Chapter II (8)

When zinc is used in fire-works, it should be remarkably fine. The powder may be very readily formed, by heating it, until it is about to fuse, and pulverizing it while hot, in a warm mortar. It is generally considered, however, that the best method of obtaining the powder of zinc, although a longer time is required, is by filing it; but the filings are more or less coarse, according to the file which is used. They may be sifted, and thus obtained of any degree of fineness. In various blue lights, in the blue flame of the parasol and cascades, and other descriptions of fire-works, it is used. It gives a more brilliant light than any other substance used for this purpose. It is frequently mixed with other substances; but, as to its peculiar properties, they remain the same. By the combustion of zinc, which follows in fire-works, it always produces an oxide. In this state, it is expelled, or thrown off.

Acetate of zinc appears to possess advantages over zinc-filing, especially as it produces the same colour, may be more readily mixed, and with more accuracy, and does not deliquesce or absorb moisture, a circumstance which must always be guarded against in artificial fire-works.

_Sec. XLIII. Of Brass._

This is a mixed metal, composed of copper and zinc. This alloy, according to the proportion of the metals, is more or less yellow, or reddish-yellow. The yellow copper, or _laiton_ of the French, the similor, Manheim gold, prince Rupert's metal, &c. are alloys of the same metals.

Zinc readily unites with copper; and the usual manner of forming brass by brass-founders, is to make a direct union between the two metals. The process, however, generally consists in mixing together granulated copper, calamine, or carbonated oxide of zinc, and charcoal in powder, and melting them in a crucible. The charcoal reduces the zinc, which then unites with the copper. The heat is kept up for five or six hours, and towards the last of the process, is raised. Zinc, in small proportion, renders copper pale, and in the proportion of one-twelfth, inclines its colour to yellow. The yellow colour increases in intensity with the zinc, until the weight of this metal in the alloy equals that of the copper. An increase of zinc, afterwards makes the alloy white. English brass contains one-third of its weight of zinc. In Germany and Sweden, the proportion of zinc varies from one-fifth to one-fourth of the copper. Twenty to forty parts of zinc, with eighty to sixty parts of copper form the _cuivre jaune_, laiton, or yellow copper of the French.

Dutch metal, or Dutch gold, is a fine kind of brass, and comes in leaf, which is about five times as thick as gold leaf. This brass is made by the cementation of copper plates with calamine, and hammered out into leaves.

According to Thenard (_Traité de Chimie_, tome i, p. 478), the French use 50 parts of calamine, mixed intimately with 20 parts of charcoal, and stratified in a crucible with 30 parts of laminated, or granulated copper. British brass consists of two parts of copper, and 1-1/8 parts of zinc, by weight.

The filings of brass are much employed in fire-works. They communicate to stars, rains, &c. a flame between a blue and green. In some, the filings of copper alone are used. A beautiful green fire, for instance, is produced by 16 ounces of gunpowder, and 3-1/4 ounces of copper-filings. Verdigris is also employed for the same purpose; but the effect is not so striking, as in that preparation, the copper is already oxidized. The effect of copper in fire-works, it is to be recollected, depends, like that of other metals, on its combustion, and consequent oxidizement. The product of the combustion of brass, is oxide of copper, and oxide of zinc.

_Sec. XLIV. Of Bronze._

The union of copper with tin, in various proportions, forms gun-metal, bell-metal, the mirrors of telescopes, and bronze.

The ductility of the copper is diminished by the tin; but its hardness, and tenacity, as well as its fusibility and sonorousness are increased.

To form a complete union of the two metals, they should be continued in fusion for some time, and constantly stirred. The tin is apt to rise to the surface, unless this precaution is used.

Bronze is usually composed of 100 parts of copper, and 8 to 12 parts of tin. It is yellow, brittle, heavier than copper, and has more tenacity.

The same metals, and in the same proportion, constitute gun-metal. In the brass ordnance made at Woolwich, the proportion of tin varies from 8 to 12, to the 100 parts of copper. The purest copper requires the most. That the alloy is more sonorous than iron, is evident from the report of brass pieces, being louder than that occasioned by iron guns.

When the alloy is 78 of copper and 22 of tin, it is chiefly used for clocks. There is, in the English metal, about five per cent. of zinc, and four per cent. of lead. The proportion of tin, in bell-metal, varies. In church bells, less tin is used than for small bells. In the latter, zinc is sometimes added.

The _Tam-tam_, or _gong_ of the Chinese, used for cymbals, clocks, mirrors, &c. contains, according to analysis, 80 parts of copper, and 20 parts of tin. The proportions, however, are not always the same.

The ancients made cutting instruments of an alloy of copper and tin. A dagger, analyzed by Mr. Hielm, consisted of 83-7/8 copper, and 16-1/8 tin. Vessels of bronze were frequently covered with silver. Some of this kind were found in the ruins of Herculaneum.

Pliny observes, that ancient mirrors were made with a mixture of copper and tin; but that, in his time, those of silver were so common, that they were even used by the maid servants. The quantity of tin, to make the most perfect speculum, depends on the quality of the copper. If the proportion of tin be too small, the composition will be yellowish; if it be too great, the composition will be of a grayish-blue colour. Mr. Edwards casts the speculum in sand with its face downwards; takes it out while red-hot, and places it in hot wood-ashes to cool, otherwise it would break in cooling. The mixture is first granulated, by pouring it into water, and then fused a second time for casting. Mr. Little recommends the following proportions: 32 parts of the best bar copper, 4 parts of brass, or pin wire, 16-1/2 of tin, and 1-1/4 of arsenic.

Whether for speculum metal, bronze, or gun-metal, the metals must be mixed exactly, and for this purpose be kept a long time in fusion, and constantly stirred; otherwise, the alloy will not be of a uniform quality, as the greater part of the copper will sink to the bottom, and the greater part of the tin rise to the surface. When we speak of _brass guns_, as that name is generally applied to them, we are to understand, that they are not made, like brass, of an alloy of copper and zinc.

The ancient metallic mirrors, which were in use before the present mirrors, or the discovery of glass, and the mode of applying to its surface an amalgam of tin, were composed of two parts of copper and one part of tin. Mr. Mudge asserts, that the best proportion for mirrors is 32 parts of copper and 14.5 parts of tin. Klaproth found a specimen of ancient mirror to consist of 32 of tin, 8 of lead, and 62 of copper. The alloys of copper and tin may be decomposed by dissolving them in an acid, the muriatic for instance, and immersing a sheet of iron, which will precipitate the copper. The tin may then be separated by immersing a plate of lead, or zinc, by either of which metals, it will be precipitated.

Bronze, being a mixed metal, in which the copper forms the principal ingredient, is sometimes used in fire-works, in lieu of copper or brass; for its effects are similar. By the combustion of bronze filings, we have an oxide of copper and an oxide of tin.

_Sec. XLV. Of Mosaic Gold._

This name, or _aurum musivum_, was given to a preparation of tin, composed of tin and sulphur. It is considered to be a persulphuret of tin.

Several methods are recommended for preparing this substance. The oldest process is to sublime a mixture of 12 parts of tin, 7 parts of sulphur, 3 parts of mercury, and 3 parts of sal ammoniac. It may be formed by heating together in a retort, a mixture of equal parts of sulphur and oxide of tin.

It is used principally for rubbing the cushions of electrical machines, and for bronzing wood. In fire-works, it is sometimes employed under the name of _gold-powder_.

It was supposed to be a combination of sulphur with the oxide of tin. Dr. J. Davy (_Phil. Trans._ 1812, p. 199) and Berzelius, (_Nich. Jour._ xxxv, 165), have proved, however, that it is nothing more than metallic tin and sulphur; the proportions of which, according to the former, are 100 of tin + 56.25 of sulphur.

Mosaic gold is of a yellow colour, resembling that of gold. It is insoluble in water, and is not acted upon by muriatic or nitric acid. The nitromuriatic, however, decomposes it. A solution of caustic potassa dissolves it, forming a green solution, which is decomposed by acids, letting fall a hydrosulphuret of tin. It deflagrates with nitre.

When it is used in fire-works, it is pulverized, and sifted. It is more generally employed as a pigment to impart a golden colour to small statues of plaster-paris. When mixed with melted glass, it is said to imitate lapis lazuli.

_Sec. XLVI. Of Iron and Steel._

Both iron and steel are used abundantly in fire-works. It would be unnecessary to detail the preparations, in which they are employed, which may be seen by a reference to the different kinds of fire, and to their respective formulæ.

Cast iron is more employed in artificial fire than forged iron or steel, at least in the preparation of some, as gerbes, white fountains, and Chinese fire.

The filings of iron and steel may be sifted through sieves. A fine hair sieve will answer for common purposes. Their fineness depends, in the first instance, on the file, which is used. Steel or iron filings are more commonly employed in the compositions for brilliant fire.

The sparks produced by cast-iron are very brilliant; but the reduction of the iron to powder, or to a degree of fineness sufficient for use, is a difficult operation. It is of too hard a nature to be cut by a file.

This operation is generally performed in the following manner: Procure from an iron foundry, some thin pieces of cast iron, such as generally run over the mould at the time of casting, and pound them on a block, made of cast iron, with an iron hammer of four pounds weight, putting, under the block, a cloth to catch the pieces of iron, which fly off. They are beaten with the hammer in this manner, until the whole is reduced to grains, which are more or less small. It is then thrown into a sieve, which should be fine, and the dust separated. This is used, in the place of steel dust, in small cases of brilliant fire. The remainder is then put into a sieve, a little coarser, and again sifted. This portion is preserved separately. The same operation is repeated, but with sieves of different sizes, till the iron passes through about the bigness of small bird shot.

The pulverization may be effected in an iron mortar, with a steel pestle, having the mortar covered in the usual manner, to prevent the escape of the finer particles of the iron.

According to a writer in the _Dictionnaire de l'Industrie_, vol. iii, p. 34, the Chinese prepare their iron-sand for fire-works by igniting iron, and plunging it in cold water. They then pulverize the scales thus formed, and pass the powder obtained, through different sized sieves, which is then called No. 1, 2, 3, 4, &c. as it is very fine or coarse. This cannot be a good method, and we doubt whether it is at present employed; because it is obvious, that the scales, in this case, consist of the metal in the state of protoxide. D'Incarville, a missionary at Pekin, obtained the process for making Chinese fire; and observes, that the pulverized cast iron they employ is called _iron-sand_, of which they have six numbers or varieties.

As the goodness of iron or steel dust, in fire-works, depends greatly on its being dry, and not oxidized or rusted; its preservation must be accordingly attended to. The usual preservative is to put it in a box, lined with oiled paper, and covered with the same, or in tin cannisters, with their mouths well closed.

When it is to be used, it is taken according to its size, and in proportion to the cases, for which the charge is intended. Large gerbes, of 6 or 8 lbs. require only the coarse sort.

As the brilliancy of the sparks, produced by the iron and steel dust, is a desideratum in the formation of some fire-works, and as this brilliancy depends upon the nature and quality of the metal, it may not be improper to offer some remarks on these subjects.

That iron, when finely divided is capable of producing sparks of fire, is a well known fact; and we see it daily in the operations of the smith, when ignited iron is hammered on the anvil. The scintillation produced by the steel, when struck with a flint, is of the same character. In the latter case, the metal is actually fused, and, when caught on a paper, and examined with a microscope, will appear globular, and partly oxidized. Hence it is, that gunpowder is inflamed by this spark, which is nothing more than highly ignited, and inflamed iron, possessing a temperature more than sufficient to inflame gunpowder.

The effect, therefore, that results from the inflammation of fire-works, in which iron or steel forms a constituent part, is nothing more than a vivid combustion of the metal; and during that process it becomes oxidized, as it does not form an acid with oxygen, like arsenic, antimony, and some other metals.

The combustion of iron or steel may be shown by a very brilliant experiment, that of burning it in oxygen gas. A steel wire, harpsichord wire for instance, formed into a spiral, with a small piece of wood dipped in sulphur, stuck on its end and then set on fire, upon being immediately introduced into a bottle, containing pure oxygen gas, will burn with great brilliancy, emitting a number of sparks or scintillations, which fall like rain. In making the experiment, some sand should be put into the bottle to prevent the sparks from breaking it. This experiment illustrates the rapid combustion of iron, or steel. For the oxygen gas supports the combustion; and while the oxygen is actually taken up by the metal, which becomes oxidized, and therefore increased in weight, in the same manner as it does when inflamed in fire-works, the caloric, the other constituent of oxygen gas, is given out in a free state, and, with the light at the same time evolved, produces the phenomena of combustion.

Many other experiments might be mentioned, in which the same effects take place, and from which the same conclusions may be drawn. But with respect to the _effect_, whether it be dull, brilliant, or very brilliant, depends more on the quality of the metal, than perhaps, on its subsequent mixture with the other materials. Crude iron, usually called cast iron, seems to possess this property in an eminent degree; but in the experiment with oxygen gas, steel is always preferable, as the combustion is more rapid, and the effect more striking. The difference, which we will not attempt to explain, may depend on the _state_, as well as the _proportion_ of carbon, which enters into crude iron, as well as steel. In one case, the combustion ensues in contact with nitre, and in atmospheric air; in the other, in contact only with oxygen gas. Be this as it may, this inference is conclusive, that, in all cases of the combustion of iron in fire-works, the metal itself unites with oxygen, and the result of the combustion is an oxide of iron; and with respect to the carbon, in both instances, it is converted alike into carbonic acid. So that whether the iron receives its oxygen from the nitre, or from the air, or from both, is immaterial, as the products are the same.

When iron is exposed to the atmosphere, it tarnishes, and is gradually changed into a brown or yellow powder, called rust. This change is owing to its combination with oxygen; and its affinity for oxygen is such, that, when the vapour of water is made to pass through an ignited gun-barrel, it is decomposed, the metal becoming oxidized, and the hydrogen, the other constituent of the water, being liberated in the form of gas.

Gun barrels are browned by a process of oxidizement. There are several processes recommended. One of which is, to rub the barrel over with diluted nitric or muriatic acid, and then, to lay it by for a week or two, until a complete coat of rust is formed. A brush, made of iron wire, is then applied; afterwards, oil and wax, and the barrel is finished by rubbing it with a cloth. The gunsmiths in Philadelphia use a mixed solution of sulphate of copper, tincture of the muriate of iron, and sweet spirit of nitre. This they apply by means of a cloth. The object is to form a rust, and to render it permanent on the barrel by hard friction along with wax. When sulphate of copper is employed, metallic copper is precipitated on the barrel. A coat of rust, put on in this manner, prevents effectually the oxidizement of the iron; and in point of utility, and the saving of labour in polishing and keeping muskets in order, the browning of barrels is certainly advantageous in the land service. At sea, in particular, where iron is more readily oxidized, this plan ought always to be adopted. With regard to the use of dragon's blood, it is entirely too temporary in its effect to be depended on. I was informed by an intelligent gunsmith, who followed the practice of browning barrels in Europe, that he has known the _browning_ to remain very perfect for years, and that the best mode of insuring its durability is to use the _steel brush_, which _carries in_, as he expressed it, the rust.

The oxides, which are formed by the union of oxygen with iron, are two; namely, the black and the red; the first being the protoxide, and the last the peroxide. The black oxide, which is formed by the combustion of iron, and by other processes, contains 56 iron + 16 oxygen. The common rust of iron is the peroxide of this metal, combined with carbonic acid. It may be formed by exposing the protosulphate of iron, or green vitriol, in solution, to the atmosphere, and then adding an alkali. This oxide contains more oxygen than the preceding; it consisting of 56 iron + 24 oxygen.

The tempering of cutting instruments, an operation which requires great delicacy and exactness, after that of hardening, is intended to obtain a fine and durable edge; and as this subject may be interesting in a military point of view, we deem the following remarks of use.

The hardening of steel instruments is performed by heating them to a cherry-red, and then immersing them in cold water. The tempering is another process, calculated, as we observed, to obtain a fine and durable edge. This is performed by heating oil to a certain temperature, and plunging the instrument into it, where it remains until the colour appears, indicative of the particular kind of temper which is intended to be given. The experiments of Stoddart, (_Nicholson's Quarto Journal_, iv, 129,) are conclusive on this subject; for his experiments prove, that, between 430° and 450° the instrument assumes a pale yellowish tinge: at 460° the colour is a straw-yellow, and the instrument has the usual temper of pen-knives, razors, and other fine edge tools. The colour gradually deepens as the temperature rises, and at 500° becomes a bright brownish metallic yellow. As the heat increases, the surface is successively yellow, brown, red, and purple, to 580°, when it becomes of a uniform deep blue, like that of watch springs. Before the instrument becomes red-hot, the blue changes to a water colour, which is the last distinguishable colour. These different shades are owing to the oxidizement of the surface of the metal; and the art of ornamenting _sword-blades_, knives, &c. long practised in Sheffield, depends on this principle. The general process is, that an oily composition is used, with which flowers and various ornaments are painted. On the application of the heat required for tempering it, that part which was covered with the composition, is not altered, whereas, the uncovered parts of the blade are changed. These ornaments, when the paint is removed, have the natural colour of polished steel. When steel is heated in hydrogen gas, no appearance of the kind takes place, a fact which shows, that it is owing to the oxidizement of the metal.

Iron is soluble in the acids. By the assistance of water, it is acted upon by sulphuric acid; the metal being oxidized, and the oxide dissolved, while hydrogen gas is evolved. The salt, formed in this case, is the sulphate of iron, green vitriol, or copperas. With muriatic, nitric, acetic and other acids, it forms various salts; and with gallic acid, when the iron is peroxidized, it forms the pergallate of iron, or common writing ink, and also the bases of black dye.

Iron unites with carbon, sulphur and phosphorus. Of the sulphurets, there are two kinds, the protosulphuret and persulphuret. The former is the magnetic pyrites, and the latter, cubic pyrites, from both of which, green vitriol is obtained by decomposition. Pyrites, we may observe, was the original fire-stone, or the _feuer-stein_ of the Germans, which was used in the place of flint. See _Beckman's History of Invention_. Iron also unites with some of the metals, forming alloys. The white iron of the French, (_Fer blanc_,) or tin plate of the English, is found to be any alloy of tin with iron, as well as a covering of tin on iron.

Sheet tin, or tinplate which is necessary in the construction of the apparatus for some fire-works, for canister shot, &c. is made by immersing sheets of iron, previously freed from rust, into melted tin. The number of dippings it undergoes, determines, in some measure, its quality and character.

The union of carbon and iron, forming very important modifications of this metal, is not only interesting in the military art, as concerns the metal for cannon, small arms, and fire-works, but also in relation to the many and highly useful compounds which result.

All the varieties of iron, which are distinguished by artists, under particular names, we may consider under the following heads: namely; cast iron, wrought or soft iron, and steel.

Cast or pig iron is the name of this metal, when first obtained from the ore. The ores of iron are various, and contain a greater or less quantity of iron, which is either combined with oxygen, or found with clay, giving rise to two important classes of iron ore, the calciform and the argillaceous. The reduction of the ore merely requires the presence of charcoal, and occasionally some addition, as limestone, when the clay iron ores are to be reduced. On the application of heat in furnaces, constructed for the purpose, the charcoal unites with the oxygen of the oxide, reducing it to the metallic state, and escapes in the form of carbonic acid; and the lime, if the ore be argillaceous, unites with the clay, forming a kind of glass, which floats on the melted metal. When the iron is suffered to run into moulds, prepared for its reception, it usually takes the name of pig iron.

Manufacturers distinguish cast iron by its colour and other qualities. The _white cast iron_ is hard and brittle, and can neither be filed, bored, nor bent. Gray mottled iron, so called from its colour, is of a granulated texture, softer, and may be cut, bored and turned on the lathe. Cannon are made of this iron. _Black cast iron_ is the most unequal in its texture, but the most fusible.

Cast iron melts at 130° of Wedgwood. Its specific gravity varies from 7.2 to 7.6. It is converted into malleable, usually called soft iron, by a process called refinement. Several modes have been adopted for this purpose. It was formerly done by keeping it in fusion in a bed of charcoal and ashes, and afterwards forging it. The hammering makes the particles of iron approach each other, and expels some impurities.

Among the various improvements for expeditiously and effectually converting crude into malleable iron, the process of Mr. Cort seems to possess advantages. The cast iron is melted in a reverberatory furnace, and the flame of the combustible is made to act upon the melted matter. It is stirred during this operation, by which means, every part is exposed to the air. A lambent blue flame begins to appear in about an hour, and the mass swells. The heat is continued about an hour longer; and, by this time, the iron acquires more consistency, and finally congeals. While still hot, it is next hammered by powerful tilt-hammers. This is called the _puddling_ process.

Iron, obtained in this way, is not however pure; for it contains either some of the other metals, or oxygen, carbon, silicon, or phosphorus.

When small pieces of iron are stratified in a crucible with charcoal powder, and exposed to a strong heat for eight or ten hours, they are converted into steel. Steel is brittle, resists the file, cuts glass, and affords sparks with flint. It loses its hardness by ignition and cooling. It is malleable at a red heat. It melts at 130 degrees of Wedgwood. By being repeatedly ignited in an open vessel, it becomes, by hammering, wrought iron.

Natural steel is that which is formed, by converting the ore first into cast-iron, and exposing it to the action of a strong heat, while the melted scoriæ float on its surface. This steel is inferior to the others. Steel of cementation is formed, on a large scale, by stratifying bars of iron with charcoal, in large earthen troughs or crucibles, the mouths of which are closed with clay. These troughs are put in furnaces, and, in eight or ten days, the process is finished. This is also called blistered steel, on account of the appearance of its surface. The tilted steel is that which is beaten out into small bars by the hammer. When broken, and the pieces again united by welding in a furnace, and made into bars, it is then called German or shear steel.

Cast steel is considered the most valuable of all the varieties; and is used for the manufacture of razors, surgeons' instruments, &c. It is, besides, more fusible than common steel, and for that reason, cannot be welded with iron. It is made by melting the blistered steel, in a close crucible, along with pounded glass, and charcoal powder. It may also be formed by melting together 30 parts of iron, 1 part of charcoal, and 1 part of glass. Equal parts of chalk and clay, put with iron in a crucible, will also produce it.

The Celtiberians in Spain had a singular mode of preparing steel. Diodorus and Plutarch both say, that the iron was buried in the earth, and left in that situation, till the greater part of it was converted into rust. What remained, without being oxidized, was afterwards forged and made into weapons, and particularly swords, with which they could cut asunder bones, shields, and helmets. This process is used in Japan, however improbable it may seem; and Swedenbourg, among the different methods of making steel, has introduced it. Bishop Watson, (_Chemical Essays_ 8vo. i, p. 220,) speaks of the same process. The fact has been verified at Gottingen; for an anvil, which had been buried in the ground for many years, was found to be extremely soft; and a part of it, which appeared in steel-like grains, possessed the properties of steel.

The sabres made in Japan, according to Thunberg, are incomparable. Without hurting the edge, they can be made to cut through a nail at one blow.

The art of hardening steel by immersion in cold water is very old. Homer (_Odyssia_ ix, 301,) says, that, when Ulysses bored out the eye of Polyphemus with a burning stake, it hissed in the same manner as water, when the smith immerses in it a piece of red-hot iron, in order to harden it. Sophocles, Salmasius, Pliny, Justin and others mention the use of water in hardening iron; but the most delicate articles of that metal were not quenched in water, but in oil. As to the opinion of the peculiar virtue of any particular water, for the purpose of hardening iron, which many have believed, it is altogether fallacious, although Vasari asserts, that the archduke Cosmo, in 1555, discovered a water, that would harden instruments, to cut, like the ancient tools, the hardest porphyry. The art of working porphyry, however, was known in every age. Beckman assures us, when treating of the processes of making steel, that the invention and art of converting bar iron into steel, by dipping it into other fused iron, and suffering it to remain there several hours, although ascribed to Reaumur, (_Art de Convertir le Fer en Acier_, p. 145), are mentioned by Agricola, Imperati, and others, as a thing well known and practised in their time.

Pliny, Diamachus, and other ancient writers mention various countries and places, which, in their time, produced excellent steel. The _ferrum Indicum_ and _Sericum_ were the dearest kinds. The former is the same as the _ferrum candidum_, a hundred talents of which were given, as a present, to Alexander in India.

Beckman thinks, that the ancient _ferrum candidum_ is the same kind of steel still common in India, and known under the name of _wootz_; some pieces of which were sent from Bombay in 1795 to the Royal Society. Its silver coloured appearance, when polished, he thinks, may have given rise to the epithet of _candidum_.

Mr. Faraday of the Royal Institution has lately examined wootz, and imitated it very accurately. The experiments may be seen in _Ure's Chemical Dictionary_, article _Iron_. It appears that the presence of silex and alumina distinguishes this kind of steel from the English. Four hundred and sixty grains of wootz gave 0.3 of a grain of silex, and 0.6 of a grain of alumina. It is highly probable, that the much admired sabres of Damascus, are made from this steel.

A small portion of silver, melted with steel, improves the latter very considerably. One part of silver and five hundred parts of steel were melted together, and every part of the alloy formed, when tested, indicated silver. The alloy forged remarkably well, although very hard, and was pronounced to be superior to the very best steel. This excellence is undoubtedly owing to its combination with the silver, however small. The alloy has been repeatedly made, and with the same success. Various cutting tools have been made from it of the best quality. The silver is found to give a mechanical toughness to the steel.

Platinum and steel, equal parts by weight, form a beautiful alloy, which takes a fine polish, and does not tarnish. This alloy is said to make the best speculum. Steel, for edge tools, is improved by this metal. The proportions, which appear to be most proper, are from one to three per cent. An alloy of 10 platinum with 80 of steel, after exposure for many months, had not a speck on its surface. Would not this alloy, as it is not oxidized, be very useful for making points for lightning rods, in lieu of iron, gold, silver, or platinum alone? The experiment is worth a trial; for nothing adds more to the safety of a magazine, or building, against the effect of lightning, than a conductor.

Iron and carbon, it appears, are capable of uniting in different proportions; hence the variety of crude iron, and the different kinds of steel. When the carbon exceeds the iron, as in plumbago, or black lead, it forms a carburet. When the iron exceeds, such compounds are properly speaking sub-carburets; under which name, we may rank all the varieties of cast iron and steel.

The hardness of iron, according to the experiments of Mushet, (_Phil. Mag._ xiii, p. 138), increases with the proportion of charcoal, with which it combines, until the carbon amounts to about 1/60th of the whole mass. This is the maximum, the metal acquiring the colour of silver. More carbon diminishes the hardness, according to its quantity. The difference in iron, whether it be the _cold-short_, or _hot-short_ iron, a matter of some consequence to the workers in this metal, was found to be owing to phosphoric acid in the cold-short, which exists with the iron. But the substance, called _siderum_ by Bergman, is a phosphuret, and not a phosphate of iron.

We have gone into this subject more fully, on account of its importance, and intimate connection with the casting of guns, and the different qualities of iron. In fire-works, it will appear obvious, that the various properties exhibited by iron are owing to the iron and carbon, to the changes which they undergo, to the combustion which necessarily ensues, and to the production of oxide of iron, and carbonic acid gas; effects that invariably take place, whether cast iron or steel be used, provided it is exposed to the action of agents, under the same circumstances and conditions.

_Sec. XLVII. Of Glass._

Glass, in the form of powder or dust, is used in fire-works. The pulverization of glass is easily performed. It may be done in an iron mortar, and passed though fine wire or brass sieves. It is used in the composition for wheels, in water balloons, cones, fire-pumps, slow white fire, &c.

Glass is nothing more than fused silica, made by exposing a mixture of silica and other substances to the action of a violent heat.

The quality of the glass depends on the proportion of silica, and the fluxes which are used in promoting its fusion; for the various kinds of glass, as white glass, green glass, bottle glass, &c. are all, in one respect, the same, though they differ in these particulars.

The glass of Saint-Gobin in France is made by fusing white sand, lime, soda, and broken inferior glass. The white goblet-glass is made of sand, potash, lime, and old glass; the quantity of potash is about fifty per cent. If green, or yellow, the colour is destroyed by the addition of black oxide of manganese; and hence that oxide is named _glass makers' soap_.

The common plate glass, for electrical machines, &c. is formed of sand, crude soda, old glass, and oxide of manganese. The bottle glass, made with the soda of marine plants, consists of sand, soda, common ashes, and old glass. Another bottle glass is made by melting common sand, black or yellow, with soda, wood-ashes, clay, and broken glass. It appears from the use of the substances which enter into, and compose, glass, that its quality is owing to the materials employed. The crystal or flint glass is a finer kind. The substances, with the proportions in which they are used, are the following:

_Parts._
White sand, 100
Red lead, 80 to 85
Calcined potash (pearl-ash,) 35 to 40
Refined nitre, 2 to 3
Black manganese, 0.06

To this composition, there are sometimes added:

_Parts._
White arsenic, 0.05 to 0.1
Crude antimony, 0.05 to 0.1

The specific gravity of this glass is 3.2. Goblets, lustres, &c. are made of it.

Flint glass, according to the English formula, is made of

Purified Lynn sand 100 parts.
Litharge or red lead 60
Purified pearlash 30

To this is added black manganese, to correct the colour, and sometimes nitre and arsenic.

Plate glass is formed of

Pure sand, 43.0 parts.
Dry carbonate of soda, 26.5
Pure quicklime, 4.0
Nitre, 1.5
Broken plate glass, 25.0
------
100.

Crown, or fine window glass, is composed of

Fine sand, 200 lbs.
Best kelp, ground, 330 lbs.

To this is added, if the vitrification is not complete, some muriate of soda. Good glass, according to Pajot des Charmes, may be made by fusing equal parts of carbonate of lime, sand, and sulphate of soda. The glass is clear, solid, and of a pale yellow. Professor Scheweigger found, that the following proportions were the best:

Sand, 100
Dry sulphate of soda, 50
Dry quicklime in powder, 17 to 20
Charcoal, 4

Broad glass is made of a mixture of soap-boilers' waste, kelp, and sand. Two of waste, one of kelp, and one of sand are the proportions generally employed. Common bottle glass is usually made of waste and river sand, to which lime, and clay, and common salt are occasionally added.

The coloured glasses are produced by various metallic oxides. The colour and beauty of precious stones are thus imitated. These colours are communicated by sundry metallic preparations, as the following: The purple powder of Cassius, with oxide of manganese, will give a red or purple according to the proportions used; zaffre, an oxide of cobalt, a blue; a mixture of oxide of cobalt, muriate of silver, or glass of antimony, a green; and oxide of manganese, a violet, &c.

The basis of all artificial precious stones, is composed of what is called glass-paste, a compound of silica, potash, borax, red lead, and sometimes arsenic. These substances are melted together. The glass, which forms the body of the artificial gem, is pulverized, and the colouring substances are blended with it by sifting; and then the whole must be carefully fused, being left on the fire for from 24 to 30 hours, and cooled very slowly. The following proportions are used for this purpose:

_Pastes._ 1. 2. 3. 4.
Rock crystal, 4056 gr. ---- 3456 360
Minium, 6300 ---- 5328 ----
Potash, 2154 1260 1944 1260
Borax, 276 360 216 360
Arsenic, 12 12 6 ----
Ceruse of clichy, -- 8508 ---- 8508
Sand, -- 3600 ---- ----

_Topaz._ No. 1, No. 2.
Very white paste, 1008 3456
Glass of antimony, 43 ----
Cassius purple, 1 ----
Peroxide of iron, (saffron of Mars,) -- 36.

_Ruby._ Paste 2880, oxide of manganese 72.

_Emerald._ Paste 4608, green oxide of copper 42, oxide of
chrome 2.

_Sapphire._ Paste 4608, oxide of cobalt 68, fused for 30
hours.

_Amethyst._ Paste 4608, oxide of manganese 36, oxide of
cobalt 24, purple of Cassius 1.

_Beryl._ Paste 3456, glass of antimony 24, oxide of cobalt
1-1/2.

_Styrian garnet_, or ancient carbuncle. Paste 512, glass of
antimony 256, Cassius purple 2, oxide of manganese 2.

The following recipes are given by M. Lancon:

_Paste._ Litharge 100, white sand 75, potash 10.

_Emerald._ Paste 9216, acetate of copper 72, peroxide of
iron 1.5.

_Amethyst._ Paste 9216, oxide of manganese from 15 to 24,
oxide of cobalt 1.

The ancient coloured glass has been much admired. The art was carried to a very great extent. Even in Pliny's time, the highest price was set upon glass entirely free from colour. He, as well as others, mentions that hyacinths and sapphires were imitated very exactly.

The emperor Adrian received as a present from an Egyptian priest, several glass cups richly ornamented with various coloured glass. Seneca speaks of the knowledge of Democritus in this art. Porta, Neri, and others, in modern times, have treated the subject in a more enlarged manner. Coloured glass was used for ornament; but Pollio relates, that Gallenius punished an impostor for selling to his wife a piece of glass for a jewel. In the _Museum Victorium_ at Rome, are several ancient artificial gems, such as the chrysolite and emerald. What materials the ancients used for colouring glass is not known. Gmelin, however, observes, that it is probable they made use of iron, by which, he adds, not only all the shades of red, violet and yellow, but even a blue colour might be communicated. Cassius discovered the powder which bears his name. He was a physician, and resided at Lubec.[22] This powder was employed by the German artists. While noticing this subject, it may be proper to state, that Libavius (_Alchemy_, 1606,) gives a process for making ruby glass. Neri, (_ars vitraria_ by Kunkel,) was acquainted with the gold-purple and its use. Glauber (_Furnus Philosophicus_, 1648) mentions the use, and gives the preparation of the powder. Kunkel made artificial rubies in great abundance, and a cup of ruby glass for the elector of Cologne. In 1679, he was inspector of the glass houses at Potsdam; and, in perfecting the art, he expended 1600 ducats, which the elector of Brandenburgh gave him for the purpose.

M. Brongniart has lately made many experiments on the subject of staining glass. The colours, however, are the same as we noticed. A green glass may be made by putting on one side of the glass a blue, and on the other a yellow. A black glass may be made by a mixture of blue with the oxides of manganese and iron. Painting on glass is an ancient art. When pieces of old painted glass are examined, they have always on one side a transparent red _varnish_ burnt into them. The moderns, however, excel in this art.

Glass is not acted upon by the acids, except the fluoric or hydrofluoric. Hence the acid of Derbyshire spar, which is a fluate of lime, is used for etching on glass, in the same manner as nitric acid is, on copper. Fluoric acid, a compound of fluorine and hydrogen, is decomposed during this action, and is changed, by the union of its fluorine with silicon, into the silicated fluoric acid.

When a quantity of alkali is used just sufficient to fuse silica, glass is the result; but when the quantity is greater, as three or four to one, the fused mass is soluble in water, and then forms the silicated alkali, or liquor of flints. From this the silica is obtained in a pure state, by the addition of an acid.

Glass, when melted and dropped into water, assumes an oval form, with a slender projection, called a tail. This is called Prince Rupert's drop. If a small part of this tail be broken off, the whole bursts into powder, with a kind of explosion. The Bologna, or philosophical phial, is a small cylindrical vessel of glass, rounded at the bottom, but open at the upper end. It is made thick at the bottom, so as not to be easily broken; but if a pebble be dropped into it, it immediately cracks, and the whole falls into pieces. In both these, (the drop and the bottle,) the glass is unannealed. When the external part of glass is suddenly cooled, the inner part is kept, as it were, contracted. Now annealing, the process of tempering glass in an oven, renders the glass uniformly alike, and capable of sustaining the variations of temperature, without breaking. By a crack or fissure, the internal parts which remained in a state of tension, endeavour to recover the full state of expansion, and consequently the glass is rent asunder.

_Sec. XLVIII. Glue and Isinglass._

Both glue and isinglass are animal products. They are used in fire-works, but always in the state of solution, as vehicles to mix up compositions in order to make them unite, and to preserve them from falling to powder. The quantity, however, is never large, or either would destroy the effect. The proportions are generally prescribed. A solution of glue is employed in the old process for refining saltpetre. See _Nitre_. In making priming paste, isinglass dissolved in brandy is sometimes used.

Glue and isinglass owe their adhesive quality to the presence of gelatin; the most remarkable property of which is, that it unites with, and precipitates the tanning principle from its solution in water. For this reason, the use of oak bark and other astringent substances, in the tanning of leather, is obvious, the gelatin of the hide or skin, uniting with the tannin and forming tanned leather. Gelatin exists in bones, muscles, tendons, ligaments, membranes and skins. Skins, especially those of old animals, furnish the best and strongest glue.

For the preparation of glue, the parings and offals of hides, pelts, and the hoofs and ears of horses, oxen, calves, sheep, &c. are first digested in lime-water to clean them; then steeped in fresh water, which is suffered to run off; and being previously inclosed in a strong linen bag, are boiled in a copper cauldron with pure water. The impurities are removed as they rise. To the solution, alum, or finely powdered lime, is added. It is then strained through baskets and allowed to settle; after which, the clear fluid is again boiled. When it becomes thick, or of a proper consistence, it is poured into moulds or frames, when it concretes into jelly. It is cut into pieces by a spade, and then into thin slices by means of wire, and finally dried on coarse net-work.

The goodness of glue is known by its brittleness, and equal degree of transparency, without black spots. It swells up in cold water, and becomes gelatinous, but does not dissolve. It is a mark of want of _strength_, when glue dissolves in cold water.

Size is also a gelatinous substance, and is colourless and transparent. Eel skins, vellum, parchment, &c. are used in its preparation. They are treated in the same manner as hides. Isinglass, or fish glue, is a finer kind of gelatin, obtained from the air bladder and sounds of different kinds of fish of the _accipenser_ genus; as the _sturio stellatus_, _huso ruthenses_, _&c._ The bladder, when taken from the fish, is washed and stripped of its exterior membrane, and then cut lengthwise and formed into rolls, or cut into strips. Isinglass dissolves in water with more difficulty than glue. A coarser kind of fish glue is made from sea wolves, porpoises, sharks, cuttle fish, the sturgeon, &c. The head, tail, fins, &c. are boiled in water, and the solution evaporated. Isinglass is used for a variety of purposes, as the making of court plaster and size, the clarification of liquors, &c.

Isinglass is almost wholly gelatin. One hundred grains give ninety-eight of soluble matter.

Gelatin constitutes the greater part of the solid parts of animals, such as bone, ligament, muscle, membrane, skin, &c. and is always extracted by boiling them in water. We need hardly remark, that it constitutes the chief part of soup, which owes its nutritive qualities principally to its presence. The portable soup is nothing more than concrete gelatin, with other substances, as spices, salt, &c.; for it contains, in a small compass, the nutritive parts of beef, veal, and other animal substances, from which it may have been prepared.

Besides the use of water for extracting, or otherwise separating, the gelatin from bone, we may separate the phosphate of lime entirely from the latter, (as these two substances constitute the greater part of bone), by the action of dilute muriatic acid, which will dissolve the phosphate of lime, and leave the gelatin.

_Sect. XLIX. Of Wood._

Of the kinds of wood, used for the preparation of coal, for the purpose of gunpowder, those should be preferred, which are light, and will give a tender charcoal. This subject was fully considered under that head.

But our intention, in noticing wood at this time, is, that it is employed in the composition of some fire-works in the form of saw-dusts, or raspings. Its use in fire-works may be considered, 1st, as producing a particular coloured flame: 2dly, as varying the character of the flame, and likewise the degree of the combustion; and 3dly, as communicating an agreeable odour along with other substances; as in odoriferous fire-works. To this, we may add its use in smoke-balls along with nitre and sulphur.

The raspings of wood are sometimes required to be extremely fine. This can only be done by employing sieves of different degrees of fineness. They should be preserved from the action of moisture.

In the composition of the new priming powder, of which chlorate of potassa is the basis, very fine raspings of a particular kind of wood are employed. So is also lycopodium for the same purpose.

By the distillation of wood, as in the process of carbonization in iron cylinders, we obtain some volatile products, the chief of which is the pyroligneous, now called the pyroacetic acid, while the ligneous fibre is converted into coal; but, in the combustion of wood, all the volatile products are expelled, some being consumed in the flame, and others, with some carbon, condensed in the form of soot, while the residue is an ash which furnishes common potash.

Ovid in his Metamorphoses, fable xvi, says--"Adomitis Athamanis aquis accendere lignum narratur; minimos cum luna recessit in orbes." This idea we know is groundless; for it is impossible, that wood, sprinkled with water, whether the waters of Athamanis, or any other, should be kindled when the moon is in the decrease, or at any time of the moon's age.

To prevent the action of fire on wood, marine salt, vitriol, and alum have all been used. Various ways of employing them have been adopted; but they do not absolutely prevent wood taking fire in an active heat. For the same purpose, (_Coll. Academ._ tome xi, p. 487,) a mixture of green vitriol, and quicklime is recommended, by which we form sulphate of lime and oxide of iron. The _Journal de Paris_ of 1781 contains various processes. At Vienna, saline substances are employed.

The combustion of wood is the same, in all cases, in which oxygen is concerned; but the products in some particulars may vary. Hence saw-dust, when mixed with nitrate of potassa, and inflamed, will burn, and produce little or no smoke, because the combustion is rapid and perfect; but when employed with sulphur and nitre, it produces much smoke. Here the oxygen is furnished by the nitre, and carbonic acid gas is formed. The same thing takes place, when a mixture of saw-dust and nitre is used in artificial fire; and, according as the decomposition is more or less rapid, the combustion will be so likewise. The particular applications of saw-dust will be noticed hereafter.

With respect to _lycopodium_ or puff ball and various species of agaric, or the medullary excrescences of trees, which are used in some preparations of artificial fire, we may observe, that the first is confined principally to theatrical fire-works, and the second to the preparation of spunk, or tinder, called also pyrotechnical sponge. See _Pyrotechnical Sponge_.

As to the substance usually called _lightning wood_, found in the hollow of the stumps of trees, and sometimes on the surface, which, from having lost its compactness and other characters of ligneous fibre, is called _rotten_ wood, it is in fact the solid part of the wood in a state of decomposition, in consequence of which, it becomes a _solar phosphorus_. It appears to owe its phosphorescent property, i. e. its power of shining in the dark, to the previous absorption of light, and not, as some have suggested, to the presence of phosphorus, or the emission of any gaseous compound, which contains it. The process of animal putrefaction will produce such appearances, but, in this case, the cause is different.

Turf or peat, a substance found, and employed as fuel, in some countries, and found in boggy situations, is partially decomposed vegetable matter, consisting of a congeries of fibres or roots. But black mould is the result of a decomposition of vegetable substances, in which the ligneous fibre is carbonized, and mixed with earth. The formation of mould, however, is owing more to the decay of leaves &c. (See _Coal_.)

Dr. Shaw (_Travels to the Holy Land_) observes, that when they were either to boil or bake, camel's dung was their common fuel; which, after being exposed a day or two in the sun, catches fire like touch-wood; and burns as light as charcoal.

_Sec. L. Of Linseed Oil._

Linseed, or flaxseed, oil is obtained by expression from flaxseed. It is a thick mucilaginous oil, when first extracted, called _raw_ oil, and in this state, is seldom used. The preparation, it undergoes before it is used as drying oil for mixing with paints, is nothing more than boiling it with litharge, or some oxide of lead, which separates the mucilage, and unites with the oil. By this treatment, it acquires the property of drying with facility, when exposed to the atmosphere.