Introduction to Bacon & the Art of Living
The story of bacon is set in the late 1800s and early 1900s when most of the important developments in bacon took place. The plotline takes place in the 2000s with each character referring to a real person and actual events. The theme is a kind of “steampunk” where modern mannerisms, speech, clothes and practices are superimposed on a historical setting. Modern people interact with old historical figures with all the historical and cultural bias that goes with this.
The Direct Addition of Nitrites to Curing Brines – the Spoils of War
I thought I would write your sister this time around but then realised that I have to finish my tale of how sodium nitrite became the most popular way to add nitrite to curing brines. It one of the most epic developments in the curing world.
From a scientific standpoint, using sodium nitrite as the source of nitrite is an important progression of the technology of bacon curing but there was a problem. The general public saw sodium nitrite as a poison and the cost was exorbitant. It would require more than just an energetic and brilliant Master Butcher from Prague to convince the world that it is an improvement in curing technology.
Early Public Perception about Nitrite
Between the mid-1800s and early 1900s, industry and informed members of the public knew nitrite as an ingredient in medication  (Vaughn E, et al.;2010; Jul–Aug; 18(4): 190–197) and sodium nitrite as an intermediary in the chemicals dye industry. (Concerning Chemical Synthesis and Food Additives) Most people, however, knew nitrite as a toxic chemical that kills livestock and people if the drinking water has even small traces of it. Such was the concern that nitrite levels in drinking water were reported in local newspapers every week to alert the public to possible contamination. It is, therefore, no wonder that the public and authorities were very skeptical about its use in food.
At the beginning of the 1900s, scientists developed a detailed understanding of the chemistry of curing which showed the priority of nitrites. In contrast to this, the general public and their elected officials were against the direct use of nitrites in food. As is many times the case, the scientific understanding was not general knowledge.
Three parts of the world now become the focus of our attention namely Prague, Germany and in the USA, Chicago. Events, dates, and places will start to overlap and two processes will become very important, the electric arc method of extracting nitrogen from the atmosphere and the Haber process.
As we do so, it is important to understand one more point in chemistry namely the close proximity of nitric oxide (), nitrous acid (), nitric acid (), nitrite (), nitrate () and ammonia (). All have a nitrogen atom as part of either the molecule or the ion. The Haber process yields ammonia () and the electric arc process, either nitrous acid () or nitric acid (). From any of these, nitrite () can be formed. (Webb, H. W.; 1923)
Germany 1910 – 1920 – the Race to Access Atmospheric Nitrogen
Austerity for the middle class in Germany during the Great War.
By the end of the war, the largest stockpiles of nitrite in the history of humanity were in Germany. It was created by the most productive chemicals industry in the world. How this happened is fascinating!
By the late 1800s, it was apparent that the world’s growing populations will not be fed unless atmospheric nitrogen can be harvested. Solving the problem of how to achieve this became one of the biggest priorities of science. After an intense search and various processes tested on an industrial scale, including the electric arc method, the German chemist, Fritz Harber finally solved the problem with the help of Robert Le Rossignol who developed and build the required high-pressure device to create ammonia from atmospheric nitrogen.
The process was first demonstrated in 1909. The German dyes manufacturer, BASF acquired the technology and under the leadership of Carl Bosch, the first Haber-process factory went into operation in Oppau, Germany in 1913. (Concerning the direct addition of nitrite to curing brine) As a direct consequence of this development, Germany was no longer reliant on saltpetre from Chili (sodium nitrate) as fertilizer to feed its massive agriculture industry. Another consequence of the Haber process is that it made World War One possible on an industrial scale. Nitrogen is key in ammunition production. Germany and its allies could escalate the war to a never before seen level.
When ammonia is made from atmospheric nitrogen, it was possible to produce nitrates and nitrites. The concept of using nitrites as a preservative in food was not something new. There are good examples of Germans toying with the use of nitrite in food, even before the war. The German scientist, Glage (1909) wrote a pamphlet where he outlined the practical methods for obtaining the best results from the use of saltpetre in the curing of meats and in the manufacture of sausages. (Hoagland, Ralph, 1914: 212, 213)
Glage gives for the partial reduction of the saltpetre to nitrites by heating the dry salt in a kettle before it is used. It is stated that this partially reduced saltpetre is much more efficient in the production of colour in the manufacture of sausage than is the untreated saltpetre (Hoagland, Ralph, 1914: 212, 213), pointing to the fact that nitrite was being considered as a preservative and for its effect of meat colour, from the earliest times. This means that by the 1910s, German scientists tried to solve the problem by still using saltpetre as a starting point to the reaction but getting to a reduced state faster. The line of thinking of using nitrate as the starting point was finally perfected by the Irish, Danes, and British who allowed the reduction to take place at the normal pace through bacterial means. In developing tank curing, there is no indication that they had any inkling of why it worked. They merely joined different known methods which resulted in faster curing in one cohesive system.
The main obstacle to using nitrite directly was still its cost. When BASF’s new Haber process came into operation, sodium nitrite became generally and cheaply available which meant for curing of meat that it could be added directly without allowing a bacterial reduction of nitrate to nitrite first. Solving the problem by using sodium nitrite was now a serious possibility. The Great War provided the environment to “motivate” the entire meat-curing industry to change from saltpetre to sodium nitrite when saltpetre was suddenly not available for curing and survival was linked to the speed of curing which all resulted in the fact that public perceptions were put aside.
It was a document from the University of Vienna which was the first breakthrough in my research which unlocked the mechanism of how sodium nitrite became the curing chemical of choice. According to it, saltpetre was reserved for the war effort and was consequently no longer available as curing agent for meat during World War One. (University of Vienna). It was reserved for the manufacturing of explosives, and for example, the important industry of manufacturing nitrocellulose, used as a base for the production of photographic film, to be employed in war photography. (Vaupel, E., 2014: 462) It gets even better. The prohibition on the use of saltpetre gives us the background of why people started using sodium nitrite as curing salt instead of saltpetre in Germany.
In August 1914, the War Raw Materials Department (Kriegsrohstoffabteilung or KRA) was set up under the leadership of Walther Rathenau. It was Rathenau who was directly responsible for the prohibition on the use of saltpetre. (11) He, therefore, is the person in large part responsible for creating the motivation for the meat industry in Germany to change from saltpetre to sodium nitrite as a curing medium of choice. It was the vision and leadership of Walther Rathenau, the man responsible for restricting the use of saltpetre, which drove Germany to produce synthesized Chilean Saltpeter. He saw this as one of the most important tasks of his KRA. He said: “I initiated the construction of large saltpetre factories, which will be built by private industries with the help of government subsidies and will take advantage of recent technological developments to make the import of saltpetre entirely unnecessary in just a few months“. (Lesch, J. E., 2000: 1)
Fritz Harber was one of the experts appointed by Rathenau to evaluate a study on the local production of nitric acid. During World War One production was shifted from fertilizer to explosives, particularly through the conversion of ammonia into a synthetic form of Chile saltpetre, which could then be changed into other substances for the production of gunpowder and high explosives (the Allies had access to large amounts of saltpetre from natural nitrate deposits in Chile that belonged almost totally to British industries; Germany had to produce its own). It has been suggested that without this process, Germany would not have fought in the war, or would have had to surrender years earlier.” (www.princeton.edu)
So it happened that Germany became the leader in the world in synthesised sodium nitrate production and it effectively replaced its reliance on saltpetre from Chile with synthesised sodium nitrate, produced by BASF and other factories. As a result of the First World War, sodium nitrite was produced at levels not seen previously in the world and in large factories that were built, using the latest processing techniques and technology. Sodium nitrite, like sodium nitrate, was later used in the production of explosives. Nitroglycerin is an example of an explosive used extensively by Germany in World War One that uses sodium nitrite in its production.
Ball-and-stick model of Amyl nitrite used in the production of nitroglycerin. Amyl nitrite is produced from sodium nitrite. The diagram shows the amyl group attached to the nitrite functional group.
Sodium nitrite and the coal-tar dye industry
The importance of the manufacturing cost of nitrite and the matter surrounding availability can be seen in the fact that sodium nitrite has been around since well before the war. Despite the fact that it was known that nitrite is the curing agent and not nitrate, and despite the fact that sodium nitrite has been tested in meat curing agents, probably well before a clandestine 1905 test in the USA, it did not replace saltpetre as the curing agent of choice. This was due to cost restrictions as much as public opinion.
The technology that ultimately is responsible for synthesising Chilean Saltpeter and made low-cost sodium nitrite possible was incubated in the coal-tar dye and textile industry and in the medical field. The lucrative textiles and dye industry was the primary reason for German institutions of education, both in science and engineering to link with industry, resulting in strong, well-organised skills driven German economy. For example, “Bayer had close ties with the University of Göttingen, AGFA was linked to Hofmann at Berlin, and Hoechst and BASF worked with Adolph Baeyer who taught chemists in Berlin, Strasbourg, and Munich.” (Baptista, R. J.. 2012: 6)
“In the late 1870s, this knowledge allowed the firms to develop the azo class of dyes, discovered by German chemist Peter Griess, working at an English brewery, in 1858. Aromatic amines react with nitrous acid to form a diazo compound, which can react, or couple, with other aromatic compounds.” (Baptista, R. J.. 2012: 6) Nitrous acid (HONO) is to nitrite (NO2-) what nitric acid (NO3) is to nitrate (NO3-). According to K. H. Saunders, a chemist at Imperial Chemical Industries, Ltd., Martius was the chemist to whom the introduction of sodium nitrite as the source of nitrous acid was due. (Saunders, K. H., 1936: 26)
The Economic Imperative
The simple fact is that ammonia can be synthesized through the direct synthesized ammonia method at prices below what can be offered through Chilean Saltpeter. (Ernst, FA. 1928: 92 and 100) Sodium Nitrite can be supplied at prices below Chilean saltpetre and this made sodium nitrite the most effective curing agent at the lowest price since World War One.
As an example of the cost differences, the price of Nitric Acid (HNO3) from direct synthesis in 1928 was $23.60 per ton HNO3 plus the cost of 606 lb. of NH3 by-product and from Chilean Nitrate at $32.00 per ton of HNO3, plus the cost of 2840 N NO3 by-product. (Ernst, FA. 1928: 112)
The Advantage of Scale and Technology
By 1927, Germany was still by far the world’s largest direct syntheses ammonia producer. Production figures for the year 1926/ 1927 exceeded Chilean saltpetre exports even if compared with the highest levels of exports that Chilean saltpetre ever had in 1917. A total of 593 000 tons of nitrogen was fixed around the world in 1926/27. Of this figure, Germany produced 440 000 tons or 74%. The closest competitor was England through the Synthetic Ammonia and Nitrates Ltd. with a total capacity of 53 000 tons of nitrogen per year. (Ernst, FA. 1928: 119, 120) In the USA, seven direct synthesis plants were in operation with a combined capacity of 28 500 tons of nitrogen per year. (Ernst, FA. 1928: 120)
Supporting Evidence from the USA
The thesis that before the war, the production of sodium nitrite was not advanced enough for its application in the meat industry (resulting in high prices and low availability) is confirmed when we consider the situation in the USA. The first US plant for the fixation of atmospheric nitrogen was build in 1917 by the American Nitrogen Products Company at Le Grande, Washington. It could produce about one ton of nitrogen per day. In 1927 it was destroyed by a fire and was never rebuild. (Ernst, FA, 1928: 14)
An article in the Cincinnati Enquirer of 27 September 1923 reports that as a result of cheap German imports of sodium nitrite following the war, the American Nitrogen Products Company was forced to close its doors four years before the factory burned down. The imports referred to, was as a result of Germany selling their enormous stockpiles of sodium nitrite at “below market prices” and not directly linked to a lower production price in Germany, even though this was probably the case in any event. (The Cincinnati Enquirer ( Cincinnati, Ohio), 27 September 1923. Page 14.)
The meat curers initially used sodium nitrite directly (i.e. not mixed with sodium chloride). It looks similar to regular table salt. Several cases of poisoning were reported including the mass poisoning of 34 people including a child who died in Leipzig. The Government promptly banned its use (Hans Marquardt , et al, 1999:21), but in the prevailing war conditions, and with the Government’s inability to stamp out the massive black market in foods, there can be no doubt that this practice persisted throughout the war.
The practice of colouring curing salt containing sodium nitrite pink, probably stems from this indecent or incidents like this, in order to prevent people from confusing sodium nitrite with table salt. The practice became law in most countries in subsequent years and the remains to this day. The Vienna University document indicates that the fast curing of sodium nitrite was recognised and after the war, the ban was lifted. Walter Rathenau’s actions may have motivated the change, but it was the developments in synthesizing ammonia, sodium nitrate and sodium nitrite which provided the price point for the compound to remain the curing agent of choice, even after the war and after the prohibition on the use of saltpetre was lifted.
By 1909, the world production of inorganic nitrogen by the electric arc method and some miscellaneous processes were standing at a combined 3000 metric tons. The Haber process was not invented yet. One year after Ladic started working as a meat curer, by 1913, the arc and miscellaneous processes yielded 18 000 metric tons and the Haber process, 7000 metric tons.
By 1917, the arc and miscellaneous processes delivered 30 000 metric tons and the Haber process, 100 000 metric tons. This was 5 years after Ladic learned the art of curing and possibly started using sodium nitrite in meat curing. Over these five years, he has seen a dramatic increase in the availability of nitrite and therefore a reduction in nitrite prices. In 1920, the Haber process delivered a staggering 308 000 metric ton of nitrogen, compared to the 33 600 metric tons of the arc and miscellaneous processes. (Scott, E. Kilburn. 1923; : 859–76)
World War One broke out on 28 July 1914 and lasted until 11 November 1918. When the war ended, Germany had huge stockpiles of sodium nitrite (along with many other war chemicals). They had to pay a massive war debt and raise the German economy from the dead. These were desperate times and Germany threw its full energy and industriousness behind this effort. The effort focused on the lucrative market of the USA.
The USA – 1910’s – Nitrite on Trial
The drama of the sale of German nitrites played itself out in the USA and particularly in Chicago. This directly led to the creation of a legendary curing salt, Prague Salt, which later became Prague Powder. We used Prague Powder during all the years that I was with Woodys. These events played out in America.
We begin our US story by looking at public and government views on nitrite. During the 1910s, the USA wrestled with the question of whether nitrites in food constitute adulteration and its consideration created its own epic drama. Vastly opposing views were held in relation to preservatives and colourants generally. Prof. Julius Hortvet, a chemist at the Minnesota Dairy and Food Commission said in an address delivered on 16 July 1907, at the Eleventh Annual Convention of the Association of State and National Food and Dairy Departments, in Jamestown, “Some state laws go so far as to inflict fine and imprisonment for making an article appear better than it really is.” He presented the opposing view when he said that he believes that “if we must have legislation in regards to this, it would be wiser to reserve it and punish the man who did not make his food product as attractive as possible.” (American Food Journal; 1907)
In his speech, he made the following prophetic comment about saltpetre which in years to come would become one of the dominant arguments for the use of nitrite in foods. He said that “we know . . that certain substances, as salt and saltpetre, have caused death from the effects of large doses.” He then draws a brilliant comparison between these products and alcohol when he said that “alcohol is classed as a poison.” His point was that what is good for alcohol, which is a poison if consumed in high concentrations and large volumes, should be good for saltpetre (i.e. limit the amount of nitrate and nitrite in foods instead of banning it altogether, as is the case with alcohol). “In short,” he said, “the whole question sometimes is relative.” (American Food Journal; 1907)
He was “not contending that certain articles commonly used in . . . . food may or may not under certain circumstances act as a poison.” He was “simply defending . . . against two possible evils: first, the addition to . . . food of any substances that will tend to augment the possibilities of harm arising from our daily diet.” His second point sounds like one directed to the use of nitrite and its medicinal use when he said that “he is secondly defending against,” the addition to . . . foods of substances having therapeutic or even toxic properties by persons unqualified to prescribe such substances.” (American Food Journal; 1907) He is possibly tripped up by a lack of scientific understanding about nitrites at the time, but both cautionary notes are commended and points that I have for years lived by.
In the 1910s, the US Department of Agriculture had the right to promulgate “standards of purity for food products and to determine what is regarded as adulteration therein.” (American Food Journal; 1907 vol 2 no 2, 15 Feb 1907, p43) Whether these standards would become law was an open question at this stage. If there was a dispute about a substance, it was heard by a special organ of the US Department of Agriculture, the Referee Board of Consulting Scientific Experts, created in 1908. The battleground about the use of nitrites itself was not the meat industry. It seems that the meat industry considered and possibly used it in secret. The battle played out in its use as a bleaching agent in flour. The controversy came to a head in a landmark court case in 1910 related to flour.
The millers were infuriated because the attorney general opted for a jury trial instead of referring the matter to the Referee Board of Consulting Scientific Experts. (Chicago Daily Tribune; 7 July 1910; Page 15) I can only suspect that the attorney general was himself against the use of nitrites in food and probably did not want scientists to decide.
A court case was brought by the US Federal Government against the Mill and Elevator Company of Lexington, Nebraska. The charge was that they adulterated and misbranded flour and sold it to a grocer in Castle, Missouri. The government seized as evidence 625 sacks of flour from the grocer. The court case lasted five weeks. The case was brought by the government under the pure food and drug act of 1906. (Chicago Daily Tribune; 7 July 1910; Page 15) This is an act “for preventing the manufacture, sale, or transportation of adulterated or misbranded or poisonous or deleterious foods, drugs, medicines, and liquors, and for regulating traffic therein, and for other purposes.” (www.fda.gov)
The government contended that “poisonous nitrites are produced in the flour by bleaching.” They did not share the view of Prof. Julius Hortvet that we looked at earlier who said that these matters are relative to the amount of the substance used since alcohol is also a poison if used in the right quantity. The Federal Government said that “any amount of poison introduced into food is an adulteration.” (Chicago Daily Tribune; 7 July 1910; Page 15)
The issue was that as much as 80% of the flour produced in the USA during that time was bleached with a nitrogen peroxide process. Flour naturally has a creamy tint. The cheaper the grade, the more creamy it is. In ages past, flour was bleached simply by age. The chemical bleaching process with nitrogen peroxide instantly changes the yellowest flour whiter than the highest grade. The process results in residue traces of nitrous and nitric acid being left in the flour which produce nitrites and nitrates. (Chicago Daily Tribune; 7 July 1910; Page 15)
The defence argued that “nitrates (and nitrites) were present in such small quantities that no man could eat enough bread at one time to be poisoned by them.” (Chicago Daily Tribune; 7 Jul 1910; Page 15) The government contended that “if this view were upheld by the courts all foodstuffs manufactured could introduce quantities of poison into their products, infinitely small in each case, but devastating in their cumulative effect.” (Chicago Daily Tribune, 7 Jul 1910, Thu, Page 15) (I will look at the arguments and provide an overview of how the international food industry answered it in the years following 1910 in a separate letter)
This was a case of huge importance to the industry as can be seen from the list of people called upon by the defence. Pierce Butler of St Paul acted as a special attorney for the defence. (Chicago Daily Tribune; 7 Jul 1910; Page 15) Whether he still had the position in 1910 when the case was heard must be verified, but he was a lawyer of such stature that in 1908, Butler was elected President of the Minnesota State Bar Association. From 1923 to 1939 he served as Associate Justice of the Supreme Court of the United States. (saintpaulhistorical.com)
Apart from Butler, “a large staff of distinguished lawyers fought for the company whose flour was seized, and for the millers of Nebraska, the millers of Kansas, and the company who makes the bleaching machines. Among the experts who testified were all the toxicologists who testified in a previous landmark case (the Swope case), professors of chemistry and medicine from twenty universities, doctors, bakers, millers, and housewives.” (Chicago Daily Tribune; 7 Jul 1910; Thu, Page 15) After seven hours of deliberation, the jury returned a verdict in favour of the government upholding the charge that the bleached flour was both adulterated and misbranded. (Chicago Daily Tribune; 7 Jul 1910; Thu, Page 15) It is fair to conclude that by 1910, nothing was more sensitive in food production than the presence of nitrites and the use of sodium nitrite in food was highly controversial.
Sodium Nitrite Tested in Meat Curing in Chicago
In the early 1900s, in Chicago, the powerful meatpacking companies set up by Phil Armour, Gustav Swift, and Edward Morris were all looking for ways to reduce steers to beef and hogs to pork in the quickest, most economical and the most serviceable manner.” (The Indiana Gazette. 28 March 1924). The earliest reference to a test of meat curing with sodium nitrite in the USA places a secret experiment conducted where sodium nitrite was used to cure meat in 1905.  This was probably done in Chicago. When the “Pure Food and Drug Act and Meat Inspection Act” of 1906 was promulgated, it made the use of sodium nitrite in food illegal. It was not specifically forbidden, but the act was applied, for example in the 1910 court case we just looked at, in such a way that it was seen as making its use in food illegal.
During the 1910s a very interesting article appeared in Chicago that places a company with the technology to produce sodium nitrite in the same city. It appeared in the American Food Journal of 15 February 1907 entitled “Cheap Nitrogen.” It said that a Chicago-based company was producing nitric acid by the electric arc method invented by Prof. Mościcki of the University of Freiburg, Switzerland, that we looked at before. The method, in reality, was able to produce both nitric and nitrous acid (US patent US1097870) and dates back to 1901. (cesa-project.eu) The article states that the process made its production “cheap enough to be commercially applicable.” (American Food Journal. Vol 2. No 2. 15 Feb 1907, p29) The entrepreneur behind this company was William M. Thomas, who set an experimental plant up in Marshfield Avenue, Chicago. His main goal was probably to produce fertilizer. (Chicago Sunday Tribune, Nov 10, 1907)
We have already referred to the electric arc method several times. Mościcki, the inventor of the process was the former assistant to Józef Wierusz-Kowalski (1896), professor of physics, and rector (provost) at Albert-Ludwigs University in Freiburg, Switzerland. Prof Mościcki was an interesting person. After a very successful academic career and a career as an inventor, he became the 3rd president of the second Polish Republic. He was in office from 4 June 1926 to 30 September 1939. Another interesting fact relates directly to his invention is that in Bern, Switzerland, his patent application was handled by none other than Albert Einstein.
“In 1905 Einstein evaluated Prof Mościcki’s special arc furnace which employed a rotating electric arc and was used for the production of nitric (and nitrous) acid…” ”The field generated by an electromagnet was used to rotate the arc. The 26-year-old physicist (Einstein) and the still young (38) but already renowned inventor and scholar (Prof Mościcki’s) met and discussed the patented idea. Einstein was curious to know why an electric arc changed its orientation in a magnetic field.” Prof Mościcki’s became a successful businessman in Switzerland. (Zofia Gołąb-Meyer Marian. 2006) 
When we looked at the career of Ladic Nachtmullner, we have seen that the first production of nitrous acid in Switzerland was in 1910, during World War One based on the invention of Prof Mościcki. This happened “immediately after his procedure was patented.” “A factory was opened in Chippis in Wallis canton, Switzerland.” “In the subsequent years, this procedure was substantially perfected and nitrous acid could be supplied not only to Switzerland but also to neighbouring countries.” (cesa-project.eu)
What is interesting in relation to Chicago is that the American Food Journal article says that the Chicago company was already in production by 1907 manufacturing nitric acid “in a small way” from free nitrogen, using the technology invented by Mościcki’s. (American Food Journal. Vol 2. No 2. 15 Feb 1907, p29) In the USA the fixation of atmospheric nitrogen was a priority and they knew they lagged behind Germany. The first US plant for the fixation of atmospheric nitrogen was built in 1917 by the American Nitrogen Products Company at Le Grande, Washington. It could produce about one ton of nitrogen per day. In 1927 it was destroyed by a fire and was never rebuild. (Ernst, FA, 1928: 14)
An article in the Cincinnati Enquirer of 27 September 1923 reports that as a result of cheap German imports of sodium nitrite following the war, the American Nitrogen Products Company was forced to close its doors four years before the factory burned down. We will consider America’s response to these cheap imports momentarily. (The Cincinnati Enquirer ( Cincinnati, Ohio), 27 September 1923. Page 14.)
We can conclude then with great certainty that there was at least one company in Chicago by 1907 that could produce sodium nitrite. Was this venture funded by the meatpacking companies? It is a question for further discovery. A much larger project got underway in 1917, but by 1923, the USA was not in a position to supply material quantities of sodium nitrite.
Nitrite Curing Known in the USA Pre-1925
A document, published in the USA in 1925 shows that sodium nitrite as a curing agent has been known well before 1925. The document was prepared by the Chicago based organisation, The Institute American Meat Packers and published in December 1925. The Institute started as an alignment of the meatpacking companies set up by Phil Armour, Gustavus Swift, Nelson Morris, Michael Cudahy, Jacob Dold and others with the University of Chicago.
A newspaper article about the Institute sets its goal, apart from educating meat industry professionals and new recruits, “to find out how to reduce steers to beef and hogs to pork in the quickest, most economical and the most serviceable manner.” (The Indiana Gazette. 28 March 1924). The document is entitled, “Use of Sodium Nitrite in Curing Meats“, and it is clear that the direct use of nitrites in curing brines has been practised from earlier than 1925. (Industrial and Engineering Chemistry, December 1925: 1243) The article begins “The authorization of the use of sodium nitrite in curing meat by the Bureau of Animal Industry on October 19, 1925, through Amendment 4 to B. A. I. Order 211 (revised), gives increased interest to past and current work on the subject.” Sodium Nitrite curing brines would therefore have arrived in the USA, well before 1925.
It continues in the opening paragraph, “It is now generally accepted that the saltpetre added in curing meat must first be reduced to nitrite, probably by bacteria, before becoming available as an agent in producing the desirable red colour in the cured product. This reduction is the first step in the ultimate formation of nitrosohemoglobin, the colour principle. The change of nitrate to nitrite is by no means complete and varies within considerable limits under operating conditions. Accordingly, the elimination of this step by the direct addition of smaller amounts of nitrite means the use of less agent and a more exact control.”
Aftermath of the Great War
At the end of World War One, England had its own stockpiles of nitrite to dispose of Sodium nitrite in the UK appeared for sale in an advertisement in the Times of London on 1 May 1919, 6 months after the armistice. (The Times, London)
The stockpile of the English was dwarfed by what was available from Germany. The German Government did not wait long before they started selling their war stockpile. An article appeared in The Watchman and Southron on 19 Feb 1921 and shows that German goods, especially chemicals have been making its way to the USA in such quantities that it was seen as a threat to the local industry.
Restrictions on German Sodium Nitrite in the USA
Our three worlds of Germany, Prague, and the USA now merge. The Detroit Free Press (Detroit, Michigan) reported on 14 Jan 1921 that “large stocks of imported sodium nitrite are offered at extremely low prices by agents of German manufacturers.”
Some of the tactics used by Germany to get goods into the USA, including goods subjected to presidential restrictions, were to import goods through the “concealment of the origin of shipment.” German chemicals, subject to such restrictions have been making their way into the USA “appearing as having been shipped from Switzerland, Italy and elsewhere. “Also, there has been extensive smuggling.” The article states that the German plans to sell their products in the USA and economic domination have been made as early as May 1919. (The Watchman and Southron, 19 Feb 1921, page 3)
Great emphasis is placed on sodium nitrite. The author of an article that appeared in The Watchman and Southron, 19 Feb 1921, misread its importance when it was reported that “sodium nitrite would seem to be of minor importance.” “Since the first of the year (Jan 1921), the Germans have glutted the American sodium nitrite market, threatening to destroy the hitherto prosperous American industry, and no relief has yet been obtained through the war trade board.” (The Watchman and Southron, 19 Feb 1921, page 3)
In April 1921, the call made in February for greater control over the import of sodium nitrite was answered when the war trade board in the USA placed an embargo on the importation of sodium nitrite. In the future, it could only be imported under license.
An article that appeared in the Detroit Free Press, 22 April 1921, reported that the goal of the embargo was to “check the heavy imports from Germany and Norway which have swamped the market in the country and reduced prices to a level below the cost of manufacture in the United States. (Detroit Free Press, 22 Apr 1921, Page 18) On 7 May 1924, The Indianapolis News, reports that the tariff for importing sodium nitrite was increased by a massive 50% from 3 cents a pound to 4.5 cents per pound. This was the maximum duty permitted under the Fordney-McCumber tariff act. The additional duty was levied in response to a petition filed by the American Nitrogen Products Company of Seattle, Washington. (Detroit Free Press, 22 Apr 1921, Page 18) In June it is reported that the measures were effective and that sodium nitrite prices were increasing. (Detroit Free Press, Detroit, Michigan, 11 June 1921, p4)
German Sodium Nitrite Appears as Curing Agent in the USA – Ingredients for Deceit.
Union Stock Yard, Chicago, 1910
Then arrived 1925 and everything seems to change as sodium nitrite became available through the Griffith Laboratories in a curing mix for the meat industry. They described Prague Salt and how they came upon the concept in official company documents as follows, “The mid-twenties were significant to Griffith as it had been studying closely a German technique of quick-curing meats. Short on manpower and time, German meat processors began curing meats using Nitrite with salt instead of slow-acting saltpetre, potassium nitrate. This popular curing compound was known as “Prague Salt.” (Griffith Laboratories Worldwide, Inc.)
In Canada, Prague Salt was classified as food adulteration. A progress report from the Canadian department of agriculture in 1925 lists the fact that “one sample of Prague salt” was tested and it was found to contain “5.87 % of potassium nitrite.” It calls it an adulteration. (Progress Report for the Years Canada. Dept. of Agriculture. Division of Chemistry, 1912)
In 1925 in the USA however, the fortunes of nitrite seem to change overnight. If the courts continue to find against the use of an ingredient in food that is seen as a food adulteration, the easiest way to solve the problem is to change the law. In Oct 1925 the American Bureau of Animal Industries legalised the use of sodium nitrite as a curing agent for meat. In December of the same year (1925) the Institute of American Meat Packers document appeared which we already referenced, “created by the large packing plants in Chicago,” entitled “The use of sodium Nitrite in Curing Meats.”
A key player suddenly emerges onto the scene in the Griffith Laboratories, based in Chicago and very closely associated with the powerful meatpacking industry. In that same year (1925) Hall was appointed as chief chemist by the Griffith Laboratories and Griffith started to import a mechanically mixed salt from Germany consisting of sodium nitrate, sodium nitrite and sodium chloride, which they called “Prague Salt.”
Probably the biggest of the powerful meat packers was the company created by Phil Armour. You will recall that Phil was the mentor who set David de Villiers Graaff on his course to build refrigerated railway cars to transport meat which became the backbone of his Anglo Boer War supply to the English forces. More than any other company at that time, Armour’s reach was global. It was said that Phil had an eye on developments in every part of the globe. (The Saint Paul Daily Globe, 10 May 1896, p2) He passed away in 1901 (The Weekly Gazette, 9 Jan 1901), but the business empire and network that he created endured long enough to have been aware of developments in Prague in the 1910s and early ’20s.
Could one of the offers of employment that Ladislav received before 1926 have been from Armour or one of the other meatpackers in Chicago? Griffith Laboratories is formed in the year following the armistice in 1919. This is the same year when the United Kingdom starts selling its sodium nitrite stockpile. Two years later, even cheaper German and Norwegian sodium nitrite start arriving in the USA. In response to this, import duties are levied against German sodium nitrite.
By April 1921, the import duties have been bolstered by a blanket embargo on importing sodium nitrite, except where a special permit is granted. In 1924, the tariffs on sodium nitrite are increased by 50% to the maximum allowed level permitted under the law. By this time, the use of sodium nitrite in curing brines were in all likelihood the norm in Chicago and the 50% increase would have impacted the bottom line of these companies.
Is it possible that by calling it the curing mix from Germany, Prague Salt (as opposed to German Salt or German Nitrites), did Griffith sidestep the import tariff and the required permit for importing sodium nitrite completely? My thesis is that it is entirely possible, even probable. It probably misrepresented the content in Prague Powder (mislabeling) as well as misrepresenting the country of origin.
Just as a side note, I have over the years seen the same trend returning to the meat industry. More and more companies pack their products without declaring the ingredients and apart from protecting the exact composition, I have seen many illegal ingredients going into meat curing in this way.
When Phil Armour passed away, his personal fortune was estimated at $50 000 000. This is almost $1,500,000,000 in 2016. So powerful were the packing companies that US anti-trust legislation was created to break these companies up. The point is that big money was at stake and a big influence on parts of the American government.
Is it possible that Prague Salt is no more than a clever name given to a curing brine? Taking the full weight of the historical context of events in Prague, Germany, and the USA into account in the 1910s and 1920s; particularly the severe measures to keep German sodium nitrite out of the USA, with the last blow being dealt, in 1924; understanding the extreme pressure on the packing houses to deliver huge volumes of bacon faster, I seriously doubt it. The name was probably deliberate in referring to the salt invented by Ladic in Prague but instead of giving him credit for the invention, it was in all likelihood a ruse to distract the attention from the real issue that German sodium nitrite was still coming into the USA despite a ban.
It seems that the name, Prague Salt was crafted to misrepresent the country of origin and possibly its real composition. Importing salt was no problem. There is a possibility, of course, based on the popularity of salt from Bohemia, and the fact that we know it was widely exported, including to Germany, that the original mix was done in Germany, could even have contained salt from Prague, mixed with German sodium nitrites. Whether this was so or not, the name had enough of a basis in reality in Ladislav Nachtmullner, Praganda and the famous salts from Prague to get it past the customs officers at the American harbours and into the meatpacking plants of Chicago and later, around the world. The fact that it was tested in Canada and found to contain nitrite shows that this was not declared at borders, at least in one of the events of the import into Canada and even though this does not prove that it was done in the US also, it builds the case for the theory that it was imported into the US without disclosure of its nitrite content at the borders.
Prof. Julius Hortvet, in his address in Pittsburgh, had these prophetic concluding remarks about the future of science in the food industry. He said that “…it is imperative that the use of colouring matter should be kept under intelligent control. Regulations of the food industries will in future depend more than ever before on the results of scientific investigations, and the laboratory will become the dominant factor in the shaping of food standards and food laws.” (American Food Journal; 1907)
The legal status of nitrites as food additive was clarified in 1925 through proper legislation, based on Prof. Hortvet’s principle of “intelligent control” when science decided the matter and it was taken out of the hands of “the court of popular opinion.” However, the involvement of the packing plants and Griffith in everything that happened in 1925 raises suspicion of collusion with the US government.
The real hero in the story is the master butcher from Prague who through practical application and the exact scientific inquiry that Prof Hortvet spoke about, developed the first commercially successful curing mix, Praganda. Unknowingly, he became the central figure in the saga about the naming of Prague Powder and the worldwide phenomena of the direct addition of nitrites to curing brines. Finally, there is Griffith Laboratories. The way in which Prague Salt came into the USA was probably not above board. They did, however, became pivotal around the world in making the direct addition of sodium nitrite through Prague Salt and later, Prague Powder a worldwide phenomenon. If Ladislav was the messiah to the bacon industry with his nitrite containing curing mix, Griffith was his St. Paul, the evangelist to the gentiles!
They preached the gospel of a new curing brine that swept the world. So much so that today, it is universally used as the curing brine of choice and only a handful of artisan curing operations still use the tank curing method. Several British processors, including Direct Table Foods from Bury St Edmunds, United Kingdom, retain Tank Curing as one of the methods used to cure bacob.
This was one of the most significant developments in the world of bacon curing. As I have said many times before, understanding the limitations and the mechanics of the system is very important to the modern-day curing plant manager. The tale of nitrite and how sodium nitrite became the curing salt of choice is riveting and involves some of the most important names in scientific history.
Well, my son, there you have it. A story of suspense, intrigue, and risk-taking! Remarkable! I am excited to see you soon during your upcoming vacation. There is a chance that Lauren may come home over the same time. What a blessing that will be to Minette and me. Liam is finishing school this year as Luan is going to Grade 1. We can all go up in Kirstenbosch with Skeleton Gorge one morning and spend the day in the Botanical Gardens in Cape Town. I can not wait to see you!
Lots of love from Cape Town,
Dad and Minette.
Difference between Fresh Cured and Cooked Cured Colour of Meat.
Mechanisms of meat curing – the important nitrogen compounds
Reaction Sequence: From nitrite (NO2-) to nitric oxide (NO) and the cooked cured colour.
Concerning the direct addition of nitrite to curing brine
Concerning Chemical Synthesis and Food Additives
(c) eben van tonder
“Bacon & the art of living” in book form
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1. The colour changes in meat.
The meat colour generally “changes” (either red, purple or brown), based on how many electrons are spinning around the iron atom which is part of myoglobin. Nitric oxide stabilizes or fixes the myoglobin colour through a reversible chemical bond. It does not colours the meat. (Pegg, B. R. and Shahidi, F.; 2000: 23 – 45) This is an important point to remember because, in the consideration of the use of nitrite in meat, nitrite can not be viewed as a meat colourant.
2. Rate of reaction.
The reaction of nitrite in meat is slow, in part due to the very small quantity used in the curing brine. The rate of reaction, as always, depends on the concentration of the reactants, the pH and temperature.
3. Nitrosating species from nitrous acid.
“The first step in the reaction sequence beginning with nitrous acid is the generation of either a nitrosating species or the neutral radical nitric oxide (NO).” (Sebranek, J. and Fox, J. B. Jn.. 1985)
The following list gives the relative reactivities of various nitrosating species, species 1 being the strongest and species 5 being the weakest.
Source: “From smoke which has many other phenolic compounds”
Source: From curing salt
Source: Found in the air.
Source: Nitrous acid anhydride
Nitrose derivatives of citrate, acetate, sulphate, phosphate.
Sources: Cure ingredients, weakly reactive under certain conditions.
I excluded those found under very acidic conditions. (Comparison by Sebranek, J. and Fox, J. B. Jn.. 1985)
4. The term “nitrite”
“The term nitrite is used generically to denote both the anion, , and the neutral nitrous acid , but it is the latter which forms nitrosating compounds.” (Comparison by Sebranek, J. and Fox, J. B. Jn.. 1985)
5. Reducing agents in the meat system.
One such mechanism for the conversion of “nitrite to nitric oxide in meat is by oxidation of myoglobin to metmyoglobin (brown coloured meat; Fe3+). This oxidation-reduction coupling produces both nitric oxide and metmyoglobin. It has been suggested by Kim et al. (2006) that metmyoglobin can be converted back to deoxymyoglobin through metmyoglobin reducing activity (MRA), a reaction facilitated by lactate. It is the enzyme activity of LDH that helps convert lactate to pyruvate and produce more NADH. Hendgen-Cotta et al. (2008) suggested that deoxymyoglobin can convert nitrite to nitric oxide and the generation of more deoxymyoglobin is likely to result in more nitric oxide (NO) from nitrite and less residual nitrite.” (Mcclure, B. N.; 2009: 28)
Several specific biochemical reducing systems have been the subject of intense investigation as far as their importance in the development of cured meat colour is concerned.
“Endogenous compounds such as cysteine, reduced nicotinamide adenine dinucleotide, cytochromes, and quinones are capable of acting as reductants for NOMb formation (Fox 1987). These reductants form nitroso-reductant intermediates with NO and then release the NO to Mb, forming a NOmetMb complex that is then reduced to NOMb. In model systems, the rate-limiting step in the production of NOMb was the release of NO from the reductant-NO complex (Fox and Ackerman 1968). Several researchers have investigated the effects of endogenous muscle metabolites including peptides, amino acids, and carbohydrates on the formation of NOMb. Tinbergen (1974) concluded that low-molecular-weight peptides such as glutathione and amino acids with free sulfhydryl groups were responsible for the reduction of nitrite to NO, which is subsequently complexed with Mb to produce NOMb. Similar work by Ando (1974) also suggested that glutathione and glutamate are involved in cured-meat colour formation. Depletion of these compounds in meat via oxidation occurs with time, but reductants such as sodium ascorbate or erythorbate are added to nitrite-cured meats before processing to ensure good colour development (Alley et al. 1992) The role of reductants in heme-pigment chemistry is somewhat ambiguous, but they can promote oxidation and even ring rupture under certain conditions. Thus to form cured meat pigment, two reduction steps are necessary. The first reduction of nitrite to NO and the second is conversion of NOmetMB to NOMb.” (Pegg, B. R., and Shahidi, F.; 2000: 44, 45)
6. Sugar as reducing agent.
“Sugars itself does not reduce dinitrogen trioxide in the way that ascorbate or erythorbate does, but it contributes to “maintaining acid and reducing conditions favorable” for the formation of nitric oxide.” (Kraybill, H. R.. 2009)”Under certain conditions reducing sugars are more effective than nonreducing sugars, but this difference is not due to the reducing sugar itself. The exact mechanism of the action of the sugars is not known. It may be dependent upon their utilization by microorganisms or the enzymatic systems of the meat tissues.” (Kraybill, H. R.. 2009)
7. Ascorbate or erythorbate supplements sugar.
An excellent reducing agent was discovered in the 1920s when ascorbate was isolated. As early as 1927, two German chemists, J. Tillmans and P. Hirsch (1927) observed that there is a correlation between the reducing capacity of animal tissue and their vitamin C content. (Concerning the Discovery of Ascorbate) . It reacts so aggressively (effectively) with nitrite, that a less effective, but more manageable cousin (an isomer of ascorbate), erythorbate turned out to be the most practical to use in curing brines along with nitrite and salt.
Ascorbate (vitamin C) reacts so aggressively (effectively) with nitrite, that a less effective, but more manageable cousin (an isomer of ascorbate), erythorbate turned out to be the most practical to use in curing brines along with nitrite and salt.
The old curing brines of the 1800s consisting of saltpeter (nitrate), sugar (create reducing conditions) (6) and salt are, therefore, equivalent to the current curing brines of nitrite (being added directly), erythorbate (reducing agent) and salt. The same general functionality at vastly reduced curing time.
Today, nitrate is still being added to many curing brines as a reservoir for future nitrite as bacteria continue to change nitrate into nitrite. This bolsters the residual nitrite levels in cured meat which is important since it was found that nitrite has a unique anti-microbial function in cured meat, in addition to its function of fixing the cured colour and contributing to the cured taste. It is unique in the sense that it is the most effective chemical control against a highly lethal pathogen, clostridium botulinum. (Concerning Nitrate and Nitrite’s antimicrobial efficacy – chronology of scientific inquiry)
Table salt remains the most important curing agent, but salt alone will not give the cured colour or taste and will not, on its own, be effective against clostridium botulinum. Sugar is still being used in many brines today, mostly to enrich the taste profile and to create browning during frying, especially in bacon. Its contribution to reducing conditions is now secondary and since the addition of ascorbate or erythorbate. Saltpeter has been replaced by sodium nitrite.
8. Nitrite as medicine.
“The organic nitrite, amyl of nitrite, was initially used as a therapeutic agent in the treatment of angina pectoris in 1867, but was replaced over a decade later by the organic nitrate, nitroglycerin (NTG), due to the ease of administration and longer duration of action.” BACK TO POST
9. Azo dye and textile colouring in 1895.
“Dyeing with Diazotised Dyestuffs
All the diazotised dyestuffs belong to the substantive group, and therefore, all that has been said with regard to these dyestuffs and their manner of application applies to the former also. In the majority of instances, however, the dyeings obtained directly are not sufficiently fast to be usable in that condition. Nevertheless, they can be converted into fast dyeings — provided the dyestuff contains free amino groups — by diazotising, followed by developing or coupling. The chemical reactions and method of procedure are just the sam.e as in the case of cotton.
In practice, the diazotising is effected in the following manner : —
The dyed and rinsed silk is entered at once into the cold diazotising bath and is worked about constantly for fifteen to thirty minutes. For every 100 parts of silk, the bath contains 3 parts of sodium nitrite dissolved in 1500-2000 parts of cold water, 8-10 parts of crude hydrochloric acid (20° Be.) being added. The operation must be conducted in wooden vats, metal vessels or fittings (lead excepted) being unsuitable. At one time, ice was used for cooling during the process, but this has been given up in favour of water at ordinary temperature, and in some cases, e. g. diazo indigo blue, the bath may be allowed to rise to 20-30° C. As a rule, the diazotisation will be complete in fifteen minutes, though some dyestuffs take longer and have to be left in the nitrite bath for half an hour. The goods are centrifuged or squeezed, contact with metal being avoided. A lead-lined hydro-extractor may be used, or else the goods must be wrapped in packing-cloth.
The intermediate diazo compound formed on the fiber is very unstable and sensitive to light, especially direct sunlight. The operation must therefore be carried on in a shady room, and care be taken to prevent any part of the diazotised goods from getting dry, or streaks and spots will be formed in the coupling stage. The diazotised material is rinsed and then immediately entered into the developing bath. The nitrite baths will keep for a considerable time and can be freshened up for use by the addition of one-third the original amounts of nitrite and acid. During the whole process the bath should smell strongly of nitrous acid. In the case of light shades, the bath may be weaker in nitrite and acid.” (Ganswindt, A; 1895: 98, 99) BACK TO POST
10. The Professional Career of Ladic
After his apprenticeship, he worked in several factories in Praha (Kracik, Beranek, Ugge-Sitanc and Miskovsky) as an assistant. His first work as a specialist in his field was with A. Chmel, Fr. Hlousek in Paha, Fr. Strnad in Lazne Luhacovice, and later in Germany, at the factories of Josef Sereda, Fr. Seidl, Zemka and Leopold Fisher in Berlin.
He worked as a “cellar man” at Josef Cifka, Vaclav Miskovsky in Praha, Kat. Rabus & Son in Zagreb, Jugoslavia,
Later he worked as a Foreman (Workman Leader) for the companies, Fr. Maly, Vacl. Havrda, A. Kadlec in Praha and Alexander Brero, Hard a/Bodensee Vorarlbersko and, in the end, he worked as a “Quick Production Specialist” for the export of hams for Carl Jorn A.-., Hamburg, Germany, Herrmann Spier, Elberfeld, Westfalsko, Karl Frank, Urach b/Stuttgart, Wurttemberg, A. Brero & Co, St. Margrethen, Switzerland.
11. The first War Raw Materials Department (KRA) in Germany was created (KRA) in mid-August 1914, as suggested by Walther Rathenau. (Vaupel, E. 2014: 462) Walter was the son of the founder of AEG and “one of the few German industrialists who realized that governmental direction of the nation’s economic resources would be necessary for victory, Rathenau convinced the government of the need for a War Raw Materials Department in the War Ministry. As its head from August 1914 to the spring of 1915, he ensured the conservation and distribution of raw materials essential to the war effort. He thus played a crucial part in Germany’s efforts to maintain its economic production in the face of the tightening British naval blockade.”
Ladislav Nachmüllner vulgo Praganda. Nachmüllnerová, Eva, Editor, 2000, Translated by Monica Volcko
1907. American Food Journal. Volume 2.Chicago Daily Tribune, 7 Jul 1910, Thu. P15Chicago Sunday Tribune, Nov 10, 1907, The Cincinnati Enquirer ( Cincinnati, Ohio), 27 September 1923. Page 14
The Detroit Free Press (Detroit, Michigan) reported, 14 Jan 1921, p 16Detroit Free Press, Detroit, Michigan, 11 June 1921, p4
Detroit Free Press, 22 Apr 1921, Fri, Page 18Ernst, FA. 1928. Fixation of Atmospheric Nitrogen. D van Nostrand, Inc.http://www.fda.gov/RegulatoryInformation/Legislation/ucm148690.htm
Gamgee, A. 1867 – 1868. Researches on the Blood. On the Action of Nitrites on the Blood. Proceedings of the Royal Society of London. Vol. 16 (1867 – 1868), pp. 339-342. Published by: Royal Society.
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Hoagland, Ralph. 1914. Coloring matter of raw and cooked salted meats. United States Department of Agriculture. National Agricultural Library. Digital Collections.
Hiemstra-Kuperus, E. 2010. The Ashgate Companion to the History of Textile Workers, 1650–2000. Ashgate Publishing, Ltd.
The Indiana Gazette, 28 March 1924The Indianapolis News, 7 May 1924, Wed, Page 1
Jones, G. 1920. Nitrogen: Its Fixation, Its Uses in Peace and War. The Quarterly Journal of Economics. Vol. 34, No. 3 (May, 1920), pp. 391-431. Oxford University Press.
Kim-Shapiro, D. B., Schechter, A. N., Gladwin, M. T. 2006. Unraveling the Reactions of Nitric Oxide, Nitrite, and Hemoglobin in Physiology and Therapeutics. Arteriosclerosis, Thrombosis, and Vascular Biology. Published online before print January 19, 2006.
Kraybill, H. R.. 2009. Sugar and Other Carbohydrates in Meat Processing. American Meat Institute Foundation, and Department of Biochemistry, The University of Chicago, Chicago, Ill. USE OF SUGARS AND OTHER CARBOHYDRATES IN THE FOOD INDUSTRY. Chapter 11, pp 83–88. Advances in Chemistry, Vol. 12. Publication Date (Print): July 22, 2009 . 1955
Ladislav Nachmüllner vulgo Praganda Nachmüllnerová, Eva. OSSIS,2000Mcclure, B. N.; 2009.
The effect of lactate on nitrite in a cured meat system. Iowa State University.Packer, L. 1996. Nitric Oxide, Part 1. Academic Press.
Pegg, B. R. and Shahidi, F. 2000. Nitrite Curing of Meat. Food & Nutrition Press, Inc.
Polenske. E.. 1891 Works from the Imperial Health office, Volume 7, Springer, Berlin, S. 471-474Progress Report for the Years Canada. Dept. of Agriculture. Division of Chemistry.
Sebranek, J. and Fox, J. B. Jn.. 1985. A review of nitrite and chloride chemistry: Interactions and implications for cured meats. J. Sci. Food. Agric. 1985, 36, 1169 – 1182.
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Scott, E. Kilburn. 1923. “NITRATES AND AMMONIA FROM ATMOSPHERIC NITROGEN. Lecture I”.
Journal of the Royal Society of Arts 71 (3702). Royal Society for the Encouragement of Arts, Manufactures and Commerce: 859–76.
Sullivan, G. A., 2011. “Naturally cured meats: Quality, safety, and chemistry”. Graduate Theses and Dissertations. Paper 12208.Sydney Morning Herald on 1 Mar 1870 (p4)
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1: Old Prague: Old Prague Logansport Pharos-Tribune Sat Oct 19, 1895Image
2: Ladislav Nachmüllner from Ladislav Nachmüllner vulgo Praganda Nachmüllnerová, Eva. OSSIS, 2000.Image
3: Ladislav Nachmüllner from Ladislav Nachmüllner vulgo Praganda Nachmüllnerová, Eva. OSSIS, 2000.Image
4: Sodium nitrite, photos by Prof Duchon.Image
5: Germany. http://theintersectionist.com/wp-content/uploads/2012/05/austerity-for-middle-class-meat-market.jpg
Image 6 and 7: Notice of sale by UK government: The Times, 1 May 1919, Thu, Page 18Image 8: Union Stock Yard, Chicago. The Modern Packing House. 1905, 1921. Nickerson & Collins.