a generic term under which may be arranged all pieces of ordnance which from their weight or form cannot be used as the personal weapon of the soldier, such as guns, carronades, howitzers, and mortars. A brief historical sketch of the substitution of these tubular propelling machines for the mechanical instruments of war which had been used before the invention, or at least the practical application of gunpowder as a propulsive agent, has been given under the article ARTILLERY; and such additional particulars will be here cited from the excellent Spanish treatise on artillery by Don Claudio del Fraxco and Don Joaquin de Bouligny, as are necessary to explain satisfactorily the progressive improvements in the manufacture of cannon. In applying the suddenly developed impulsive force of ignited gunpowder to the propulsion of heavy projectiles, it is necessary to inquire what should be the properties of the material to be used in the manufacture of the tube, cylinder, or cannon, in which the powder is intended to be ignited, and from which the projectile is to be propelled. Such material then should possess hardness sufficient to resist the shock of the projectiles; should be capable of resisting the chemical action of the air, or of the compounds generated by the combustion of gunpowder, and augmented in their destructive agency by the heat produced by ignition; should possess sufficient elasticity to resist a disruption of continuity, or a permanent change of condition, resulting from the vibrations produced, either in rapid transport or by frequent discharges; and also a tenacity sufficient to resist the enormous pressure exercised by the elastic gases at the first moment of their development, which has been estimated by Prechill so high as 18,000 atmospheres, and by Hutton as 20,000, or even in the latter case at about 15,000 lb. per square inch of the bore of the tube or cannon. A deficiency in any one of these properties must lead to the rapid deterioration of the cannon: as want of hardness to the indentation, scratching, and grooving of the bore; want of elasticity to a change in its form and a diminution of its strength after every discharge; want of tenacity to a partial separation of its parts under pressure, and, finally, to decided fracture. It often happens that guns which have withstood the severe trial of proof charges, and have been subjected afterwards to much firing, suddenly burst under the effects of a very moderate charge; a result which must be attributed to a deficiency in one or more of these important properties, and which renders very doubtful the propriety of subjecting guns to excessive proof, by which they are often, though imperceptibly, much deteriorated.
The only simple substance in which the properties of hardness, elasticity, and tenacity are sufficiently blended together to produce an efficient result (for it must be observed, that to a certain extent they are opposed to each other), is iron; excluding, of course, from that term cast-iron, as being a compound or carburet. Various attempts, therefore, have been made from a very early epoch, to manufacture guns of wrought or forged iron, and only a few months have passed since a gun of this description, invented by Captain Simons, Royal Engineers, was submitted to trial by the artillery authorities. There can be little doubt, indeed, that excellent guns might be manufactured from forged iron, and should it be found possible hereafter, either by rifling the bore of guns, or by altering the form of the shot, to diminish the charge of powder, as in the Minie and similar rifles, it is by no means improbable that forged iron will again be adopted as a material for field guns. The difficulty of completely purifying iron from the sulphur and phosphorus usually associated with it, and which render it brittle, naturally led to many failures in the early days of artillery; and it was thus that James II. of Scotland perished before the walls of Roxburgh in 1460, from the bursting of a bombard formed of large iron bars, strengthened and bound together by iron hoops. Notwithstanding these defects, all the guns of the fifteenth century were manufactured in this manner; and the system of forging was so improved, that guns were even made of a single piece, in spite of the great labour and difficulty of managing such heavy masses in the frequent heatings to which it was necessary to subject them in forging. The manufacture of forged cannons was again revived after having been long abandoned; and in 1758, a gun weighing 1600 pounds was forged in Paris, and six years afterwards several guns of various calibres were forged in Spain. In 1813, the St Etienne Iron Company of Lyons proposed to the French government to supply guns of forged iron from their establishment at the rate of eight 24-pounders each day, and forwarded as a specimen an 8-pounder. This gun was proved by four discharges, with 3 lb. of powder, 1 ball, and two wads, one above the powder and the other above the ball; and then by five discharges with 4 lb. of powder under the same circumstances; the recoil being 24 feet in the first four, and 35 in the last five discharges.
The extreme lightness of such guns—a 16-pounder French, about equal to our 18-pounder, weighing about 1650 lb., and a 24-pounder French, equal to a 27-pounder English, about 2100 lb. only—would have rendered the recoil with ordinary charges so excessive, and the destructive effect on the carriage so great, that they could not have been satisfactorily employed in the field; still, however, it should be always remembered, that iron has great advantages over all other simple metals for the manufacture of guns, that it is quite possible to forge good pieces of artillery of iron at two-thirds the cost of bronze, and that it is desirable in the field to obtain as large a calibre for the discharge of spherical and other case shot as is consistent with a reasonable weight, which, perhaps, will hereafter be effected more readily by forged iron than in any other way. Where a long range, and in consequence a powerful charge of powder, are indispensable, this form of gun can scarcely, under existing circumstances, be adopted; or, at least, until some means of diminishing the shock and the recoil, by the intervention of springs, has been discovered; and even then it will be necessary to move the same weight, taking the gun and carriage together, though distributed in a different way.
The precise date of the first cast-iron guns is not known, but it has been asserted by General Haguenein, that a piece of this description at Bois-le-Duc bears the date 1411. Some doubt, however, has been expressed on this subject; and it has been thought more probable, with reference to the invention of high smelting furnaces, to suppose this date 1511. In 1540 Ralph Page cast eight iron guns at Rackstadt; and in 1547 the use of such artillery began to become general, and was for nearly a century exclusively adopted in some countries. In France cast-iron guns were not manufactured before 1600; but so evident were the advantages to be gained by their use, both as regards the qualities of the guns and their moderate cost, that they were speedily adopted in most countries; foundries for iron guns having been established in Silesia in 1470, in Germany in 1577, in Saxony in 1594, in the Hartz in 1626, and in Sweden in 1640; one foundry alone, in the latter country, having been said to have supplied for some time from 400 to 500 cannons annually.
All these pieces of ordnance were cast hollow until 1729, when a horizontal boring machine was established at Lyons, and, after some trials made in 1734, M. Maritz abandoned hollow casting at Strasburg in 1744–45, and adopted the boring machines.
Maritz, who was appointed, in 1755, inspector-general of the foundries of France, did much to perfect the art of solid casting and boring; but, in attempting to obtain a metal which should be easily turned and bored, he led to many failures in the proof, in consequence of which his system was combated by the celebrated Montalembert, and subsequently, in 1764, the department of the Marine undertook the manufacture of its own cannons. These imperfect trials led to the resumption, for a time, of hollow casting; but an examination of specimens of ancient guns has shown that the real defect was in the very imperfect casting of early times, fragments of metal unreduced being sometimes found imbedded, as it were, in a paste, very much like the condition of crystals in porphyry.
In 1770 Wilkinson established at Indret a reverberatory furnace, and introduced moulding in sand, as explained by Monge some years afterwards; and in 1780 reverberatory furnaces were applied to the re-smelting of iron for cannons in France, Silesia, Germany, and the Low Countries. In Sweden the use of reverberatory furnaces did not gain ground, as the excellence of its ores rendered them less necessary than in other countries. The efficiency of cast-iron guns was amply tested and proved in the siege of Ciudad Rodrigo in 1812, in the subsequent siege of Badajoz, and in that of St Sebastian in 1813; as the guns used were not deteriorated by the hard work of either of these memorable sieges. At that of Badajoz more than 36,000 projectiles were discharged, and each 24-pounder contributed to that total about 1250 rounds; but, notwithstanding this general success, many examples might be cited of guns bursting in action, which at least point to the necessity of still further improvement, and, it may be added, of a reconsideration of the system of proof.
Whilst the properties of pure iron are so eminently suited to the manufacture of guns, it is necessary to guard against purity, the presence of any of those minerals which in nature are so often associated with it, and which are removed only with great difficulty, as their presence even in small quantities deteriorates the metal. Sulphur, in the proportion of $\frac{1}{10}$th per cent., renders it friable and brittle when hot, and tends to produce white metal. Phosphorus, in the proportion of $\frac{1}{20}$th per cent., renders it soft and easily worked when hot, but brittle when cold. Antimony renders it brittle when hot, and friable when cold; as does arsenic if in considerable quantity. Manganese augments the hardness of iron without affecting its tenacity, but it prevents the formation of gray metal. Silicon, even in the proportion of $\frac{1}{100}$th per cent., renders iron brittle. Of other metals, tin in the proportion of 1 per cent., gives iron a fine grain and increased hardness, and renders it more sonorous, but at the same time more brittle when cold. Copper, increasing the hardness and tenacity of iron but in the proportion of $\frac{1}{4}$th per cent., renders it brittle when hot. Titanium renders the ores refractory, but gives to the metal tenacity and hardness. Zinc, chrome, gold, bismuth, and cobalt, in small quantities, do not affect the quality of iron. Nickel renders it fusible, soft, and tenacious. Silver and platinum in small quantity give it hardness and tenacity, and the presence of aluminium causes it to lose the latter property. From a consideration of these results, it is manifest that little can be expected in such a manufacture as that of cannon from any system of alloying iron, and that the main object is to ensure its absolute purity.
In Sweden the magnetic iron ores are abundant, forming extensive masses in the granite rocks. They are a mixture of the protoxide and peroxide of iron, in the proportion of 31 protoxide to 69 of peroxide. All these magnetic ores are not equally suited for this purpose, and those are preferred which are highly crystalline in structure. The Swedish iron enjoys a well-merited reputation; and the Swedish foundries of Finspong, Aker, and Stassjo, have supplied artillery not only to Sweden, but to Norway, Denmark, Russia, Piedmont, Naples, and Egypt. The metal for the casting of cannon is obtained both in Sweden and Norway directly from the ore, which is smelted with wood in high furnaces, composed of two truncated cones joined at their bases, the lower and shorter being inverted, and connected with the chamber or crucible which receives the melted metal. The height of these furnaces varies from 30 to about 43 feet, according to the fuel made use of, and about 13 feet of the upper cone form the air or draught chamber.
Mr Moritz Meyer has given the following rules for selecting the metal for casting cannons. The metal which produces the best cannons is that which, cooled in small pieces, a fitting of a clear gray colour, is very finely granular, and exhibits metal on the surface distant small white facettes like crystals, with a metallic lustre, whilst the general surface is of a greasy lustre. Poured into an empty mould, the surface remains concave with sharp edges, and without hollows or air-bubbles. Cooled in large masses as for cannon, it assumes on the surface a well-defined clear gray colour, and produces an iron of an interwoven texture. The principal mass presents a fine white grain, and contains small separated groups of graphite-like stars, which in very good iron should not be much less nor greater than pin heads; and in lesser number they are uniformly disseminated over the whole mass, though in fracture these stars appear more numerous and larger towards the edges. These groups assume sometimes an ellipsoid figure, crystallized like hematite. The rays of these stars should be so small as scarcely to be discernible by the eye alone; for when larger and more visible, or as it were like lamellae, the iron will be much weaker. The white metal appears to envelope these black groups, and whilst the former is attacked only with difficulty by the file, the latter are rapidly worn away. The recent fracture feels very harsh, and catches the fingers as if bristled with hooks. When turned in a machine, the surface seems as if marked by lines of cleavage, and the graphite groups appear of a stronger tint and more deeply incrustated.
Much difference of opinion has existed respecting the comparative merits of a clear gray, and of a dark or dull gray metal; and doubts have been expressed as to the rules or principles of Mr Meyer; but this at least is evident, that the condition of the metal in respect to the distribution of the plumbago is very peculiar, and that the greatest care must be necessary to insure satisfactory results in casting cannon, more especially those of large size.
In this country, in France, Germany, and the Lower Countries, from the difference of ore used, the first metal obtained in the smelting furnaces cannot, as in Sweden, be cast at once in cannons, but must be again melted in reverberatory furnaces, by which process the extraneous bodies still combined with the iron are removed, and the excess of carbon driven off as carbonic acid—the success of this process depending on the quantity of air admitted to the surface, and the manner in which the flame is directed over the metallic bath. This second reduction of the metal, though adding to the expense, has its advantages, as it enables the founder to mix together the products of different smeltings, and thus to correct the defects of some of them, and to use up the fragments of old guns, and generally to obtain with greater certainty a good metal.
The results of analyses of cast-iron by Gay-Lussac are as follows:
| Gray metal obtained with Charcoal. | |-----------------------------------| | From Carbon, Silicium, Phosphorus, Manganese, Iron, Total. | | Champagnes, 2:100 1:060 0:809 trace 95:971 100 | | Nivernais, 2:254 1:030 1:043 do. 95:673 100 |
| With Charcoal and Coke mixed. | |-------------------------------| | Carbon, Silicium, Phosphorus, Manganese, Iron, Total. | | Berry, 2:319 1:920 0:188 trace 95:573 100 |
| With Coke alone. | |------------------| | Carbon, Silicium, Phosphorus, Manganese, Iron, Total. | | Wales, 2:450 1:620 0:780 trace 95:150 100 | | Do., 2:552 1:200 0:440 do. 95:810 100 | | Do., 1:965 3:000 0:492 do. 94:842 100 | | Franche Comté 2:800 1:160 0:351 do. 95:680 100 | | Creuzot-Haute Saone 2:021 3:490 0:604 do. 93:885 100 |
The general result being, that the metal is a mixture of a carbide (carburet), in which one atom of carbon is combined with four of iron, and of a silicide of similar constitution, or quadrabasic. It had long been a received opinion that the iron guns of France were inferior to those of both Sweden and England, but Soult, when minister of war in 1832, sent two artillery officers into Sweden to study the manufacture there, and admirals Rigui and Duperré, on the part of the marine, sent officers also both to Sweden and England. At Aker and Finspong in Sweden, and at Carron these officers had guns cast of three several calibres, viz., 8-pounders, 18-pounders, and 30-pounders, which were subsequently submitted to proof in France, when it is asserted that the Carron guns stood in order of resistance the fourth or last, the French the second, and one or other of the Swedish guns in every trial the first. Whatever may be thought of these reported results, the example of the French may well be imitated by us so far as regards the personal examination by well-instructed artillery officers, not only of foreign cannon foundries but also of our own; and it would be very desirable to have specimens of guns corresponding to our own authorized calibres cast at the most celebrated foreign foundries, such as those of Sweden already named, and that of Liège, to be used in comparison with our guns. In the furnaces of Liège the hot-blast has been adopted.
The proofs to which iron guns are subjected before they are received as fit for service vary in different countries. In some each piece is proved by itself, in others only one is proved out of each distinct lot supplied by the founder. In France and Belgium iron guns are proved one by one, each gun being fastened to a strong stage or platform of wood, fixed firmly in an ordinary battery so as to prevent recoil, and in this condition making two discharges with a load of powder equal to one-half the weight of the projectile, two balls, and two wads, or one to each ball. In Sweden from three to ten discharges are made from each gun, with charges of powder varying from \( \frac{1}{2} \) lbs. to \( \frac{3}{4} \) lbs. of the weight of the projectile, and a quantity of balls, after which the guns are carefully examined to ascertain the extent, if any, of deterioration; and should one gun explode still more attention is bestowed on the examination of the others. At the beginning of this century General Hellwig proposed a system of proof varying in strength according to the weight of the gun. For a 27-pounder cannon, weighing 170 times the weight of the projectile, six discharges were to be made, the first two with \( \frac{1}{4} \) lb. of powder and two balls, the next two with \( \frac{1}{2} \) lb. and a cylinder 4 calibres long, and the last two with \( \frac{3}{4} \) lb. of powder and two balls. Gazarian substituted a different principle of proof, which has since been adopted in Sweden, the Low Countries, and Germany, and which may be called a metal proof. Bars of a determinate size were constructed of the metal used in any particular cast, and loaded until they broke, the result being supposed to afford a test of the quality of the gun; but as such a trial as this can take no account of the imperfections which are liable to be engendered in the very operation of casting large masses, by irregular cooling, or solidification, and other causes, it is evident that no satisfactory theoretical relation can be established between the weight which breaks a bar and the force which bursts a gun. Chemical proofs are equally unsatisfactory, as it is impossible that they should embrace all the possible physical defects of a gun, which may be so local as easily to escape notice in this way. In England the proof is of two kinds—the first instrumental, being directed to the examination of the bore, having previously tested the general dimensions and weight of the gun; and the second a fire-proof, all the other proofs (by searcher, by water, and by sun) being only means of detecting any deterioration from the firing. In respect to general dimensions, not more than \( \frac{3}{4} \) of an inch variation is allowed; in the diameters of the bore not more than \( \frac{1}{3} \) inch in 42 to 18-pounders, and \( \frac{1}{2} \) inch in 12 to 6-pounders; and in the position of the bore as regards the axis \( \frac{1}{3} \) in the 42 to 18-pounders, and \( \frac{1}{4} \) in the 12 to 6-pounders. In the fire-proof, each gun is discharged twice with charges exceeding one-half the weight of the projectile, excepting in the 68 and 56-pounders; one shot and two high junk wads, the actual charges being as below:
| Nature of gun | 42 | 32 | 24 | 12 | 9 | 6 | 3 | |---------------|----|----|----|----|---|---|---| | Charge in lbs.| 25 | 21 | 18 | 12 | 9 | 6 | 3 |
The proof charge of the 68-pounders is 30 lbs., and that of the 56-pounders 28.
After the firing the searcher is used, and any cavity of of an inch depth behind the first reinforce, or one of 25 before it, condemns the gun. Water is then forced into the gun by an engine, in order to detect fissures by its percolation through the metal, and subsequently the bore is examined internally by light reflected from a mirror, in order to detect minor flaws by their retention of water, which constitutes the sun proof. Should any one gun of a lot burst, all the others are subjected to another proof.
In respect to these modes of proof by firing with extraordinary charges of powder, it may be justly objected that they are rather proofs of the strength of a gun before firing than of its strength after firing; and it is scarcely possible that the discharge of an extreme load should not more or less modify the condition of an iron gun in respect to its power of resistance. It is thus that guns are found to burst unexpectedly in service with ordinary discharges, which have gone through the proof without exhibiting any deterioration; and this is by no means surprising, as the locality of the injury may often be entirely out of the reach of the test devised for its detection. In the proof charges used in our service there is even an unnecessary exaggeration of the principle in guns of the lesser calibres; for though in the 24-pounder the proportion of the weight of the gun to that of the projectile is as 233 to 1, whilst in the 12-pounder it is 196 to 1, the proof charge in the first is only three-fourths of the weight of the projectile, or 2-25 times the service charge, and in the last equal to that weight, or three times the service charge; and it is difficult to account for such high proof charges, unless the object of proof were to determine the absolute strength of the gun rather than simply to ascertain its ability to resist a regular charge under ordinary circumstances. It may be justly said that firing a few rounds with a moderate charge, combined with a knowledge of the quality of the metal and of the care used in casting and boring, would insure more effectively safe ordnance than the use of excessive charges; but this requires that the gun foundries should be under an artillery inspector as they are in Spain, the foundry of Trubia having been especially established by the Spanish government for that purpose.
At present the greater portion of the iron guns are cast for the ordnance by Messrs Walker of Gospel Oak, and by the Low Moor Company in Yorkshire, for which Mr Hood is the agent. The guns are cast solid, are then bored and brought to Woolwich, and having been previously weighed, are subjected to the proofs already detailed. Taking the average of ten years, 64 in a thousand are rejected by the instrumental proof, or about 6½ per cent., and 44 in a thousand, or about 4½ per cent. by the fire proof; and this latter number is sufficiently great to warrant the belief that many more may have suffered considerable deterioration under so severe a trial, from the defective elasticity of cast-iron, although of a nature to escape detection by the searcher, or by the auxiliary water and sun proofs. It may be here observed that the Sardinian government have obtained iron ordnance from one at least of the Yorkshire foundries, as many of the guns mounted upon the new works of Genoa are of their make; and in respect to their mounting, they possess the peculiarity of being placed on iron garrison carriages, so high as to fire "en barbette" over the parapet with only a very slight elevation of the mound or platform on which they rest. This arrangement is intermediate between the ordinary garrison carriage and a traversing platform, and may under some circumstances have its advantages.
The insufficiency of mechanical means to construct easily and cheaply wrought-iron guns, as well as the impossibility of giving to cast-iron a large amount of elasticity without interfering with its hardness, have led to the proposal of strengthening the cast-iron gun by reinforces of wrought-iron. Several modes have been devised of effecting this object; that of M. Thiery consists in the use of both bars and hoops applied in the following manner. Bars of the same length as the piece are heated to a suitable temperature, and then arranged in grooves prepared for the purpose in the interior of the mould, at about 8 inches apart, the number and thickness of the bars depending on the calibre of the gun. Making the cast afterwards with care, it is found that the bars adhere firmly to the cast metal, and though on the surface they are found to have undergone a steel-like modification, they retain internally the texture of wrought iron. This gun is moulded without trunnions, so that the bars extend its whole length, and protect the breech as well as every other portion of the gun. In the bars are notches at regular intervals to receive the binding hoops which, being put on at a white heat, grip the bars firmly in cooling. One of these hoops is considerably strengthened, so as to receive and support the trunnions which are welded on to it. An 8-pounder corresponding to an English 9-pounder constructed in this manner, with 12 bars and 36 hoops, the former ¾ths and the latter ¼ths inch thick is stated to acquire, by such an armature, resisting power so great that it is probable a 9-pounder might be bored up to a 12-pounder, and be then efficient for the projectile and charge of that calibre; and thus, that it would be possible to replace bronze field-guns by iron guns of this description at about one-fourth the cost. It should be observed, that casting without the trunnions simplifies the process of moulding, and induces more uniformity in the cast; but the subsequent operation of attaching the trunnions by welding them to the hoops is not without much mechanical difficulty.
The necessity of casting guns of sufficient weight to prevent a violent recoil, and the consequent rapid deterioration of the carriage, will doubtless render our authorities disinclined to adopt guns of this description; but in mortars intended to be fired at high angles, the use of a wrought-iron armature would render the adoption of very heavy projectiles more practicable than they are at present, and it is thus that in Belgium mortars of the calibre of 23½ inches, and capable of projecting a shell weighing half a ton, are secured from bursting by wrought-iron hoops.
It has been proposed to cast a compound gun of iron and bronze, and it is said that a gun of this description was cast in India in 1666. In modern times several such guns have been constructed; as at Strasbourg in 1802 and 1819, at Turin in 1812, and by M. Martin in 1821 and 1822. The object of such a system is to obtain a core of either wrought or cast iron for the bore of the gun, and by covering it with a metallic envelope of higher elasticity and tenacity to diminish the chances of explosion. It is said that in these experiments a perfect union was established between the bronze and iron; but that the results of proof were not satisfactory. Again, in 1826, three 24-pounders were made on this principle, the bore in one having been formed of short tubes of forged iron placed one above the other, so as to give the necessary length of bore, whilst in the two others tubes were used only of sufficient length to form a chamber for the charge and ball, the tubes being either of wrought or cast iron.
When it is remembered that the great defect of bronze guns is, that they rapidly wear, or, as it is technically called, serve trial droop at the muzzle in active service, it may be suggested that this union of a wrought-iron bore, with a casing of bronze, deserves a trial at our arsenal, and seems to admit of very easy manipulation.
The attempts which have been made to use mixtures of alloy of iron and copper by melting the two metals in separate furnaces, and then mixing them in a reservoir before taking copper, the cast, scarcely require observation; as the great difference in the fusibilities and affinities for oxygen of the two metals, as well as the small affinity of one for the other, render such alloys unnatural. Under this term may be arranged all alloys of copper, whether binary or ternary. The epoch of the first economical application of copper is lost in the darkness of the most remote antiquity; and the first use of an alloy of that metal in the construction of arms must be also referred to a very early epoch, as bronze is mentioned by Homer. The ruins of Pompeii and Herculaneum have exhibited to the moderns the skill in working bronze attained by the ancients; and the numerous Celtic swords and other warlike implements discovered in Ireland and other countries testify to the fact, that bronze was the material commonly used for the manufacture of arms, before the more intractable metal iron had been brought under sufficient control, partly to replace it for that purpose, and entirely for many others.
Tin, the other constituent of true bronze, was also known from the very earliest epoch; but zinc was not known in Europe as a distinct metal till the twelfth century, when it was introduced as such from China; and it was only about the middle of the last century that the method of extracting it from its mineral ores was discovered. The ancients, however, had unconsciously applied zinc to practical purposes in the manufacture of brass, which they produced by the direct action of the ores of zinc, either blende or calamine, on copper. The name zinc was given to the metal by Paracelsus at the beginning of the sixteenth century.
In respect to the first use of bronze cannon, the Spanish authors we have so freely cited state that the Moors used machines of cast metal for projecting stones in 1220, which may be assumed to have been bronze cannon, as the art of casting iron is of so much more recent date—at least the art so far as concerns the casting of large objects. The train which was prepared for the Andalusian war, in the reign of Henry III., in 1406, consisted of 6 bombards, and 100 lesser pieces, many of which were doubtless bronze guns; the probability indeed is, that the Spanish Arabs were our first instructors in this branch of war, just as they appear to have been our precursors in the institutions of chivalry, and that these warlike arts passed from them, through the Spaniards, to the other countries of Europe. In the wars of Charles V. against Francis I. of France, a great quantity of bronze cannons of various kinds, cast at Malaga, were used in the emperor's army, and so rapidly were such instruments of war multiplied, that Philip III., in 1609, issued an ordinance by which the number of bronze cannon foundries was limited to four within the peninsula, and four in the Spanish territory without it; and the number of calibres restricted also to four, a remarkable anticipation of a wise simplicity in the arrangements of war. The oldest bronze gun, with a legible date attached, now existing in Spain, was found in the Alhambra of Granada, in 1814, and was cast in 1501. Several others of the date of 1542 are also in the Alhambra, and one of probably much greater antiquity, which bears, in Gothic characters, this inscription, "Preceptum mei dominat facio, fugite a me omnes." In France, at Toulouse, there is a bronze gun cast in 1438, and in 1478 Louis XI. ordered artillery of this description to be cast at Paris, Orleans, and Tours, the epoch of which was marked by the death, at Tours, of the founder, Jean Moqué, who was killed by the bursting of one of his own guns. In Germany bronze guns were cast at Augsburg in 1372, and in Italy in 1399, and it is very probable that both countries derived the art from Spain. In England the industrial resources of the country have naturally led to a preference for iron guns; but it would appear, from the fact that bronze guns formed part of the armament of the Mary Rose, sunk off the coast of France in 1545, that at least prior to that date bronze guns had been used, if not cast, in England. The curious compound guns of the date 1426, formed of iron bars with a brass cylinder as part of the bore, connected with a moveable breech, belong to the section of forged guns.
The bronze guns cast before the middle of the last century are supposed, from such chemical examinations as have hitherto been made, to have been formed of a ternary compound of copper, tin, and zinc. The latter, as before observed, derived from the calamine ore, a carbonate of zinc. Bronze. Early guns made of a ternary compound of copper, tin, and zinc. The latter, as before observed, derived from the calamine ore, a carbonate of zinc. Bronze.
| Copper | Keller | Bachman | Other founders | |--------|-------|---------|---------------| | Tin | 7-8 | 8-6 | 11-1 | | Zinc | 0-7 | 1-3 | 2-9 |
The zinc being introduced into the compound through the intervention of its binary compound with copper, a proportionate quantity of brass having been actually used in forming the metal for casting. The ternary gun-metal has even very recently had its advocates, and it is said to be still used in Denmark; but when the difficulty of insuring certainty in the proportions of the alloy with a metal like zinc, so volatile at a very moderate temperature, is considered, there can be little reason to depart from the binary compound now generally adopted.
The proportions adopted are different in different countries; in France, 11 per cent. of tin; in Spain the same for large calibres, or 8 per cent. for small calibres and for mortars and howitzers; and in England 10 per cent.; and in our service the proper line appears to have been drawn in respect to the use of iron and bronze—the heavy ordnance of garrison and siege artillery being constructed of iron, and the lighter ordnance for the field of bronze.
Of the several modes of casting which have been adopted at different times and in different countries, two only are at present in use in cannon foundries, namely, casting in sand, and casting in prepared earth or mould; the first for iron and the second for bronze ordnance. By casting iron guns in sand, a hard skin, as it were, forms on the metal, and it is unnecessary to subject the gun to turning, and this is gaining a great advantage in iron guns.
The sand for dry sand mouldings is made by mixing a dry sand quantity of sharp refractory sand with water in which clay moulding has been diffused. After the mixture is thoroughly made, if a handful is grasped, and on opening the hand the sand retains the form given it, then the consistence of the mixture is good. The sand should have the following qualities:
1. It should not be fusible by the heat of melted cast iron; if it were, it would adhere to the metal, and make the surface of the gun rough. 2. It must be sharp, and composed of angular particles; if the particles of the sand were round, it would not hold together on taking out the model. 3. It must not contain too much clay, for in that case it would crack in drying. 4. It must contain a certain proportion of clay, to retain the form that the model impresses on it.
For dry sand moulding, a pattern of wood may be used, turned exactly to the form of the gun; or, to avoid expansion from humidity, the model, or pattern as it is termed in the foundries, may be of metal. Brass or pewter are preferable to iron for making patterns, as a smooth surface may be more easily given them, so that they may leave a correct impression, and may come out well from the sand. The metallic pattern is hollow, that it may be lighter and more easily handled; it is also in different pieces; and each piece fits into the adjacent piece by a rebate.
The length of each piece of the model should be a very little greater than the given length of the corresponding part of the gun, because the length of the mould is the length of the gun whilst hot, and this is longer than the length of the gun when it comes to the temperature of the atmosphere, at which temperature the dimensions of the guns are given. It has been estimated that some kinds of cast iron contract six hundredths of an inch in a foot in passing from the liquid state to the temperature of the atmosphere. This contraction is not considerable enough to be taken into consideration in the diameter of the pattern. The shrinking of the sand in drying, though not considerable, tends likewise to make the piece shorter, and is another motive for making the pattern a little longer than the dimensions taken from a gun at the usual temperature. The patterns of the trunnions are attached to the pattern of the second reinforce by screws, so as to be unscrewed and separated when the pattern is to be lifted out of the sand.
The gun-box, in which the dry sand mould is to be formed, is of cast iron, and cast in sand. It consists of several portions; each of these portions has a flange, by which it is fixed to the others, and the whole, when connected together, form the gun-box. In the flanges are holes through which bolts are passed; the bolts are secured by wedge-formed keys; thus the different parts of the box are firmly held together. The two portions of the gun-box which contain the breech-ring and cascabel are single, not being divided longitudinally. Each of the other five transverse portions is divided longitudinally into two. A handle is fixed to each portion of the box, for the purpose of moving it. The upper transverse portion AA contains the gun-head. In each of the two portions BB, which contain the second reinforce, there is a lateral projection for the trunnions. The figure represents the gun-box with the breech lowermost, in the position in which it is placed when the metal is poured in.
To make the mould, the pattern of the breech is first placed on a board, and the corresponding portion of the gun-box is put over it, and sand is rammed between the pattern and the box. The flat exposed surface of the sand is painted over with blacking, which consists of charcoal and clayed water, that there may be no adhesion with the sand of the next portion of the mould. The pattern of the first reinforce is now fitted into the pattern of the breech, and the corresponding portions of the first reinforce box adjusted on the flange of the breech-box. Sand is well rammed, in small quantities at a time, between the pattern and the box; and the upper flat surface of the sand is painted over with blacking. The mould is completed by adding the remaining pieces of the model and of the box, one above another, ramming the sand, and painting the transverse surface of the sand at the top of each division of the box with blacking. The sand must be strongly and equably rammed, that every part of its surface may be able to resist the pressure of the liquid metal. Three little wedges are interposed between the two adjacent transverse portions of the box, that the sand may project a little, so that after it is dry it may be flush with the box; if this were not done, there would be an interval between the adjacent surfaces of the sand, through which the metal would pass and form a fin.
When every part is moulded, the box is taken to pieces, and the parts of the pattern are carefully taken out of the sand, for which purpose they are first struck with a wooden mallet. Each part of the mould is then carried separately to the stove to dry. The stove is a room twelve or fifteen feet square, with large iron doors on one side; the fire is made in a large conical grate placed on the middle of the floor; the smoke issues by an aperture in the brick ceiling. The heat in this stove is considerable, but it must not be so great as to make the boxes red hot; for then, by the expansion of the iron, the mould would be injured; the moulds take about fifteen hours to dry in this situation. When the moulds are taken out of the stove, their interior surface is painted over with a coat of blacking, that there may be no adhesion between the mould and the metal.
The pieces of the gun-box containing the mould are then taken to the pit, and being carefully placed the one upon the other by the crane, they are put together, and secured mould by their bolts. The mould is placed with the breech undermost; the axis of the mould is made perpendicular to the horizon by a plumb-line, that the weight of the melted metal may press equably, and not more on one side of the mould than on another. It is not necessary that sand should be rammed round the mould, the box being strong, and its parts firmly bound together, so as to require no additional support. The mould is now in a position for the metal to flow into it through its open end, which is the extremity of the head.
The pig-iron from which the gun is to be made is melted in a furnace, called an air-furnace in the iron foundries, and termed by some authors a reverberatory furnace. The flame of pit-coal is carried by a current of air so as to play upon the pig-iron. The stack of the chimney is 40 feet high. By the pressure of the rarefied external air on the lower part of the rarified column of air in the furnace and chimney, the current of air through the furnace is produced. The grate G is larger than any other transverse section of the furnace. (See figure next page.) The furnace has three openings; one, C, for introducing the coals; the second, P, which has a sliding brick door, with a counterpoise, serves for introducing the pig-iron. The third, I, is for the purpose of stirring the metal, and taking out the melted iron for small castings by iron ladles coated with clay, and made red hot. This third opening has a door of fire-brick; the joints between the door and the door-frame are luted. In the middle of the door is a hole, through which the state of the melted metal may be seen. There is likewise a smaller opening, T, for letting out the melted metal.
The furnace and stack are of brick. The interior of the furnace is a coating of fire-brick, nine inches thick, detached and separate from the outer coat and the other parts of the building, in order that the heat may not melt the common brick of which the outer parts are composed. The fire-brick is made of refractory clay, which, containing little iron, and little or no calcareous matter, burns white, and sustains a great heat without melting. These bricks are made of Stourbridge clay, or of a light-bluish gray stratified clay, found in the strata that accompany coal in some of the collieries in Scotland. The clay is first ground, the pieces of ironstone picked out, and then made into bricks. In making the interior coating of the furnace, the bricks must be built with moistened fire-clay, and not with lime-mortar. The quantity of metal put into the furnace should be equal to the weight of the solid unheated gun with its head, and something more in case of need. It requires a large air-furnace to contain metal enough for one large gun.
The pig-iron for guns should be gray, that kind having most tenacity; while pig-iron is too brittle, and so hard that the head cannot be cut off, nor the gun bored.
A bed of sand, N, is made in the furnace, on which the charging pig-iron is to be laid. The furnace is heated to a white heat, till the sand is vitrified, which is known to have taken place by touching the surface of the sand with an iron ringard. The brick door is then lifted up, and the pig-iron is Cannon laid on the bed of sand. The heat should be applied so as to produce a speedy fusion; for if the iron is long exposed to heat before melting, a portion of its carbunculous matter is burnt, and it passes from the state of gray cast-iron to that of white. In situations where pit-coal cannot be had, wood may be used in the air-furnace; but the heat given by wood is not so great as that produced by pit-coal. To obtain the utmost heat that the wood is capable of affording, it should be well dried, cut into small logs, and the logs should be placed with their end upon the grate.
The pig-iron melted by the flame playing on it flows down into a cavity, L, which has a hole T, opening outwardly, and stopped with clay. When the hole is forced open by a workman, the metal issues and is conveyed by a gutter formed of sand to the gun-mould, into which the melted metal falls through the open end of the head. The sand forming the gutter should be in a proper state of moisture. If it is too dry, some pieces of it will be carried away by the metal. Across the gutter is a dam composed of an iron plate luted, and dipping a little below the surface of the metal to retain the scoria. This dam is driven down to stop the current of metal when the mould is full. The metal is also skimmed, as it passes along, by a skimmer, composed of a rod of iron terminated by a flat semi-elliptical piece luted and made red hot. It is sometimes the practice to plunge a piece of green wood for a short time into the head whilst liquid. This is with a view to prevent honeycombs, and its action may be to metallize any oxidated particles of the metal, and that the vapour from the green wood, rising to the surface of the metal, may carry with it small air bubbles, or other extraneous bodies that would, if they remained, occasion cavities in the metal.
The figure is a transverse section of the air-furnace. C is the opening through which the coals are introduced. P, the opening at which the pig-iron is thrown in. T, the hole through which the metal is let out. The metal flows into the casting-house. O, the floor of the casting-house. In this floor is the pit in which the moulds of large goods are sunk, that the metal may flow down into them. I, the door, with a hole in it, for seeing the state of the melted metal.
G, the grate. L, the lower part of the cavity of the furnace, into which the metal, as it is melted, flows. S, steps leading to A, the ash-pit. N, bottom of the furnace, lined with sand. H, chimney; the height of the stack is forty feet from the surface of the ground. The stack is strengthened in different places by iron bars. X. F is the mass of building which forms the foundation built below the surface of the ground to support the weight of the furnace and stack. R, the surface of the ground out of doors. CPNLH is the course that the flame takes.
The guns are not cast from the blast-furnace, where the Not cast ironstone is melted, as the quality of the metal would be un-certain, and might vary from one cast to another, by causes blast furnaces either unknown, or not under the control of the iron-master. On the other hand, in the air-furnace, pig-iron of a quality proper for making guns is put in, and the quality of the iron is not materially altered by the process of melting.
The head of the gun is like the jet (gate or geeet of the The head. workmen) of any other casting. Whilst the whole is liquid, the head is a column of liquid metal that acts by its height, exerting pressure on the metal that forms the body of the gun. The metal subjected to this pressure whilst liquid is less subject to porosity when cooled. The head also furnishes metal to fill up the cavities that occur in the piece by the contraction and crystallization of the metal whilst it is passing to the solid state. All the great contractions and crystallizations are thus transferred to the surface of the head, which is found to be composed of large cavities, sometimes containing cast-iron crystallized in a fern-leaf shape. The head also serves to receive any impurities that may have escaped the attention of those appointed to skim the iron as it flows along the gutter.
In 10 or 12 hours, the piece is sufficiently cool to be removed. It is then stripped of the mould, and taken to the boring-mill, to undergo the operations described under our article Boring of Cannon. Mortars, howitzers, and car-ronades, are moulded, cast, and bored in the same way as long guns.
Pit-coal cannot be employed entire in the blast-furnace; the bituminous part would be conglutinated by the heat, and the furnace would be choked, and the materials would no longer descend gradually as they ought to do. The coal is therefore burnt to drive off its bitumen, and it is then in a state of cinder, and called coke. It requires a larger mass of coke than of charcoal to smelt ironstone. Hence the coke blast-furnaces are large, and the machines employed to blow them are more powerful than the wooden spring bellows invented in Germany in 1620, and which continue to be employed in the charcoal iron-furnaces in Germany and France. Bellows connected by leather, and worked by water, were used to blow the blast-furnaces at Carron at the commencement of that establishment in 1760. Some time after, these bellows gave place to blowing machines, composed of pistons working in iron cylinders, constructed by the celebrated Smeaton, and described in his reports. The blowing machines of the blast-furnaces in Britain are now always composed of pistons moving in iron cylinders. The improvements in the steam-engine have rendered practicable the working of blast-furnaces in situations where there is no fall of water; and, on the other hand, the manufacture of the various parts of numerous steam-engines has called forth the abilities and ingenuity of the iron-founder.
In consequence of the advanced state of the English cast-iron manufacture, several foreign nations have been desirous of introducing the English method, and have procured English workmen for that purpose. In this way iron-works on the English plan were erected in Russia about 1780, in Silesia in 1790; and in France, at Creuzot, 12 miles south of Autun, there were three English coke blast-furnaces begun about 1790, under the direction of William Wilkinson.
The improvements in casting cannon, as in other arts, Progress of have been gradual. They are now always cast solid, except the art of experience having shown that guns cast solid are stronger, and casting less liable to burst than those cast hollow, and that the bore cannon is freer from honeycombs, and more likely to have the same axis with the piece. The second of these qualities is still more certainly attained by the practice now in use of making the gun itself revolve whilst boring; in this way, as long as the boring bar remains unmoved, the axis is right; but if the boring bar has a conical motion, then the point of the bit is out of the axis; when the boring bar was made to revolve, the bore might deviate greatly from the axis. The improvements in the casting of cannon have kept pace with the improvements in the manufacture of cast-iron.
The art of casting iron was known to the ancients, as appears from a small antique statue of Hercules of cast-iron, dug up at Rome. In China it appears to be practised with a dexterity visible in the Chinese specimens of many other arts. In modern Europe it has grown with the general advancement of society, and has now arrived at a high state of perfection. In the Prussian dominions small statues and other objects are cast in iron, and then bronzed; and from the great taste with which they are designed are highly ornamental; but in none of the other countries of Europe has so large a capital been embarked in the manufacture of cast-iron goods as in England, and their use, in some shape or other, is general throughout the British dominions. Pit-coal has been the main instrument in the development of this highly important manufacture, and Great Britain is indebted to its possession of such vast coal deposits for the extension and success of its iron-works. Pit-coal began to be used for smelting ironstone in 1619, the first operation having been performed in Worcestershire by Dudley, who describes the process in a book entitled Metallum Martis. The manufacture of cast-iron was not much advanced 100 years afterwards; for, in the first half of the eighteenth century cast-iron goods were imported from Holland, and the Dutch chimney backs, with the figure of a parrot, are yet to be seen in old country houses in Scotland. The minerals used are the hematites of Ulverstone, and the neighbourhood of Whitehaven, which, being very rich in iron, are carried by sea to smelting furnaces of other parts of Britain; and the argillaceous iron ore which is interstratified with the beds of coal of the great coal-fields, on which, therefore, the principal iron-works of Great Britain have been established.
Bronze cannons are cast in earth or prepared mould, which is composed of clay, sand, cow-hair, and horse-dung. The clay, from its tenacity, the facility with which it can be moulded into any shape, and its property of hardening on drying, forms the basis of all moulding earths, whilst the defects it possesses of cracking and shrinking as it dries, are corrected by the addition of sand or silicious earth. Sands or earths containing much calcareous carbonate should be rejected, as the disengagement of carbonic acid upon contact with melted metal would produce air-bubbles; and ochreous earths should be also rejected, as the metallic oxides they contain may vitrify the first coats of the mould. The cow-hair adds to the tenacity of the earth, by binding its parts together, and diminishes the contraction or shrinking; and the horse-dung renders the paste more unctuous and cohesive, and more readily dried. All these substances undergo distinct preparative processes before they are mixed together, in order to free them from extraneous substances, and to make them fit for blending readily together; the earth being first mellowed by exposure in pits when moistened by a sufficient quantity of rain-water.
Three descriptions of moulding loams are used in the French foundries, viz., fine earth, putty, and common earth. The fine earth is a mixture of four parts of mellowed clay and one part of horse-dung, which is allowed to rest in the tubs for at least eight days, and is then used as a pulp, after having been passed through a very fine sieve. The putty consists of four parts of fine earth passed through a coarser sieve, or a perforated copper basin of three parts of silicious sand, and 4th part of cow-hair. Common earth consists of two parts of mellowed clay, one of rather coarse silicious sand, one-half part of horse-dung, and one-half part of cow-hair. Each of these compounds is prepared separately on an oak table, and the various substances of which they consist are arranged in layers one upon the other, and then carefully triturated together with proper tools, so as to ensure a smooth and homogeneous mixture. The proportions vary in different foundries; but it is necessary to keep to moderate and fixed quantities of cow-hair and horse-dung, as these substances burn, and if in too great quantity may produce cavities in the coats of the mould into which the metal, when in fusion, would necessarily filter. In Spain the common earth is made by spreading on the table 584 lb. of prepared clay, and over that 36 lb. of horse-dung; and as a third layer 2½ lb. of cow-hair; 69 lb. of water being then added, and left for 1½ hours, so as to allow the whole mass to be penetrated by the water, when the operation of mixing commences, and is continued for about three-quarters of an hour, after which it is generally found that the three materials have been perfectly combined together.
The operation of moulding is divisible into two parts, namely, the preparation of the model and the formation upon the model of the mould.
The model, as well as the mould, is formed of three distinct parts, namely, the models of the body of the gun, comprising part of the first and the second reinforces, the chase, and the muzzle; of the breech and casable, and of the head metal. The model of the body of the gun is built up on a conical spindle of wood, either of pine or fir, which is supported horizontally, by its ends resting in the sockets of the vertical end-pieces of a frame firmly fixed to the ground. The large end of the spindle has a shoulder in the shape of a truncated cone, which, resting in a hollow or notch of the frame, prevents any longitudinal motion, and this shoulder is terminated by a square head pierced with lever holes, into which the handles are placed, by which the model and the mould in progress of formation may be turned as required. Each frame supports two spindles placed opposite each other, but in reverse positions, so that two models may be prepared at once. In well-arranged foundries the frames are constructed of cast-iron, and made moveable on trucks and rails, so that their position may be shifted; and as it is necessary to dry the model and mould in course of formation, the frames are placed over a brick pavement made slightly concave for the reception of the fuel. The external form of the model is regulated by a profile board, to one edge of which is attached throughout its length an iron plate cut so as to correspond exactly to the various rises, depressions, mouldings, &c. of the intended gun. This profile is fixed to the uprights of the frame, either horizontally at the level of the axis of the spindle, or vertically below the spindle; and as the spindle is turned round during the process of forming the model, every part of it is reduced to its true shape and size, or rather to a size somewhat greater, as the profile is so placed as to produce an increase in the diameter of the gun of about half an inch, which allows a sufficient thickness of metal for the operation of turning. The spindle and profile-board being properly placed, the first act of the moulder is to fix brackets, shaped to the swell of the muzzle, at regular intervals all round the smaller end of the spindle, and to fasten them on with long nails; he then covers the spindle with straw-rope, winding it round from the muzzle end backwards; and when the rope circles have sufficiently bound the brackets which define the swell of the muzzle, he withdraws the nails by which they had been at first secured in position, and continues the straw coating until there remains only an interval of one or two-tenths of an inch between it and the profile-board, which space is then filled up by a coat either of prepared clay, or plaster of Paris, the last layer being put on in a finely liquid state, so as to fill up all cracks, and efface any defects; the spindle being turned during the operation, so as to bring every point of the surface into contact with the profile-board, by which it is as it were turned into proper shape. The model of the body of the gun being thus finished, the models of the trun- nions and dolphins (if any) are next attached to it. These models are made of plaster, cast in plaster moulds; and those of the trunnions are, from their bulk, cast hollow. The trunnions and dolphins having been carefully secured in their proper places by straps, and cemented on by liquid plaster the model is complete, and the workman then pro- ceeds to form the mould upon it.
The model is first brushed over with a wash either of finely comminuted and well-washed ashes, or with tan- ashes diffused in water, the object of this coating being to prevent adhesion between the model and the mould. The ash-coat being perfectly dry, the moulder applies three suc- cessive coats of putty loam, being in all about \( \frac{3}{4} \)ths of an inch thick, all being slowly dried in the air, with a mixture of putty and common loam. Several other coats are then added, gradually increasing in thickness, and dried by artificial heat so as to render them hard enough to resist the point of a knife; and these are followed by thicker layers of common moulding loam, until a thickness of about \( \frac{2}{3} \) inches in guns of large calibre, and \( \frac{1}{2} \) inches in those of lesser calibre has been attained. The surface is then carefully smoothed, and any irregularities having been removed by the application of a profile-board, the first armature is fixed, which consists of flat bands of iron of the length of the mould, secured by circular iron bands at fitting intervals; these hoops being well closed by iron wire. In guns of large calibre, such as the French 16-pounder and 24-pounder, 10 or 12 bands, and 16 or 20 hoops are used. The bands and hoops are 2 inches wide; the bands being \( \frac{3}{4} \)ths of an inch thick, and the hoops between \( \frac{3}{8} \)ths and \( \frac{5}{8} \)ths. Before putting on the bands some iron wire is wound round the mould at both ends and at each side of the trunnions, and by this wire the bands are tied down to the mould, and thus kept firmly in place until the hoops have been put on and closed. The armature being thus fixed, the moulder fills up all the spaces between the bands and hoops with common loam, and puts fragments of brick into any open spaces between the bands and hoops. He then applies over the whole surface a new coat of coarse loam, which he dries as before, and continues the operation, by successive coats, until the mould has ac- quired a total thickness of 5 inches for large calibre, and 4 inches for small; and as these dimensions have been found sufficient to insure stability in the mould, they should not be exceeded, as a greater thickness would only add to the difficulties of drying and baking. The moulder now smooths and trims this last coat, and having strengthened the region of the trunnions by hoops let into the substance of the loam, proceeds to attach the second armature of bands and hoops, which are somewhat stronger than the first, and ter- minated by hooked ends, by which they may be secured to the bands of the breeching and head-metal moulds; on this second armature one or two more coats of loam are spread, and the whole being smoothed by the hand, the mould is complete. The spindle and the straw bands are now with- drawn, and such portions of the plaster which do not come off with the straw being carefully extracted, as well as that which formed the moulds of the trunnions and dolphins, the mould is ready to be baked. The models and moulds of the breeching and head-metal are formed upon the same prin- ciples as that of the body of the cannon, except that in the model of the breeching, an iron axis is used instead of the wooden spindle; the axis and profile-board being sometimes horizontal for small calibres, and vertical in large calibres, in consequence of the greater thickness and heavier arma- ture of the moulds. The moulding with a vertical axis is carried on over a small round furnace heated with wood, and surmounted by a cast-iron drum, which can be raised or depressed for either moulding or drying. The axis is in this case fixed, being firmly attached at its base to the plat- form of the furnace, and the profile-board is moveable, being fixed to an iron plate, which turns on a shoulder of the axis.
The model being finished, the mould is formed upon it in the same manner as in that of the body of the gun; but the second armature is replaced by an envelope of iron or bronze, called the goblet mould, into which the mould is cemented either with plaster or loam, and from which it acquires strength to support the whole weight of the metal. The mould being completed is then dried by fire, and this is effected at Toulouse by a circular furnace with a central hearth sufficiently large to dry ten moulds at once; the ten stoves being arranged circularly round the hearth, and covered as required by a drum of sheet-iron. The model of the tail piece itself of the cascabel is made of bronze, and is used for all guns of the same calibre. The final harden- ing or baking of the moulds requires special precaution in respect to that of the body of the gun, on account of its length, and it is therefore effected in the casting-pits by sus- pending the mould over a small temporary brick furnace, which is removed after the operation. The three pieces which constitute the whole mould of a cannon being now ready, they are lowered into the pit and properly adjusted to the breech below and the dead-head above, each part being firmly secured to the other two by iron wire passed round the hooked ends of the iron bands of the armature, and the joints well plastered with moulding loam. The mould now forms one complete whole, and the moulds of all the cannons to be cast at the same time are carefully arranged in the pit, so that their summits should all be on the same level, and the top of the dead-head level with the lower discharging hole of the furnace. The whole pit is now filled up with slightly damp earth, put in by successive layers, gradually increasing in thickness from below upwards, and carefully rammed with an iron rammer. In the moulds of large guns, the breech and body of the gun are first connected together, and the dead-head mould fixed on when the pit has been filled up to the level of the muzzle. The ram- ming is a delicate operation, and much care is required to avoid a blow on the trunnion portion of the mould, an acci- dent which in some foundries is guarded against by small stakes placed around the trunnions as a guide to the work- man. When the filling has come up to about \( \frac{1}{2} \) inch of the discharge hole of the furnace, canals are formed in the earth of the pit for conveying the melted metal to the dif- ferent moulds, the sides and bottoms being of bricks well cemented and plastered with moulding putty, and the pit is then filled up to its summit, when everything is ready for the casting. The system which has been here described is that adopted in the great cannon foundries in France, in which country even siege guns of the largest calibres are manufactured of bronze, and is, with some slight modifica- tion, that of our own arsenal.
Shell Moulding.—This description of moulding is also effected in loam, but far more expeditiously than the pre- ceding. The model is either of wood or brass turned to the exact shape of the particular gun, with the addition of the dead-head; and serving, therefore, for all guns of that calibre. It is divided into two halves by a plane passing through the axis; and one half being placed on a horizontal plank, the model is covered by a coat of moulding loam sufficiently soft to be readily applied to the model by the simple pressure of the hand, and about \( \frac{1}{2} \) inches thick. Numerous holes are then made over the surface with the finger to the depth of about one-third of an inch, and the whole is dried with lighted charcoal placed in lumps upon it until it has begun to harden, when a thick coating of plaster is applied, which fills also the holes, and thus binds the two coats together. An armature is now applied con- sisting of strong iron bars, both longitudinal and transverse, fixed one to the other by rivetted bolts, and over this arma- ture a second thick bed of plaster; so that the armature is as it were imbedded between the two coats. The one half being finished, the mould is turned over, and the model having been taken out, the hollow is thoroughly dried by live coals, and the interior surface brushed over by a liquid paste of clay to fill up cracks or other defects, when an ash coat is applied as in ordinary moulding to prevent adherence. It should be observed that the models of the trunions and dolphins are made separate, and are attached to the body of the model by long screws, being removed by unscrewing when the mould has been completed. The two halves are now carefully adjusted to each other, and secured by bolts passing through the transverse bars of the armature; after which the joints are plastered up and the mould is complete for lowering into the casting pit.
Another mode of shell-casting is only a slight modification of the above: the model is laid with its longitudinal axis horizontal, and one-half immersed in a bed of sand. Upon that part of the model which projects above the sand successive coats of loam are applied, and dried one by one by fire, till the model is covered with a coat of loam four or five inches thick, when an iron carcass is applied, and over the carcass another coat of loam. The mould with the model in it is now turned, so that the half already covered with loam shall be lowermost. The plain surface of the loam which had been in contact with the sand is painted over with a coat of blacking, composed of finely-powdered charcoal mixed with clayed water; this prevents the adhesion of the flat surface with the loam that is to be laid on it in order to form the mould of the other half of the gun, now of course uppermost. The two halves are secured together in the manner before described; but this method has the advantage of securing precision in the structure of the two parts by forming one upon the other. Both these methods were in use in the French foundries towards the end of the last century, but have been abandoned, as it was found impossible to prevent an escape of the more liquid portions of the metal, surcharged with tin at the line of junction. Guns cast in this way exhibit along the lines of junction, even after turning, long white streaks, which are only so many spots of tin which has filtered through, and it was therefore found impossible to secure homogeneity in the mass by this system. The process of forming the model will be better understood by the accompanying woodcut, which represents the spindle at that stage of the work where the straw-rope is wound round it, the brackets fastened on towards the lesser end, giving an approximation to the form of the muzzle. The description will, it is believed, render the remaining portion of the process sufficiently intelligible.
The importance of casting with a dead-head is very great, as the weight of the column of fluid metal forces the lower portions into all the sinuosities of the mould, and insures a homogeneous structure with a proper density. The following table gives the result of French experience as regards the weight of the dead-head, as it is evident that an excess of weight would endanger the deterioration of the mould, whilst too little weight would lead to imperfections in the mass; hence it is very important to have some guide in determining the weight from such extended experience:
**Weight of French Cannon in their different States, and dimensions of their Dead-Heads, 1838, in Kilogrammes, the Kilogramme equal to 2½ lb. Avoirdupois.**
| NATURE OF CANNON | WEIGHT OF CANNON | Length of Dead-Head in metres (1 metre = 3.281 feet) | Diameter of Dead-Head in metres | |------------------|-----------------|-------------------------------------------------|--------------------------------| | | Rough, with Dead-Head. | Finished. | Weight of Dead-Head. | Douai. | Toulouse. | Strasbourg. | Douai. | Toulouse. | Strasbourg. | | Siege guns | 24 cwt. | 5400 | 5290 | 6028 | 2754 | 2764 | 2560 | 1554 | 1635 | 2196 | 184 | 138 | 152 | 0.400 | 0.395 | 0.450 | 0.440 | 0.440 | | | 16 cwt. | 4050 | 3880 | 4817 | 5015 | 2033 | 2016 | 1217 | 1533 | 1984 | 195 | 140 | 148 | 0.330 | 0.323 | 0.390 | 0.475 | 0.350 | | Guns of position | 12 cwt. | 3200 | 3023 | 3308 | 1508 | 1574 | 1583 | 981 | 1187 | 1387 | 191 | 147 | 144 | 0.304 | 0.295 | 0.350 | 0.430 | 0.370 | | Field guns | 12 cwt. | 1950 | 2333 | 1971 | 868 | 890 | 884 | 642 | 1018 | 689 | 145 | 135 | 140 | 0.280 | 0.280 | 0.350 | 0.350 | 0.350 | | | 8 cwt. | 1700 | 1620 | 1735 | 592 | 585 | 589 | 709 | 730 | 881 | 204 | 122 | 134 | 0.265 | 0.240 | 0.300 | 0.310 | 0.260 | | Howitzers, Siege | 22 cwt. | 3474 | 2840 | 3468 | 1241 | 1231 | 1244 | 1686 | 1131 | 1229 | 138 | 112 | 163 | 0.411 | 0.404 | 0.400 | 0.442 | | | (centimetres = 0.92 Inch) | | | | | | | | | | | | | | | | | | Howitzers, Field | 16 cwt. | 2275 | 2265 | 2818 | 852 | 879 | 887 | 894 | 857 | 1407 | 177 | 118 | 163 | 0.305 | 0.290 | 0.350 | 0.390 | 0.290 | | | 15 cwt. | 1722 | 1489 | 1702 | 585 | 584 | 585 | 749 | 496 | 757 | 132 | 94 | 135 | 0.255 | 0.250 | 0.310 | 0.325 | 0.285 | | Howitzers, Mountain | 12 cwt. | 386 | 362 | 457 | 101 | 98 | 101 | 193 | 134 | 224 | 100 | 60 | 62 | 0.185 | 0.183 | 0.180 | 0.220 | 0.184 | | Mortars | 32 cwt. | 3764 | 3708 | 3591 | 1294 | 1304 | 1294 | 1979 | 2081 | 1808 | 170 | 138 | 138 | 0.457 | 0.433 | 0.469 | 0.450 | 0.450 | | | 27 cwt. | 2960 | 2846 | 2687 | 908 | 930 | 915 | 1685 | 1634 | 1429 | 179 | 148 | 150 | 0.380 | 0.367 | 0.420 | 0.430 | 0.370 | | | 22 cwt. | 1500 | 1121 | 1176 | 293 | 288 | 288 | 1015 | 600 | 697 | 135 | 105 | 100 | 0.318 | 0.311 | 0.300 | 0.376 | 0.340 | | | 15 cwt. | 345 | | | | | | | | | | | | | | | |
**Remarks.—** At Douai the dead-head is a truncated cone, the greater circle next the piece—both diameters given in the table. At Toulouse the dead-head is cylindrical, except the small piece merging in the mould of the body of the cannon, which is a truncated cone. At Strasbourg, in guns and howitzers, a truncated cone commencing at the swell of the muzzle, and then cylindrical; in mortars of 32 and 27 cwt., partly cylindrical and partly a truncated cone; in mortars of 22 cwt., two cylinders of different diameters. It appears from the data given, that the weight of the dead-head in a French 8-pounder, equivalent to an English 9-pounder, is to that of the whole mass to be cast, as 1 to 2½ths, or about 1694 lb., and that its length is about 4½ feet, this height of metal being necessary to ensure a sufficient pressure. (T. H. F.)