Chapter 6.03 Saltpeter’s ancient history

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Saltpere is found around the world, but nowhere in bigger and better volumes and quality as in India.  Here they mine saltpeter from the earth and thousands of small villages are engaged in its production.  (Crookes, W.  1868/ 69:  153)  In countries such as these, with a warm climate and high rainfall, “ammonia resulting from the putrefaction and decay of nitrogenous materials is washed into the soil by rainfall, to be oxidized by bacteria, yielding nitrate. . .  In India, saltpeter is leached from the ground as sheets of water left by monsoon flooding evaporate. A crust of saltpeter, including mineral salts, spreads across the ground, and can be dug up and refined into pure potassium nitrate.”  (Frey, James W.   2009)

It was this vast quantity of Indian saltpeter and the European and English desire to get their hands on it that resulted in the establishment of the East Indian companies in England and Holland.  The Dutch East Indian Company, in turn, established Cape Town and in a way, we can say that Cape Town exists because of the saltpeter trade.   It was in the first place not used to cure meat, but in the production of gunpowder and as a fertiliser to increase crops to feed the ever-growing population of the world.  It was the arms-race of the 16th 17th and early 18th  century and the desire of all great nations.

It’s not only mined from the earth, but it also grows like fungus on the walls of cellars and around toilets.  (Drs. Keeton, et al, 2009:  6)  (8)  It seems as if it occurs wherever urine and dung occur such as in bat caves.  Peter Whitehorn, the Elizabethan theorist said that saltpeter ‘is a mixture of many substances, gotten out of fire and water of dry and dirty ground.’    “It could sometimes be found as an efflorescent or ‘flower that growth out of new walls, in cellars, or of that ground that is found loose within tombs or desolate caves where rain can not come in.’  But saltpeter could also be nourished or encouraged to grow by adding ‘the dung of beasts’ to the earth.  A distinction was made between ‘natural saltpeter’ which only needed to be scraped from walls, and ‘artificial saltpeter’, which required digging and refinement.  The two kinds ‘partook of the very same virtue’ (according to Whitehorn, relaying Biringuccio) except that some /beasts, converted into earth, in stables or in dunghills of long time not used”. (Cressy, David, 2013: 16)

Jeppe continued unabated.  “In Germany, they developed technology whereby they created their own saltpeter.   The average German farmer is so skilled in its production that Germans authors, writing on this subject, did not even bother to give the detail of its production.”  The German method centered around the use of niter beds (managed heaps of vegetable matter mixed with excrement and dung) created by farmers from which niter rich material was removed and saltpeter extracted.

The best description of its production in Europe from the mid to late 1500’s came to us from Lazarus Ercker (1530-1594), chief master of the mines of Emperor Rudolph II in Bohemia.  He wrote arguably the most detailed account on the production of saltpeter in ‘The right and most perfect way of the whole work of saltpetre’.   A German translation appeared in Prague in 1574 and in Frankfurt in 1580.  (Cressy, D.  Saltpetre, State Security, and Vexation in Early Modern England:  5)

Still, despite the impact of the renaissance and tremendous advances in fields of biology and the natural sciences, people could only appreciate saltpeter by what it did without any understanding of how it worked.  (Cressy, D.  Saltpetre, State Security, and Vexation in Early Modern England:  5)

In the late 1770’s a chemical instructor said about saltpeter, “‘we are much in the dark as to the origin and generation’ of saltpeter, though we knew it to be ‘found among earth and stone that have been impregnated by animal and vegetable juices susceptible of purification, and have long been exposed to air. . . . It is the product of the elements deposited in the bosom of the earth, and may not be improperly called the universal and unspecific mercury”.  (Cressy, David, 2013:  14)

“Written knowledge of saltpeter filtered into England in 1540 with Vannoccio Biringuccio’s De la pirotechnia.  This work was eventually translated into English and included accounts of the making of explosives. (Cressy, David, 2013:  14)  Saltpeter being one of the main ingredients in gunpowder.

In England, they harvested saltpeter earth and extracted it from the niter enriched soil.  Saltpetermen scoured the English countryside and dug up any place where the ground could have been impregnated with animal and human urine and dung.  Saltpetermen received authority from the king to dig up any soil from which saltpeter could be extracted to the great frustration of the people of England.  Their work and the irritation it brought to the English people became a political issue during the time when England was a monarchy and after the civil war.  Dove coves or pigeon houses were favourite sites because of their concentration of the sheltered droppings.  “A skilled prospector would know how to soil rich saltpeter for ‘by the taste of the tongue it may be felt if it be biting, and how much”.  (Cressy, David, 2013:  16)

In 1588 a man by the name Lucar wrote in Collequies Concerning the Art of Shooting in Great and Small Peeses of Artillerie, ““digging the earth out of floors in cellars, vaults, stables, ox-stalls, goat or sheep-cotes, pigeon house, or out of the lowermost rooms in other houses.”  This reflects the practice in Tudor England’s roving saltpetermen.”  (Cressy, David, 2013: 17)

Barrels full of dung rich earth would be set on a framework so that water introduced at the top would trickle down to a catchment tube at the bottom.  Further refinement took place through filtration.  The whole process would take a week or more.  (Cressy, David, 2013: 17)

In general, Europe and England struggled to produce enough saltpeter.  After 1850’s the East Indian Company solved the supply problem of Saltpeter by importing it from India where it occurred naturally and was also efficiently produced. (Cressy, David, 2013:   25)  Some of the saltpeter were imported in a refined state and some to be refined in England.

Trade in saltpeter from India to London, Amsterdam, Lisbon and Stockholm and to my current home city, Copenhagen dominated.  Saltpeter was one of the largest commodities by volume for the Dutch East Indian Company.  (Frey, James W.   2009.) (9)  Its ships that sailed past our Cape Town brought vast quantities of unrefined saltpeter to be sold to England and European countries.

The state of ignorance as to the workings of saltpeter continued until in France, Antoine Lavoisier wrote in 1777 his groundbreaking works Instruction sur l’établissement des nitrières et sur la fabrication du salpêtreand  Publiée par ordre du roi, par les Régisseurs généraux des Poudres & Salpêtres where the link with nitrogen was made.  The breakthrough came in 1770 when he analysed nitric acid as a component of saltpeter. (Mauskopf, MSH.  1995:  96) (10)  

Lavoisier is the father of industrial chemistry.  By the time of his death, a good understanding of saltpeter’s chemical origin had been achieved.  (Mauskopf, MSH.  1995:  116)  The mystery was unraveled.  The compound is potassium nitrate.  It is the nitrate in Saltpeter which Ed Polenski’s speculated about, that is turned into nitrite through bacterial action that may be ultimately responsible for curing meat.

The brine mix that we use at Uncle Jeppe’s curing plant is fifteen pounds of salt, two and one-half ounces of crude East Indian Saltpeter and ten gallons of water with three-quarters of molasses.  The meat is emerged in this mix and cures in between forty to forty-five days, ready for smoking. (Shenango Valley News (Greenville, Pensylvania), 26 January 1883, page 3)

Jeppe’s lecture on saltpeter was one of the highlights of my time in Denmark.  He showed how the knowledge of its composition, being a compound chemical of potassium and nitrate (nitrogen and oxygen), became the key for Ed’s speculation that nitrite may be present in the mix after the 21 days of curing.  If soil and water bacteria turn nitrate into nitrite within 21 days, he developed the hunch that the exact same removal of the one “loose” oxygen atom from nitrate through bacteria, will probably turn nitrate into nitrite in curing brines also.  His hunch was right.

The lunch hour in Jeppe’s office seems too short.  He told me that this is a small part of the story.  Discoveries in a desert in Chile lead to war over saltpeter.  How was the action of bacteria discovered that remove one oxygen atom from nitrate to turn it into nitrtite?  How is nitrate formed?  So many questions to tackle over the next few weeks.  I am insanely excited to be here and learn these things.

I borrowed Uncle Jeppe’s notebook to copy the quotes he read.  I promised him that I would return it after the weekend.  I have many other things that I can copy from his book on Saltpeter but for today, what I have written will suffice.  Tomorrow is Monday and I will post your letter on my way to work.

I hope you are well my boy and that you continue to work hard at school!  Please be sure to keep an eye on your sister.  Remember that while I am gone you are the man of the house and you must take care of the woman.

(8)  Wall saltpeter (calcium nitrate), formed by nitrifying bacteria and found as an efflorescence on the walls of caves and stables, was gathered in China and India long before the Christian era. (Drs. Keeton, et al, 2009:  6)

(9)  “BETWEEN 1601 AND 1801, ships made thousands of voyages carrying goods from Asian ports to the primary European markets for East Indian commodities: Amsterdam, London, l’Orient, Copenhagen, Lisbon, and Stockholm. On average, these Indiamen measured 1,000 tons burden, with approximately 2,830 [m.sup.3] of cargo space. Sixteen percent of this cargo space, according to the normal practice of East India captains, consisted of saltpeter–some 452.8 [m.sup.3] of nitrates, weighing 1.6 metric ton”  (Frey, James W.   2009)

The British took over the Subah of Bengal from the VOC in 1757.   “The subsequent defeat of a VOC expeditionary force at Bedara in 1759, and the British defeat of the Mughals at Buxar in 1764 secured Company control over Bihar and permitted the monopolization of the saltpeter trade. The significance of these events cannot be underestimated. By seizing Bengal, the British exerted mastery over 70 percent of the world’s saltpeter production during the latter part of the eighteenth century.”  (Frey, James W.   2009)

(10)  One of Lavoisier’s major achievements of the 1770’s (and the one of particular interest to us) : the analysis of nitric acid.”  (Mauskopf, MSH.  1995:  96)

“Lavoisier’s chemical discoveries and reformulation, enabled him to delineate the chemical reaction that produced (explosive) gases : between the nitric acid component of saltpeter and the carbon in the charcoal.” (Mauskopf, MSH.  1995:  105)

He wrote the landmark paper in the spring of 1776 “in which Lavoisier demonstrated that nitric acid was a compound of nitrous gas with the portion of the pure air (la portion la plus pure de l’air) by decomposing the acid into these gases and then reconstituting it from them, and asserted for the first time that this “was a constituent of all acids and a principle of acidity” (la portion la plus pure de l’air).  (Mauskopf, MSH.  1995:  107)

“Saltpeter is a “borderline” substance between the organic and the inorganic world. Although clearly a neutral salt like other mineral salts, it only seemed to come into existence in the presence of organic substances in a state of decay. There was, therefore
a debate in the century before Lavoisier took up the subject over how this substance originated and whether or not vital processes were essential for its formation.”  (Mauskopf, MSH.  1995:  108)

“According to Macquer, three theories were current. The oldest one posited a non-vital origin of saltpeter (or at least of nitric acid) in the air. The other two, formulated in the eighteenth century, related nitric acid’s origin to organic processes. Lemery the Younger
postulated a completely organic origin : nitric acid developed in vegetable and animal substances. The theory of Georg Ernst Stahl, was, in a sense, the mean between the other two vis-a-vis organic and inorganic origins; moreover, it offered a chemical analysis
of nitric acid. To Stahl, this acid was a compound of the universal acid (vitriolic) and phlogiston. Although the source of vitriolic acid lay in the ambient air, this acid could only be converted into nitric acid through the agency of organic putrefaction, which liberated
the necessary phlogiston.”

“The origin and chemical nature of the fixed alkali component were only somewhat less obscure than that of nitric acid. “Fixed vegetable alkali” was one of a class of three alkaline substances (the other two were mineral and volatile alkali) that possessed many
common features. Two of these alkalis (vegetable and volatile) were thought to have organic origins while the mineral alkali, or, at least, its principal salt, common salt, was felt to be, in Macquer’s words, “a production of nature, and […] it does not belong to the plant kingdom or the animal kingdom, it is stored in the class of minerals. It is for this reason that we gave his name alkalile iTAlkali mineral” (une production de la nature, & […] il n’appartient ni au règne végétal, ni au règne animal, on le range dans la classe des minéraux. C’est par cette raison, qu’on a donné à son alkalile nom iTAlkali minéral).

. While alkalis, like acids, were distinct chemical substances operationally, they were not yet ontologically separate (nor would they be fully for Lavoisier).” (Mauskopf, MSH.  1995:  108)

“Lavoisier succeeded both in decomposing nitric acid with mercury into its components gases in succession “the rudy,  nitrous gas” and then “the portion of the pure air” (la portion la plus pure de l’air)  from the calx of mercury which had formed in the meantime and in reconstituting the acid from just these components gases over water. With this analysis, Lavoisier was moving towards a clear differentiation of acids into chemically distinct species (albeit with a common “acidifying principle”, a point also enunciated in this paper for the first time.” (Mauskopf, MSH.  1995:  108)

“By 1777, Lavoisier had reached the conclusion that the traditional (i. e. Macquerian) view of the role of the wood-ash treatment was indeed correct : it was necessary to employ wood-ash preferably both intermixt with saltpeterish earth and as a lessive in that earth’s first purification. His conclusion was based on systematic study of the tamarisk ash used by Parisian saltpetermen ; the crucial tests were of : 1° washed ash mixed with a) mother liquid of raw saltpeter and b) an artificial liquid of “chalk cham loin cloth” (craie de champagne)  dissolved in very pure nitric acid; and 2° the same tests using unwashed ash. In the first set of tests, no saltpeter was obtained; the second yielded 7 ounces. Prior to the reports on the tests, Lavoisier had given the results of his analyses of the Parisian ash itself : he had found various salts including «sélénite», «tartre vitriolé» (selenite, tartar vitriolated) , Glauber salt and common salt.

At first surprised at the production of saltpeter in the second set of tests with unwashed ash, Lavoisier soon produced more tests and a chemical explanation : «… il ne m’était pas possible de douter qu’il ne se fût opéré unedouble décomposition en vertu d’une double affinité; que, d’une part, l’acide vitriolique qui entre dans la composition de ces sels ne se fût combiné avec la terre calcaire de l’eau-mère pour former de la sélénite, et que, de l’autre, l’acide nitreux ne se fût emparé de la base alcaline du sel de Glauber et du tartre vitriolé pour former de véritable sal pêtre.»  Translate:  “it was not possible for me to doubt that he would have made unedouble decomposition under a dual affinity; that, on the one hand, the corrosiveness acid in the composition of these salts was not combined with the ground limestone mother liquor to form selenite, and, on the other, acid nitrous was not captured the alkali and Glauber’s salt to form tartar Vitriolated real sal Petre”

As confirmation, Lavoisier combined the mother liquids of « very pure » niter with solutions of vitriolated tartar and other vitriolates. In all cases, selenite and a niter of whatever base of the vitriol were formed. He concluded :« // est évident, d’après tout ce qui vient d’être dit, que les cendres qu’on emploie dans la fabrication du salpêtre ne servent pas seulement en raison de la partie alcaline qu’elles contiennent à nu; qu’elles agissent encore en raison de la partie alcaline qu’elles contiennent dans un état de neutralité, et combinée avec l’acide vitriolique. Ainsi, peu importe qu’on emploie, pour décomposer l’eau-mère et pour la convertir en vrai salpêtre, un alcali fixe à nu, ou un sel vitriolique à base d’alcali; l’effet est le même, et l’acide nitreux, dans les deux cas, va chercher de préfé rence l’alcali contenu dans le sel, et en déloge l’acide vitriolique. »  Translated:  Is clear from all that has been said, that the ashes that employed in the production of not only serve saltpetre because they contain the alkaline part exposed; they act yet because of the alkaline part in a state that they contain neutrality, and combined with the vitriolic acid. Thus, regardless of we used to split water mater and to convert it into real saltpeter, alkali fixed bare or vitriolic based salt alkali; effect is the same, and nitrous acid, in each case, pref fetches ence alkali content in salt, and removes the vitriolic acid.”  (Mauskopf, MSH.  1995:  112, 113)

Those days seem far away. Uncle Jeppe is teaching me the basics of meat curing.  The magical salt that accomplish curing is called saltpeter.

For many years we did not know what saltpeter is composed off.  We knew what one could do with it.  It is a salt that is used for explosives, meat curing, to fertilize crops, cool beverages and by the late 1800’s, even as a treatment for blood pressure.  In many regards, saltpeter was the subject of an arms race between nations in the middle ages as they jostled for superiority in matters pertaining to ammunition and agriculture.  Saltpeter was the key ingredient in both these.

By far the largest natural deposits were found in India (potassium nitrate) and the East Indian Companies of England and Holland were in large created to facilitate its acquisition and transport.  Later, massive deposits of sodium nitrite were discovered in the Atacama Desert of Chili and Peru and became known as Chilean Saltpeter.

At a few places, some peoples of the ancient world cured their meat with saltpeter and enjoyed its reddening effect, it’s preserving power and the amazing taste that it gave.  It was, however, not widely used until the 1700’s when it became more commonly used and by 1750, its use was probably universal in curing mixes.

The ancients could not tell if saltpeter occurred naturally or was it something that had to be nourished or cultivated by humans. Later we worked out that both are true.  It was found naturally and the technology of producing it became common knowledge among farmers in Germany.  Generally, when the ancients managed to get hold of it, they wondered how to take the impurities out of the salt which gave inconsistent results in curing meat, fertilising fields and in the quality of gunpowder produced from it.

People were baffled by its power.  Almost every great civilization used it in one way or the other.  Romans used it to cure meat as early as 160 BCE.  The Chinese and Italians used it to make gunpowder.  There is a record of gunpowder being used in India as early as 1300 BCE, probably introduced by the Monguls.  It was used since ancient times as medicine and as fertilizer. (Cressy, David, 2013:  12)   Saltpeter was used in ancient Asia and in Europe from the 1500’s to cool beverages and to ice foods.  (Reasbeck, M:  4)  The first reported references to the characteristic flavor of cured meat produced by the addition of saltpeter during meat preservation and curing were made as early as 1835.  (Drs. Keeton, et al;  2009)  Some speculated that it contained the Spiritus Mundi, the ‘nitrous universal spirit’ that could unlock the nature of the universe!  (Cressy, David, 2013:  12)

Peter Whitehorney, the Elizabethan theorist who wrote in 1500’s, said about saltpeter, “I cannot tell how to be resolved, to say what thing properly it is except it seemeth it hath the sovereignty and quality of every element”.  Paracelsus, the founder of toxicology who lived in the late 1400’s and early 1500’s said that “saltpeter is a mythical as well as chemical substance with occult, as well as material connections.”  The people of his day saw  “a vital generative principle in saltpetre, ‘a notable mystery the which, albeit it be taken from the earth, yet it may lift up our eyes to heaven’”   (Cressy, David, 2013:  12)

From the 1400’s to the late 1800’s scientific writers probed the properties of this magical compound.  “Saltpeter encompassed the “miraculum mundi”, the “material universalis” through which ‘our very lives and spirits were preserved.  Its threefold nature evoked ‘that incomprehensible mystery of … the divine trinity,’ quoting Thomas Timme who wrote in 1605, in his translation of the Paracelsian Joseph Duchesne.  “Francis Bacon, Lord Chancellor and Privy Councillor under James I, described saltpeter as the energizing “spirit of the earth.””   (Cressy, David, 2013:  14)

From as early as the mid-1600’s, important observations started to emerge about saltpeter but without any real experimental basis.  Some of these conclusions were based purely on speculation but were remarkably accurate.  Johan Rudolph Glauber (1604-1670) detected it in plants, animals, and soil in 1658 .  He speculated on the chemical relationships that bind them together. Despite the fact that he did not do many experiments on plants, he suggested the efficacy of saltpeter in plant nutrition.  He called it “the Universal Menstruum,” since by it, “he wrote. .. every pure Sand destitute of all fatness is quickly so fatted . . . we affirm that the Salt-Petre was of necessity in the Herbs, & Grass, afore the Beasts feeding on them ….”  (Aulie, R. P.; 1970:  440)

In 1676 Edme Mariotte (1620-1684) quite brilliantly speculated about the role of the atmosphere in plant nutrition, despite not having any experimental basis for his speculation.   He correctly stated that “these volatile salts, etc., are mixed in the air with aqueous vapors, etc., and fall again with the rain formed with these vapors onto the surface of the ground.  There they penetrate together as far as then roots of plants, where they enter with some particles of soil…” (Aulie, R. P.; 1970:  440)

From the earliest times, the study of saltpeter was done concurrently with a study in fertilisers and explosives. Beginning with the work of John Woodward (1665 – 1728) of the Royal College of Physicians, the speculation on saltpeter and fertilisers of the 17th century ended and made way in England for a much more practical approach to agriculture.  The French chemists, like Boussingault, took up the challenge of rigorous scientific research on the subject.

Another French Chemist, Louis Lemery (1677-1743), “showed for the first time that saltpeter is of organic origin and that it cannot be considered a mineral. In his 1717 paper, “On the Origin of Nitre,” he described its slow production in the superficial layers of the soil. He also recognized the reciprocal relationships that characterized plants, animals, and the soil, while denying the previous “nitro-aerial matter.”  (Aulie, R. P.; 1970)

There is an interesting reason behind the changes in focus between the English and the French.  England gained access to the saltpeter fields in India reducing the national priority of understanding it in order to manufacture it.  The French, on the other hand, never had access to natural saltpeter and it had to find better ways of producing it in order to satisfy the demand of its enormous military and, I am sure, their farmers.

The practical approach of the English to fertilizers became an important backdrop of the future work of the brilliant French chemist Jean-Baptiste Joseph Dieudonné Boussingault (1 February 1801 – 11 May 1887).  Boussingault would become one of the most prolific scientists in terms of the research on nitrogen and is rightly credited for laying the foundation for the discovery of the nitrogen cycle.  (Aulie, R. P.; 1970)

The next major milestone on the road to the full realization of the role of nitrogen in nutrition was the identification of “nitrogen as a gas in the atmosphere, and as a constituent of both animal and plant tissues”.  These occurred in the last quarter of the eighteenth century as a combined achievement of English and French chemistry. (Aulie, R. P.; 1970)

“By 1772 the English pneumatic chemists had isolated “mephitic air,” but they had not yet established its elemental nature.  The French quickly saw the importance of the English gas studies and, beginning with Antoine Laurent Lavoisier (1743-1794), rapidly incorporated them into their own work. They invented the names azote and nitrogene for the new gas, established its elemental nature, determined its quantitative percentages in nitric acid, ammonia, and saltpeter, and began to detect les azotates de potasse in many plants, all before the close of the eighteenth century.” (Aulie, R. P.; 1970)

The chemical elements of potassium, nitrogen, and oxygen as constituents of saltpeter were identified even though there remained uncertainty about the exact ratio of atoms.  The value of nitrogen in plant and animal nutrition was elucidated by scientists, particularly by Boussingault.  His work laid the foundation for the discovery of the role of microorganisms in fixation of nitrogen as well as the reduction of nitrates to nitrite and ammonia.

The next few years saw scientists and in particular, Boussingault, starting to understand the value of nitrogen in plant and animal nutrition.  A key question that had to be answered was the source of the nitrogen.  One of the possible sources that was still being looked at with great interest was atmospheric nitrogen.  Another, more obvious source, at this time, due to the long and well documented use of saltpeter, was nitrates.

Boussingault turned his attention in 1855 to conducted research on nitrates as a source of plant nitrogen.  This naturally led him to inquire how they are formed in the soil.  He asked the question “if nitrates and ammonium salts are interchangeable in the soil, and which is the more efficacious; is one or the other actually the form in which nitrogen is absorbed by plants? Furthermore, did nitrates act essentially like alkali salts because of their sodium or potassium content, or like ammoniacal salts?” (Aulie, R. P.; 1970)

“Beginning with Boussingault in 1855, various workers attempted to settle these questions with the view of determining how plants get their nitrogen. These essentially chemical attempts continued until the late 1870’s, when the modern biochemical interpretation began to emerge.  Kuhlmann thought that nitrates were formed by the oxidation of ammonia in the soil. As a corollary to this view, he also maintained that the utility of nitrates was due to their deoxidation into ammonium compounds in the soil. Noting the constant association of organic materials with nitrification, although, to be sure, missing the importance of microorganisms, he went on to assert that putrid fermentation was a necessary condition for this nitrification.” (Aulie, R. P.; 1970)

“In the spring and summer of 1855, Boussingault examined this hypothesis by investigating the influence of potassium on Helianthus argophyllus, or the sunflower. He wished first to test whether putrescible organic material in the soil was absolutely indispensable for the absorption of the nitrogen of nitrates, and second, to determine whether there was a prior transformation into ammonium compounds.” (Aulie, R. P.; 1970)

“The first part of this hypothesis was easy to test, which he did, by using an artificial soil free of all organic materials. In his first experiment, he reported to the Academie that his sunflowers flourished in a soil composed of calcined sand and ash, when watered with a solution containing 1.11 grams of potassium nitrate (saltpeter).”  (Aulie, R. P.; 1970)

“He showed that all the nitrogen could be accounted for by the potassium nitrate (saltpeter). Although Boussingault could not then test for the nitrate “ion,” the contemporary ideas of “equivalents” allowed him to determine the relative proportions of nitrogen and potassium both in the soil and in his experimental plants. At the time he began his nitrate work, there was still confusion about the number of atoms that would combine to make a compound. But chemical equivalents were directly measurable, and this concept Boussingault readily used to good advantage, as did many chemists of his day.  Dictionaries and texts gave the composition of potassium nitrate as KO,AzO5.146.” (Aulie, R. P.; 1970)

Boussingault reasoned that by determining the ratio of alkali to nitrogen in his test plants, and comparing this figure with the known value for niter, he would be able to draw a conclusion with respect to its possible prior transformation in the soil. The data show that the action of potassium nitrate was manifest in the absence of decomposing organic material. But did the nitrogen enter as a nitrate or as ammonia? The answer to this question depended on the ratio of potassium to nitrogen in the soil.”  (Aulie, R. P.; 1970)

“Boussingault considered his figures close enough to warrant the conclusion that potassium nitrate was absorbed as such by each equivalent of potassium, at least in this experiment, without prior transformation in the soil. Transformation into an ammonium salt prior to absorption would have resulted presumably in different analytical results, owing to the escape of volatile ammonia. His control plant languished in the absence of potassium nitrate; a slight increase in nitrogen he attributed to a visible cryptogamic contamination.” (Aulie, R. P.; 1970)

“From the beginning of his career, Boussingault was aware that nitrogen was far from the only useful element in plant nutrition. As early as 1841 he was “certain that many calcium and mineral salts are indispensable for the development of plants.”  His work on nitrates in the late 1850’s was an experimental confirmation of his earlier views. Having demonstrated qualitatively in 1855 with Helianthus the pronounced growth that results with a regimen of potassium nitrate (saltpeter), Boussingault in 1857 then went on to demonstrate the quantitative effects produced in this plant by both mineral and nitrogen components of fertilizer on the elaboration of organic materials.”  (Aulie, R. P.; 1970)

Saltpeter, nitrogen and its role in plant and animal, including human nutrition, the nitrogen cycle, nitrifying and denitrifying bacteria are all integrally connected fields of study.  It encompasses chemistry, biochemistry, bacteriology, nutrition, medicine and meat science and even today the various complex mechanisms associated with its efficacy as fertiliser and curing agent is not fully understood by science.

Another interesting link between Polenske and Boussingault is the way in which Polenske sought to determine the nutritional value of cured beef.  He looked at amongst other, the nitrogen content.  This had its origin in work done by Boussingault and Magendie.

“Franqois Magendie (1783-1855) reported in a classic study in 1816 that dogs could not survive on a diet of non-nitrogenous food alone.  He wrote that “It would be of fundamental importance in the history of nutrition, if the source could be determined of the nitrogen which is found in such great abundance in the animal body”.  It was this study of Magendie that gave Boussingault the “clue on which he promptly acted in his first research work. This clue was the identification of nitrogen as an important ingredient in animal diet.”  It was on the basis of this work that Dr. Polenske wrote his 1891 article, examining the nutritional value of cured beef by focussing on its nitrogen content.  The obvious loss of nitrogen in the curing process caused him to view cured meat as inferior to fresh meat.  (Aulie, R. P.; 1970)  Even today, it is a recognised fact that nitrogen is an important ingredient in a healthy diet.



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