02: Nitrogen chemistry en route to Cape Town

August 1892

Dear children,

Today I boarded the Union Shipping liner of Donald Currie & Company en route to Cape Town. Oscar sent me a telegraph message two weeks ago announcing the plans of James and Christel to get married.

An investor in our cause to set up a bacon curing plant in Cape Town saw this as an ideal opportunity to get me home. I can report on what I have learned; assist Oscar in designing the new plant to be erected at the back of the Combrinck & Co. building in Newmarket street; above all, I can see the two of you and Ava.  It is a welcome break before I return to London and the forests and fields of Bristol, Calne and Peterborough.


James and Christel have been friends since university. They formally saw each other for 6 months and in accordance with all sense and sensibility, got engaged 2 months ago. James is Oscar’s youngest brother and took over the financial affairs of our company. He gambled a lucrative career in the Bank of the Netherlands with his move to Woody’s, which I am confident, will pay off handsomely.

Together, Ava and I have hiked up Table Mountain a few times with him and Christel and I consider it a great privilege to know them. He is an upstanding citizen and Christel is everything a good wife should be.

Her dad knows Livingston, being a seasoned explorer himself. When Oscar, David and I met in Copenhagen, Oscar told me that Christel’s dad is travelling through Kazakhstan.  I am looking forward to hear his many stories at the wedding. Martin Sauer from Denmark’s dad also knows Livingston. He has been in Rhodesia to help farmers set up pork farms. Maybe they know each other.


From Ava, I hear that you both have taken a keen interest in chemistry.  Uncle David promises to take you two along to the reading room (1) in Cape Town one day.  The reading rooms in Copenhagen and now in London and Bristol, where I have been staying with Kevin, is the source of endless pleasure.

I am sure you will find it equally engaging in years to come.  It is the gateway to the world.  Where printed newspapers and posts link our globe and knowledge are shared within weeks of a discovery or an event or a newsworthy happening.  It is an indispensable tool to the scientist and businessman alike and the fact that Cape Town has its own is just marvellous.

On the steam liner I picked up an old copy of the Marion Record from Marion in Kansas, published 4 years ago on Friday, 15 July 1887.  The journalist entitled his piece, About Nitrogen.  I am not sure how it survived these four years, but I am thankful that I found the article.  It gives me much insight into matters that Uncle Jeppe in Denmark taught me and its content provides occasion for contemplation and reflection in order to answer important questions.

Back in England I have been challenged by a chemistry student on the subject of brine formulations and microbiology.  In Denmark I become convinced that it may be a good idea to slightly acidify our bacon brine, that is, to lower the pH to a range between 5 and 6. My reasoning is that microorganisms prefer a higher pH and grow faster, spoiling meat and causing illness.

One evening a few friends from the processing industry and I were discussing this theory over drinks in a pub in London when an objection was raised by a chemistry student who was listening to our conversation, that acidifying the brine will cause nitrite to rapidly change to nitric oxide.  This would, according to him, have two detrimental effects. On the one hand it would release nitric oxide, a corrosive gas, into the atmosphere to the detriment of staff working in the curing room and on the other hand, it would deplete the available nitrite in the brine, thus removing the substance that cures the meat.

In order to look into the matters, I have to refresh my own memory on matters of chemistry.  I have to review nitrogen, nitric oxide and the other oxidation states of nitrogen and acidification.  What is acidification and how it will interact with nitrogen and its many forms.  It is therefore a good opportunity to introduce you to the subject more thoroughly.


Farmers all around the world heard about nitrogen and its value in the soil.  It is a gas that forms part of our atmosphere.  We estimate, at least 4/5th.  The rest, roughly 20%, is oxygen.  (2)  (Marion Record, p3: About Nitrogen)

Up to the present time, its relation to the animal and plant world has not been clearly understood.  It is found in the tissue of all animal structures and in all plants.  Exactly how nitrogen, which exist as a gas, tightly bound in pairs and requiring enormous energy to separate, end up in plants and animals, is an important question to the farmer     (Marion Record, p3: About Nitrogen) and the starting point of our chemistry review. 

The article from the Marion Record reminded me that the role and effect of nitrogen in human and animal tissue is relevant not just to the living but also to pork from which we make bacon.  The art of bacon is the art of the manipulation of the properties of meat through nitrogen, sodium and chloride.  I told you about the pioneers who discovered these elements and processes in Lauren learns the nitrogen cycle and The micro letter.

It is important to know a few of the other chemical elements at work in our industry.  Nitrogen is the basis for the earliest food colouring industry, an attempt to make our meals look more appetising. (see Concerning chemical synthesis and food additives)  Nitrogen is the link between fertilizer, food processing and war since the same power fires bullet, provides nutrition to plants and cures meat for future consumption.


Nitrogen gas molecule (N2)

Nitrogen was so named by the early chemists as the generator of nitre.  Nitre is also called saltpeter, something you are familiar with by now.

Nitrogen was independently discovered by two scientists.  In 1772, by the Scottish physicist, Daniel Rutherford  (Marion Record, p3: About Nitrogen) and in the early 1770’s by a Swedish chemist, Carl Scheele.  “Rutherford named his discovery “noxious air,” because animals were not able to breath in it.  Scheele called it “foul air.”  (Farndon, J, 1999: 9)

In one of my first letters, I wrote to you about the French chemist, Antoine Lavoisier (1743 – 1794) who realized that air was basically a mixture between two gasses, oxygen and nitrogen.  He burned mercury in a closed jar and found that a 5th of the air combined with the mercury to form a red powder, mercury oxide.  No matter what he did, the rest stayed a gas.  Mice died in it and a candle could not burn in it.  “Lavoisier decided that air is made of two gases.  One, which he called oxygen, was the gas that burned with the mercury.  The other he called azote from the Greek for ‘no life.’  It later came to be known as nitrogen, because it can be generated from niter, the common name for sodium or potassium nitrate or saltpeter” (Farndon, J, 1999: 9)

Nitrogen comes into our lives through the power of lightning and the small microorganisms that I have written about in my previous letters.  Let’s first look at nitrogen that falls from the skies.


Nitric Oxide (NO)

Nitrogen gas exists as two atoms, tightly bound in one molecule (N2).  The bonds between the atoms are so strong that it doesn’t normally react with anything else.  Lightning provides enough energy to break these strong bonds which now makes the nitrogen available to react with other elements.  (Farndon, J, 1999: 10)

One of these elements is oxygen.  When they react, they form nitrogen monoxide (NO).  Nitrogen monoxide is a colourless gas, also called nitric oxide or nitrogen oxide.  The nitric oxide is heated due to the energy from the lightning flash that created it.  (Farndon, J, 1999: 10)

The reaction is written as follows:

N2 (g) + O2 (g)  lightning —> 2NO (g)


Nitrogen dioxide.
Nitrogen dioxide. (NO2)

Other sources of nitric oxide, besides lightning, are certain bacteria and volcanos.  (Air Quality Guidelines, 2000:  chapter 7).  As it cools down, it reacts further with the oxygen molecules around it to form nitrogen dioxide.  One nitrogen atom attached to two oxygen atoms and forms nitrogen dioxide. “It is a poisonous, brown, acidic, pungent gas”.  (Farndon, J, 1999: 12)  Nitrogen dioxide is however mainly formed in the atmosphere through it’s a reaction with ozone (O3).

Like nitrogen, oxygen occurs as two oxygen atoms, bound in one molecule.  Ultra-violet light and lightning cause the two tightly bound oxygen atoms to separate and react, either with other single atom oxygen molecules or with more stable two atom oxygen molecules.  In the latter case, three oxygen atoms are bound into one molecule (O3). (3)  (Wikipedia, Ozone)  It is not very stable and quickly breaks down into one oxygen atom (O) and or two oxygen atom molecules or it reacts with nitric oxide to form nitrogen dioxide.  (Huffman, R. E.; 1992: 210) (Air Quality Guidelines, 2000:  chapter 7)

The reaction occurs as follows:

NO (g) + 1/2O2 (g) —> NO2 (g)


Nitric Acid (HNO3)

Nitrogen Dioxide (NO2) reacts with more oxygen and rain drops to form nitric acid (HNO3) which falls to earth and enters the soil to provide nutrients for plants.  (Ramakrishna, A.; 2014: 14) Nitric acid (HNO3) is also known as aqua fortis and spirit of niter.  (Wikipedia, Nitric Acid)

This puzzling phrase, “spirit of” something seems to have been used generally by chemists when they did not really know what it was.  The particular phrase, “spirit of niter” was puzzling to even  Robert Boyle in the 1650’s and 60’s.  (Rattansi, P.;1994: 66)

The reaction occurs as follows:

3NO2 (g) + H2O —> 2HNO3 (aq) + NO (g)

Nitric acid is highly reactive and combines with salts in the soil, converting it to nitrates which in turn become food for the plants.  (Ramakrishna, A.; 2014: 14)  It is this reaction of nitric acid with salts that create sodium nitrate  or calcium nitrate or potassium nitrate that are used as fertilizer or in gunpowder or to cure bacon.

It has been discovered that curing happens much faster if nitrite is used directly.  Bacteria are responsible for changing nitrate to nitrite when it is injected into meat as a curing agent, just as it is done by bacteria in soil.  Nitrite (NO2) is the same as nitrate (NO3), with one less oxygen atom.  By using nitrite directly, curing is accomplished much faster since the reduction to nitrite takes time.


Ammonia (NH3)

Nitrogen comes into our lives from the atmosphere, but despite the fact that “nitrogen oxides trapped in rocks and sediments probably represent a larger total quantity of nitrogen, this nitrogen, for the most part, is not accessible to living organisms.”  (Igarashi, Y. and Seefeldt, C. L..  2003)   Most nitrogen enters our world through special bacteria that take nitrogen from the atmosphere and combine it with another important chemical element, hydrogen, to produce ammonia.  (www.eoearth.org)

There are many bacteria who achieve this conversion through various means, but a common denominator is that they all use the most interesting enzyme, nitrogenase.  It is this enzyme that is responsible for changing N2 to ammonia.  The general N2 reduction reaction catalyzed by these enzymes is typically presented as follows:

N2 + 8 e− + 16 ATP + 8 H+ → 2 NH3 + 16 ADP + 16 Pi + H2  (Igarashi, Y. and Seefeldt, C. L..  2003)

This amazing enzyme has the ability to break to very strong N2 molecule and form ammonia.  “Ammonia is easily manipulated by biological cells and by converting it into ammonium (NH4+) and other compounds such as nitrate and nitrites.”   (Dincer, I. and Zamfirescu, C.; 2011: 706)  Interestingly enough, a small amount of ammonia is also produced through pressure and energy from lightning.  (Krasny, M. E.; 2003: 46)

Bacteria with this remarkable ability are found in fresh water, soil and in seawater.  A few of these bacteria live in a special relationship with plants where both benefits in special ways.  The bacteria live in the roots and supply the plant with nitrogen.  In turn, the plant supplies the bacteria with sugars and other carbon compounds.  Examples of these plants are alfalfa, clover, peas, peanuts and beans.  (Krasny, M. E.; 2003: 46)

Ammonium (NH4+) is taken up by the plants and incorporated in amino acids, the building blocks of proteins.  When animals or humans eat the plants, the nitrogen is taken up in their bodies in the form of amino acids and proteins.  (Krasny, M. E.; 2003: 46)

“Similar to Carbon, organic nitrogen is returned to the atmosphere when plants and animals die and are decomposed.  Bacteria first break protein and amino acids back down into ammonium.”  The process now becomes complicated as some ammonium is taken up again by plants and used by the plants to build amino acids and protein.  Some are broken down further by bacteria into nitrite (NO2)and nitrate (NO3).  Nitrate (NO3) itself can be taken up directly by the plants. Some of the nitrate are transformed by bacteria into gaseous nitrous oxide (N2O), nitric oxide (NO), or nitrogen gas (N2), which are released into the air.  Some nitrate makes its way into streams, lakes and groundwater.  (Krasny, M. E.; 2003: 46)

Lauren and Tristan, now that I have painted the landscape of how nitrogen moves through its various oxidation states we can look at acidity.  Then we will try and write the reaction that occurs when a brine mix containing nitrite is dosed with an organic acid such as acetic acid, in order to reduce the pH.  We will then try and predict how much nitrite is converted into nitric oxide and why this happens. Lastly, we will see if this is a reaction that should be a concern to us. This will deal with the particular question that I was challenged about in the pub in London.

I also want to learn more about nitric oxide (NO) and its role in curing of meat.  Some interesting studies are coming out that it may be nitric oxide that is ultimately responsible for bacon curing.

I am looking forward to give you the letters I am writing on the streamliner personally and read them to you in the evenings after supper.  When I close my eyes, my spirit floats to our living room in Cape Town where, after supper, we sit and first read and then talk until the evening sun sets over the Atlantic in all its brilliance.

I dream about being home and enjoying Ava’s home cooked meals and telling you first-hand about all my adventures.  The quest of setting up a bacon curing plant in Cape Town in becoming the most interesting adventure I have ever imagined.

Much love!

Your Dad.


(c) eben van tonder

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1. Reading Room in Cape Town

2.  This estimation is accurate, even by today’s reckoning.

3.  In 1930 S.Chapman, a British scientist, proposed a theory of the formation of ozone in the stratosphere (known as Chapman mechanism).


Air Quality Guidelines – Second Edition.  2000. Published by the WHO, Regional Office for Europe, Copenhagen, Denmark.

Butcher, S. S.. et al.  1992.  Global biogeochemical cycles. Academic Press, Inc.

Dincer, I. and Zamfirescu, C.  2011.  Sustainable Energy Systems and Applications.  Springer Science + BusinessMedia, LLC.

Farndon, J.  1999.  The Elements, Nitrogen.  Marshall Cavendish Corporation.

Huffman, R. E..  1992.  Atmospheric Ultraviolet Remote Sensing.  Academic Press, Inc.

Igarashi, Y. and Seefeldt, C. L..  2003.  Nitrogen Fixation: The Mechanism of the Mo-Dependent Nitrogenase.  Article from Critical Reviews in Biochemistry and Molecular Biology, 38:351–384.  Robert. Taylor and Francis Inc.

Krasny, M. E..  2003.  Invasion Ecology.  NSTA Press.

Langa, S. L..  1999.  The Impact of Nitrogen Deposition on Natural and Semi-Natural Ecosystems.  Springer Science+Business Media.

Marion Record, Marion, Kansas.  Friday, 15 July 1887. About nitrogen, p3

Ramakrishna, A.  2014.  Goyal’s IIT FOUNDATION COURSE CHEMISTRY.  Roshan Lal Goyal for Goyal Brothersn Prakashan.

Rattansi, P..  1994.  Alchemy and Chemistry in the 16th and 17th Centuries.  Kluwer Academic Publishers.

http://www.eoearth.org/view/article/170977/  Atmospheric Science. Earth’s atmospheric air.


Image references

Image 1:  Union-Castle liners in Cape Town harbour. Early 1900s, from https://en.wikipedia.org/wiki/Percy_Molteno

Image 2:  Dinitrogen molecule: https://en.wikipedia.org/wiki/Diatomic_molecule

Image 3:  Nitric Oxide:  https://en.wikipedia.org/wiki/Nitric_oxide

Image 4:  Nitrogen dioxide.  https://en.wikipedia.org/wiki/Nitrogen_oxide

Image 5:  Nitric Acid.  http://900igr.net/kartinki/khimija/Primenenie-kisloty/004-TSarskaja-vodka.html

Image 6:  Ammonia.  https://en.wikipedia.org/wiki/Ammonia

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