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The following is taken from Chamber's Library of Universal Knowledge.*
"GUNPOWDER a well known explosive mixture composed of sulphur, niter and charcoal. Of use in several trades, its principal employment is in the discharge, for war or sport, of projectiles from fire arms, and in the processes of blasting during mining or quarrying. The history of gunpowder has been already given under fire-arms (q.v.), and it will therefore be only necessary now to consider the chemical action which takes place when the powder is ignited, and then to proceed to a short description of the manufacture.
Extreme care is requisite in securing the purity of the ingredients entering into the composition of gunpowder. The principal impurity of niter or saltpeter is chloride of sodium, or common salt, which, in consequence of its tendency to absorb moisture from the atmosphere, would have a very injurious action on gunpowder by weakening its power. The details of the process of purification of the niter would be out of place in this article. The sulphur may be purified either by fusion (where the heavier impurities sink and the lighter ones may be removed by skimming) or by distillation. The preparation of the charcoal is a most important point. It should be light and porous, should yield a very small amount of ash, especially of carbonate of potash and other deliquescent salts and should contain little moisture. The woods yielding the best charcoal for gunpowder are black alder, poplar, spindle-tree willow and dogwood, the last named giving off the largest volume of gas when ignited with a given weight of niter, and being on that account especially used for rifle powder.
A vast number of experiments have been made at different times, and by different nations, to discover the proportions of niter; sulphur, and charcoal best adapted for the production of different kinds of gunpowder; and upon the whole there has been great uniformity in the results, as may be seen from the following table of the percentage composition of the powder of different nations:
Kinds of Powder Charcoal Sulphur Niter Authority
Austrian war powder 13.1 11.3 75.6 Linck.
English (Waltham Abbey)
war powder 13.7 10.1 76.2 Ure.
Russian war powder 17.7 11.7 70.6 Meyer.
Italian sporting powder 18.2 8.6 73.2 Prechtl.
Chinese gunpowder 23.1 15.4 61.5 Prechtl.
Note: Chem Reaction 13.3 11.9 74.8 Chambers
The chemical processes which occur in the ignition of gunpowder are commonly described as follows: When the powder is ignited, the oxygen of the niter combines with the charcoal or carbon to form carbonic acid, the potassium combines the sulphur to form sulphide (or sulphuret) of potassium, and the nitrogen is liberated: the reaction being shown in the equation KO,NO5+ S + 3C = 3CO2 + N +KS. Powder consisting of one equivalent each of niter and sulphur and three equivalents of carbon would contain 74.8 percent of niter, 11.9 percent of sulphur, and 13.3 percent of charcoal which approximates very closely to the Austrian powder in the above table. It is easily shown that one volume of such powder would yield 296 volumes of mixed carbonic acid and nitrogen gases, after the ordinary reduction for temperature and pressure, although from the intense heat developed at the moment of explosion the actual dilatation amounts to at least 1500 times the volume of the powder employed. The only solid residue, supposing the equation to represent the true reaction, is sulphide of potassium (KS) and part of this is volatilized by the heat of the explosion, causing the whitish smoke by its combustion, while the part that is not burned gives the peculiar odor to the washings of the gun-barrel.
If a larger proportion of charcoal is added, more or less carbonic oxide gas is generated as a product of combustion. Blasting powder is so composed that, theoretically, it should yield on explosion a mixture of carbonic oxide and carbonic acid gases, and leave a residue of bisulphide of potassium; the reaction being expressed by the equation: KO,NO5+ 2S+4C = 2CO2 + N + KS2 A powder composed according to this formula would contain 64.4 per cent of niter, 20.4 per cent of sulphur, and 15.2 per cent of carbon; and the proportions actually employed are 65, 20, and 15, respectively.
Recent investigations of Bunsen and Schischkoff (Poggendorff's Annalen, Bd. 102, p.321) show that in reality the chemical reactions are very far from being as simple as those given in the preceding paragraphs; the solid residue consisting of various compounds of potassium (sulphate of potash being in the greatest quantity), with portions of niter and carbon.
The ignition of gunpowder must be distinguished from combustion. The powder is ignited when a portion of it begins to develop light and heat; this in granulated gunpowder communicates from grain to grain with the utmost rapidity; but still, it is important to bear in mind, by successive ignitions. Combustion means the final and total decomposition of each grain separately, and the complete liberation of its component gases. In gunpowder these phenomena follow each other so rapidly, that, unless the mass is spread over a considerable space, they appear simultaneous. The heat spread around by each grain during its combustion suffices to ignite all other grains within a sphere of six times its own diameter. This serves to account for the almost instantaneous communication of the flame throughout the whole quantity exposed. The granulation of gunpowder has a great influence on the rapidity of its ignition; the larger the grain, the more rapid is the ignition, but the slower the combustion. On the other hand, small-grained powder ignites more slowly, and burns with greater speed. When mealed or finely powdered gunpowder is employed, it readily inflames, from the presence of the ordinary ingredients; but there being no interstices, the conflagration spreads but slowly, and therefore the decomposition is proportionately retarded. It thus happens that mealed powder exhibits less explosive power and less rapidity of combustion the closer it is pressed together, a circumstance taken into account in the manufacture of fireworks.
In rifled guns and muskets, where it is desired that the projectile should expand to the shape of the grooves, it is obviously best to have a powder which, by very rapid ignition, creates the utmost sudden expansion, and which, by continued combustion, maintains an increasing degree of heat, which shall further augment the explosive force of the gasses evolved up to the period of time at which the projectile is driven from the muzzle of the weapon. With this object, large-grained powder is clearly the most suitable, although a contrary view has been long accepted; and that to so great an extent, that some among the recent inventors of rifled arms have had to complain that the only gunpowder they could obtain has been far too good for their purposes.
Process of Manufacture --
The three ingredients being taken to separate mills, are reduced by successive grindings to impalpable powder. The several materials are then taken to the mixing-house, where they are weighed out into their respective proportions. The charcoal is spread in a trough, and the sulphur and niter being sifted upon it, the whole are incorporated, though imperfectly, by the hands. The next process is in the powder-mill, where the mixture is ground between millstones, and thoroughly incorporated in a wet state. So dangerous is this part of the manufacture, that makers are forbidden to grind more than 42 lbs. in the same house at one time; all the bearings of the machinery are of copper, lest heat should be generated by friction. According to the quality intended is the time during which this trituration is continued, from one hour to six being that usually employed, and three hours the period in the government factory. The powder, completely pulverized and caked by the moisture and the pressure, leaves the mill in small lumps, called mill-cake. This mill-cake is then spread between copper plates in layers about 3 in. thick, and is subjected to an immense pressure either by a screw-capstan or by a hydraulic engine.
The next operation is graining, a process to which, as already explained, gunpowder owes its rapidity of ignition, and its consequent explosive powder. This is performed by forcing the mill-cake through minute holes in a circular parchment sieve, the sieve being kept by mechanism in rapid revolution. The grains thus formed are, however, of very various sizes; and that the gunpowder should be homogeneous, it is necessary that they should be sorted into the several sizes. This is done by intervention of a series of sieves of different degrees of fineness.
Since the introduction of the immense modern cannon, it has been found necessary to make powder with very large grain, even larger than hazel nuts, this is called pebble powder, and is now in general use.
The last processes are drying, glazing, and freeing from dust. The first is effected by heating the powder to a point sufficient to drive off moisture; the second, by the friction of the grains together in a revolving cylinder; the third, by the centrifugal action caused by the powder being twisted round at great speed in a gauze cylinder, when the dust (formed in the polishing) flies off the gauze, and the bright grains remain as finished gunpowder.
This is the modern system, a system involving considerable personal risk at every stage; for the fine dust becomes so diffused through the atmosphere in the mills that the slightest spark would blow the whole into the air in a moment. The early process of manufacture was, however, more dangerous. What with the stirring, and pounding, and spirit** (which our forefathers used instead of water, in the idea that a strong fluid would impart strength to the mixture.) It was probably to the impurity alone of the materials that the operators were indebted for not being blown to pieces.
The following are the chief properties of gunpowder. Good powder should be perfectly uniform in texture, and should not present any light specks or glittering points. The grains should be sufficiently hard not to be easily crushed by the fingers, or to soil them, or a piece of paper by mere contact. If inflamed on white paper, it should blacken it but slightly, should on no account set fire to it, and should leave only a very slight residue. The temperature at which it explodes has been carefully studied by Violette, who obtained the following results.
Angular grains Pulverized
Blasting powder explodes at: 518degrees 509 degrees
War powder explodes at: 528.5 519.5
Sporting powder, fine, explodes at: 536 514.5
Sporting powder, extra fine: 603 518
The most combustible of these powders was the one containing the largest amount of sulphur, which is the ingredient most ready to enter into ignition. When gunpowder is exposed to a heat of 500 degrees, the whole of its moisture is expelled, and the niter and sulphur are reduced to the fluid form. On cooling, such powder is found to be intensely black, and the grain has become indurate, and no longer able to imbibe moisture. Powder is inflamed by any burning substance, by red-hot metal, by the electric spark, or by the violent concussion even by comparatively soft bodies, if it be sufficiently powerful. For example, powder place upon lead, or even on wood, may be ignited by the shock of a leaden bullet fired at it. Its specific gravity is about 1.8.
The nature of the residue which is left after the ignition of the powder has been already explained. The fouling caused by this residue is avoided to some extent by the lubrication of the barrel with a little fatty matter.
Gunpowder factory--
Royal, at Waltham abbey, an establishment in which much of the gunpowder
required for the British army and navy is made. It is built on all the
newest and most approved principles to insure safety, economy, and
efficiency; but even here accidents occasionally happen in this dangerous
manufacture, and roofs and sides, purposely left loose so as to offer but
little resistance, are scattered to the winds. Between the different mills
mud-banks are raised, and groves of trees thickly planted, to lessen the
concussion, and, as far as possible, limit the catastrophe when one house is
unfortunately exploded. A series of raised canals, at the same time, is
ready to flood the whole place, or to afford a precarious shelter to the men
employed if time be available to make use of it....'
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*The above description of gunpowder manufacture is from Chamber's Library of Universal Knowledge. A reprint of the last (1880) Edinburgh and London Edition of Chamber's Encyclopedia. In fifteen volumes. This reprint was published by the American Book Exchange in New York in 1880. Copious Additions were made by American Editors who used the technique of regular type to draw attention to these from these additions as opposed to Chamber's edition in which bold-faced type is used for the headings. There were no changes, as the editor stated; Scrupulous care has been taken not to mutilate or modify the original text of the edition of 18-0, no changes have been made except such verbal alterations as are required by the omission of the woodcuts.'
Gunpowder manufacture in the United States dates from the initial settling of the colonies. Guano from caves was a ready source of the nitrate (nitre or niter) that when removed from the sodium salt by use of wood ash became potassium nitrate. It has been reported that during the War between the States, night soil or honey pot contents were saved and used as a source of organic nitrogen that could be converted to nitrate, probably by a means not unlike that described in fruit of the stable.
The chemical works of DuPont at Hopewell, Virginia have long since been abandoned but evidence of their production of explosives can be easily seen by the widely separated structures in which gunpowder was produced (Not unlike those described in the Chamber's Encyclopedia.)
Another web site that may be of interest is:
The site provides a means of making saltpeter from manure and urine based on
a recipe from Birringucchio (Pyrotechnia, 1540).
>From An Introduction To The Study of Chemistry by Ira Remsen, which was published in 1904 by Henry Holt and Company comes the following description of the production of potassium nitrate. "When refuse animal matter is left to undergo decomposition in the presence of bases, nitrates are always the end products. Advantage is taken of this fact for the purpose of preparing saltpetre artificially, the process being carried on on the large scale in the saltpetre plantations.' In these, refuse animal matter is mixed with earthy material, wood-ashes, etc., and piled up. These piles are moistened with the liquid products from stables. After the action has continued for two or three years the outer crust is taken off and extracted with water. The solution thus obtained contains, besides potassium nitrate, calcium and magnesium nitrates. It is treated with a water extract of wood-ashes or with potassium carbonate, by which the calcium and magnesium are thrown down as carbonates..."
Now you might ask, exactly how long does the process take to form traces of ammonium nitrate (and other salts) and when does the reaction reach equilibrium. While to my knowledge this has not been pursued, I can add a bit of commentary on the process. Current technology permits the detection of even tiny traces of nitrates.
In a recent trip through the airport at Raleigh North Carolina, the lady checking baggage asked if my bag could be set aside for further investigation. Of course I agreed, and she used a system that looked no more sophisticated than a Kimwipe on a stick. She said the bag could be reclaimed, so I asked what this was all about. She said it was a test for explosives. Now why was this particular bag singled out? At least one answer is that we have cats in the house and from time to time they have the unpleasant habit of marking objects. While the odor of urine was certainly not present on the bag, you have to wonder if the sensitive detectors did pick up minute traces of nitrate that may have been formed from urea in cats urine(?)
While much is said in the above article about the danger of manufacture of gunpowder, the production of ammonium nitrate by chemical processes is no less hazardous. Chemical plants that convert ammonia to ammonium nitrate use a process of oxidization which in more than a few cases has resulted in massive explosions.
It is most unfortunate that ammonium nitrate has achieved notoriety as an ingredient in the making of bombs as it is one of the best nitrogen fertilizers. Plants use the nitrate form much more readily than ammonia. In fact calcium nitrate is a preferred fertilizer for tomatoes and such. The calcium component helps prevent blossom-end rot and the nitrogen promotes growth giving higher yields.
It seems what the ingenuity of chemist and chemical engineers have contributed, the twisted minds of a few individuals takes away. Such it is with gunpowder as well. As an ingredient of fireworks, material for mining and blasting there really is no substitute. Unfortunate it is that gunpowder also has the unpleasant role in destroying life as well.
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