Chapter II (3)

Coal prepared in the manner above stated, is liable to many foreign admixtures, nor can the process be so well regulated as to produce coal of a uniform quality throughout. The present improved process has many advantages, as experience has proved. It consists in charring the wood in confined vessels, made of iron. These are usually cylindrical, furnished with an iron cover, and placed in furnaces. The pyroacetic, formerly called the pyroligneous, acid, which is formed in the destructive distillation of wood, is caught for use. This acid is useful to the calico printer, dyer, &c. in making their iron liquor, and when purified, is employed in Europe in the place of vinegar, as it is more pungent, and highly concentrated.

When pine and various kinds of wood, which yield turpentine, are carbonized, we obtain tar during the process.

Chaptal informs us, that tar is obtained from the wood of the trunk, branches, and roots of the pine, which are heaped together, covered with turf, and set on fire to produce a close combustion, in the same manner as for making charcoal. The oily parts which are disengaged, trickle down, and are received in a gutter, which serves to convey them to a tub. The most fluid part is sold under the name of huile de cade; and the thicker part is the tar used for paying or painting the parts of shipping and other vessels.

According to the wood submitted to the process of charring, the products are, more or less, various; but in all cases it is only the solid part, or ligneous fibre, that furnishes the coal. By the ordinary process we obtain sundry volatile products, among which are pyroacetic acid and carburetted hydrogen gas.

When wood is carbonized in the usual manner, it yields from 16 to 17 parts of charcoal in the hundred; but when the operation is conducted in close vessels, the product is 28 per cent. a saving of eleven or twelve per cent. By this difference in the quantity, it appears that eleven or twelve per cent. is burnt in the common process.

M. Mollerat was the first who tried the experiment with iron cylinders.

M. Vauquelin (_Annales de Chimie_, tome lxvi, p. 174) has given some observations on the carbonization of wood in close vessels, predicated on a Memoir of M. Mollerat; both of which are interesting. The apparatus used by M. Mollerat is described by Thenard, (_Traité de Chimie_, iii, p. 373,) to be composed of two parts, viz: a furnace with a moveable dome, and a cylindrical kettle, or vessel of iron sufficiently large to contain a cord of wood. It is furnished with a cover and pipe. The pyroacetic acid is collected. Smaller cylinders are preferred, because the wood is ignited more readily and the charcoal is more of a uniform quality.

From 100 parts of the following named woods, Messrs. Allen and Pepys (_Phil. Trans._ 1807) obtained the following proportional parts of charcoal:

Beech 15.00
Mahogany 15.75
Lignum Vitæ 17.25
Oak 17.40
Fir 18.17
Box 20.25

See also the experiments of Mr. Mushet, in the third volume of Tilloch's _Magazine_.

It appears by the _Annales de Chimie_, vol. 66, and the _Retrospect of Discoveries_, vol. vi, p. 100, that three brothers have established at Pellerey, near Nuits, Cote d'Or, a manufactory on a large scale, for making charcoal in close vessels.

The quantity of charcoal they obtained is double that by the usual mode, while it requires only one-eighth part of wood to be consumed in the distillation; it is also better than the common, as a given quantity evaporates one-tenth more water than the other; hence iron masters may obtain twice as much iron from the use of a given quantity of wood; and in addition to this, there is also prepared a number of other articles, of each of which in order.

350 kilogrammes (700 lbs.) of wood, yield 25 or 30 of tar, which retains so much acid that it is soluble in water; but when it is washed, and rendered thick by boiling, for some time, it offers more resistance to water. If mixed with one-fifth of rosin it is rendered equally fit for the use of ships, &c. as the common tar.

Four sorts of vinegar are prepared, all of which are perfectly limpid, which do not, like the common, contain any tartar, malic acid, resinous or extractive matter, nor indeed any mineral acid, lime, copper, or other substances. The simple vinegar marks--2° hydrometer for salts, at 12° centigrade thermo. it is stronger tasted than common vinegar, and produces a disagreeable irritation. The aromatic vinegar is prepared with tarragon, the smell is agreeable, but it has the same fault as the former. The vinous vinegar is formed by adding some alcohol to simple vinegar; it has a very sensible odour of acetic ether; the alcohol softens the flavour in some degree, but the vinegar is still very sharp. The acid, called strong vinegar, is in fact a very good acetic acid at 10-1/2° hydr., it is very white, clear, and sharp, without the usual burnt flavour, and seems to form the basis of the preceding kinds. It can be sold for 8 or 9 francs (7s.) per lb. which is only half the price of that distilled from verdigris. Although not so agreeable to the taste as common vinegar, these new kinds are more elegant to the eye, and do not mother.

The editor of the Retrospect makes the following observations:

The proprietors of this manufactory seem to be perfectly aware of all the several productions which could be prepared from the refuse of their principal object; and we have no doubt but that the substances they procure in this manner will amply compensate them for the use of the capital that must be invested in building the furnaces.

The nature of the vessels in which they distil the wood is not mentioned, but they are probably cast iron retorts, or vessels of a similar nature, in which a distillation _per latus_ takes place. The application, therefore, of lord Dundonald's furnaces for procuring coke to this purpose would be still more advantageous.

A cubic yard of wood yields 100 quarts of acid liquor, besides 50 or 60 lbs. of thick oil.

The method of making charcoal of a _uniform quality_, for which a Mr. Kurtz has taken out a patent, is the following:

A sheet-iron chest, which has a cover that fits it tight, and a pipe, or tube, that descends nearly to the bottom, and coming out from its side above, is fixed in brick work. In this the billets of wood are put. Fire is then made underneath. It is obvious, that the wood is kept at one temperature from its being immersed in vapour, as the vapour cannot escape at the top, but must descend to the bottom, and then proceed up the pipe, by which it is conveyed away. The effect is, that the charring process goes on regularly, and the wood is charred equally. The carbonization is finished when the vapour ceases to appear, and nothing but carburetted hydrogen gas escapes. The charring of bones is performed in iron cylinders, furnished with tubes to receive, and convey away, the impure ammonia.

In the manufacture of powder, particular kinds of wood are selected for carbonization. These are generally, willow, hazle, maple, poplar, linden, buckthorn, or alder, or those which are tender and light, because, as they are less dense, and consequently more friable, they enflame and consume more rapidly: they are known in the arts by the name of _white wood_. When a less sudden effect is to be produced with the gunpowder, and the combustion prolonged, as in some sky-rockets, the charcoal of hard wood is to be preferred, such as the oak, beech, &c. When the wood is gathered, the bark is removed, and the wood exposed to the sun to dry: it is then cut into billets, and charred. The ashes, if any be formed, are to be carefully separated.

In considering the use of charcoal, therefore, for the preparation of gunpowder, we are to direct our inquiries to the choice of wood for carbonization, and the best process for carbonizing it. All light woods, we remarked, as the linden, willow, poplar, &c. furnish the lightest coal, and on that account are preferred. It is remarked, that tender wood, besides making a light, friable, and porous coal, is more combustible than ordinary hard, and more compact wood, and the coal that it furnishes leaves less residue after combustion.

Many experiments have been made with coal prepared from different kinds of wood, with a view of ascertaining the kind best adapted for the manufacture of gunpowder. M. Letort, at the powder mills of Essonne, in France, instituted a number of experiments of this kind. He made gunpowder with the coal of several kinds of wood, and compared its effects by a mortar eprouvette. The result was, that the powder made with the coal of poplar, was the strongest; and the other powder, made with the coal of the linden, willow, &c. was of the same quality throughout. As to the second inquiry, it is hardly necessary to repeat, that for the complete and thorough carbonization of the wood, to produce at the same time coal of a uniform quality, the process of charring in iron cylinders or close vessels, is to be preferred. The point to be attended to is, to bring the wood to a complete state of ignition, and consequently to disengage all the volatile or fluid parts. When the gas (carburetted hydrogen) ceases to appear, it is a criterion that the operation is finished. This gas, it is to be recollected, will come over even after the whole of the wood is completely ignited. The first volatile product is the pyroacetic acid. Some saturate the acid liquor with chalk, and decompose the acetate of lime with sulphate of soda, and separate the acetic acid from the acetate of soda by distillation with sulphuric acid. The acetic acid is then tolerably pure, and may be diluted for use.

It is observed, however, that when charcoal, prepared in iron cylinders, is designed for gunpowder, the last portion of vinegar and tar must be allowed to escape, and the reabsorption of the crude vapours prevented, by cutting off the communication between the interior of the cylinders and the apparatus for condensing the pyroacetic acid, whenever the fire is withdrawn from the furnace. If this precaution be not taken, the gunpowder made with the charcoal would be of inferior quality.

On a large scale, when the object is also to prepare the vinegar of wood, a series of cast-iron cylinders, about four feet diameter, and six feet long, are built horizontally, in brick-work, so that the flame of one furnace may play round about two cylinders. Both ends project a little from the brick-work. One of them has a disc of cast iron well fitted and firmly bolted to it, from the centre of which disc an iron tube about six inches diameter proceeds, and enters at a right angle, the _main_ tube of the refrigeration. The diameter of this tube may be from 9 to 14 inches, according to the number of cylinders. The other end of the cylinder is called the mouth of the retort. This is closed by a disc of iron, smeared round the edge, with clay lute, and secured in its place by wedges. The charge of wood for such a cylinder is about 8 cwt. The hard woods, oak, ash, birch, and beech, are alone used. Fir does not answer. The heat is kept up during the day-time, and the furnace is allowed to cool during the night. Next morning the door is opened, the coal removed, and a new charge of wood is introduced. The average product of crude vinegar is 35 gallons. Its total weight is about 300 lbs. But the residuary charcoal, according to Ure, (_Chemical Dictionary_), from whom we have taken this account, is found to weigh no more than one-fifth of the wood employed. The crude pyroacetic acid is rectified by a second distillation, in a copper still, in the body of which about 20 gallons of viscid tarry matter are left for every 100. Its acid powers are now superior to the best household vinegar in the proportion of 3 to 2. Ure observes, that by distillation, saturation with quicklime, evaporation of the liquid acetate to dryness, and gentle torrefaction, the empyreumatic matter is so completely dissipated, that on decomposing the calcareous salt by sulphuric acid, a pure, perfectly colourless, and grateful vinegar rises in distillation. Pyroacetic acid is said to be a powerful antiseptic. M. Monge, Dr. Jorg, and more lately, Mr. Ramsay, of Glasgow, have made experiments with it. Fish dipped in it have been preserved for many days, and meat treated in the same manner, has also been preserved from putrefaction.

With respect to the pulverization of charcoal, the operation is so exceedingly simple, that we deem it unnecessary to notice it. It is obvious, that mortars, mills, &c. may be used, with fine or coarse sieves. For fire-works, charcoal is frequently pulverized in a leather sack, in the same manner as grained powder is reduced to meal-powder. It may be made either coarse or fine, to answer different purposes, by employing sieves of different kinds. Charcoal may be separated from nitre and sulphur, in gunpowder, by a simple process, which may be seen by referring to the section on gunpowder.

The quantity of carbon in coal, is directly proportionate to the quantity required for the decomposition of nitrate of potassa, a fact necessary to be considered in the theory of the action of charcoal in gunpowder. Thus, Mr. Kirwan found that, 12.709 of carbon are necessary to decompose 100 of nitrate of potassa. It will be easy to deduce the quantity of carbon, in a given weight of coal, from the quantity of nitrate of potassa it is capable of decomposing. The experiment is made very readily by fusing in a crucible, five hundred or more grains of nitre, and when red-hot projecting by degrees the powdered coal on the nitre. When the detonation produced by one projection of coal has ceased, add a new portion till it produces no farther effect.

Charcoal may be made intensely black, resembling ivory black, according to M. Denys-de-Montfort, (_Bibliothèque Physico-Economique_, for March 1815,) by pulverizing it very fine, mixing it with wine lees, and drying the mixture, and then subjecting it to a strong heat in a covered crucible, or other vessel.

_Sec. VII. Of Gunpowder._

Having remarked, that the quality of gunpowder depends upon the purity of the materials, of which it is formed, and that they should be prepared in a state of purity; the subject that will now particularly claim our attention, is the proportions of the ingredients, their mixture, and the final preparation of gunpowder for use. To this, we purpose to add, the theory of its explosive effects, the different modes of proving it, and the experiments necessary to determine the quality of its respective ingredients, on all which we will be as brief as the importance of the subjects will admit. Previously, however, it may be interesting to notice the _history of gunpowder_, the invention of which has so completely changed the art of war.

The history of gunpowder has been fully treated by many writers of eminence; but by none more largely, and, at the same time, more satisfactorily than by the French. Beckman, in his History of Inventions, is full on this subject. Our purpose is not to go into details, as it would enlarge our volume, to the exclusion, perhaps, of other and more important matter. We shall, therefore, confine ourselves to a few facts and observations.

Notwithstanding much has been written on the subject, the original invention of gunpowder seems to be in obscurity. By whom, and at what time it was invented, is a question not fully settled. It is said to have been known in the east from time immemorial, and whatever claim Roger Bacon, who died in 1292, may have had to the discovery, or that he knew the properties of gunpowder, it is certain, that the use of fire-arms was then unknown in Europe.

Professor Beckman, who examined all the authors extant on the origin of gunpowder, is of opinion, that it was invented in India, and brought by the Saracens from Africa to the Europeans, who improved the preparation of it, and employed it in war, as well as for small arms and cannon.

M. Langles, who read a memoir on this subject to the National Institute, in 1798, observes, that the Arabians obtained a knowledge of gunpowder from the Indians, who had been acquainted with it from the earliest periods. The use of it was forbidden in their sacred books, the veidam or vede. It was employed in 690 at the battle near Mecca. As nitre was employed in all probability in the Greek fire, invented about the year 678, it is supposed, that that composition gave rise to the invention of gunpowder.

Various prescriptions, or formulæ, have been given for the preparation of this fire. The oldest is by princess Anna Commena, in which, however, there is only resin, sulphur, and oil. Beckman observes, that the first certain mention of saltpetre will be found in the oldest account of the preparation of gunpowder, which, in his opinion, became known in the thirteenth century, about the same time that the use of the Greek fire, of which there were many kinds, began to be lost. The oldest information on this subject is to be found in the works of Albertus Magnus, and the writings of Roger Bacon. The true recipe for making the Greek fire, and the oldest for gunpowder, were found in a manuscript, preserved in the electoral library at Munich. Various copies of this manuscript were made. Bacon employed this writing, which was mentioned by Jebb, in the preface to his edition, from a copy preserved in the library of Dr. Mead. Whether the writer was Marcus Græcus, is of no moment; for Cardan observes, that the _fire that can be kindled by water_, or rather not extinguished by water, was prepared by Marcus Gracchus.

The former Marcus, mentions two kinds of fire-works; and the composition, which he prescribes for _both_, is two pounds of charcoal, one pound of sulphur, and six pounds of saltpetre, well powdered and mixed together in a stone mortar.

Friar Bacon, who lived three centuries after Græcus, was in possession of the recipe. It was concealed, however, from the people, veiled in mystery. In his treatise _De Secretis Operibus Artis et Naturæ, &c._ the secret of the composition is thus expressed: "sed tamen salispetræ, LURU MOPE CAN URBE et sulphuris; et sic facies tonitrum et corruscationem, si scias artificium." _Luru mope can urbe_, is the anagram for _carbonum pulvere_. Bacon supposes, that it was with a similar composition that Gideon defeated the Midianites, with only three hundred men. Besides the use of gunpowder in the 9th century, in the war between the Tunisians and the Moors, in which the former are said to have employed "certain tubes or barrels, wherewith they threw thunderbolts of fire," the Venetians employed it against the Genoese, and it was reprobated as a manifest contravention of fair warfare.

Peter Mexia, in his "_Various Readings_," relates, that the Moors, being besieged, in 1349, by Alphonso the eleventh, king of Castille, discharged a kind of iron mortars upon them, which made a noise like thunder. This, with the sea-combat between the Tunisians and the Moors, stated on the authority of don Pedro, bishop of Leon, places the invention much earlier than by some writers.

Polydore Virgil ascribes the invention of gunpowder to a chemist, who, having put some of his composition in a mortar, and covered it with a stone, was blown up, in consequence of its accidentally taking fire. The person here alluded to, according to Thevet, was a monk of Friburg, named Constantine Anelzen. Others, as Belleforet, with more probability, hold it to be Bartholodus Schwartz, or the black, who discovered it, as some say, about the year 1320. Du Cange, however, remarks, that there is no mention made of gunpowder in the registers of the chamber of accounts in France, as early as the year 1338. Roger Bacon knew of gunpowder, near one hundred years before Schwartz was born. (See the invention of cannon, in _military fire-works_, fourth part.)

It is certain, that Albert de Bollstædt indicated the constituent parts of gunpowder, when he says, in his _Mirabilis Mundi_, "Ignis volans, accipe libram unam, sulphuris, libras duas, carbonas salicis, libras sex, salis petrosi, quæ tria subtilissime terantur in lapide marmorea; postea aliquid posterius ad libitum in tunica de papyro volante, vel tonitrum faciente ponatur.

"Tunica ad volandum debet esse longa, gracilis, pulvere illo optime plena, ad faciendum vero tonitrum brevis, grossa et semiplena."

Gunpowder was of a much weaker composition than that now in use, or that described by Marcus Græcus. Tartalgia, (_Ques. and Inv._ lib. 3, ques. 5), observes, that, of twenty-three different compositions, used at different times, the first, which was the oldest, contained equal parts of the three ingredients. When guns of modern construction came into use, gunpowder of the present strength was introduced.

The strength of powder depends upon the proportions of the ingredients, they being pure; and Mr. Napier observes, (_Trans. Royal Irish Academy, ii._) that the greatest strength is produced, when the proportions are, nitre, three pounds, charcoal, nine ounces, and sulphur, three ounces. The cannon powder was in meal, and the musket powder in grain.

In the time of Tartalgia, the cannon powder was made of four parts of nitre, one of sulphur, and one of charcoal; and the musket powder of forty-eight parts of nitre, seven parts of sulphur, and eight parts of charcoal; or of eighteen parts of nitre, two parts of sulphur, and three parts of charcoal.

The intimate mixture, therefore, and the determinate proportions of saltpetre, charcoal, and sulphur, form gunpowder; the different qualities of which, depend, as well upon the proportions which are used, as on the purity of the materials, and the accuracy with which they are mixed.

Gunpowder is reckoned to explode at about 600° Fahr; but, if heated to a degree just below that of faint redness, the sulphur will mostly burn off, leaving the nitre and charcoal unaltered.

The saltpetre should be perfectly refined, and entirely free from deliquescent salts; the sulphur as pure as possible, and, for that reason, a preference should be given, to that which is sublimed, or distilled; and the charcoal should be prepared in iron cylinders, as described under that head, from woods, which are light and tender, as the linden, willow, hazle, dogwood, etc.

There is a considerable difference in the proportions used by different nations; but, from the many accurate and conclusive experiments of the French chemists, their formula is certainly the most perfect. In English powder, three-quarters of the composition are nitre, and the other quarter is made up of equal parts of charcoal and sulphur; but sometimes, to seventy-five parts of nitre, fifteen of charcoal is used, adding ten of sulphur. Their government powder is the same for cannon, as for small-arms.

According to a number of experiments, made at Grenille, it was found, that the proportion of saltpetre in gunpowder, must be in a given ratio with the charcoal, so that the latter might effectually decompose it in the act of combustion; and hence the ratio is as 12 of the latter to 75 of the former, and these, with 12 of sulphur, are the proportions generally employed. Ruggeri (_Pyrotechnie Militaire_, p. 91,) gives, as the proportions, 12 parts of saltpetre of the third boiling, 2 parts of charcoal, and 1 part of sulphur. The proportions, used in Sweden, are 75 saltpetre, 9 sulphur, and 16 charcoal; in Poland, 80 saltpetre, 8 sulphur, and 12 charcoal; in Italy, 76 saltpetre, 12 sulphur, and 12 charcoal; in Russia, 70 saltpetre, 11 sulphur, and 18-1/2 charcoal; in Denmark, 80 saltpetre, 10 sulphur, and 10 charcoal; in Holland, 76 saltpetre, 12 sulphur, and 12 charcoal; in Prussia and Austria, 78 saltpetre, 11 sulphur, and 11 charcoal; and in Spain, 77 saltpetre, 11-1/2 sulphur, and 11-1/2 charcoal.

According to Klaproth and Wolff, (_Dictionnaire de Chimie_, translated into French by MM. Lagrange and Vogel), Berlin powder is composed of three-quarters nitre; one-eighth sulphur, and one-eighth charcoal; Chinese powder, of 16 parts nitre, 6 charcoal, and 4 sulphur; Swedish powder, of 75 parts nitre, 16 sulphur, and 9 charcoal; the powder of Lissa, of 80 nitre, 12 sulphur, and 8 charcoal; and English powder, on the authority of Beckman, as follows: Powder for war, 100 parts of nitre, 25 charcoal, and 25 sulphur; musket powder, 100 nitre, 18 sulphur, and 20 charcoal; pistol powder, 100 nitre, 23 sulphur, and 15 charcoal; strong cannon powder, 100 nitre, 20 sulphur, and 24 charcoal; strong musket powder, 100 nitre, 15 sulphur, and 18 charcoal; and strong pistol powder, 100 nitre, 10 sulphur, and 18 charcoal. German powder, for war, is composed, generally, of 0.70 saltpetre, 0.16 charcoal, and 0.14 sulphur. A small portion of gum is sometimes added, to make the grain firmer; but such additions retard the combustion, and the effect.

The addition of gum arabic, however small, must injure the quality of gunpowder, although it has the effect of making the grain firmer, and less liable to fall into meal powder. The grain is also made heavier, and less liable to absorb moisture. M. Proust, in his second memoir on gunpowder, mentions the use of icthyocolla, a fish glue, for the same purpose; and, nevertheless, speaks of some advantages that the gunpowder, prepared with it, possesses.

It is observed by Mr. Coleman, of the Royal Powder Mills of Waltham abbey, that it is not exactly ascertained, whether there is any one proportion, which ought always to be adhered to, and for every purpose. We have no hesitation in believing, for our own part, that the French formula is the most correct, from the numerous experiments made at the royal manufactory at Essone, near Paris.

A very considerable variation is found in the proportions of the ingredients of the powder of different nations and different manufactories. The powder made in England, is the same for cannon as for small arms, the difference being only in the size of the grains; but in France, it appears, that there were formerly six different sorts manufactured; namely, the strong and the weak cannon powder, the strong and the weak musquet powder, and the strong and the weak pistol powder. The following are the proportions in each, though the reason of this nicety of distinction is not very obvious. For the strong cannon powder, the nitre, sulphur, and charcoal were in the proportions of 100 of the first, 25 of the second, and 25 of the third: for the weak cannon powder, 100, 20, and 24: for the strong musket powder, 100, 18, and 20; for the weak, 100, 15, and 18: for the strong pistol powder, 100, 12, and 15; for the weak, 100, 10, and 18.

The Chinese powder appears, by the analysis of Mr. Napier, to be nearly in the proportions of 100 of nitre, 18 of charcoal, and 11 of sulphur. This powder, which was procured from Canton, was large-grained, not very strong, but hard, well coloured, and in very good preservation.

The following proportions are _now_ used in France, for the manufacture of gunpowder for war, for hunting, and for mining.

For war. For the chase. For mining.
Saltpetre, 75.0 78 65.
Charcoal, 12.5 12 15.
Sulphur, 12.5 10 20.

After having made choice of the materials, the nitre being pulverized, is passed through a brass sieve; the sulphur is pulverized by means of a muller, or other contrivance, and also sifted in a bolter; the quantities are then weighed, as well as the charcoal.

The mixing of these substances is performed in a series of mortars, hollowed out of a strong piece of oak wood; and by the aid of pestles or stampers, which are set in motion by machinery and water power, the mixture is thoroughly made. The end of the stampers is usually covered with, and sometimes made of, brass, and the mortars are also, in some powder mills, lined with brass. The mill has generally two rows of mortars and stampers, of ten each. The nitre, sulphur, and charcoal, in proper proportions, are put into each mortar. The charcoal is first introduced into the mortar, being sometimes previously pulverized; then wetted with water, and the pounding is continued for thirty minutes. The nitre and the sulphur are then added, and the whole is stirred with the hand. More water is then added; it is again stirred, and the operation of pounding is continued. The object of adding the water is to prevent the so called volatilization of the ingredients, and to give the mixture the consistency of paste, and at the same time to prevent the explosion of the powder; a circumstance, which must be always guarded against.

After the operation is continued for half an hour, the pounders are stopt, and the powder is then _re-exchanged_ by means of copper or brass ladles; that is to say, the powder of the first mortar is removed, and put into a box, and the contents of the second mortar are put into the first, that of the third is put into the second, that of the fourth into the third, &c. in succession, and in the last, the contents of the first mortar.

We make, in this manner, twelve exchanges, allowing one hour between two, and adding water from time to time, to the mixture, and especially during the summer months. After this, the pounders are again set in motion, for the space of two hours, and the operation is finished. Fourteen hours are generally required to complete the mixture, which is then in the form of paste. It is then granulated. After being partially dried, the graining is performed by passing it through sieves, which are more generally formed of parchment. These sieves are made to work horizontally, and the powder is caught in vessels placed beneath. The size of the grain depends on the sieve; hence, fine grain, or coarse grain powder is thus obtained. In the sieve is usually placed a contrivance to break the masses, and to cause the powder to pass through in grains. After this, the powder is again passed through a second sieve, commonly called a _grainer_, the holes of which are of the same diameter as the powder we wish to obtain. It is then put into another sieve, which permits only the dust to pass, whilst the grain-powder remains. As the powder, however, contains some grains too large, as well as others too small, we may separate the former by a fourth sieve, of a suitable size. The dust and fine grain are carried to the mill, and worked over. The powder for war, and for mining, is dried immediately after the graining.

Formerly, the powder was dried in the open air, by spreading it on tables lined with cloth, or in oblong boxes; but serious inconveniences resulted from it, and, particularly, the powdermakers were obliged to watch the temperature, as well as the state of the atmosphere. When the latter was moist, the _drying_ was suspended.

M. Champy, however, has obviated these inconveniences by a very advantageous process, which consists in raising the temperature of the air to 50 or 60 degrees, and causing it to pass from the chamber in which it is heated, through cloths, on which is spread a bed of powder, of a certain thickness. By this means, large quantities of powder may be dried, in all seasons of the year, in a short time, and at little expense. In whatever manner the _drying_ is performed, there is always more or less _dust_ formed, which, to make the grain of one uniform appearance, must be separated by a hair sieve. This operation is called the _dusting_.

Whether we adopt the plan recommended by M. Champy, or heat the rooms for the drying of powder to a certain temperature, by means of steam pipes, a plan which presents every advantage, or use the old mode, the effect is the same.

The musket, or _hunting powder_, undergoes an operation more than the powder for war, namely, that of glazing, which is performed before it is dried. With the exception of this process, it is made in the same manner, using, however, a finer sieve in granulating it. The glazing has for its object the smoothing, or removing the asperities of the grain, and to prevent its falling into dust, and soiling the hands.

The powder intended for glazing is first exposed an hour to the sun on one cloth, in winter, and between two cloths in summer, in order to dry it more perfectly, which is very necessary before the operation of glazing. For this purpose, it is put into a vessel like a barrel, which is turned horizontally upon its axis, by machinery. This barrel is furnished with bars that go across, intended to augment the friction, or rubbing of the grain, and expedite the process. The barrels are made to turn slowly, to avoid breaking the grain, and at the expiration of eight or twelve hours, the glazing is finished, the powder having acquired a sufficient hardness and polish. After removing the powder, the dust is separated in the usual manner.

_Gunpowder-mills_ are mills, in which powder is prepared, by pounding and beating together the ingredients of which it is composed. They are always worked by water-power, and as there are generally many of them belonging to the same manufactory, one dam of water will furnish a sufficient supply. In the construction of powder-mills, the frame of the house is made very stout, and the roof put on lightly, so that in case of explosion, it may be carried off easily, and thus give vent to the powder, without much injury to the works. The lights, to enable the work to be carried on at night, are placed on the outside of the building, beyond the reach of the powder, and by means of glass windows, the light passes into the mill. It is lamentable, indeed, that so many accidents occur in the operation of making powder. This may take place, as it has to our knowledge, by the friction of the pounders. Their weight, the rapid succession of the blows, and the dryness of the powder, are the principal causes of such accidents, and sometimes by the inattention of the workmen, suffering nails, and the like, to get among the materials. I once witnessed the effect of an explosion of the kind, in the neighbourhood of Frankford, in the vicinity of Philadelphia, at the old and well-known powder mills, at that place. It was produced, in consequence of the friction, by the neglect of the men not adding water at a proper time, to keep the materials moist. The mill in which the explosion took place was not much injured; but the roof, together with the men, were sent a considerable distance. Some of the latter fell into the mill-race, and were much injured. The effect, however, did not stop here; for the fire communicated, strange as it may appear, to some of the other mills, although at some distance, and blew them up. Several explosions have happened at the same mills.

An experiment, made at the same works, by the then proprietor, the father of the late commodore Decatur, by putting the nitre, charcoal, and sulphur, into a barrel, with iron balls covered with lead, which was turned upon its axis, terminated in the same way. It exploded, but no other injury or accident was sustained. On examining the balls, we found, that the lead was entirely worn off, and the explosion must have been owing to the iron. This experiment was performed, in order to find if the mixture could be made in this manner, a plan which was afterwards adopted in France, with success, but brass balls were used. In a series of essays, which I wrote for, and published in, the Aurora, in 1808, on the "_Application of Chemistry to the Arts and Manufactures_," as manufactures are vitally important to the _practical_ independence of this country, I mentioned the subject of gunpowder, and the different modes of preparing it, and among which, the various experiments on this subject.

The machinery, required in gunpowder mills, is exceedingly simple. The power of the water, which may be given by an overshot, or undershot wheel, is communicated to the parts of the mill, which perform the work. Thus it is, that pounders, like the snuff, or plaster-paris mill, are put in motion, by a horizontal shaft, furnished, at different distances, with pieces of wood, which, by the revolution of the shaft, and meeting with the projecting pieces from the pounders, raises them in succession. They fall, then, in the same order of succession, in the respective mortars.

The mortars of the powder-mill, are hollow pieces of wood, capable of holding twenty pounds of paste, composed of the substances before mentioned, which are incorporated by means of the pestle. There are usually twenty-four mortars in each mill, where are made, each day, four hundred and eighty pounds of gunpowder; care being taken, to sprinkle the ingredients with water, from time to time, lest they should take fire. This precaution is absolutely necessary, and if attended to, would prevent many of the explosions, which, unhappily, take place, in the manufacture of powder. The friction must be great, and, therefore, the increase of temperature, occasioned in this manner, ought to be guarded against. This can only be done, by diminishing the time, or number of the blows, or by proportioning the weight of the pestle, and the frequent addition of water. The last is the most certain, and indeed, the water is in some respects, necessary to promote a more intimate mixture of the materials. The observations of M. David, on the use of water in the manufacture of powder, are certainly correct. The pestle is a piece of wood, ten feet high, and four and a half inches broad, armed at the bottom with a round piece of metal. It weighs about sixty pounds.

Having mentioned one cause of the explosion of powder-mills, that of friction produced by the pestle, we find that it has been accounted for on another principle. The _Annales de Chimie_, tome xxxv, mentions some instances of spontaneous combustion in powder mills. It is well known, that charcoal has the property of absorbing several gases, and the observations of Rouppe and Berthollet, on this subject, are conclusive. It is also known, that charcoal, which contains hydrogen, when exposed to atmospheric air, will absorb oxygen, and form water; and during this combination, heat must be generated, by the emission of caloric from the oxygen gas. It is said, then, that in cases of spontaneous combustion, when nitre, sulphur, and charcoal, are mixed together, (unless water be added to prevent it), this effect will ensue, and fire be produced. We know, however, that percussion is one source of heat; and in truth, if that opinion be well founded, percussion itself may facilitate the union of hydrogen, with the oxygen of the air, and necessarily operate as a secondary cause of such explosions.

Another opinion has been advanced by Bartholdi, to account for the spontaneous combustion in powder mills: namely, that charcoal sometimes contains phosphorus, combined with hydrogen, which, by the action of the pestle, is disengaged in the form of gas, and inflames, the moment it comes in contact with the air. Others again suppose, that it sometimes contains pyrophorus.

Pulverizing the charcoal, in the first instance, by itself, and adding water, during its mixture, from time to time, a measure proposed in 1808, by M. David, and now generally adopted, will prevent such accidents; for it appears, they have not occurred in France, since the adoption of this plan. Some remarks on spontaneous combustion, may be seen in the article on _artificial volcanoes_.

M. Sage, (_Journal de Physique_, vol. lxv, p. 423, or _Nicholson's Journal_, vol. xxiii, p. 277), has written on the spontaneous ignition of charcoal, and adduced some facts on the subject; by which it appears, that M. de Caussigni was the first, who observed, that charcoal was capable of being set on fire, by the pressure of mill stones.

Mr. Robin, commissary of the powder mills of Essonne, has given an account, in the _Annales de Chimie_, of the spontaneous inflammation of charcoal, from the black berry bearing alder, that took place the 23d of May, 1801, in the box of the bolter, into which it had been sifted. This charcoal, made two days before, had been ground in the mill, without showing any signs of ignition. The coarse powder, that remained in the bolter, experienced no alteration. The light undulating flame, unextinguishable by water, that appeared on the surface of the sifted charcoal, was of the nature of inflammable gas, which is equally unextinguishable.[17]

The moisture of the atmosphere, of which fresh made charcoal is very greedy, appears to have concurred in the development of the inflammable gas, and the combustion of the charcoal.

It has been observed, that charcoal powdered and laid in large heaps, heats strongly.

Alder charcoal has been seen to take fire in the warehouses, in which it has been stored.

About thirty years ago, M. Sage saw the roof of one of the low wings of the mint set on fire by the spontaneous combustion of a large quantity of charcoal, that had been laid in the garrets.

Mr. Malet, commissary of gunpowder at Pontailler, near Dijon, has seen charcoal take fire under the pestle. He also found, that when pieces of saltpetre and brimstone were put into the charcoal mortar, the explosion took place between the fifth and sixth strokes of the pestle. The weight of the pestles is eighty pounds each, half of this belonging to the box of rounded bell metal, in which they terminate. The pestles are raised only one foot, and make forty-five strokes in a minute.

"In consequence of the precaution now taken," M. Sage observes, "to pound the charcoal, brimstone, and saltpetre separately, no explosions take place; and time is gained in the fabrication, since the paste is made in eight hours, that formerly required four and-twenty.

"Every wooden mortar contains twenty pounds of the mixture, to which two pounds of water are added gradually. The paste is first corned: it is then glazed, that is, the corns are rounded, by subjecting them to the rotary motion of a barrel, through which an axis passes: and lastly, it is dried in the sun, or in a kind of stove.

"Experience has shown, that brimstone is not essential to the preparation of gunpowder; but that which is made without it falls to powder in the air, and will not bear carriage. There is reason to believe, that the brimstone forms a coat on the surface of the powder, and prevents the charcoal from attracting the moisture of the air.

"The goodness of the powder depends on the excellence of the charcoal; and there is but one mode of obtaining this in perfection, which is distillation in close vessels, as practised by the English.

"The charcoal of our powder manufactories is at present prepared in pots, where the wood receives the immediate action of the air, which occasions the charcoal to undergo a particular alteration."

In 1724, (_Coll. Academ._ t. v, p. 413,) M. de Moraler proposed a new mode of mixing the materials for gunpowder. In 1759, M. Musy proposed another method to prevent explosions; and in 1783, the baron de Gumprecht constructed a very ingenious powder mill, a model of which he presented to the king of Poland, whose approbation it received.

There is an account in detail, of the results of the experiments made by MM. Regnier and Pajot Laforet, with different fulminating powders, in the _Archives des Découvertes_, iii, p. 337. These experiments, although interesting in a philosophical view, cannot be of service in the present case. They were made with gunpowder, fulminating silver, fulminating silver and mercury combined, fulminating mercury alone, &c. See also the _Bulletin de la Société d'Encouragement, cahir 65_.

The observations of M. Proust (_Journal de Physique_ for May, 1815) on the mixing of powder, and the consequences that result by following the old process, may be consulted.

The process of manufacturing gunpowder, which we have described, is followed in all, or the greater part of the factories of France. It is, however, tedious, and not exempt from danger. The same process, with some modifications or improvements, is adopted in this country; but of all our gunpowder manufactories, that of the messrs. Dupont of Brandywine, Delaware, has heretofore produced the best powder. Powder, however, equally powerful, has been made in other factories.

The improved process of M. Champy, which, in many respects, is superior to the foregoing, is the following:

1. The nitre, sulphur, and charcoal are first reduced, separately, to very fine powder. This operation is performed in barrels, which are made to turn upon their axis, similar to the barrel-churn, and the substances are introduced gradually. Balls, made of an alloy of copper and tin, are then put in, which by their action reduce the substances to powder.

2. The second operation has for its object, the intimate mixture of the ingredients. The quantities to be mixed are weighed, and put into a drum with a quantity of shot, which is made to revolve during an hour and a quarter. In this manner, three hundred pounds of the mixture are at once operated upon.

3. The mixture is then moistened with water. About fourteen per cent. is added. It is then passed through a sieve made with round holes, and then put into a drum, and submitted for a half hour, to a rotary motion. A number of small round grains are thereby formed, which are separated from the mass by means of a sieve, the holes of which are very small.

4. When a sufficient quantity of these grains are procured, they are put into another drum, of a suitable size, with one and a half times their weight of the original mixture. The drum being put in motion, some water is added, which serves to make them increase in size, by constant rubbing: at the end of a certain time, the whole becomes granulated, or perfectly round. The density of the grains depends on the mixture, and the time they were kept in motion.

5. The powder being thus grained, is passed through sieves, whose holes are of different diameters; and hence it is divided into three kinds: _viz._ cannon powder, musket powder, and fine grained powder.

6. Finally, the powder is dried, and preserved in the usual manner. Its strength is equal to that made by the old process, and is perfectly round.

It may be proper to observe, that this process presents many important and decided advantages. Although, in our description, we have not gone into details, yet the whole operation will be seen at one view. It was practised in France, by its inventor, M. Champy, and, besides being introduced into the United States, it has also been adopted in Prussia.

M. Proust endeavoured to show, that charcoal made of shoots or branches, makes the best powder, and will mix with more facility with the nitre and sulphur; and in employing the ordinary charcoal, two hours beating is necessary to obtain a perfect mixture. The pestles, as Chaptal observes, usually make fifty-five strokes in a minute. Their weight is various; he gives them at eighty pounds.

M. Carney discovered a new process for the fabrication of powder, and although Chaptal himself made some advantageous changes in the process, yet the merit of the discovery he gives entirely to Carney. The process of M. Champy, is in some particulars the same. It will be sufficient, however, to observe, that it is reduced to three heads: _viz._

1. The pulverization, and sifting of the materials;

2. Mixing the materials intimately in vessels similar to casks; and,

3. Giving the mixture the necessary consistence, and the final granulation.

For some details of the process, the reader may consult Chaptal's _Chimie Appliqué aux Arts_, tome iv, p. 145.

Chaptal is of opinion, that Carney's mode of fabricating powder, presents many advantages, among which he considers the facility of its formation, economy in the expense, and the superiority of the powder. In a memoir on the subject, and the formation of powder at Grenelle, Chaptal has described the process very minutely.

Bottée and Riffault reduce the manufacture of gunpowder in France to the following heads:

1. The mixture of the ingredients. This relates to the manner of uniting the nitre, charcoal, and sulphur, the quantity of the composition put into each mortar, and observations respecting the manipulation.

The time required for reducing gunpowder to its proper consistency, and for effecting the mixture is termed by the French, _Battage_. They are usually twenty-four hours, (or eight according to the new mode,) in pounding the materials to make good gunpowder. Supposing the mortar to contain sixteen pounds of composition, it would require the application of the pestle 3500 times each hour.

The order in which they are beaten, and mixed, is as before given, and also the rechanging, or transferring the materials from one mortar to another.

2. _Granulation_, (_Grenage Fr._) This operation consists, as before observed, in passing the mixture through different sized sieves, employing also parchment sieves, and afterwards separating the dust by a fine sieve. The size of the grain depends altogether on the sieve. Hence we have cannon-powder, gunning or musket-powder, pistol-powder, and mining-powder. Superfine powder is the very small grained.

3. _Glazing._ (_Lissage Fr._) This operation takes off the asperities of the grain, renders it hard and less liable to soil the hands, and gives it a kind of lustre. It is only used for fine powder, such as the pistol, and hunting-powder. Cannon powder is never glazed. It is performed in a barrel-shaped vessel, which is made to revolve on its axis, like the ordinary barrel-churn. The quantity of powder glazed in one of these barrels at a time, in France, is 150 kilogrammes.

By the rotary motion, the grains of powder rub against each other, by which each grain becomes smooth, and receives a polish. According to the motion of the barrel, so is the glazing more perfect. This, however, is regular. After the operation, which continues several hours, the dust is separated from the grain by a sieve. The state of the atmosphere influences the process. If dry, the grain receives a better polish; if wet or damp, the operation is retarded, and the gloss imperfect. It has been customary to introduce a very small portion of finely pulverized plumbago, (carburet of iron), in order to give the grain a better polish. But such additions, however small, are obviously injurious to the powder. It is said that it prevents the absorption of moisture. Powder, which has been glazed with black lead, (plumbago), may be known by its peculiar shining lustre, and also by experiment. M. Cagniard Latour made some experiments with glazed powder, which may be seen in the work of Bottée and Riffault, p. 233.

4. _Drying._ (_Séchage. Fr._) The drying of powder is performed in two ways, _viz._ by exposure to the sun, and by exposure to heat in close rooms. The English mode, that of drying by steam pipes, MM. Bottée and Riffault are of opinion, presents many advantages, and particularly that the powder may be dried in all weathers, and with perfect safety.

The mode of drying gunpowder by the vapour of water, (confining it, however, in iron pipes or vessels,) was suggested in 1781, and 1787. See _Mémoires de l'Académie des Sciences de Suede_, 1781, the _Journal des Savants_, 1787, and the _Transactions of the Society of Arts_, vol. xxiv. Mr. Snodgrass, in the last work, gave an account of a method of communicating heat by steam, by using pipes of cast iron, for which the society of arts voted him forty guineas.[18] Chaptal (_Elements de Chimie_) has some judicious remarks on the exsiccation of powder.

The experiment made at Essonne near Paris, by M. Champy, in 1808, on a contrivance for the drying of powder, was satisfactory. This experiment may be seen in page 242 of Bottée and Riffault.

5. Dusting, (_Epoussetage_.) This operation is confined merely to the sifting. It is nothing more than the separation of the dust from the grain, which we have before noticed. The dust is put in the mortars, and worked over.

6. _Barrelling &c._ After the powder has gone through the several operations described, it is then put into barrels, and taken to the magazine.