The number of hands through which a common table-knife passes in its formation is worthy of being known to all who use them. The bar steel is heated in the forge by the maker, and he and the striker reduce it in a few minutes into the shape of a knife. He then heats a bar of iron and welds it to the steel so as to form the tang of the blade which goes into the handle. All this is done with the simplest tools and contrivances. A few strokes of the hammer in connexion with some trifling moulds and measures, attached to the anvil, perfect, in two or three minutes the blade and its tang or shank. Two men, the maker, and striker, produce about nine blades in an hour, or seven dozen and a half per day. The rough blade thus produced, then passes through the hands of the filer, who files the blade into form by means of a pattern in hard steel. It then goes to the hafters to be hafted in ivory, horn, &c. and then to the finisher. In this profession, every table-knife, pocket-knife, or pen-knife, passes, step by step, through no less than 16 hands or 144 separate stages of workmanship.

Sheffield employed about 15,000 persons in these departments, four years since:

Besides those who are employed in Britannia-metal ware, smelting, optical instruments, grinding, polishing, &c. &c. making full 5,000 more. There are full 1,700 forges engaged in the various branches of the trades, and of course as many fires.

Why are the most minute instruments generally made with good steel?

Because it is much more ductile than iron: a finer wire being drawn from it than from any other metal.

Why is Wootz or Indian steel the most valuable for making edge tools?

Because it is combined with a minute portion of the earths, alumina and silica; or rather perhaps, with the bases of these earths. Whether the earths are found in the oar, or are furnished by the crucible in making the steel, is not certainly known; nor is the Indian steel-maker probably aware of their presence. Wootz, in the state in which it is imported, is not fit to make into fine cutlery. It requires a second fusion, by which the whole mass is purified and equalized, and fitted for forming the finest edge instruments.Brande.

Why does a razor operate best when dipped in hot water?

Because the temperature of the blade has then been

raised, and the fineness of the edge proportionally increased.

In some experiments, the knife edges attached to the pendulum described by Captain Kater, in Phil. Trans. 1818, on being carefully hardened and tempered in the bath at 432°, were, on trial, found too soft. They were a second time hardened, and then heated to 212°, at which point the edges were admirably tempered. This, it will be remembered, is the heat of boiling water, and further illustrates the preceding question.

In the manufacture of a razor, it proceeds through a dozen hands; but it is afterwards submitted to a process of grinding, by which the concavity is perfected, and the fine edge produced. They are made from 18. per dozen, to 20s. per razor, in which last the handle is valued at 16s. 6d.-Scissors, in like manner, are made by hand, and every pair passes through sixteen or seventeen hands, including fifty or sixty operations, before they are ready for sale. Common scissors are cast, and when riveted, are sold as low as 48. 6d. per gross! Small pocket knives too are cast, both in blades and handles, and sold at 6s. per gross, or a halfpenny each! These low articles are exported in vast quantities in casks to all parts of the world.

ZINC.

Why is Zinc useful in the arts?

Because, in combination with copper or tin, in various proportions, it forms some of the most useful compound metals or alloys. Thus, with copper, it constitutes brass, pinchback, and tombac; with little copper, Prince's metal;* with tin and copper, bronze. Roofs covered with zinc are very numerous in the Low Countries but have one bad quality. In cases of fire, the zinc being very combustible, soon becomes inflamed, and falling all around, occasions great danger

*See DOMESTIC SCIENCE, page 65.

to those who approach the building. In short, zinc is the most combustible metal we have. If beaten out into thin leaves, it will take fire from the flame of a common taper.

Why has the oxide of zinc been substituted for white lead in house-painting.

Because it preserves a good colour much longer: it is not, however, of so perfect a white as lead.

TIN.

Why did the ancients mix tin with their copper coins and edge tools?

Because it occasioned the coins to wear longer, and it imparted sufficient hardness to the copper to render it capable of forming very good cutting instruments. Mr. Parkes, in analysing several Roman brass coins, from various periods of the Empire, found tin to be a component part in all of them.

Why is not Spanish tin used in this country?

Because it bears a prohibitory duty of 30l. per cent. It is raised in great quantities in South America, and is very pure, but not so neatly manufactured as the Cornish tin. According to Aristotle, the tin mines of Cornwall were known and worked in his time. Diodorus Siculus, who wrote 40 years before Christ, describes the method of working these mines, and says, that their produce was conveyed to Gaul, and thence to different parts of Italy. The miners of Cornwall were so celebrated for their knowledge of working metals, that about the middle of the 17th century, the renowned Becher, a Physician of Spire, and tutor of Stahl, came over to this country to visit them.

A celebrated tin mine was the famous wherry mine, near Penzance. The shaft through which the miners went down to work, was situated nearly 100 yards below water mark. "The opening of this mine" says Dr. Maton, "was an astonishingly adventurous un dertaking. Imagine the descent into a mine through the sea, the miners working at the depth of 17 fathoms

ARTS AND MANUFACTURES.

below the waves; the rod of a steam engine, extending from the shore to the shaft, a distance of nearly 120 fathoms, and a great number of men momentarily menaced with an inundation of the sea, which continually drains in no small quantity through the roof of the mine, and roars loud enough to be distinctly heard in it." The working of this mine was wholly given up in the year 1798.

Such is the mineral wealth of Cornwall, that it contains more men, who possess fortunes, sprung from the mines, of five and from that to twenty thousand pounds, than there are in any other county of England, excepting the metropolis and its vicinity; and there are some instances of individuals acquiring from fifty to two hundred thousand pounds, from the mines, and by a fortunate course of trade.

Why should tin be chosen for its lightness?

Because its purity is in exact ratio with its levity; while gold, on the contrary, unless alloyed with platinum, is fine in proportion to its density.

Why is tin so important to the dyer?

Because it is employed to give a brightness to cochineal,* archil, and other articles used in forming reds and scarlets; and to precipitate the colouring matter of other dyes. For these purposes it is previously dissolved in a peculiar kind of aqua-fortis, called dyers' spirit.

Tin is consumed in large quantities by the dyers; it is also used for covering sheet iron to prevent its rusting, and in forming plumbers' solder, speculum metal, pewter, and some other alloys. Its oxides are used in polishing glass, in glazing some kinds of earthenware, &c.

Why is tin-plate so called?

Because it is made by dipping clean iron plates into melted tin. When tin-plate is washed over with

* See ZOOLOGY-Insects, page 258.