104 OF gun-meta'l.

a sufficient degree of hardness, since in firing with {hot, thebore of the gun is never injured; but as it is not sufficientlytenacious to resist the force of powder in very long sieges, itbecomes necessary to supply this defect by adding to thestrength, and consequently to the weight of the guns, toprevent their bursting: wherefore 32 pounders with properreinforces are too heavy, and are only used on board of shipsof war, 24 pounders being the largest piece of iron ordnancethat is used in land service.

15. The iron of the second smelting is heated and weldedwith a forge hammer to increase its malleability and tenacity:this operation is frequently repeated to separate the earthyheterogenous particles. When thus worked, it obtains thename of forged iron, and is less hard but much more tena-cious than before; It is esteemed of the best quality whenmalleable, both hot and cold, and, when it yields to the file;but when it breaks and splits under the hammer, it is not sogood. A very violent and long continued heat is necessaryto fuse forged iron ; and from its softness, it is only used inthe construction of fire-arms of small calibre, from whichleaden bullets are projected, as wail-pieces, musquets, pistols,&c. since from its great tenacity the barrels may be made verythin.

16. Copper is generally found mixed with other metallicand volatile substances; according to the nature and propor-tion of which the operation of purifying must be varied. Itsometimes happens that a vein of a copper mine will furnishfor a considerable time, an ore easily refined ; but at lengthits quality alters, which induces a necessity of multiplyingand even diversifying the processes of refining. In all cafesit is first fluxed; whence a regulus or mixed metal, calledblack copper is obtained ; which is unmalleable and of differentqualities according to the nature and proportion of the hete-rogeneous substances.

17. To purify black copper, the chymists use the cupelalmost the same manner as the refiners of gold and silver:but the common method is to roast and afterwards smelt it;that during the roasting, the volatile particles may be sub-limed ; and that when in fusion the other heterogeneous sub-stances may be converted into scoriae: the metal obtainedfrom this process is called copper, and is generally run intothin cakes, which are very full of cavities and spungy.