The art of casting iron was known to the ancients, as appears from a small statue of Hercules. of cast-iron, dug up at Rome. In China it appears to be practised with a dexterity visible in the Chi nese specimens of many other arts. In modern Europe it has grown with the general advancement of society, and has latterly attained to a high degree of improvement in this Island, where individuals having the command of capital, and the power of making advances for the salaries of workmen and the construction of buildings, were induced to form large establishments for the melting of iron stone, and for the manufacture of cast-iron. In alto serves to receive any impurities that miry have escaped the attention of those appointed to skim the iron as it flows along the gutter.
In ten or twelve hours, the piece is sufficiently cool to be removed. It is then strippedof the mould, and taken to the boring-mill, to undergo the opera tions described under our article BORING OF Can non. Mortars, howitzers, and carronades are mould ed, cast, and bored in the same way as long guns.
The English Board of Ordnance is supplied with iron guns by contract. The contractors are those iron-masters Who offer the guns at the lowest price, and the guns are cast at their works in the country. The guns are sent to Woolwich to be examined in respect to their dikeensions, the coincidence of the axis of the bore With that of the piece, the position of the touch. ale, and to undergo a proof by pow der. It is also tried whether water can be forced through the gullstance of the gun. If any cavities called be. found in the bore, the piece is rejected. The proofs- are at the risk of the con tractors, wholgenerally examine and prove the guns at their bet ire !wilding them to Woolwich. Unserviceable gone ate taken to the triangle, where a large mass of cast-iron is let fall upon the gun, i from a height of 40 or 50 fbet. It is thus broken into pieces of a size fit for being introduced into the air-furnace to be re-cast. Some brass gulls are cast and bored in the foundery of the Board of Ordnance at Woolwich.
Cast-iron guns have the advantage of not suffer ing any injurious alteration ftom the heat of repeat ed feting. Brass guns, when fired rapidly in succes sion, droop at the muzzle. Cast-iron guns alone are used on board British- ships ; brass guns are non principally used for field•neces. Brass guns, in strict and precise language, might be called bronze guns, as the word brass most commonly used to denote a composition of copper and zinc, whereas, in gun-meta; there is generally little zinc, and often" none. Copper shine as too soft, so that the guns that
have been made of it were cut and furrowed by the hall in firing. Use is made, therefore, of a of copper and tin ; this composition being harder gleancopper. Copper and tin separately are soft" and malleable ; when combined they form a compo sition that is hard and brittle ; and these two quali ties are increased by augmenting the relative quan tity of tin. Different proportions have been em ployed for guns; by weight of copper, and I of tin, is a proportion that is found to give, the re quisite hardness, and not too much, nor too great brittleness. The copper is' first melted., and the tin is added. If the tin were melted first, and the cop per added, much of the tin would be oxidated be fore the combination took place ; the metal, during the process, is stirred with a rod of green wood.
Bell-metal is a combination of copper and tin in other proportions. It is made hard by means of tin, in order that it may be sonorous. It contains 25rr tent. of tin, and is too brittle and too hard for making guns. Jo the year 1794 the Revolutionary Govern ment of France obtained gun-metal by depriving bell-mend of a part of its tin. Bell-metal was heat ed with the contact of air, and stirred to oxidate the France cast-iron is little used ; many of the articles which in England are of cast-iron, being there of wrought-iron, copper, earthenware, or wood. In the Prussian dominions, the art of casting statues and small medals, in cast-iron, is successfully practised. But in none of the other countries of Europe is cast iron so generally used, and nowhere is it manufac- , tured on so large a scale, and with the employment of so much capital, as in Britain.
Pit-coal has been the main instrument in this ex tensive manufacture. As it gives a better heat for the melting of cast-iron, and saves the great extent of ground required for rearing wood, the greatest part of the cast-iron in Britain is now extracted from the ironstone, and made into castings by pit-coal.
i Pit-coal began to be used in smelting of ironstone in 1619. This first operation was performed in Wor cestershire, by Dudley, who describes his process in a book, entitled, Metallum Mortis. The manufac ture of cast-iron was not much advanced one hun dred years after; for in the first half of the eighteenth century, cast-iron goods were imported into some part of Britain from Holland. And the Dutch chim ney-backs, with the figure of a parrot, are to be seen in old country houses in Scotland to this day.