Tuesday, March 22, 2016

The History of Saltpeter - VII

In our last post, we looked at how instructions by Professor Joseph LeConte enabled the Confederate States of America to obtain saltpeter. However, that was not the only way that they obtained their saltpeter. We will look at a couple of other methods in today's post.

The Confederate States of America had formed the Nitre and Mining Bureau during the Civil War, to help with production of war materials such as saltpeter, sulfur, iron, lead, copper etc. Along with distributing instructions to farmers on producing saltpeter in their farms, they also tried to obtain it in other ways.

The first way was by mining in caves. Caves that contain a large population of bats, naturally have bat dung collecting on the floor for centuries. If the floor of the cave is made of limestone, this means that the ground will be slightly alkaline. Coupled with the facts that the temperature and humidity of caves tends to stay consistent and caves also provide shelter from sun and rain means they provide pretty good conditions for the growth of certain types of bacteria that decompose organic dung into saltpeter.

One of these caves was Lookout Mountain Cave near  Chattanooga, Tennessee. The owner of this cave was one Robert Cravens, who contracted to supply the Tennessee Military and Financial Board with 20,000 pounds of saltpeter in 1861 and later handed it over to the Nitre and Mining Bureau in 1862.

Another cave was Nickajack Cave, which is located in Marion County, Tennessee, just west of Chattanooga. This cave was first mined for saltpeter by Colonel James Orr in 1800. At this time, the land was owned by the Cherokee tribe and mining was done with their permission. Saltpeter from this mine was used by US forces during the War of 1812. By the time of the US Civil War, the mining operation on this cave was also run by the above mentioned Robert Cravens, and he later on handed over the saltpeter mining operation to the Nitre and Mining Bureau as well.

Another cave that is located in Eastern Tennessee is Worley's Cave (which is also known as Morrell's Cave or Morrill's Cave). This cave was originally on the property of one Elias S. Worley. Later on, a local resident named John Morril led many explorations of the cave during the early 1900s, which led to different variations of the spelling, Worley's Cave, Morrell's Cave, Morril Cave, Morril's Cave etc. The US Board on Geographical Names settled on officially calling it Morrell's Cave in 1980, but several locals refer to it by the original name, Worley's Cave. This was a very important source of saltpeter during the Civil War.

Organ Cave in Greenbrier County, West Virginia, was also known for its niter. General Robert E. Lee's men mined this cave. The soil is rich in calcium nitrate, which was then converted to potassium nitrate by combining with wood ash.

One of the major areas for armaments production in the south was Selma, Alabama. There was a large iron works and foundry in Selma, it was somewhat centrally located and also had good railroad connections. There was an army arsenal, a shipyard and factories to produce gunpowder here. Several Confederate rifles, cannon and ironclad warships were produced here. While there were niter beds in and around Selma, these were not enough to meet confederate needs, therefore, more niter beds were needed and for this, more raw materials (i.e. dung and urine) were needed. Enter a lawyer named Jonathan Haralson.

Jonathan Haralson

Jonathan Haralson was the son of Colonel William Browing Haralson and his wife, Temperance Martin Haralson, who were rich farmers. He went to the University of Alabama and became a lawyer in the early 1850s, settling in Selma, where he also was active in the local Church. During the Civil War, he became an agent for the Nitre and Mining Bureau in the Selma area. As saltpeter could not be procured in enough quantities from caves, he ran the following ad in a local newspaper called the Selma Sentinel on October 1st 1863:

"The ladies of Selma are respectfully requested to preserve all their chamber lye collected about their premises for the purpose of making Nitre. Wagons with barrels will be sent around to gather up the lotion"
(signed) Jon Haralson
Agent, Nitre and Mining Bureau

What he was suggesting was for the Southern women to collect and contribute their urine to the war effort. On seeing the wagons making their daily rounds through the streets of Selma, a local resident, one Thomas B. Wetmore, was inspired to write a poem, which became a somewhat popular song of that era, sung to the tune of "O Christmas Tree" (or "O Tannenbaum" for German speakers):

John Haralson! John Haralson!
You are a funny creature;
You've given to this cruel war
A new and curious feature.
You'd have us think, while every man
Is born to be a fighter,
The women, bless the pretty dears
Should save their pee for nitre.

John Haralson! John Haralson!
Where did you get the notion
To send barrels around our street
To fill them with that lotion?
We thought the girls work enough
With making shirts and kissing:
But you put the lovely dears
To patriotic pissing.

John Haralson! John Haralson!
Pray do invent neater
And a somewhat less immodest way
Of making your saltpetre.
Indeed, the thing is so very odd,
Gunpowder like and cranky,
That when a woman lifts her skirt
She shoots another Yankee!"

The reader can click the above link to hear a rendition of this song (though the above rendition contains one stanza that actually came later: read on for details)

Of course, Jonathan Harrolson wasn't going to let Thomas Wetmore get away with his poem, so he composed a reply in return (What? You thought only modern-day rappers have beefs with each other? This stuff has been happening for centuries.)

The women, bless their dear souls,              
And everyone for war                            
To 'soldier boys' they'll give them shoes,              
Their stockings by the score                     
They'll give their jewels all away,              
Their petticoats to boot                            
They'll have saltpetre, or they'll shout,                     
In earnest phrase--'Wet more'!                     

The women, were it not for them
Our country would be lost;
They charm the world, they nerve our hearts
To fight at every cost.
What care they how our powder's made?
They'll have it, or they'll bore
Through mines or beds in stables laid,
And, straining, cry 'Wet more'!

Women, yes they stoop to conquer
And keep their virtue pure;
It is no harm to kill a beast
With chamber lye I'm sure.
But powder we are bound to have,
And this they've sworn before;
And if the needful thing is scarce,
They'll 'press' it and 'Wet more'!

Soon after this, a widow from the Union side, living in Boston, decided to stir the pot even more and composed her own poem:

Jon Haralson!Jon Haralson!       
We read in song and story                            
That women's in all these years,                     
Have sprinkled fields of glory;              
But never was it told before                     
That how, midst scenes of slaughter                     
Your Southern beauties dried their tears              
And went to making water.                            

No wonder, Jon, your boys were brave
Who would not be a fighter
If every time he shot his gun
He used his sweetheart's nitre?
And, vice verse what could make
A Yankee soldier sadder
Than dodging bullets fired from
A pretty woman's bladder.

They say there was a subtle smell
That lingered in the powder;
And as the smoke grew thicker,
And the din of battle grew louder
That there was found in this compound
This serious objection;
The soldiers could not sniff it in
Without a stiff erection.

After the Civil war ended, Jonathan Haralson was elected as a judge in the Alabama Supreme Court, where he served for several years. Incidentally, a former slave owned by him, Jeremiah Haralson, who was freed in 1865, went on to become the first African-American member in the Alabama House of Representatives in 1870 and the third African-American Congressman in America in 1875. Judge Jonathan Haralson threw in his support for Congressman Jeremian Haralson, to ensure that he would be welcomed into the House of Representatives, and the congressman in turn, sought a general amnesty for former Confederates (who were temporarily barred from office), to help create harmony between blacks and whites, in an act of reconciliation after the war.

In our next few posts, we will study some of the developments of saltpeter mining in England and India.

Tuesday, March 15, 2016

The History of Saltpeter - VI

In our last post, we studied the early history of saltpeter and gunpowder manufacturing in the United States. Where we last left off was where Du Pont started his plant in Brandywine Creek, Delaware, followed by other manufacturers, notably Hazard Powder Company, Oriental Powder Company and Laflin Powder Company. These companies were all located in the northern parts of the US.

Then, when the Civil war started, most of the factories were on the Union side. The Confederate forces found that they were woefully short of war materials: they had only a couple of small arsenals, one large iron manufacturer and few ships in its navy. In order to build up needed materials, they formed the Nitre and Mining Bureau, which was in charge of obtaining materials such as copper, iron, lead, sulfur, saltpeter etc. In fact, they are best known for their saltpeter production efforts.

The Confederate States Secretary of War gave the following order on April 15th 1862: "Military commanders are directed and officers of the Niter Bureau are authorized to seize niter in the hands of private individuals who either decline to sell it or ask more than 50 cents per pound for it.... All quartermasters are directed to give precedence in transportation to niter over all other Government stores."

Some caves in the south had limestone floors and cave dirt from these were rich in saltpeter deposits from bats and other cave dwellers, Caves in Selma, Alabama and Sullivan County and Marion County, Tennessee were exploited for saltpeter, but it wasn't enough to meet demand. Therefore, the confederates turned to Joseph LeConte, a professor of chemistry and geology at South Carolina College in Columbia, South Carolina, to teach them how to make saltpeter from niter beds.

Professor Joseph LeConte. Click on the image to enlarge. Public domain image.

Professor LeConte published a pamphlet to be used by farmers to produce saltpeter in their plantations. He does acknowledge that this is a slow process, even saying in the bottom of his pamphlet: "It will be seen that under the most favorable circumstances saltpetre cannot be made in any considerable quantity in less than six or eight months, and that if we commence now the preliminary process of preparing black earth, so as to insure a sufficient and permanent supply, results cannot be expected under eighteen months or two years. Let no one be discouraged by this fact, under the idea that the war may not last so long, and all their work may be thrown away. There is every prospect now of the war continuing at least several years, and of our being thrown entirely on our own resources for war materials. Besides, even if the war should be discontinued, the work is by no means lost. The method of preparing and making saltpetre-beds is precisely the most approved method of making the best manure, and all the labor and pains necessary for the preparation of black earth, and the construction of saltpetre-beds, and which I hope to induce my fellow-countrymen to undertake under the noble impulse of patriotism, ought to be annually undertaken by every planter, under the lower impulse of a wise self-interest, and would be amply rewarded in the increased production of field crops."

Click on the image to enlarge.

He starts off by explaining how saltpeter is formed in nature:
The general conditions necessary to the formation of saltpetre are: 1st, the presence of decaying organic matter, animal or vegetable, especially the former; 2nd, an alkaline or earthy base, as potash or lime; 3rd, sufficient moisture; 4th, free exposure to the oxygen of the air; and 5th, shelter from sun and rain.
        These conditions are often found in nature, as in the soil of all caves, but particularly those in limestone countries; and still more frequently under a concurrence of circumstances which, though not strictly natural, is at least accidental, so far as the formation of nitre is concerned, as in cellars, stables, manure-heaps, &c. In crowded cities, with narrow, dirty streets and lanes, the decomposing organic matter with which the soil is impregnated becomes gradually nitrified, oozes through, and dries on the walls and floor of the cellars, as a whitish crust, easily detectible as saltpetre by the taste. The same salt may be found in the soil beneath stables of several years' standing, particularly if lime or ashes have been used to hasten the decomposition of the manure; also in the earth of sheep and cattle pens, if these have remained several years in the same position; also in the soil beneath manure-heaps, particularly if lime or ashes have been added to them, as is common among farmers in making compost. It is very important, then, that the soil of such caves, cellars, stables, pens and manure-heaps, as described above, should be tested for saltpetre. If the salt exists in considerable quantities, it may be detected by the taste; if not, a small quantity of the earth may be leached, and the ley boiled down to dryness, and then tested by the taste. If there be still any doubt, any chemist or educated physician may test it. If the earth contains saltpetre in sufficient quantities, it must be leached, and the salt crystallized, by methods which we have described below.
He then goes on to say that natural sources are not sufficient for the demands of war and therefore goes on to describe how to make it using niter beds:
By these means, if diligently used in all parts of the State, it is hoped that an immediate and not inconsiderable amount of saltpetre may be obtained. It is not believed, however, that the supply thus obtained will be sufficient for the exigencies of the war. It is very important, therefore, that steps should be taken to insure a sufficient and permanent supply of this invaluable article. This can only be done by means of nitre-beds. I proceed, then, to give a very brief account of the method of making these.
The rest of his instructions are reproduced below. He gives a few methods of preparing niter beds from various European sources: the French method, Prussian method, Swedish method and Swiss method. The spelling is reproduced exactly as in his document (which is why spellings like "nitre" instead of "nitre", "mould" instead of "mold" etc. show up in the notes below)


The most important prerequisite in the construction of nitre-beds in such manner as to yield nitre in the shortest possible time, is a good supply of thoroughly rotted manure of the richest kind, in the condition usually called mould, or black earth. It is believed that in every vicinity a considerable supply of such manure may be found, either ready prepared by nature, or by the farmer and gardener for agricultural and horticultural purposes. To make the bed, a floor is prepared of clay, well rammed, so as to be impervious to water. An intimate mixture is then made of rotted manure, old mortar coarsely ground, or wood ashes (leached ashes will do), together with leaves, straw, small twigs, branches, &c. to give porosity to the mass, and a considerable quantity of common earth, if this has not been sufficiently added in the original manure-heap. The mixture is thrown somewhat lightly on the clay floor, so as to form a porous heap four or five feet high, six or seven wide, and fifteen feet long. The whole is then covered by a rough shed to protect from weather, and perhaps protected on the sides in some degree from winds. The heap is watered every week with the richest kinds of liquid manure, such as urine, dung-water, water of privies, cess-pools, drains, &c. The quantity of liquid should be such as to keep the heap always moist, but not wet. Drains, also, should be so constructed as to conduct any superfluous liquid to a tank, where it is preserved and used in watering the heaps. The materials are turned over to a depth of five or six inches every week, and the whole heap turned over every month. This is not always done, but it hastens very much the process of nitrification. During the last few months of the process, no more urine, nor liquid manure of any kind, must be used, but the heaps must be kept moist by water only. The reason of this is, that undecomposed organic matter interferes with the separation of the nitre from the ley. As the heap ripens, the nitre is brought to the surface by evaporation, and appears as a whitish efflorescence, detectible by the taste. When this efflorescence appears, the surface of the heap is removed, to the depth of two or three inches, and put aside under shelter, and kept moist with water. The nitre contained is thus considerably increased. When the whitish crust again appears, it is again removed until a quantity sufficient for leaching is obtained. The small mound which is thus left is usually used as the nucleus of a new heap. By this method it is believed that an abundant supply of nitrified earth, in a condition fit for leaching, may be obtained by autumn or early winter.

        I have spoken thus far of the method of preparing a single heap, or nitre-bed, such as any farmer or gardener may prepare with little trouble. But where saltpetre is manufactured on a large scale, as in the saltpetre plantations, many such beds are made and symmetrically arranged, so as to economize space; all under the same roof, with regularly arranged drains, all leading to a large cistern. In such plantations everything may be carried on with more economy, and with correspondingly increased profits.

Preparation of Mould

        I have supposed that there is already a considerable supply of rotted manure, prepared for other purposes, in a condition fitted for making nitre-beds; but after the present year this precarious supply must not be relied on. Systematic preparation of mould or black earth must be undertaken. The process of preparation is so precisely similar to that of compost manure that little need be said, the chief difference being the greater richness in nitrogenous matter in the case of compost intended for nitre-beds. First prepare a floor of well-rammed clay; on this place a layer of common soil, mixed with broken old mortar or ashes, six or eight inches thick; then a layer of vegetable matter -- straw, leaves, rank weeds, &c. then a layer of animal matter, dung, flesh, skin, scrapings of drains, sinks, &c. then another layer of mixed earth and mortar or ashes, and so on until a heap six feet high is made. Brush and sticks are often introduced, also, to increase the porosity of the mass. The whole is protected from the weather, and watered every week or two with urine or dung-water, until the organic matter is entirely decomposed into a black mass. This will take place in about a year, or perhaps less, in our climate. The whole is thoroughly mixed, and is then fit for making nitre-beds, as already explained.

        Thus it is hoped that the preparation of saltpetre may be set on foot at once in three different stages of advance, viz.: by the collection of already nitrified earth; by the making of nitre-beds from already formed black earth; and by the preparation of black earth. By leaching, the first would yield immediate results, the second in six or eight months, and the last in about eighteen months or two years.

        The method I have given above is that of the French. Other methods are precisely the same in principle, and differ only slightly in some of the details. The best of these is the

Prussian Method

        Five parts of black earth and one of spent ashes or broken mortar are mixed with barley straw, to make the mass porous. The mixture is then made into heaps six feet high and fifteen feet long with one side perpendicular (and hence called walls), and the opposite side sloping regularly by a series of terraces or steps. Straight sticks are generally introduced, and withdrawn when the mass is sufficiently firm. By this means air and water are introduced into the interior of the mass. The heap is lightly thatched with straw, to protect from sun and rain. The whole is frequently watered with urine and dung-water. The perpendicular side being turned in the direction of the prevailing winds, the evaporation is most rapid on that side. The liquid with which the heap is watered is drawn by capillarity and evaporation to this side, carrying the nitre with it, and the latter effloresces there as a whitish crust. The perpendicular wall is shaved off two or three inches deep as often as the whitish incrustation appears, and the material thus removed is kept for leaching. The leached earth, mixed with a little fresh mould, is thrown back on the sloping side of the heap, and distributed so as to retain the original form of the heap. Thus the heaps slowly change their position, but retain their forms. This method yields results in about a year-- probably in our climate in eight months.

Swedish Method

        Every Swede pays a portion of his tax in nitre. This salt is therefore prepared by almost every one on a small scale. The Swedish method does not differ in any essential respect from those I have already described. First a clay floor; upon this is placed a mixture of earth, mould, spent ashes, animal and vegetable refuse of all kinds. Small twig branches, straw and leaves are added, to make the mass porous; a light covering, to protect from weather, frequent watering with urine or dung-water, and turning over every week or two. The process is precisely the same as the French, except that the process of preparation and nitrification are not separated. I only mention it to show that nitre may be made by every one on a small scale. By this method the beds are ripe in two years-- perhaps in less time in this country.

Swiss Method

        The method practiced by the small farmers in Switzerland is very simple, requires little or no care, and is admirably adapted to the hilly portions of our State.

        A stable with a board floor is built on the slope of a hill (a northern slope is best), with one end resting on the ground, while the other is elevated, several feet, thus allowing the air to circulate freely below. Beneath the stable a pit, two or three feet deep, and conforming to the slope of the hill, is dug and filled with porous sand, mixed with ashes or old mortar. The urine of the animals is absorbed by the porous sand, becomes nitrified, and is fit for leaching in about two years. The exhausted earth is returned to the pit, to undergo the same process again. This leached earth induces nitrification much more rapidly than fresh earth; so that after the first crop the earth may be leached regularly every year. A moderate-sized stable yields with every leaching about one thousand pounds of saltpetre.


        When the process of nitrification is complete, the earth of the heaps must be leached. Manufacturers are accustomed to judge roughly of the amount of nitre in any earth by the taste. A more accurate method is by leaching a small quantity of the earth, and boiling to dryness, and weighing the salt. There is much diversity of opinion as to the per centage of nitre necessary to render its extraction profitable. The best writers on this subject vary in their estimates from fifteen pounds to sixty pounds of salt per cubic yard of nitrified earth. The high price of nitre with us at present would make a smaller per centage profitable. This point, however, will soon be determined by the enterprising manufacturer.

        In the process of leaching, in order to save fuel, we must strive to get as strong a solution as possible, and at the same time to extract all or nearly all the nitre. These two objects can only be attained by repeated leachings of the same earth, the ley thus obtained being used on fresh earth until the strength of the ley is sufficient. A quantity of nitrified earth is thrown into a vat, or ash-tub, or barrel, or hogshead with an aperture below, closely stopped and covered lightly with straw. Water is added, about half as much in volume as the earth. After stirring, this is allowed to remain twelve hours. Upon opening the bung, about half the water runs through containing, of course, one-half the nitre. Pure water, in quantity half as much as first used, is again poured on, and after a few moments run through. This will contain one-half the remaining nitre, and therefore one-fourth of the original quantity. Thus the leys of successive leachings become weaker and weaker, until, after the sixth leaching, the earth is considered as sufficiently exhausted. The exhausted earth is thrown back on the nitre-beds, or else mixed with black earth to form new beds. The leys thus obtained are used upon fresh earth until the solution is of sufficient density to bear an egg. It then contains about a pound of salt to a gallon of liquid.


        The ley thus obtained contains, besides nitrate of potash (nitre), also nitrate of lime and magnesia, and chlorides of sodium and potassium. The object of the next process is to convert all other nitrates into nitrate of potash. This is done by adding wood ashes. The potash of the ashes takes all the nitric acid of the other nitrates forming the nitrate of potash (nitre), and the lime and magnesia are precipitated as an insoluble sediment. Sometimes the ashes is mixed with the nitrified earth and leached together, sometimes the saltpetre ley is filtered through wood ashes, sometimes the ley of ashes is added to the saltpetre ley. In either case the result is precisely the same.


       The ley thus converted is then poured off from the precipitate, into copper or iron boilers. It still contains common salt (chloride of sodium) in considerable, and some other impurities in smaller, quantities. It is a peculiarity of nitre, that it is much more soluble than common salt in boiling water, but much less soluble in cold water. As the boiling proceeds, therefore, and the solution becomes more concentrated, the common salt is, most of it, precipitated in small crystals, as a sandy sediment, and may be raked out. Much organic matter rises as scum, and must also be removed. When the concentration has reached almost the point of saturation, the boiler must be allowed to cool. This is known by letting fall a drop of the boiling liquid upon a cold metallic surface; if it quickly crystallizes, it is time to stop the boiling. It is now poured into large receivers and left to cool. As the ley cools, nearly the whole of the nitre separates in the form of crystals, which sink to the bottom. These are then removed, drained by throwing them in baskets, and dried by gentle beat. The mother-liquor is either thrown back into the boilers, or else used in watering the heaps. The product thus obtained is the crude saltpetre of commerce. It still contains fifteen to twenty-five per cent. of impurities, principally common salt (chloride of sodium), chloride of potassium and organic matter. In this impure form it is usually brought to market.

        There is still another process, viz: that of refining, by which the whole of the impurities is removed. This is seldom done by the manufacturer, but by a separate class, called the refiners.


        One hundred gallons of water is poured into a boiler, and crude saltpetre added from time to time, while the liquid is heating, until four thousand pounds are introduced. This will make a saturated solution of nitre. The scum brought up by boiling must be removed, and the undissolved common salt scraped out. About sixty gallons cold water is now added gradually, so as not to cool the liquid too suddenly. From one to one and a-half pounds of glue, dissolved in hot water, is added, with stirring. Blood is sometimes used instead of glue. The glue seizes upon the organic matter, and they rise together as scum, which is removed. Continue the boiling until the liquid is clear. The liquid is then suffered to cool to one hundred and ninety-four degrees, and then carefully ladled out into the crystallizers. These are large shallow vats, with the bottom sloping gently to the middle. In these the cooling is completed, with constant stirring. In the process of cooling nearly the whole of the nitre is deposited in very fine, needle-like crystals, which, as they deposit, are removed and drained. In this condition it is called saltpetre flour. The object of the constant stirring is to prevent the aggregation of the crystals into masses, from which it is difficult to remove the adhering mother-liquor. The saltpetre flour is then washed of all adhering mother-liquor. For this purpose it is thrown into a box with a double bottom; the lower bottom with an aperture closely plugged, and the false bottom finely perforated. By means of a watering pot a saturated solution of pure nitre is added, in quantity sufficient to moisten thoroughly the whole mass. After remaining two or three hours to drain, the plug is removed and the solution run out. This is sometimes repeated several times. The saturated solution of nitre cannot, of course, dissolve any more nitre, but dissolves freely the impurities present in the adhering mother-liquor. Last of all, a small quantity of pure water-- only about one pound to fifty-three pounds of the nitre to be washed-- is added in the same manner, and run off at the end of two hours. The nitre is now dried by gentle heat and constant stirring, and may be considered quite pure, and fit for the manufacture of gunpowder.


        As the value of crude saltpetre depends upon the quantity of pure nitre which it contains, it is important to give some simple methods of estimating its purity:

        1. The first method is founded upon the fact, already alluded to, that a saturated solution of any salt will not dissolve any more of that salt, but will freely dissolve other salts. Twelve ounces of crude saltpetre is well ground, and twelve ounces of a saturated solution of pure nitre added. The mixture is stirred fifteen minutes, allowed to settle, and the liquid carefully poured off. Six to nine ounces more of the saturated solution of nitre is again poured on, the mixture stirred ten minutes, and the whole thrown on a filter, and allowed to remain until thoroughly drained. The filter, with its contents, is then pressed upon blotting paper, or slab of plaster, or other absorbent substance-- the nitre carefully removed and dried, and carefully weighed. The loss of weight indicates the impurity originally present in the crude saltpetre. About two per cent. should be deducted from the estimate of impurity, or added to the estimate of pure nitre; since, although a saturated solution of nitre will not dissolve any more pure nitre, still, if any common salt be present, a small additional quantity of nitre is taken up.

        2. Another method of estimating saltpetre is founded upon the fact that nitre mixed with charcoal and heated is entirely converted into carbonate of potash, while common salt is not affected. If the saltpetre be mixed with charcoal alone, the reaction is apt to be violent and explosive. To moderate the violence of the action, the saltpetre must be largely mixed with common salt, which does not interfere with the reaction. One part crude saltpetre, four parts common salt, and one-half part charcoal, are mixed and thrown gradually in a red-hot crucible, or else heated in an iron spoon, until reaction ceases. The whole of the nitre is now changed into carbonate of potash, which may be dissolved in water and filtered. The solution thus obtained, being alkaline may be estimated by the quantity of sulphuric or other acid of known strength necessary to completely neutralize it. This is done by means of the instrument called the alkalimetre. One part of pure potassa corresponds to 2.14 parts of nitre; or one part carbonate potassa corresponds to 1.46 parts nitre. The objection to this method is, that it requires the use of the alkalimetre; and, therefore, a degree of care and an amount of accuracy which can hardly be expected in practical men.

        3. The third method of estimation depends upon the fact that a strong hot solution of nitre crystallizes on cooling, and that the temperature at which crystals begin to deposit (or point of saturation) depends upon the amount of nitre present in the solution, irrespective of the presence of impurities. In one hundred parts of hot water is dissolved forty parts of crude saltpetre. A very delicate thermometer is introduced, the liquid allowed to cool slowly, and the temperature at which crystals begin to deposit is accurately observed. The higher the temperature, the larger the quantity of nitre present in the solution, and, therefore, the purer the saltpetre. Tables have been constructed giving the saturating point for solutions containing different quantities of nitre.

        I have constructed, from materials derived from the best French authorities, a table which is sufficiently complete and accurate for all practical purposes.

        In a saturated solution of nitre, one hundred parts by weight of water at

  • 32° contains 13.32 parts of nitre.
  • 33° contains 13.64 parts of nitre.
  • 34° contains 13.97 parts of nitre.
  • 35° contains 14.31 parts of nitre.
  • 36° contains 14.66 parts of nitre.
  • 37° contains 15.02 parts of nitre.
  • 38° contains 15.40 parts of nitre.
  • 39° contains 15.79 parts of nitre.
  • 40° contains 16.19 parts of nitre.
  • 41° contains 16.50 parts of nitre.
  • 42° contains 16.91 parts of nitre.
  • 43° contains 17.33 parts of nitre.
  • 44° contains 17.76 parts of nitre.
  • 45° contains 18.20 parts of nitre.
  • 46° contains 18.66 parts of nitre.
  • 47° contains 19.13 parts of nitre.
  • 48° contains 19.61 parts of nitre.
  • 49° contains 20.10 parts of nitre.
  • 50° contains 20.60 parts of nitre.
  • 51° contains 21.12 parts of nitre.
  • 52° contains 21.65 parts of nitre.
  • 53° contains 22.20 parts of nitre.
  • 54° contains 22.76 parts of nitre.
  • 55° contains 23.23 parts of nitre.
  • 56° contains 23.81 parts of nitre.
  • 57° contains 24.40 parts of nitre.
  • 58° contains 25.00 parts of nitre.
  • 59° contains 25.60 parts of nitre.
  • 60° contains 26.21 parts of nitre.
  • 61° contains 26.82 parts of nitre.
  • 62° contains 27.44 parts of nitre.
  • 63° contains 28.07 parts of nitre.
  • 64° contains 28.70 parts of nitre.
  • 65° contains 29.34 parts of nitre.
  • 66° contains 30.09 parts of nitre.
  • 67° contains 30.74 parts of nitre.
  • 68° contains 31.40 parts of nitre.
  • 69° contains 32.08 parts of nitre.
  • 70° contains 32.77 parts of nitre.
  • 71° contains 33.48 parts of nitre.
  • 72° contains 34.20 parts of nitre.
  • 73° contains 34.94 parts of nitre.
  • 74° contains 35.69 parts of nitre.
  • 75° contains 36.46 parts of nitre.
  • 76° contains 37.25 parts of nitre.
  • 77° contains 38.05 parts of nitre.
  • 78° contains 38.85 parts of nitre.
  • 79° contains 39.65 parts of nitre.
  • 80° contains 40.46 parts of nitre.
  • 81° contains 41.27 parts of nitre.
  • 82° contains 42.09 parts of nitre.
  • 83° contains 42.92 parts of nitre.
  • 84° contains 43.76 parts of nitre.
  • 85° contains 44.62 parts of nitre.
  • 86° contains 45.50 parts of nitre.
  • 87° contains 46.42 parts of nitre.
  • 88° contains 47.33 parts of nitre.
  • 89° contains 48.26 parts of nitre.
  • 90° contains 49.20 parts of nitre.
  • 91° contains 50.16 parts of nitre.
  • 92° contains 51.13 parts of nitre.
  • 93° contains 52.11 parts of nitre.
  • 94° contains 53.10 parts of nitre.
  • 95° contains 54.10 parts of nitre.

        By comparing the quantity of pure nitre, as determined by inspection of the table, with the quantity of crude saltpetre dissolved, the percentage of pure nitre may be easily calculated. Thus, if crystals begin to deposit at 68°, the quantity of nitre contained in a hundred parts of water is 31.40 parts; dividing this by 40 parts crude nitre, originally dissolved, gives 76 per cent. of pure nitre in the sample examined. In the foregoing example I have used 40 parts crude saltpetre; but we are by no means limited to this number. On the contrary, in our climate a larger quantity, as 50, or even 60, parts is preferable. For it will be observed that at 80° more than 40 parts of nitre are soluble in 100 parts of water, and that, therefore, in our summer weather, if only 40 parts of crude saltpetre are used in the experiment, artificial cold will be necessary to produce crystallization. To avoid this inconvenience, it is only necessary to use a larger proportion of crude saltpetre in the experiment. Thus, if 50 parts are used, and crystallization commences at 80°, the quantity of pure nitre, by the table, being 40.46, the per centage is 40.46 / 50 = 80.9. For higher summer temperature, it will be, of course, necessary to use a still larger quantity of crude saltpetre in the experiment. This method has the advantage of great ease and rapidity of execution.

After the Civil War ended, Professor LeConte lost his inherited lands and wealth. The Southern Carolina College was reformed as the University of South Carolina and he went back to his professorship in chemistry and geology, but he was not comfortable working there. Therefore, he and his brother moved west to the newly founded University of California, where they were some of the first hired faculty members. He taught geology and botany at Berkeley, California and explored the nearby mountains. He became good friends with John Muir and co-founded the Sierra Club.

In our next post, we will look at some other ways the Confederates tried to obtain saltpeter supplies.

Sunday, March 13, 2016

The History of Saltpeter - V

In today's post, we will look at the early history of saltpeter production in the US.

When the early colonists from England arrived in the US in 1620 and established a colony in Plymouth, Massachusetts, they brought supplies of gunpowder from Europe. However, as the Massachusetts Bay Colony began to grow, it became necessary for the settlers to start manufacturing their own gunpowder locally, because they could not depend on supply ships reliably coming across the ocean from England.

Since there were no known deposits of natural saltpeter in the area, the settlers began to make saltpeter plantations, using the same techniques that were in use in England. The first reference to saltpeter manufacture comes from an order of the General Court of Massachusetts, dating from June 6th, 1639, where it granted 500 acres of land at Pecoit to one Edward Rawson, "so as he goes on with the powder if the saltpeter comes." By 1640, a saltpeter house was operational in Boston. By 1642, the General Court of Massachusetts  passed an order to promote public safety "by raising and producing such materials amongst us, as will perfect the making of gunpowder, the instrumental means that all nations lay hold on for their preservation etc., that every plantation within this colony shall erect a house in length 20 or 30 foote, and 20 foote wide within one-half year next coming, &c., to make saltpeter."

In 1666, we see two more orders passed in the General Court of Massachusetts. The first dating from May 23rd states, "whereas, there is necessity of having supply of gunpowder in this jurisdiction, and forasmuch as Sergt. Richard Wooddey, of Boston, in the county of Suffolk, and Mr. Henry Russell, of Ipswich, in the county of Essex, have been and are upon the work, and in preparation for saltpeter, for their future encouragement, or any other that shall appear to attend the promoting thereof, this Court doth declare and order that the said Richard Wooddey and Henry Russell are impowered to go on and proceed in the said work." It then grants them special permissions to build their business. The second order from October 10th states that "whereas the Court hath encouraged and authorized some persons to make gunpowder, and have promised to enable them thereunto by such public and necessary orders as may conduce to the effecting of the same, the consideration whereof hath moved the Court hereby to order and enact, that the selectmen of every town (where the powdermakers authorized by this Court shall desire it) be authorized and required hereby to make and execute such orders in their respective towns as they shall judge meet, with the advice of skilful men, for increasing and procuring of saltpetre, and to impose such penalties as the selectmen shall deem meet, not exceeding ten shillings for one offence, upon all persons that shall neglect or refuse to perform such order or orders for the propagating and increasing of saltpeter in their respective towns; and moreover, the said selectmen are further impowered to choose and appoint an officer or officers, and to allow him a convenient stipend annually for his pains out of the fines or otherwise, to look to the executing such orders as they shall make in their behalf."

The next big event we see is from 1675, when a powder mill was built in Milton, Massachusetts. It was water powered and built near the Neponset river. In August 1675, Governer Leverett wrote to this friend and revealed, "We are upon a work for making powder and have erected a mill in order thereunto at Neponset, about six miles from Boston. Our difficulty will be for peter, which we must, in our beginning, have from without us, but hope, in time, may raise it amongst us." The last sentence shows that the sources of saltpeter for this mill were still uncertain at this point.

Interestingly, as the colonies developed, Great Britain started to produce gunpowder based on cheap saltpeter imports from India (we will study that trade soon). Therefore, it actually became cheaper for Americans to import their gunpowder from England and this led to many powder mills in America closing down. Then, when the American revolution started, there was only one gunpowder mill in America, the Frankford Powder Mill, built by Oswald Eve in Frankford, Pennsylvania. However, this mill was pretty small and could only supply the American forces with small amounts of gunpowder. It was recorded that Oswald Eve signed a contract on January 11th 1776, with the Continental Congress, to supply gunpowder at $8 per hundredweight. In order to ensure that his was not the only mill to make gunpowder, Congress approved the construction of the Continental Powder Mill on February 16th 1776, on French Creek, eight miles from Valley Forge, based on the techniques learnt from inspecting Eve's mill. As it happens, Congress wasn't entirely certain about Eve's patriotism and suspected that he was dealing with the British as well. Therefore, eight other mills operated by other private businessmen were also contracted to supply additional materials. Eve's mill was later seized by the British forces in September 1777, when they captured Philadelphia. Eve was subsequently accused of treason by Congress for trading with the British and had to flee the US.

It must be noted that the new powder mills could not supply the needs of the Americans, because they couldn't obtain enough saltpeter. Desperate for gunpowder, American forces tried to get it by capturing supplies from the British. Both George Washington and Congress ran separate operations to raid a British magazine on the island of Bermuda. When the situation was very dire, help came from the other European nations. Dutch merchants were already trading with American ships and then, the French got into the act. The French had built up their saltpeter plantations with the help of gifted chemists such as Antoine Lavoisier (the father of modern chemistry) and they had plenty of supplies of saltpeter and gunpowder. The French were able to supply enough to meet the needs of America. In fact, if it wasn't for French supplies of gunpowder, American forces would never have been able to continue the war of independence.

The importance of being self-reliant on gunpowder was not lost on America's founding fathers and therefore, efforts were made to build up supplies after the American revolution. American ships began to import raw saltpeter from India, but the quality of gunpowder produced was not very good. Then, in 1800, a rich Frenchman named Éleuthère Irénée du Pont escaped with his family from the French revolution and came to America.

Éleuthère Irénée du Pont

Before he came to America, the young du Pont had studied for some years under the famous chemist, Antoine Lavoisier, who was a friend of his father. He had also worked in the Regie des poudres, the French government agency responsible for manufacturing gunpowder. From Lavoisier, he learned the latest techniques in manufacturing nitrates. Later on, he gave up his chemistry career and began to help his father run a publishing house. Then the French revolution happened and he and his father were arrested and nearly executed. They decided to flee France with their families and come to America. Meanwhile, his former mentor, Antoine Lavoisier, was not so lucky and was executed by guillotine during the French revolution.

When Du Pont first came to America in 1800, he didn't actually want to go into the gunpowder manufacturing business. As it happened, the quality of gunpowder manufacturing in the US was very bad. The story goes that Du Pont went hunting with a certain Major Louis de Tosard, who was a former French artillery officer who had also escaped from the French Revolution and was employed by the US army to buy gunpowder supplies. During the hunting trip, Du Pont's gun misfired and he commented that despite the high price of gunpowder in the US, it was of very poor quality. That's when he thought about his earlier career in making gunpowder in France. He arranged with Tousard to tour American gunpowder factories and came to the conclusion: "There already exist in the United States, two or three mills, which make very bad powder and which do however a very good business. They use saltpeter from India, which is infinitely better than that which is produced in France, but they refine it badly."

Du Pont decided that he could use his experience from France to better refine the saltpeter and thereby produce higher quality gunpowder. With his father's support, he began to raise capital in France to build a new factory in America and also arranged to import machinery from France. The new E.I. du Pont de Nemours and Company gunpowder mill was established in 1802 on the Brandywine Creek in Delaware. Initially, the mill was just a saltpeter refining factory, but they soon moved into manufacturing gunpowder as well. Within a few years, his company became the largest gunpowder manufacturer in the United States and the Federal government became one of his biggest customers. The company he founded would go on to become one of the largest and most successful American corporations in history and is currently the world's fourth largest chemical company.

Other American companies that were founded after Du Pont include the Hazard Powder Company (founded 1832), the Oriental Powder Company and the Laflin Powder Company (the last two being owned by members of the Laflin family, who had a history of making gunpowder since the American revolution). By the time of the Civil war, these four companies were supplying most of the gunpowder to the Union side.

In our next post, we will study how saltpeter was manufactured by the Confederate forces, during the Civil war.

Tuesday, March 8, 2016

The History of Saltpeter - IV

In our last couple of posts, we saw the basics of saltpeter extraction and also an insight into the bacterial and chemical processes involved. As we saw previously, it was the job of saltpeter men to go around the country and locate soils rich in nitrates, so that saltpeter could be extracted from them. They often found these lands close to places where organic materials decomposed, which were sheltered from rain and sun. This usually meant digging in cellars and stables of various farms. However, the formation of saltpeter in these areas was a slow process and the supplies could not keep up with the demand. Therefore, people began to prepare special areas to produce saltpeter. These areas were called niter beds (or nitre beds, if you're used to British spelling). Other names for these include nitraries and saltpeter plantations. We will study how these worked in today's post.

Niter Beds. Click on the image to enlarge. Public domain image from a woodcut from 1598.

Workers would prepare long trenches lined with clay and pile on heaps of manure, rotting leaves, plants and urine, arranged with layers of limestone and ash in between, and small twigs, branches and straws in the middle, to give the mixture sufficient porosity. Such heaps can be seen as C in the image above. The sides of the various heaps protect each other to some degree from wind and weather. Every week, the workers would keep the heaps moist by adding more urine, dung water, water from drains etc. The idea was to keep the heaps moist, but not too wet. Urine from drinkers of beer and wine were in much demand, as it was thought that this resulted in superior quality of saltpeter. The process needed to be somewhat carefully controlled because if it was overdone, the production rate of saltpeter would actually decrease.

Meanwhile, the workers would collect pure rainwater in a large vat (A in the image above), as it is a relatively pure source of water without any minerals dissolved in it. They would also collect wood (D in the image) to be used to prepare ashes and for boiling the liquids later on. After about a year, the heaps would be ripened enough and a saltpeter digger (E in the image above) would dig into them and take them into buildings B and A for processing.

Click on the image to enlarge. Public domain image.

Inside, they would use the pure rainwater to dissolve and leach the saltpeter crystals from the compost heap and then use the wood to boil the water and extract the crystals from it, as described in the posts previously.

As can be imagined, running a nitrary (saltpeter plantation) meant that the smell was very nauseating. In fact, one of the major qualifications to be a nitrary manager or worker was to be able to tolerate the incredible stench produced. That's why many of these operations were located out in the countryside, away from most people.

The remains of what once used to be the largest nitrary in Dijon, France. This was originally out in the countryside, but is now a residential neighborhood of the city. The only hint of what used to be here is the street sign. In the inset, it says "Rue de la Raffinerie" (i.e.) "Street of the [saltpeter] refinery."
Click on the image to enlarge.

These nitraries were dedicated to producing saltpeter and some countries (e.g. France, Sweden, Germany, colonial-era America etc.) introduced laws requiring people to set aside X amount of land in each village for niter beds. A well run operation could produce, every two years, about 2-4.5 kg. (about 5 to 10 pounds) of saltpeter per cubic meter of dirt. It was a slow, painstaking, dirty and labor-intensive job, but for several countries, it was necessary for their survival.

In our next post, we will look into the works of a certain Professor Joseph Leconte, who wrote a pamphlet on the production of saltpeter during the Civil war.

The History of Saltpeter - III

In our last post, we studied one of the techniques of producing saltpeter. We did promise there that we will study another method using niter beds. But, before we dive into that topic, let's cover a few more things that were left out in our previous post.

First, in case the reader is wondering, it is not possible to simply pick up a pile of fresh dung and urine and manufacture saltpeter that way. The dung and urine need to ferment for a while (at least 6 months or more), with sufficient moisture and shelter from rain and sun, and the soil needs to be alkaline and have certain compounds and not grow any crops on it.

Since we have the benefit of modern chemistry and biology knowledge, let us try to understand what is actually happening. First, when animals and people produce a large amount of urine and dung, under the right conditions, certain bacteria will turn the urea into ammonia and then combine that ammonia with oxygen in the air to produce nitrate ions. Now, these nitrate ions are looking to combine with other minerals. If the soil contains minerals such as calcium carbonate (limestone), magnesium carbonate or potassium carbonate, these minerals with react with the nitrate ions being produced by the bacteria, to form calcium nitrate, magnesium nitrate, potassium nitrate etc. Now if plants are allowed to start growing here, they will absorb the nitrates and grow tall and green, but there will be no saltpeter produced, since the plants use up the nitrates in the soil (nitrate compounds have been used as fertilizer for this reason). However, in stables, the animals will eat any plants and therefore, the nitrates can continue to form under the floorboards and walls of adjacent buildings. Similarly, if the ground is porous and dry, plants won't grow well and therefore nitrate crystals can form on it.

Now remember that we said that nitrates such as calcium nitrate, magnesium nitrate, potassium nitrate etc. are formed. Of these, only potassium nitrate is useful to us for gunpowder. The other two nitrates absorb too much water from the air and this reduces their explosive strength. The trick is to separate the potassium nitrate from the others. An Arab scientist from Syria named Hassan Al-Rammah described how to do so, in his book from 1270 AD titled "al-Furusiyya wa al-Manasib al-Harbiyya" (i.e. "The Book of Military Horsemanship and Ingenious War Devices"!) The details in his book seem to indicate that the method is of Chinese or Indian origin. The method described consists of dissolving all the nitrates in water and mixing in a lot of wood ash (which contains a lot of potassium in the form of potassium carbonate). The potassium ions in the wood ash replace the calcium and magnesium ions in calcium nitrate and magnesium nitrate and leave behind potassium nitrate, which can be crystallized. The knowledge of this method went westwards via the Italians and spread to the rest of Europe. A version of this method was described in the previous post.

All of this seems very obvious to us readers, who have had the benefit of knowledge passed to us by hundreds of scientists and inventors over many centuries. However, for people living in the 13th to 18th centuries, who did not have the knowledge of chemistry and biology that we do, the formation of saltpeter crystals was practically magic. They understood that decomposition of organic matter might have something to do with it, but they could not explain why saltpeter crystals would form under stables and cellars, but not in the open fields where dung is also found, and also why saltpeter crystals would not always form under stables if the weather conditions weren't right (the role of certain types of bacteria in the nitration process wasn't fully understood until the late 19th and early 20th century). The source of dung also had an effect on whether saltpeter was produced or not. While it was known that seabird guano was good for fertilizer, it wasn't as good for saltpeter production. However, some soil found under dove cotes (i.e. houses for pigeons and doves) was found pretty rich in nitrates. Stables provided with porous floors, such as straw and ashes, allow the formation of saltpeter. Some caves with limestone floors and filled with bats, would provide good saltpeter from the bat guano piles which were centuries old. Another puzzle was why sunlight and rain affected the production of saltpeter. Again, they didn't fully understand the roles of bacteria, soil chemistry, other minerals etc. This is why the role of the saltpeter men in various countries became so important, because people couldn't guarantee that saltpeter crystals would form at any particular location and it was left to saltpeter men to sniff around and find rich deposits of saltpeter. Since it was such a vital ingredient of gunpowder, they were given permission by their country's rulers to dig literally anywhere and given state protection from angry landowners.

In our next post, we will start looking into niter beds.

Friday, March 4, 2016

The History of Saltpeter - II

In our last post, we studied the components of gunpowder and noted that the key one was potassium nitrate, whose source was from saltpeter. As we noted earlier, the other components of gunpowder were relatively easy to obtain, but this one was not. We will study the history of saltpeter production in this post.

In the fifteenth and sixteenth centuries in Europe, saltpeter's purpose was well understood in the manufacture of gunpowder, but its sources were not. People were not too sure if it could be mined as a mineral or grown in a field like crops. As late as the 1770s, one noted chemistry lecturer admitted that 'we are much in the dark as to the origin and generation of saltpeter', although he knew that it was to be found around 'earth and stones that have been impregnated with animal or vegetable juices susceptible of putrefaction, and have long been exposed to the air... It is a product of elements, deposited in the bosom of the earth... and may not improperly be called the universal and unspecific mercury.' As saltpeter is found as an efflorescence on the surface of the earth, it was assumed by many chemists that it was of aerial origin. In 1821, John Davy, the brother of noted chemist, Sir Humphry Davy, after examining some niter-yielding caverns of Sri Lanka, concluded that it was formed from the nitrogen and oxygen in the air. Around 1890 is when the role of bacteria in the nitrification process was understood. In fact, the full process of nitrification was not understood until the twentieth century.

In some parts of the world blessed with the optimum weather conditions and soil chemistry, saltpeter could be mined right off the ground. However, there are few places in the world with this correct mix of factors: parts of Northern India, Egypt, Spain and the Atacama desert in South America are some of the well known ones. Northern India, in particular, was well known for its saltpeter trade and this was exported to the middle east in the thirteenth and fourteenth centuries, and from then on, to Europe. However, others had discovered artificial methods of making saltpeter as well and these came to European notice as well. We will study the artificial methods of making saltpeter first.

The technology of making saltpeter by artificial means seems to have been invented in Asia and spread westwards into Europe. As might be expected, the Italian states, especially Venice, with their trading interests with the Turkish empire and the middle east, were the first Europeans to gain the knowledge from Asia, of how to produce saltpeter by artificial means. The metallurgist, Vannoccio Biringuccio, from Siena, wrote a well-known book on metalworking, De La Pirotechnia, which was published in 1540, shortly after his death. In this book, along with dealing with metals and alloys, there are notes devoted to saltpeter production. It is known that Biringuccio had a monopoly on saltpeter production in Siena around 1524, so he must have had knowledge of the process before then. This book was copied by several authors and eventually translated into English, and this is how the knowledge of the process gradually spread northwards in Europe.

In most of Europe, and England in particular, they were initially content to simply purchase the ingredients and finished gunpowder from other sources. In particular, trading with the Mediterranean countries for sulfur, saltpeter and gunpowder and northern European countries for saltpeter and gunpowder. Northern Europe was preferred as a source of gunpowder because the commodities were strategically located for military operation on the European continent.

England's need for gunpowder accelerated under King Henry VIII. When he invaded France in 1513, his army carried 510 tons of gunpowder with them, but the siege guns consumed 32 tons of powder a day. Very soon, he was importing gunpowder from other European countries. He commissioned a German named Hans Wolf to travel 'from shire to shire, to find a place where there is stuff to make saltpeter of.' His successor, Queen Elizabeth I, faced the Spanish Armada, and caused the demand for gunpowder to go even higher. She granted a Dutchman, one Gerard Honrick, the sum of 300 pounds, to teach her subjects the art of saltpeter making. His rules:

  1. Black earth, the richer the better. The color shows the rich organic decomposition.
  2. Urine - especially from those that drank wine of strong beer
  3. Dung - especially from horses fed with oats
  4. Lime made from oyster shells or plaster of Paris
The moistened ingredients were to be layered in beds to which ashes were added (ashes from oak leaves being recommended) and the resulting salts were to be leached out and boiled to form the crystals of saltpeter.

The following instructions come from a book called De re Metallica (it means, On the Nature of Metals in Latin), written by Georg Bauer, better known by his pen name of Georgius Agricola. It was published in 1556 and undoubtedly influenced by the above mentioned De la Pirotechnia. This was an influential book in the fields of chemistry and mining and remained an authoritative text on mining for 180 years after its publication. There is a chapter on saltpeter extraction, which we will describe below:

Click on the image to enlarge. Public domain image.
A - Reduction Pan, B - Large Vat, C - Plug, D- Tub, E - Crystallization vat.

Saltpeter diggers would dig up soil found near stables or dovecotes, where there was a strong concentration of dung. The best saltpeter came from a dry, slightly fatty earth, which if retained for a while in the mouth, has an acrid or salty taste. Then, they would take a large vat, (B in the figure above), and fill it with layers of this soil and a powder in layers of a palm deep. The powder consists of two parts of unslaked lime and three parts of ashes of oak, holmoak, Italian oak or Turkish oak or some such suitable material. Alternate layers of soil and powder are filled in the large vat, to about three quarters of a foot from the top. Then water is added until the vat becomes full. As the water seeps into the material, it dissolves the saltpeter. Then the plug (C in the figure above) is pulled and the solution is drained into smaller tubs (D in the figure above). The solution is then poured into a caldron or reduction pan (A in the figure above), which is a flat shallow pan made of copper, which is placed on top of a fire. Here, the solution is boiled for several hours until about half of the water evaporates, and the solution is allowed to settle down. Any impurities in the solution form a dirty scum on top, which is then removed. Then it is boiled again and lye and rock alum are added to remove any further impurities and it is boiled again leaving behind a concentrated solution of saltpeter liquor. Then the concentrated solution is transferred to crystallization vats (E in the figure above). These vats have copper rods that act as nucleation sites for crystals of saltpeter to form on them. After three of four days, the rods are removed and the saltpeter crystals scraped off them. The solution left behind in the vats is partially used to wash the crystals after they are scraped off, and the rest of it is reboiled to concentrate the solution even more. The washed saltpeter crystals are placed on boards to drain and dry up.

Of course, as the demand for gunpowder and hence, saltpeter, went up due to the numerous wars in Europe, stables and dovecotes didn't provide enough saltpeter. The next solution was niter beds, which we will study in our next post.