CHAPTER II.
OF THE SUBSTANCES USED IN THE FORMATION OF FIRE-WORKS.
Sect. I. Of Nitrate of Potassa, or Saltpetre.
Nitrate of potassa, nitre, or saltpetre, is composed, as its name expresses, of nitric acid, and potassa. When pure, it contains, according to Kirwan, potassa 51.8, nitric acid 44, and water 4.2 in the hundred. This salt, when pure, or even mixed with other saline substances, is recognised by placing it on hot coals. Slight detonations, and a hissing noise, with a vivid combustion take place. It is also decomposed by sulphuric acid, and the nitrous vapour is apparent from its smell and colour.
Nitrate of potassa crystallises in six-sided prisms, terminated by six-sided pyramids. Its specific gravity is 1.933. Its taste is sharp and cooling. One part is soluble in seven parts of water, at the temperature of 60 degrees, and in rather less than its own weight of boiling water.
It melts in a strong heat, and by cooling congeals into an opaque mass, called crystal mineral, or sal prunelle.
Exposed to a red heat, it disengages oxygen gas, and passes to the state of a nitrate; at a higher temperature, this is decomposed, and oxygen, azote, and a portion of nitrous acid, which has not been decomposed, are evolved. What remains is potassa. When projected on ignited coals, it burns brilliantly. Detonation also ensues by mixing nitre and charcoal, and throwing the mixture into a red-hot crucible. The residuum is carbonate of potassa. Fourcroy (Système des Connoissances Chimiques, Tome iii, p. 124.) observes, that metals, with nitrate of potassa, will decompose this salt, and produce different coloured flame, extremely brilliant, on which account such substances are used in fire-works.
The alchymists believed, they could obtain, from nitre, a liquor, which would constitute, with other substances, the philosopher's stone. The clyssus of nitre, they imagined, possessed wonderful properties. The decomposition of nitre by charcoal, they effected in two ways, viz. by submitting the mixture to the action of heat in a crucible, or, otherwise in an earthen or iron retort. In the latter case, they collected a fluid, principally water, containing some carbonic acid, and the aeriform product they suffered to escape. The residue they named nitre fixed by charcoal, or, the extemporaneous alkali of nitre. When, in the place of charcoal, a mixture of sulphur and nitre was projected into a red-hot crucible, they obtained a saline substance, to which they gave the name of sal polychrest. This is the same as vitriolated tartar, or sulphate of potassa, and is that salt which is formed in the distillation of nitric acid from nitre, and sulphuric acid. The crystal mineral, of some of the old pharmacopœias, was nothing more than nitrate of potassa fused with a portion of sulphur, and, therefore, a mixed salt, consisting of nitrate and sulphate of potassa.
Nitrate of potassa, distilled with half its weight of sulphuric acid, furnishes nitric acid, or concentrated spirit of nitre. This, diluted with about an equal weight of water, forms the aqua fortis of the shops.
A mixture of nitre and phosphorus, if struck with a hammer, produces a violent detonation. Nitre oxidizes all the metals at a red heat, even gold and platinum.
Nitre and sulphur, thrown into a red-hot crucible, produces an instantaneous combustion, accompanied with a great disengagement of light and heat. Sulphurous acid gas, with sulphuric acid, is produced.
Equal parts of cream of tartar, (supertartrate of potassa,) and nitre, deflagrated in a crucible, form white flux. Two parts of tartar, and one of nitre, treated in the same manner, produce black flux.
Three parts of nitre, one part of sulphur, and one part of sawdust, mixed together, form the powder of fusion.
When three parts of nitre, two parts of potash, and one of sulphur, all previously well dried, are mixed together, the compound is called pulvis fulminans, or, fulminating powder. A small portion of this powder, or as much as will lay on a shilling-piece, put on a shovel, and exposed to heat, will first melt, become liver-coloured, and then explode with great noise. The theory of this explosion is, that a part of the sulphur, and the potassa unite, and form a sulphuret; the sulphuret then decomposes water, and produces sulphuretted hydrogen gas, which appears to be decomposed by the nitric acid; and there results sulphurous acid gas, water, and, as Thenard observes, protoxide of azote, azotic gas, and sulphate of potassa. The loudness of the report depends on the combustion of the whole powder at the same instant, which is secured by the previous fusion it undergoes. Gunpowder, on the contrary, burns in succession, although apparently instantaneous. In using common potash, there is also, as the alkali contains it, carbonic acid, given out in the state of gas. In fact carbonic acid appears to assist the explosive effect of this powder, for when it is prepared with potash, containing little carbonic acid, its detonating power is considerably less.
Nitre likewise enters into the composition of another fulminating powder, invented by Dr. Higgins. Higgins's fulminating powder is composed of three and a half parts of nitre, two parts of crude antimony, and one part of sulphur. This is used in the same manner as the former.
Nitre enters into the composition of gunpowder, which we shall notice under a separate head. The proportions of nitre, sulphur, and charcoal, for the formation of gunpowder, which are considered the best, are, 75 parts of nitre, 121/2 of charcoal, and 121/2 of sulphur.
The new powder of MM. Gengembrie and Bottée, which inflames by percussion, but without explosion, is composed of 21 parts of nitre, 54 parts of chlorate of potassa, 18 parts of sulphur, and 7 parts of lycopodium.
A mixture of nitre and crude antimony projected into a red-hot crucible, produces a deflagration more or less rapid, forming a composition which is used in pharmacy, and medicine.
The quality of saltpetre may be determined by a variety of experiments. Fire-workers judge of its quality by the colour of its flame.
The flame should be white. If it be green or yellow, it is said to be impure.
Nitric acid, obtained by distilling saltpetre and sulphuric acid, has a powerful effect on inflammable substances. If nitric acid, or in preference, the fuming nitrous acid, be poured on spirit of turpentine, especially if it be old, it will inflame. To succeed, however, in this experiment, a small portion of sulphuric acid is usually added to the nitric acid. As this effect is owing to the facility, with which the acid parts with its oxygen to inflammable bodies, other essential oils, besides turpentine, will have the same effect. If the same acid is poured on finely pulverized charcoal, or on lampblack, combustion will also take place. When oils are used, water as well as carbonic acid is produced, and when charcoal or lampblack, carbonic acid alone. There is also a large quantity of carbon, in the former instance, which remains on the plate, or dish. M. Delametherie (Journal de Physique, 1815) has shown, that olive oil may be converted into a substance, resembling, and having many of the properties of, wax, by mixing it with a given proportion of nitric acid. The acid is decomposed, deutoxide of azote is formed, and the oil acquires a hard consistence. A candle made with this artificial wax, he observes, burns with a clear light and without smoke. The experiment with the glace inflammable is on the same principle.
Morey (Silliman's Journal, vol. ii, p. 121.) states a singular experiment, in which nitre is used; viz: If to tallow or linseed oil, a small quantity of saltpetre be added, and the temperature raised to nearly that of the boiling point, the saltpetre appears to be dissolved by the oil; they will evaporate together, and the mixture, or the vapour, will burn, wholly excluded from the atmosphere.
Saltpetre was one of the substances employed by the alchemists. It appears from the memoir of Geoffroy, (Coll. Academ. 1722,) that the object of the alchemists was twofold; the transmutation of metals, and particularly what were denominated the baser metals into the precious, which they pretended to effect by a universal spirit, the grand elixir, the philosopher's stone, &c. and the reduction of metals to their earths. Alchemy was introduced into Europe by the crusaders, and it is remarkable, that, in the reign of Henry IV, an act was passed to make it felony to transmute metals. Mr. Boyle, aware of its absurdity, suggested the propriety of repealing that act, which was done. One of their powders was composed of nitre, cream of tartar, and sulphur.
Preparation. Although nitrate of potassa is generated in abundance, particularly in the East, yet in all countries, where the circumstances are favourable to its production, it is found. It never occurs, native, in very large masses. It is generally found in an efflorescence, on the surface of the soil, or in caverns. It never exists in the soil more than a few yards beneath the surface. We may remark, that native nitre has never been found in pure clay, or pure sand, except in the rock-ore, as it is called, of the western United States. It is often found in caverns, and fissures in calcareous rocks.
In the East Indies, the districts which furnish saltpetre, are swept at certain seasons of the year. This is repeated two or three times a week; for the saltpetre again appears in the same places, in the form of efflorescence.
It is supposed that some countries furnish saltpetre, in consequence of the drought, which continues for some time. At Lima, M. Dombay informs us, there is seldom rain; and the fields, which serve as pasturage for beasts, are so much covered with saltpetre, as to be removed with the spade. There must then be a rapid formation of nitre. M. Talbot observes, that in the meridional provinces of Spain, the earth frequented by animals, contains it, ready formed. When saltpetre became an article of importance, the rulers of Germany, &c. justified themselves in exclusively carrying away the incrustations of walls from private houses, which, when it could be used, became accessorium fundi. Accordingly this regale, as it was called, was extended every where, and was generally unpopular. In 1419, Gunther, archbishop of Magdeburgh, issued the first grant, which was the right of searching saltpetre and boiling it, during a year, in the district of Gibicherstein, for which the person, to whom it was granted, was to pay a barrel of saltpetre, and deliver to the archbishop the remainder at a certain price.
The succeeding archbishop, Frederick, let, in 1460, to a burgher of Halle, all the earth and saltpetre that could be collected in the bailiwick of Gibicherstein, for four years, at the annual rent of a given quantity of refined saltpetre. Bishop Ernest, in 1477, let, for his time, the privilege of collecting saltpetre. In 1544, saltpetre was collected, in the same manner, from the rubbish before the gates of Halle; and in the year following, the magistrates of Halle erected a powder mill, and had saltpetre works. John VI, archbishop of Triers, granted similar privileges in 1560. The saltpetre regale, was long known, and confirmed by a Brandenburgh decree in 1583.
Old walls, and the vicinity of stables, frequently exhibit saltpetre in the state of efflorescence. It was the ancient scrophula contra lapides, represented as a kind of leprosy. For the spontaneous production of nitre, animal and vegetable substances, in a state of decomposition, and the presence of dry atmospheric air are necessary. That lime, and the calcareous carbonates also promote its formation, there can be no doubt.
Notwithstanding the large quantity of saltpetre collected in the East Indies, we are told, that two-thirds of the whole are annually sent into China, and other parts of Asia, to make artificial fire-works. The pyrotechny of the Chinese is said to be very perfect; in variety and beauty, some writers assert they exceed all other nations. There is a natural nitre bed at Apulia, near Naples, which affords 40 per centum of nitre. Pelletier, (Ann. de Chim. tome xxii.) has published an analysis. The cavity of Molfetta is one hundred feet deep, containing grottos or caverns. Nitrate of potassa is found in the interior, in efflorescence or crusts, attached to compact limestone. On removing these efflorescences, others appear. The soil in this cavity is richly impregnated with nitre.
In Switzerland, the farmers extract an abundance of saltpetre from the stalls under their cattle. During the American revolution, when every expedient was resorted to, to obtain a supply of this article, the floors of tobacco houses, &c. were dug up and lixiviated. In the reign of Charles the First, certain patentees were authorised to dig up the floors of all dove-houses, stables, &c. the floors being again laid with mellow earth.
The Ukraine, Podolia, Hungary, Spain, Italy, Peru, and India, furnish more or less of this salt, which is extracted by lixiviating the earths that compose the soil. The springs, in particular districts of Hungary, contain it.
We are informed, (Ann. de Chim. xx. 298,) that, during the second and third years of the French Republic, the government required every district to send two intelligent young persons to Paris. This convocation, consisting of nearly eleven hundred persons, received regular instruction from their first chemists, partly concerning the manufacture of cannon, and partly respecting the manufacture of saltpetre and gunpowder. This body of pupils was afterwards distributed among the different establishments in proportion to their abilities, and saltpetre was soon furnished in abundance.
In the United States, we have an abundant source of saltpetre in the nitre caves of the western country. There is now no occasion for lixiviating the soil of tobacco houses, or of stables, or the refuse of old buildings, the preparation of artificial nitre beds, as adopted in France, or for any other expedient, to furnish a supply of saltpetre; these caverns, which are calcareous, producing it in great abundance. The earth of these caves does not, however, contain pure nitrate of potassa, but generally a mixture of this salt and nitrate of lime, a calcareous nitrate which constitutes the principal part. The latter is changed into nitrate of potassa, as we shall observe more particularly hereafter, by making a lixivium of the earth in the usual manner, and passing it through wood ashes. The alkali, which the latter contains, decomposes the nitrate of lime, by uniting with the nitric acid; hence the fluid, which passes through, is nitrate of potassa or saltpetre. This is evaporated, and suffered to crystallize. It is then the crude, or rough nitre, which is purified, principally by re-solution, and crystallization.
The saltpetre makers, at the caves, have found, that two bushels of ashes, made by burning the dry wood in hollow trees, afford as much alkali as eighteen bushels of ashes obtained from the oak. Notwithstanding the nitre earth contains a mixture of the nitrates of potassa and lime, nitrate of potassa, nearly pure, has been discovered. It is sometimes found in the fissures of sandstone, or among detached fragments. Some of these masses are said to weigh several hundred pounds.
Besides these caverns, which have been accurately described by Dr. Brown, in the Transactions of the American Philosophical Society, (vol. v, vi.) similar caverns have been discovered in Tennessee, and in some parts of Virginia and Maryland. At Hughes' cave near Hagerstown, in Maryland, this salt has also been made.
We are of opinion, that most of the calcareous caverns in the United States, if carefully examined, might be found to contain nitre, or at least, the calcareous nitrate, which is readily converted into nitre by lixiviation with wood ashes, or the addition of a due quantity of potash.
Professor Cleaveland, in noticing the saltpetre caves of the western country, observes, (Elementary Treatise on Mineralogy and Geology,) that one of the most remarkable of these caverns is in Madison county, on Crooked Creek, about sixty miles S. E. from Lexington. This cavern extends entirely through a hill, and affords a convenient passage for horses and wagons. Its length is six hundred and forty-six yards; its breadth is generally about forty feet; and its average height, about ten feet. One bushel of the earth of this cavern, commonly yields from one to two pounds of nitre; and the same salt has been found to exist, at the depth of at least fifteen feet; even the clay, a fact which seems rather remarkable, is impregnated with nitrate of lime. Kentucky also furnishes native nitre under a very different form, and constituting what is there called the rock ore, which is in fact a sand stone, richly impregnated with nitrate of potassa. These sand stones are generally situated at the head of narrow vallies, which traverse the sides of steep hills. They rest on calcareous strata, and sometimes present a front from sixty to one hundred feet high. When broken into small fragments, and thrown into boiling water, the stone soon falls into sand; one bushel of which, by lixiviation and crystallization, frequently yields ten pounds, and sometimes more than twenty pounds of nitrate of potassa. The nitre from these rocks contains little or no nitrate of lime. This account is corroborated by Dr. Brown,[13] to whom our author is indebted for his remarks.
In a memoir in the American Philosophical Transactions by Dr. Brown, then of Lexington Kentucky, we have a description of a nitre cave on Crooked Creek, with the process for extracting the saltpetre. From this memoir, the following extracts are made: The water which percolates through the cave in summer, as the walls and floor are dry in winter, condenses upon the rocks, and the substance thus formed, has the same properties as the salt obtained by lixiviating the earth of the floor. As far as the workmen have dug, the earth is strongly impregnated, every bushel of which, upon an average, furnishes one pound of nitre. The same earth will be again impregnated, if thrown into the cave. What length of time it requires to saturate it, is not known.
The workmen have different modes of forming an opinion with regard to the quantity of nitre, with which the earth may be impregnated. They generally trust to their taste; but it is always considered as a proof of the presence of the nitre, when the impression made one day on the dust by the hand or foot disappears the day following. Where there is a great deal of sand mixed with the dust, it is commonly believed that a small quantity of potash will suffice for the operation. The method of making saltpetre, usually practised in Kentucky, is as follows:
The earth is dug, and carried to hoppers of a very simple construction, which contain about fifty bushels. Cold water is poured on it for some time, and in a day or two, a solution of the salts runs into troughs placed beneath the hoppers. The lixiviation is continued as long as any strength remains in the earth. The liquor is then put into iron kettles, and heated to ebullition; it is afterwards thrown upon a hopper containing wood ashes, through which it is suffered to filtrate. As the alkaline part of the ashes is discharged before the nitrate passes through, the first runnings of this hopper are thrown back, and after some time, the clear solution of nitrate of potassa runs out, mixed with a white curd, which settles at the bottom of the trough. This clear liquor is boiled to the point of crystallization, then settled for a short time, and put into troughs to crystallize, where it remains twenty-four hours; the crystals are then taken out, and the mother water thrown upon the ash hopper, with the next running of the nitrate of lime. When the quantity of the nitrate of lime is too great for the portion of ashes employed, the workmen say their saltpetre is in the grease, and that they do not obtain a due quantity of nitre. If too much ashes are used, they say it is in the ley; and when it is left to settle previous to crystallization, a large quantity of salt will be deposited in the settling troughs, which they call cubic salts. These salts are again thrown upon the ash-hoppers, and are supposed to assist in precipitating the lime from the nitrate of lime, and in the opinion of the workmen are changed into pure saltpetre. To make a hundred pounds of good saltpetre at the great cave, eighteen bushels of oak ashes are necessary; ten of elm, or two of ashes made by burning the dry wood in hollow trees. The earth in some caves does not require half this quantity of wood ashes to decompose the earthy salts.
When wood ashes cannot be obtained in sufficient quantity, they make a lixivium of the earth, and boil it down, which they call thick stuff. This is put in casks, and transported to a place where ashes can be had. When dissolved and passed through wood ashes, it is changed, as in the former process, into saltpetre. Having thus given the Doctor's account, let us inquire, in the next place, into the theory of the process.
The theory is very evident. The mixed nitrate, consisting of variable proportions of nitrate of lime and nitrate of potassa, is extracted from the saltpetre earth by water, which dissolves it. Now, as the affinity of nitric acid for potassa is greater than for lime, and consequently potassa will decompose nitrate of lime, when the lixivium is passed through wood ashes, the potassa they contain will unite with the nitric acid, and the lime be separated, which remains in the hopper. The liquor holds in solution no other salt than nitrate of potassa, provided the quantity of alkali in the wood ashes be sufficient to effect the decomposition;—if more, it will pass through in an uncombined state; and if less, the liquor will contain nitrate of lime. As the alkali contains more or less carbonic acid, the decomposition is not a case of single but of double affinity, in which we form, at the same time, a carbonate of lime.
When the solution is boiled, and set aside in the troughs to crystallize, the nitre will form in a regular manner. The mother water, or the fluid which remains after the crystallization, may contain, from the circumstance before stated, either potash, or undecomposed nitrate of lime—hence it is thrown on the hopper in a subsequent operation.
The nitre, however, as made at the caves, is called rough or crude nitre. Before it is used for the manufacture of gunpowder, and other purposes, it is purified or refined. This operation, which we shall notice more fully hereafter, is nothing more than the separation of all earthy salts, and the alkaline muriates and sulphates; in other words, the conversion of the whole by the separation of foreign substances, into pure nitrate of potassa.
The mode of treating the rock ore, or sand rocks, which contain nitre, is the same as before given. It contains more nitrate of potassa, and therefore requires less potash, and in some instances, the nitre is perfectly pure. The sand rocks often yield twenty or thirty pounds per bushel. A mass of pure nitre, weighing sixteen hundred pounds, has been discovered. Smaller masses have also been found.
The rocks which contain the greatest quantity of nitre are extremely difficult to bore, and are tinged brown or yellow.
Saltpetre makers find it to their interest to work the rock ore in preference to the calcareous nitrate, as it yields more nitre.
It is a fact well known, that foreign saltpetre contains a variety of deliquescent salts, or those salts which attract and absorb moisture and also common salt. The efforts of European refiners are directed to their separation. The saltpetre of the Western country, Dr. Brown assures us, does not contain common salt.
Dr. Brown, in Silliman's Journal, i, p. 147, in a letter to professor Silliman, observes, that there exists a black substance in the clay under the rocks, of a bituminous appearance and smell. This black substance, it appears, accompanies the sand-rock nitre, and is the same as that found in Africa, which also accompanies nitre in that country. Animal matter seems to have existed in the nitre caves of Africa, forming, as Mr. Barrow expresses it, either a roof or covering; no such matter, however, has ever been found in or adjacent to the nitre caves of the Western country.
The observations of Mr. Barrow on the subject of the saltpetre of Africa may be interesting to the reader. He observes, (Southern Africa, p. 291,) that, about twelve miles to the eastward of the wells, (Hepatic Wells), in a kloof of the mountain, we found a considerable quantity of native nitre. It was in a cavern similar to those used by the Bosgesmans for their winter habitations. The under surface of the projecting stratum of calcareous stone, and the sides that supported it, were incrusted with a coating of clear, white saltpetre, that came off in flakes. The fracture resembled that of refined sugar; it burnt completely without leaving any residuum; and if dissolved in water, and thus evaporated, crystals of pure prismatic nitre were obtained. This salt, in the same state, is to be met with under the sand-stone strata of many of the mountains of Africa. There was also in the same cave, running down the sides of the rock, a black substance, that was apparently bituminous. The peasants called it the urine of the das. The dung of this gregarious animal was lying upon the roof of the cavern to the amount of many wagon loads.
The Rev. Mr. Cornelius, in describing a cave in the Cherokee country at Nicojack, the north west angle in the map of Georgia, (Silliman's Journal, vol. i, p. 321,) observes, that it abounds with nitrate of potassa, a circumstance very common to the caves of the Western country, and is found covering the surfaces of fallen rocks, but in more abundance beneath them. There are two kinds; one is called the "clay dirt," the other the "black dirt." The earth, however, contains calcareous nitre, and for that reason an alkaline lixivium is employed. In short, the process employed there is the same as at the other saltpetre caves which we have described. One bushel of the clay dirt yields from three to five pounds of nitre, and the black dirt from seven to ten pounds. It seems also, that the same dirt, if carried back to the cave, will become impregnated with nitre.
Mr. Cornelius remarks, that these caves have been used by the natives as burial places; in one of which he counted a hundred human skulls in the space of twenty feet square; and infers, that, by the decomposition of animal matter, the acid of nitric salts arises, and therefore that this may have occasioned the formation of the nitrates of potassa and lime.
At Corydon, in Indiana, there is a cave, which, according to Stilson's account, contains both nitrate of lime, and nitrate of magnesia. It is not worked.
Kain, in his remarks on the Geology and Mineralogy of East Tennessee, (Silliman's Journal, vol. i, p. 65,) observes, that the numerous caves which have been found in the Cumberland mountains, and other parts of Tennessee have been very productive of nitrate of potassa; and in confirmation of the remarks before made, he adds, in investigating the causes that have given rise to these salts, that wild animals burrow in these caves; that, when pursued by the hunter, they make them the places of their retreat, and probably die there; that the aborigines have made them a place of burial; and that the streams of water, which flow through them, in wet weather, carry with them not only great quantities of leaves, but many other vegetable productions.
Without offering any theory, by which we may account for the formation of nitre, in nitre caves, or in situations which cannot be influenced by the putrefactive process, we may merely remark, that as nitric acid is composed of oxygen and azote, there must be some operation unknown to us, by which the union of these elements takes place. Nascent azote must unite with the base of oxygen gas; but whence, in saltpetre caves, proceeds the azote and the oxygen? It appears that calcareous bodies facilitate the formation of nitre, as they do in artificial nitre beds. The greater part of the nitrous earth is lime; and it also appears, that the same earth, after the extraction of the saltpetre, will again furnish it. We know that lime is a compound of a base called calcium united with oxygen; but in what manner it promotes the union of azote and oxygen, or furnishes either one or the other of these bodies, or perhaps both, is altogether uncertain. Nor can we account for the formation of potash in the native nitre of the nitre caves. In other situations, as for instance where nitrous efflorescence appears on the earth, and in artificial nitre beds, in which animal and vegetable substances are in the act of decomposition by the putrefactive fermentation, we may account for the generation of nitric acid.
It is extremely probable, that the azote of the atmosphere, and oxygen may combine spontaneously, under particular circumstances, in various operations of nature. Azote, it is known, forms with oxygen two gases, a protoxide and deutoxide, and the same elements in other proportions form nitric acid. Some condition, unknown to us, must, as an operating cause, produce this compound. As a condition for its generation, the presence of calcareous and alkaline matter, favours the formation of nitric acid. Of this fact, we have sufficient proof, in the generation of nitre in artificial nitre beds. But, with respect to natural causes, although the facts themselves are conclusive, we know little or nothing.
Atmospheric air is a mixture, or compound, according to some, of two gases, oxygen and azote, with carbonic acid; but the proportion of the latter rarely exceeds two per cent, while the quantity of oxygen is about twenty-two. It is a solvent, as well as a vehicle, and hence may contain water, gaseous fluids, &c. Miasmata, which is contained often in the air, are vapours or effluvia, that affect the human system, and bring on diseases, of which the principal are the intermittent, remittent, and yellow fevers, dysentery and typhus. That of the last is generated in the human body itself. The same, or analogous causes, that produce the formation of nitric acid, may, under other circumstances, cause the formation of miasmata; for moist vegetable and other matter, in some unknown state of decomposition, generates it, and is known to have caused the yellow and other malignant fevers. (See an admirable work on the causes, &c. of the yellow fever in Philadelphia, by Samuel Jackson, M. D. president of the board of health, etc. in reply to the observations of Dr. Hosack.) The contagious virus of the plague, small pox, etc. as it operates in a more limited distance than marsh, or other miasmata, is communicated only in certain localities, and through the intermedium of the atmosphere. As to the chemical nature of miasmata, there can be no doubt that azote, under some form of combination, is one of its component parts, and one of the causes of disease. Is not cyanogen, or carburet of azote, perhaps combined with hydrogen, in the form of hydrocyanic or prussic acid, the substance, or principal substance, which forms the miasmata, that engenders the yellow fever? What compounds may be formed of hydrogen, sulphur, phosphorus, carbon, and azote, so as to produce miasmata, that will act specifically on the system for the production of intermittent, remittent, yellow, typhus, and other fevers?[14] This inquiry, permit me to add, is one of no small moment, as it involves in it a question of great importance relative to the origin of yellow fever. While we thus digress, in noticing the compounds of azote, let us briefly remark, as an indisputable conclusion, that the same causes of malignant disease in the West India islands, operating under similar circumstances in every respect, may engender the same disease in our cities.
The atmosphere is subject to changes of various kinds, and may be considered not only as a solvent, but a repository for different foreign bodies. Electricity, an agent so essential in the economy of nature, has its ends, its uses; and while, no doubt, it unites hydrogen with oxygen, in the most elevated regions of the air, and forms water, it may act under particular circumstances to produce a union of azote and oxygen so as to generate nitric acid. Dr. Priestley, (Transactions of the American Philosophical Society,) detected nitric acid in snow. But of all atmospheric phenomena, the formation of meteorolites, or meteoric stones, is the most wonderful. If they be really formed in the atmosphere, there can be no doubt, that the elementary principles which compose them must exist in it; and that the phenomenon denominated meteoric, in such cases, is no other than the operating cause, by which meteoric stones are generated.[15]
Animal substances furnish azote, as it is one of their constituent parts; and in the act of its separation, by uniting with oxygen, principally furnished by the air, it forms nitric acid; which, attaching itself to the alkali of the vegetable matter, or the lime usually added to nitre beds, or to other salifiable bases, forms either nitrate of potassa, nitrate of lime, or a nitrate of the particular base. The lixiviation of the nitrous substances, and the use of wood ashes, or potash itself, will produce saltpetre.[16]
Brongniart has given the following process for purifying or refining saltpetre: Pulverize the impure nitre, and wash it three times in cold water, in the proportion of 35 lbs. of water, to 100 lbs. of the salt, taking care to pour off the water before another portion is added. These washings separate the greater part of the muriate of soda, and the deliquescent salts, such as nitrate of lime. When thus washed, the nitre is to be dissolved in half its weight boiling water. On cooling, the salt begins to crystallize, and, by agitating the liquid during the process, minute crystals are obtained. These crystals when dried are to be washed in 5 lbs. of cold water for every 100 lbs. of the salt, and then dried in a temperature of forty-five degrees.
In India, where nitrate of lime also occurs, but in situations different from those in the United States, the natives extract the saltpetre by a process similar to that we have described. They refine it by solution in water, evaporation, and crystallization. In France, the potash of commerce is used; and the nitrates which are decomposed, are those principally of lime and magnesia.
According to the analysis of M. Pelletier, and the experiments of professor Vaizo, in 1781, they found the calcareous earth of the cave at Naples, to contain forty or forty-two to the hundred, of nitrate of potassa. (See Annales de Chimie, tome 23.)
In 1792, M. Pickel announced the discovery of native saltpetre, in a quarry in the neighbourhood of Wurtzburgh. M. de la Rochefoucald discovered nitre in the neighbourhood of chalk in France, in the departments of Seine and Oise. MM. Lavoisier and Clouet, made a number of researches with the same view. Since that time, saltpetre, or nitrous earth has been found in several of the departments of France; and it appears reasonable to conclude, that in all situations favourable to the generation of nitre, where the same causes operate, nitre must occur in more or less abundance.
From the rubbish of old buildings, saltpetre is obtained in some quantity. Old plaster is said to give five per cent. The soluble salts it contains, are six in number, viz: nitrate and muriate of lime, nitrate and muriate of magnesia, and nitrate of potassa, and muriate of soda. Now it is obvious, that besides the decomposition of the earthy nitrates, the earthy muriates also are decomposed by the potash, leaving in solution, besides muriate of soda, if it is not decomposed, by the potash, (which has this effect,) muriate, as well as the nitrate of potassa. To refine the saltpetre prepared in this manner, consists in separating the muriates. The proportions, in which these salts are to each other in a hundred parts, are stated by Thenard, (Traité de Chimie, Tome ii, p. 485,) to be ten, nitrate of potassa, seventy, nitrates of lime and magnesia, fifteen, marine salt, and five, muriates of lime and magnesia.
The mode of extracting saltpetre, and the various processes which have been adopted for refining it, in France, and on the continent generally, have but one object,—that of lixiviating the substances which afford it, and subsequently, separating all foreign salts. The best memoir was written by count Chaptal, occupying forty-seven pages in the Annales de Chimie, tome xx. In this he explains the theory at large. In the same work, tome xxiii, there is also a paper by Guyton, and many other memoirs of the same character. In Chaptal's Chimie Appliqué aux Arts, tome iv, p. 119, in Thenard's Traité de Chimie, tome ii, p. 485, and in the Annales de Chimie et de Physique, tome v, p. 173, the subject is ably treated.
We will now give the process of extracting saltpetre from the rubbish of old buildings, principally plaster, as adopted in France. The lixiviation, in the first place, is performed in the following manner: a certain number of casks or tubs, thirty-six for instance, is placed in three ranges. These tubs are pierced laterally near their bottom, by a hole of about half an inch in diameter, and closed with a cork; they are placed above a trough connected with a reservoir. There is put then into each tub a bucket full of the plaster, previously pounded, which is supported in the casks by cross sticks, a certain distance from the hole, so as not to obstruct the passage of the fluid. After this, a bushel of wood ashes is added, and the tubs are then filled with the plaster. Water is then put into the tubs of the first row, and after some time, the stop cocks are turned; water is then put into the tubs of another row, and the lixiviation is continued until the fluid indicates the zero of Beaumé's areometer. The saline waters, which are thus obtained, are divided into three parts, in proportion to their specific gravity, or quantity of salt they contain. The lixivium, of five degrees of the areometer, is known under the name of eaux de cuite. The waters, which are marked between three and five degrees, take the name of eaux de forte; and those below three degrees are called eaux faibles. According as the waters are weak, they are made to run through another range of tubs, in order to saturate them.
When strong and weak solutions are made to pass through the tubs in the same manner, proceeding from the second row to the third, and from the third to the first, the earths plaster, &c. being renewed, the lixiviation is not interrupted.
The lixiviation, it appears, is thus continued; for we obtain, at the same time, weak waters from the second row, the strong waters from the third, and the boiling waters, or those fit to be put into the boilers, from the first.
When a sufficient quantity of the strong solution is obtained, it is put into the copper, or boiler, and evaporated. During the evaporation, there is a scum formed, and sundry earthy substances, in the form of a mud, are deposited. This is usually caught in a vessel placed in the boiler, which is raised from time to time, by means of a rope, moved through a pulley, and fastened to a chain from the handles of the vessel. The solution is concentrated until it indicates the strength of twenty-five degrees of Beaumé's areometer. It is then mixed with the mother water of the preceding boiling, and a concentrated solution of the potash of commerce is added, until the precipitation ceases. The sulphate of potassa may be used for the same purpose, at least to decompose the nitrate of lime; but it must be used in the first instance, and the operation finished in the common way, by the addition of potash. The precipitation being finished, that is to say, the nitrates of lime and magnesia, being transformed into nitrate of potassa, the hot liquor is then carried in a large tub, called the reservoir, and placed on the edge of the boiler. As soon as the insoluble salts, which the solution contains, are deposited there, which takes place immediately, the liquor is drawn off clear by cocks, which are adapted to the tubs, and received into the boiler, previously cleaned. The deposite obtained in the boiling, is washed with a certain quantity of the solution, which becomes clear, and is then mixed with the preceding liquor.
From what has been said, the liquor must contain a great quantity of nitrate of potassa, a small quantity of the salts of lime and magnesia, and all the marine salt contained in the plaster. It is frequently the case, that the liquor contains muriate of potassa, and a small quantity of sulphate of lime. It is, therefore, submitted again to evaporation. When it is at the forty-second degree of concentration, some part of the marine salt separates, which rises to the surface, and is taken off, and drained through an osier basket placed over the boiler. The solution being concentrated to the forty-fifth degree of the hydrometer, it is put into copper vessels, in which, by cooling, it crystallizes. The salt is then separated from the mother water, drained and coarsely bruised, and afterwards washed in a certain quantity of the first boiling. It is now in a state to be delivered to the central administration, under the name of crude saltpetre, or saltpetre of the first boiling.
The crude saltpetre contains about seventy-five per cent of nitrate of potassa. The quality may be determined by treating it with a saturated solution of pure nitrate of potassa, which cannot dissolve any more of the nitrate, but will dissolve any foreign salts. The twenty-five parts of the foreign substances, contained in the crude saltpetre, are composed of a large quantity of marine salt, and of a small portion of muriate of potassa. It is necessary to separate them, and other foreign substances. The operation for this purpose, is called the refining of saltpetre.
The refining of saltpetre is founded principally upon the property, which nitre has, of being more soluble in warm water, than the muriate of soda, and muriate of potassa. Thirty parts of saltpetre, and six parts of water are put into a boiler and the liquor is heated. By this means, there is precipitated a large quantity of marine salt mixed with muriate of potassa. A small quantity of water is added from time to time, to keep the nitre in solution.
When the foreign salt is not fully deposited, the liquor is clarified, and more water is added, sufficient to form ten parts, including that which has already been poured upon it. The liquor is removed, when it is clear and less heated, and put into copper vessels, where it is agitated to prevent crystallization, and to effect the pulverization of the saltpetre.
The saltpetre obtained by this process is not sufficiently pure. The purification is completed by washing it with water saturated with nitre, which dissolves the foreign substances. This washing is completed in a vessel, the bottom of which has been pierced with holes. The nitre, however, is left some hours in contact with the water, when the latter is permitted to run out. When the solution is of the same degree of concentration as that of the saturated water, the operation is finished. The nitre is dried for use.
The old process of refining saltpetre is thus described: Put into a copper, one hundred pounds of nitre, and fourteen gallons of water; let it boil gently half an hour, removing the scum as it forms; then stir it, and before it settles put it into filtering bags, which must be suspended from a rack. Put under the filters glazed earthen pans, to receive the liquor; in which place sticks for the crystals to form on. In two or three days, it will all crystallize.
In some saltpetre works, sulphate of potassa is used with advantage. This salt is furnished in abundance, by the combustion of a mixture of nitre and sulphur, in the manufacture of oil of vitriol. It forms the residue after the combustion. It is likewise produced in the preparation of nitric acid, in the decomposition of nitrate of potassa, by sulphuric acid. It may, therefore, be obtained in quantity, from the oil of vitriol manufacturers, and the aquafortis distillers. It is usually called vitriolated tartar.
It is known that sulphuric acid forms, with lime, an almost insoluble compound, called sulphate of lime, or gypsum; and hence, when sulphate of potassa is mixed with a solution of nitrate of lime, nitrate of potassa is formed, which remains in solution, and sulphate of lime is precipitated. The same effect takes place with all earthy nitrates. For the application of sulphate of potassa, in this way, we are indebted to M. Berard. It might be advantageously employed in decomposing the calcareous nitrate of the nitre-caves of the western country.
M. Longchamp has recommended the use of sulphate of soda, or Glauber's salt, for decomposing the muriate of lime, which exists occasionally in impure nitre. These two salts reciprocally decompose each other; sulphate of lime is precipitated, and muriate of soda remains in solution. The latter is separated by evaporating the nitrous solution.
M. de Saluces (Mémoire de l'Académie des Sciences de Turin, Année, 1805 à 1808,) has proposed a new process for purifying nitre. It consists in filtering it through argillaceous earth, or clay. Although the process is highly spoken of, yet we can see no particular advantage it possesses.
Chaptal observes, that the process mostly in use is that of dissolving 2000 pounds of crude saltpetre in a copper boiler, in 1600 lbs. of water. As the solution is made by the heat, the scum, which forms, is taken off. Twelve ounces of glue, dissolved in ten pints of boiling water, and mixed with four pails full of cold water, are then added. This addition cools the solution. As to the manipulations of the process, they have been given. The principal thing to be attended to, is to separate the marine salt, which is done during the boiling.
To pass this saltpetre through a second operation, in order the more to purify it, it is again dissolved, in the proportion of 2000 pounds, in one-fourth of its weight of water. Heat is applied. The scum is separated; a solution of 8 ounces of glue in one or two pails full of water is then added. After the solution becomes clear, it is suffered to cool, and at the expiration of five days, it will crystallize, or form in a mass, which is then exposed to the air six or eight weeks to become completely dry.
In treating of the formation of nitre in France, Bottée and Riffault (Traité de l'Art de Fabriquer la Poudre à Canon,) consider it under the following heads:
1. The constituent principles of nitre; its generation, and the theories respecting it. In this article, the composition of nitric acid and its union with potassa, and the production of artificial nitre, are taken into view.
2. Nitrous earths, and substances which yield saltpetre. This subject comprehends a view of the substances, which contain saltpetre, as well as those which afford it by nitrification.
3. The preparation of the substances to produce saltpetre. This article relates to the manipulations required for the production of nitre.
4. The manner of lixiviating saltpetre earths. The lixiviation is an important part of the process, however simple it may appear; as upon its accuracy depends the quantity of the product.
5. The treatment of the different waters (lixiviums) with potash, sulphate of potassa, and wood-ashes. This article points out the use of potash in decomposing the earthy salts, such as nitrate of lime; of sulphate of potassa, which converts the nitrate of lime by double decomposition into nitrate of potassa, the sulphate of lime being precipitated; and of wood-ashes, which act in the same manner as potash, as they contain this alkali.
6. The evaporation of saltpetre waters, and the crystallization of nitre. In this article, they consider the separation of foreign alkaline salts, as muriate of soda, and the crystallization of the nitre, to obtain it in a state of purity.
7. The treatment of the mother water of crystallization. This article refers to the manner of using the mother water, in order to obtain more nitre from it, and its employment in lieu of fresh water for other lixiviums.
8. The refining of saltpetre by the old process. They describe here the old process, in which a variety of substances were used to purify the saltpetre, but which is now generally abandoned, or laid aside.
9. The process of refining saltpetre, as adopted in the establishments of the administration. Under this head they give, in detail, the process employed throughout France, as uniform and the same, in every refinery.
10. The manner of proceeding in the examination of various kinds of saltpetre in the magazines of the administration. This article relates to the different modes of examining saltpetre.
11. On the manufacture of potash and pearlash. This subject is important, as potash is an indispensable article in the preparation of saltpetre, and the formation of the alkali may be considered as of primary magnitude in establishments, conducted upon so large a scale as those of France.
It is thus, that a regular system is adopted, by the French government, for the production of saltpetre; and we may add also, for the manufacture of gunpowder, which we notice in that article.
It may be proper to mention some facts, respecting the formation of nitre-beds, and the means adopted, in this way, to obtain saltpetre, and to offer, at the same time, some observations on this mode of obtaining nitre.
The Mémoires de l'Académie des Sciences, 1720, contain the observations of M. Bouldoc, relative to the process of lixiviating saltpetre earths. Lacourt published a pamphlet some years after, entitled, Instruction concernant la Fabrication du Saltpetre. Various dissertations appeared on the same subject. In 1775, the French Academy of Sciences proposed a prize-question, which produced a more thorough investigation. The Memoirs of Thouvenal, of the Chevalier de Lorgna, and of MM. de Chevrand, and Ganivel, were highly approved, some of which took the prize. Chaptal, who has done more, perhaps, than any other person in France, to promote this all-important object, published, in 1794, an excellent dissertation, founded on experiment and observation. This Memoir was published in the Journal des Arts et Manufactures, t. iii, p. 12.
Kirwan (Geological Essays, p. 143,) remarks, that the saline crust, which is found on the walls of the houses of Malta, is owing to the walls being built of fine grained limestone. When wetted with sea-water, it never dries. The crust is nitrate of potassa, nitrate of lime, and muriate of soda, and is some tenths of an inch thick. Under this crust, the stone moulders into dust. When the first falls off, it is succeeded by a second, and so on, until the whole stone is destroyed. This particular effect, however, is attributed to the presence of marine salt.
Mr. Kirwan observes, that, "M. Dolomieu shows, at the end of his Tract on the Lipari Islands, that the atmosphere of Malta, in some seasons, when a south wind blows, is remarkably fouled with mephitic air; and, at other times, when a north wind blows, remarkably pure; and hence, of all others, most fit for the generation of nitrous acid." Mr. Kirwan remarks, "How the alkaline part of the nitre, which is one of the products resulting from the decomposition of this stone, is formed, is as yet mysterious: Is it not from the tartarin lately discovered in clays and many stones?" He adds, after speaking of animal and vegetable decomposition, "I should rather suppose, that the alkali is conveyed into these earths by the putrid air, than newly formed; and the reason is, that tartarin, (potash,) notwithstanding its fixity, is also found in soot; and, in the same manner, may be elevated in putrid exhalations."
Artificial nitre-beds consist of the refuse of animal and vegetable substances, undergoing putrefaction, mixed with calcareous earth; the refuse of old buildings, particularly plaster; earths from the vicinity of inhabited buildings; blood, urine, &c. They are covered, from the rain, by a shed, open at the sides. Cramer, an author of credit, informs us, that he made a little hut, with windows to admit the wind. In this, he put a mixture of garden mould, the rubbish of lime, and putrid animal and vegetable substances. He frequently moistened them with urine, and in a month or two found his composition very rich in saltpetre, yielding at least one-eighth part of its weight. The practice of obtaining nitre from nitre beds, was followed in France and Germany. It is extracted and refined by the process already given.
When oxygen gas is presented to azote at the moment of its liberation, nitric acid is formed. As ammonia is the result of animal putrefaction, or is formed in the process, hydrogen must unite also with azote. The azote is furnished by the animal substances. These facts being known, we are enabled to account for the generation of nitric acid, and, consequently, of the earthy and other nitrates, in artificial nitre beds.
In noticing this subject, it is unnecessary to quote the opinion of Stahl, who believed that there was but one acid in nature, the sulphuric; and that nitric acid was the sulphuric acid, combined with phlogiston, which he affirmed was produced by putrefaction; nor is it necessary to mention the opinion of Lemery, who believed that nitre exists ready formed in animals and vegetables by the processes of vegetation and animalization. The experiments of the French philosophers have put these opinions at rest.
Thouvenal discovered, that nothing more was necessary for the production of nitre than a basis of lime, heat, and open air; so that nitre beds, formed of putrefying animal and vegetable substances, with the conditions thus stated, must produce saltpetre; a fact which experience abundantly justifies.
The process for the formation of nitre, is called nitrification.
Although animal substances, by putrefaction, furnish azote, and nascent azote unites with facility with the oxygen of the atmosphere, by which nitric acid is generated—(hence the spontaneous decomposition of nitre composts)—yet Vauquelin is of opinion, that the presence of calcareous or alkaline substances is indispensable, and that the production of carbonate of ammonia from the animal matter, is another compound, which results from the same decomposition. Ammonia is produced by the union of azote and hydrogen, and carbonic acid by that of carbon and oxygen. He considers then, that the presence of lime, magnesia, potash, &c. determines the union of the azote with oxygen, and of course, the formation of nitric acid; and as this acid unites with one or other of these substances, according to circumstances, we have either nitrate of lime, or of magnesia, or nitrate of potassa. The idea that water is decomposed in the change which animal and vegetable substances undergo, in the process of nitrification, is contrary to observation; for the presence of air in dry situations, is indispensable to the process.
If a compost, made up of animal, vegetable, and calcareous substances, and put in small beds or heaps, and covered with a shed open at both sides, be frequently turned to admit new surfaces to the air, and occasionally moistened with urine, &c.—nitric acid will be generated as the putrefaction goes on. When this process is suffered to proceed until the decomposition is complete, and the beds then lixiviated, the quantity of nitre will be considerable. In all cases, we are to observe, that, as various earthy nitrates are produced, and mostly nitrate of lime, potash, or wood-ashes which contain this alkali, are to be used.
It was long since shown by Glauber, that a vault plastered over with a mixture of lime, wood-ashes, and cows' dung, soon becomes covered with efflorescent nitre; and that, after some months, the materials yield, on lixiviation, a considerable proportion of this salt. M. de Roder, speaking of nitrous walls, observes, that the efflorescence of nitre on them is in consequence of the stone, lime, and sand employed in the building.
What is denominated the saltpetre rot, is an efflorescence observed on the walls of old buildings, and on the ground. Dr. C. F. Gren, professor at Halle, in Saxony, (Principles of Modern Chemistry, vol. ii, p. 128), very justly remarks, that, among the matters capable of corruption, those are the most convenient in making nitre, which contain the greatest portion of azote, of which animal substances are the first; among which he enumerates flesh, blood, skins, excrements of animals, old woolen stuffs, and urine. He also mentions marsh plants, green herbs, mud from streets trodden by cattle, and the ground from marshes or bogs. As a compost he adds, that the ground from church-yards, where corpses have successively, and during a long series of years, undergone corruption, would be the best for artificial nitre beds. On the subject of nitre beds, the reader may consult the Recueil de Mémoires et de Pièces sur la formation et la fabrication du saltpetre, à Paris, 1786, 4to. These remarks on the generation of nitre, although of more ancient date, are confirmed by James and Herman Boerhaave, (Chemistry, &c.) Hoffman, (de Salium Medicorum, et de Præstantissima Nitri Virtute), Stahl, (de Usu Nitri Medico), Neuman, (chemical works), and Lewis, (Materia Medica)—all of whom have written more or less on the formation of saltpetre; to which we may add the observations of Parr, (London Medical Dictionary, vol. ii, p. 24.)
The process for extracting saltpetre from damaged gunpowder is nothing more than putting it into a boiler, and adding water sufficient to cover it. On applying heat, the nitre will be dissolved. If any scum forms, it must be removed. When the solution is effected, pour it on a sufficient number of filters, and collect the fluid which passes through. The residue may be treated with more water, and the whole again filtered. After boiling the solution, set it aside to crystallize. The sulphur may be recovered, by subliming the residue in a temperature not sufficient to inflame it. The charcoal may be used again for the same purpose.
Saltpetre, when properly refined, does not contain any foreign salts, and its purity may be known by a variety of experiments, as follows: make a solution of the salt in distilled water, and filter it through paper. Put a portion of it in a wine glass, and add a solution of carbonate of potassa. To another portion, add a small quantity of muriate, or in preference, nitrate of barytes. To a third portion, add nitrate of silver. If the fluid in the first glass remains clear, without any turbidness, we are to infer the non-existence of earthy salts; if turbid, that it contains lime, or some other earth, either in the form of a nitrate or muriate. The addition of oxalate of potassa to another portion of the solution will show the presence of lime by forming a precipitate, and the addition of carbonate of ammonia, and then of phosphate of soda, will indicate magnesia. If the second glass remains transparent, it shows that neither sulphuric acid, nor any of the sulphates are present. If the fluid in the third glass continues also clear, we infer that none of the muriates exist. These experiments are sufficient to show the purity of saltpetre. It would afford perhaps more satisfaction to institute also the same experiments on other samples of nitre, by which a comparison may be formed of the relative purity of each. To make an analysis of the salt, with the view to determine the proportion of the foreign substances would be altogether unnecessary for common purposes. A regularly defined crystal would, in a great measure, point out its purity. The double refined saltpetre is chemically pure. Artificers determine the purity of nitre by its flame; if white, they call it pure, if yellow, impure.
The same reagents may be used in the examination of gunpowder, as we shall notice hereafter. If a portion of powder be mixed with distilled water, the water will dissolve only the saline substances, leaving the charcoal and sulphur. When the whole is thrown on a filter, the fluid, which passes through, will contain the saltpetre, and foreign salts, if any are present. The same experiments may then be performed with the solution, and the quality of the nitre, of which the gunpowder was made, be determined. Some gunpowder absorbs a large portion of water, which is owing to the presence of deliquescent salts. These salts may be detected by proceeding in the way we have pointed out. The art of refining saltpetre is so well known of late in the United States, especially by the Messrs. Dupont of Brandywine, Delaware, that our gunpowder is of a very superior quality. I have examined various specimens of this saltpetre, and gunpowder made with it, and could not detect any of the sulphates or muriates, either alkaline or earthy. For the manufacture of gunpowder, and fire-works generally, the nitre, it may be observed, cannot be too pure.
In pyrotechny, it is necessary to have the nitre in powder. Pulverizing it in a mortar is a tedious method, if a large quantity is required for use. There is an advantage, likewise, in the mode we will describe; because the saltpetre, besides being extremely fine, is made perfectly dry. Put into a copper kettle, whose bottom must be spherical, fourteen pounds of refined saltpetre, with two quarts or five pints of water. Put the kettle on a slow fire, and if any impurities rise and form a scum, remove them; keep constantly stirring with two large spatulas, till the water evaporates, and the nitre is reduced to a powder. This will be perfectly white, and almost impalpable. If it should boil too fast, remove the kettle, and set it on wet sand, which will also prevent the nitre from adhering to the pot. It should be kept in a dry place. This process of powdering saltpetre is performed on a large scale for the manufacture of gunpowder.
This salt has been recommended in lieu of nitre, for preparing certain fire-works; but we confess, we can see no particular advantage in using it. It has the property of attracting humidity from the air, and on that account is rendered unfit for the manufacture of gunpowder. This salt is composed of nitric acid and soda. It was formerly called cubic nitre. It may be formed, very readily, by saturating nitric acid with soda, and evaporating the solution. It crystallizes in rhomboidal prisms. It may be formed more economically, by mixing together the solutions of nitrate of lime and sulphate of soda, filtering the mixture, and evaporating the filtered liquor. It will be sufficient to observe, that it deliquesces, or absorbs moisture, and in the fire, that its phenomena are the same as those of nitre. It does not melt so readily.
Used in the same proportion as nitre, it will form a gunpowder, which soon, however, spoils by exposure. It will, like nitre, communicate a yellow colour to the flame of alcohol. Experiments were made with this salt, with the view to the fabrication of gunpowder, by MM. Bottée and Riffault. Their conclusions, as we have stated, may be seen in their work on gunpowder. Professor Proust says, that five parts of nitrate of soda, with one of charcoal, and one of sulphur, will burn three times as long as common powder, so as to form an economical composition for fire-works.
The cubic nitre, and the nitrum flammans were known, and so called, by the older chemists. The former we have seen, is the nitrate of soda, and the latter, is a combination of nitric acid and ammonia. Nitrate of soda, consists of 6.75 acid + 3.95 soda.
Nitrate of ammonia possesses the property of exploding; and, when exposed to a temperature of about six hundred degrees, is decomposed, furnishing the nitrous oxide, called also the protoxide of azote, and exhilarating gas, besides water. Nitrate of ammonia is composed of 6.75 acid + 2.13 ammonia + 1.125 water.
Sec. III. Of Chlorate of Potassa.
This salt, formerly called hyperoxymuriate of potassa, is used for sundry preparations, and especially for experimental fire-works. It is prepared by dissolving one part of carbonate of potassa in six parts of water, and saturating it with chlorine, formerly called oxymuriatic acid gas. This operation is usually performed in a Woulfe's apparatus. The gas, as it proceeds from the retort or gas bottle, is brought in contact with, and passes through, the fluid. It is formed by pouring liquid muriatic acid on the black oxide of manganese, or by pouring sulphuric acid on a mixture of muriate of soda, and the black oxide. When the saturation is nearly complete, crystals fall down. These being dissolved in boiling water, and the solution allowed to stand, pure chlorate of potassa will be formed.
This salt is composed of 9.5, chloric acid, and 6 potassa; and chloric acid is formed of 28.87, chlorine, and 32.28, oxygen. It is to the oxygen in the salt, that its particular properties in fire-works are to be ascribed.
This salt is decomposed by all combustible bodies, and detonations generally accompany the decomposition. Hence it is used in a variety of experiments, some of which we will give.
Three parts of the salt and one of sulphur detonate when rubbed in a mortar. The same mixture, struck with a hammer on an anvil, produces a loud explosion. Phosphorus detonates with this salt either by trituration or percussion. The quantity of each should not exceed a grain. Treated in the same manner with almost all the metals, the same effect takes place. Cinnabar, antimony, pyrites, &c. produce the same effect. Nitric acid, poured on a mixture of this salt with phosphorus, produces flashes of fire. A mixture of the chlorate and white sugar, when touched with sulphuric acid, immediately inflames. Hence it is used in the preparation of pocket lights; the mixture being put on a common sulphur match, and immersed in sulphuric acid. The same preparation of sugar and chlorate of potassa, put over a tube used for firing artillery, will set fire to the priming fuse, by dropping on it sulphuric acid. Owing to this effect, M. Gassicourt (Archives des Découvertes), recommended a similar mixture for discharging cannon by means of this acid. As it contains a large quantity of oxygen, that gas may be obtained from it by distillation. Light decomposes it. It should, therefore, be excluded from the light.
As this salt, when mixed with inflammable substances, detonates when struck with a hammer, it has been used for the purpose of inflaming gunpowder without the use of the flint and steel. There are several formulæ given for the purpose. We remarked, when treating of the general theory of fire-works, that the Rev. Alexander Forsyth discovered a new kind of gunpowder, which inflames merely by percussion; that the gun-lock, which he contrived, was calculated for firing cannon, as well as musquetry; that it was so contrived as to hold forty primings of such powder; and that the act of raising the cock primes the piece. In his composition, each charge of priming contains no more than one-eighth of a grain of chlorate of potassa. Since that period, it appears, that the lock, as well as the powder, has been improved, although neither of them is in general use. Thenard, (Traité de Chimie, tome ii, p. 559, troisième édition), has given a formula for preparing a priming powder of this salt, adapted to the new lock, which is made by mixing it with 0.55 of nitrate of potassa, 0.33 of sulphur, 0.17 of the raspings of peach-wood passed through a fine sieve, and 0.17 of lycopodium, or puffball. (See Inflammable Powder.)
This salt also produces powerful effects with charcoal and sulphur. Three parts of it, with half a part of sulphur, and half a part of charcoal powder, produce most violent explosions. Two persons, in 1788, lost their lives by it. If this mixture be thrown into concentrated sulphuric acid, a brilliant flame is produced. Such mixtures, we are informed, will explode spontaneously. It should not, for that reason, be kept prepared. Chlorate of potassa has been used in the place of nitre, for the manufacture of gunpowder, in consequence of its decomposition by charcoal. From its explosive effects, M. Berthollet was induced to propose it as a substitute for nitre. The proportions used by Chaptal, (Chimie Appliqué aux Arts, tome iv, p. 198), are six parts of chlorate of potassa, one of sulphur, and one of charcoal. They are to be mixed in a marble mortar with a wooden pestle. The first experiment was made at Essone, in France, in 1788. No sooner, however, had the workmen begun to triturate the mixture, than it exploded with violence, and killed two persons.
The force of this gunpowder is greater than that of the common sort; but the danger of preparing it, and even of using it, is so great, that these circumstances will always prevent its introduction. A salt, containing so much oxygen, and so loosely combined, that even the slightest friction, in contact with inflammable bodies, will separate it, must, of necessity, prevent its use in that way.
The experiments, which were made at the arsenal at Paris, on the 27th of April, 1793, comparing the effects of muriated powder, and the superfine common powder, have given us the following results:
1st. By the eprouvette of Darcy, consisting of a cannon, which, being suspended to the extremity of a bar of iron, described by its recoil an arc, of which the degrees can be measured.
| Recoil. | |||
| 2 drachms | muriatic powder, | 15 deg. | 2/20 |
| 2 —— | do do moistened, | 14 — | 1/20 |
| 2 —— | common powder, | 10 — | 7/20 |
| 2 —— | common powder, | 10 — | 1/20 |
| 3 —— | muriatic powder, | 20 — | 9/20 |
| 3 —— | common powder, | 16 — | 6/20 |