The numerous materials from the three kingdoms hitherto described, with but three exceptions, namely, clay, horn, and tortoiseshell, are used in the simple natural states in which they are found, without any change of form beyond that of reduction, as the finished works are in almost every case produced by cutting or chipping away the portions in excess; the works are consequently smaller than the rough masses from within which they are obtained, and the fragments cannot be re-united without the aid of some artificial means, such as screws, rivets, or cements.

Several of the substances now to be considered, differ greatly from all the foregoing materials, by possessing in various degrees of excellence, the properties of fusibility, malleability, etc. These assist in various ways in the first separation of the metals from the earthy bases in which they are found; also in the perfect combination of the smallest particles, either of one single or of different kinds, into solid masses; and in the conversion of these by the agency of the crucible, the hammer, and various attendant means, to that endless variety of forms in which the metals are used, many of which are merely a state of part-manufacture or what may be called a "transition" stage.

The chemist enumerates forty-one different metals; of these many are entirely confined to the laboratory, part are only used in the chemical arts, and those to which I propose to refer as connected with our subject, are but fourteen, namely, Antimony,

Bismuth, Copper, Gold, Iron, Lead, Mercury, Nickel, Palladium, Platinum, Rhodium, Silver, Tin, and Zinc.

Of these, mercury is always fluid in our latitudes, and antimony and bismuth arc brittle metals, consequently they are not used alone in construction,and pure nickclalthough malleable is rarely so employed; subtracting these reduces the number to ten.

Palladium, platinum, and rhodium are principally used on account of their infusibility and resistance to acids, for a few purposes connected with science; their abstraction reduces the number to seven. Gold and silver are mostly reserved for coin, and articles of luxury, so that taking away these also, the majority of the works of mechanical art fall exclusively on five, namely, copper, iron, lead, tin, and zinc. These five practical metals, if the term may be allowed, are again virtually extended by an infinitude of combinations, or alloys, principally amongst themselves, although with the occasional introduction of the metals before named, and some few others.

Of all the metals however, iron is the one to which from its manifold changes and adaptations, and from its abundance, the most importance is to be attached; so much so, that were we compelled to the choice, it would be doubtless politic to sacrifice all the others for its possession. It is subjected to several of the methods of treatment, common to the other ordinary metals, and to a variety of changes no less important peculiarly its own.

On these several grounds, therefore, the principal share of attention will be devoted to iron and its several modifications, and it is intended as a general illustration, to commence with a slight sketch of the manufacture of iron from the ore, into cast-iron, wrought iron, blistered, shear, and cast-steel; and its part manufacture for the purpose of commerce, into ingot, bar, sheet and wire. This will be followed by its further preparation, by forging, into some of the elements of machinery and tools; the various changes of hardening and tempering, applied under a variety of circumstances will be then described.

It is proposed subsequently to consider the thirteen other metals, both in their simple and alloyed states, which will lead to a general outline of the methods of casting objects of various forms, and also of the practice of soldering, which is dependent on the fusible property of some of the metals.