It is the first day of autumn. Denmark is not home, but there is a beauty to this world. Copenhagen is an amazingly beautiful city. It is much smaller than I thought it would be, but it is very organised. The buildings are old and beautiful!
Andreas become a brother. He is an amazing soccer player. I cant keep up with him, either when I play with or against him. I try to teach them to play cricket and rugby, but its difficult. I have given up to the great amusement of his dad (and relief of Andreas).
Even autumn is colder than the coldest winters we have in Cape Town. As the cold sets in I miss you guys more every day. I miss Ava! I wish I was there to go on a long hike across Table Mountain! To sit at the kitchen table as she cooks one of her legendary lunches! I miss my dad. I miss Oscar and our crazy late night dreaming.
It seems to me that all great dreams begin on horseback, on a farm, looking for stray cattle. The vlaktes of the Wes Transvaal seem so far. Like a dream.
I remember the day after we tasted the pork that we tried to cure on Oscar’s farm with the saltpetre that we bought from the Danish spice trader in Johannesburg and discovered that the pork was off. We were so disappointed!
Trudie told us that we must have done something wrong. We were sure that we did everything that the Danish guy told us.
The next day Ou Jantjie came to the house and told us that he saw some of Oscar’s cattle on Atties farm, close to the dam, nearest to Atties house. The off-tasting pork was out of our minds and we were on Poon and Lady, riding to look for the cattle.
Oscar said that Trudie is right. That we must have done something wrong and that we must learn much more. I think he knew from the beginning how difficult it would be to take David Graaff on when it comes to curing bacon. Oscar’s mind is fast.
I reminded him that the spice trader said that if we really want to learn how its done, that we must get on the next steam ship leaving the Cape for Copenhagen. We decided to get everybody who will support the dream together for a meeting at his house one evening. Then we will decide.
The wind was in our faces and we had great dreams. I am learning how important those initial dreams are. It is like building up steam pressure before the engine start to turn the big pistons on a steam ship. If the pressure is not build up first, it will never be enough for the first “turn”. As soon as its turning, momentum takes over and the engine takes on a life of its own. The initial dreams are the building up of pressure.
This art of curing meat has been developing over thousands of years. On the one hand, people wanted to prevent meat from spoiling and on the other hand, cured meat developed into a culinary delicacy. The key ingredient is saltpetre (1).
Jeppe and I have the best of times during lunch time. He would go through the relevant scientific discoveries of the previous few years, pointing out the direct application on the science and art of curing bacon.
In my previous letters, I explained how nitrate, the power in saltpetre, is really all around us as a cousin of nitrogen, one of the most abundant elements on earth. I introduced you to some of the remarkable people who were responsible for these discoveries. Where possible, I tried to give you a small glimpse into the methods used in the discovery. The how and why behind curing bacon is after all the reason why I am here.
Bacteria play an important role in the curing of bacon (Dikeman, M, Devine, C: 436). Certain bacteria is responsible for making people very sick and we must do everything possible to prevent and eliminate them from our food. It is also bacteria which are responsible to change the ammonia to nitrite, nitrite into nitrates and back into nitrogen gas. Bacteria in certain plant roots convert nitrogen from the air directly into nitrate or plant food. Bacteria that produce nitrate and nitrite!
With sea storms, lighting, small microorganisms and fish in the sea, it is not surprise that nitrate is present in sea salt. Rivers and rainwater wash nitrates into underground salt caverns that bubble to the surface as salt springs and we harvest salt from it with nitrates in. In caves, the urine and droppings of bats create saltpetre (McCarty, M, et al. 1981: 2-3). The nitrates link up with potassium or calcium to form Saltpeter.
In England, Scandinavia, Europe and India saltpetre is created by human endeavour. Governments and farmers covet it as an ingredient in gunpowder, as fertilizer for crops and for curing meat. Its chemical composition unlocked by the French chemist Antoine Lavoisier between 1770 and 1777. (Mauskopf, MSH. 1995: 96)
So we have nitrate (NO3-) bonding with the alkali metal, sodium (Na), potassium (K) or with the alkaline earth metal, calcium (Ca) or nitrogen with hydrogen to form ammonia (NH3). All three harnessing the essential power of hydrogen (H). (3) This process is pervasive on earth.
Nitrate teams up with potassium or calcium in nature and with another element. Sodium!
Sodium nitrate occurs naturally in the driest place on earth, the Atakama desert in South America. (Wikipedia, Atacama_Desert) From 1830, Chilean Saltpeter or sodium nitrate was mined from the Atakama Desert in Chile and Peru. (Myers, RL. 2007: 229) Chilean Saltpeter, as it is called, was changed into potassium nitrate (1) and traded all over the world.
Between 1879 and 1883, a war was fought between Chile and Peru. At the heart of the war was control over nitrate rich deposits. (Wikipedia, War_of_the_Pacific)
These nitrite deposits in Chili was the largest deposits anywhere on the planet and became pivotal in the production of gunpowder. The role as fertiliser was however the focal point of its application towards the end on the 1800’s with Germany, the largest single consumer of this commodity. (Wisniak, J, 2001: 427 – 438)
Early chemists were unable to distinguish between sodium nitrate and potassium nitrate. It was found that sodium nitrate were not well suited for use in gunpowder due to its hygroscopy. (Whittaker, CW, 1932: 3) On the other hand, it is exactly this ability that makes sodium nitrate better suited for use in a bacon cure.
J. Bohn was the first person to distinguish between the crystal of potassium and and sodium nitrates in about 1683. The difference was again emphasised by J. G. Wallerius in 1750, J. B. L. Rome de l’Isle in 1783 and R. J. Hauy in 1801. (Whittaker, CW, 1932: 3)
Getting back to bacteria, they can have a good or a bad effect on meat and they play an important role in how nitrate ends up in saltpetre and how saltpeter affects meat. In my previous letter I went to great lengths to show you how nitrogen finds its way into the life cycle of plants and animals and into the salts.
I told you about the HB de Saussure (1740 – 1799), our Alps climbing scientist who had an idea that nitrogen was absorbed into the plants through the roots. I wrote about Justics von Liebig (1803 – 73), the father of the fertilizer industry who discovered nitrogen as essential plant nutrient. About Louis Pasteur who first described the nitrogen cycle and the importance of micro-organisms in fermentation. Hermann Hellriegel (1831-1895) and Martinus Willem Beijerinck discovered how bacteria in the roots of certain plants were able to convert atmospheric nitrogen into ammonium. How Berthelot described in 1885 that lightning disrupts the tightly bound oxygen and nitrogen molecules in the atmosphere as another important method, used by nature to form nitrates or plant food.
If Dr. Ed Polenski is right that bacteria is responsible for changing nitrates in saltpetre into nitrite in curing brine, the question is that if the key curing ingredient is nitrite and not nitrate, is there a way for us to produce nitrite and add it directly to the meat as curing agent?
This will reduce the time needed for the curing process, which is at the moment approximately three weeks. (6) (5) (Gouverneur Emerson . 1858: 1031)
Jeppe showed me a description of curing bacon in the American Encyclopedia of 1858. It is a good description of how we do it at his pork company.
A statement is made that curing bacon is done with a mixture of “half a pound of bay salt (sea salt), a quarter of a pound of saltpetre, and one pound of very course sugar, or treacle.” They also say that “Very excellent bacon may be made with common salt alone, provided it is well rubbed in, and changed sufficiently often. Six weeks in moderate weather, will be sufficient for the curing of a hog of 12 score.” (Gouverneur Emerson . 1858: 1031)
Have a look at the description of curing bacon with no saltpetre. Only with bay salt (sea salt). The salt must be changed sufficiently over a longer period of time, which will make sense if nitrate is present in the salt in any case, only in smaller concentration than in saltpetre. (Gouverneur Emerson . 1858: 31) The longer curing time required will also give enough time for bacteria to change the nitrate into nitrites, just as in Dr Ed’s experiment.
Addition of saltpetre and not just sea salt probably ensures that there is a sufficient quantity of nitrite available in the curing salt since the concentration of nitrates in natural salt will probably vary greatly and have a huge effect on the speed and quality of curing.
Two remarkable men were responsible for discovering the microscopic world of bacteria and micro-organisms that Dr Ed thought was responsible for changing nitrate into nitrite in his experiments. Bacteria and micro-organisms were discovered between 1665 and roughly 1678. These men responsible were Robert Hooke and Antoni van Leeuwenhoek. (Gest, H. 2004)
It came about after the discovery of the microscope. The first illustrated book on microscopy was Micrographia, published by Robert Hooke in 1665. (Gest, H. 2004)
On 23 April 1663, Mr Hooke reported on two microscopic observation to the Royal Society, one of leaches in vinegar and another of mould on sheep skin. So opened up to human kind the magical world of the minute! The microscopic!
It was the astonishing Antoni van Leeuwenhoek from Holland who introduced us to many micro realities of our world. Here is an interesting list of some of the discoveries of this remarkable man:
In 1674, in a single vial of pond scum that he had taken from the Berkelse Mere, a small lake near Delft, he discovered and described the beautiful alga Spirogyra, and various ciliated and flagellated protozoa.
He found in 1674 that yeast consists of individual plant-like organisms.
In 1675 he discovered and accurately described and differentiated red blood cells in humans, swine, fish and birds.
In 1677 he was the first to observe sperm cells in humans, dogs, swine, mollusks, amphibians, fish and birds.
In 1679 and 1684 he described the needle-shaped microscopic crystals of sodium urate that form in the tissues of gout patients in stone-like deposits called “tophi”. In 1684, he correctly guessed that much of the pain of gout is caused by these sharp crystals poking into adjacent tissues. More than a century would pass before any further advance in the understanding of gout.
He found and described in 1680 foraminifera (single-celled protists with shells) in the white cliffs of England’s Gravesend and nematodes in pond water.
Between 1680 and 1701 he carried out many microdissections, mainly on insects, making an enormous number of discoveries: He wrote extensive accounts of the mouthparts and stings of bees. He was the first to realize that “fleas have fleas”. His keen perception enabled him to correctly conclude that each of the hundreds of facets of a fly’s compound eye is in fact a separate eye with its own lens. This outlandish (but true) idea was met with derision by visiting scholars.
The big breakthrough came in 1683. In his most celebrated attainment, he discovered the bacteria in dental tartar, including a motile bacillus, selenomonads and amicrococcus. (www. Vanleeuwenhoek)
16 October 1674, Antoni wrote a letter describing his study of the tongue of an ox and his observations of the taste buds. On 24 April 1676 Antoni studied pepper water that has been sitting for three weeks under his microscope. He observed small organisms that he called “little eels” (animalcules). What he was looking at were bacteria. He has discovered a world that we knew very little about!
Antoni was responsible, not just for discovering bacteria, but for discovering important classes of bacteria. He was among other responsible for identifying anaerobic bacteria. (7) (8) In a letter dated 14 June 1680 to the Royal Society, he described his discovery. This would become very important in considering the action of bacteria in meat systems, but more about this later.
The important point about bacteria that I want you to focus on is that it plays and pivotal role in the nitrogen cycle as described by Louis Pasteur. It continues the very same interaction with family members of nitrogen in curing of meat and in meat being cured. (Dikeman, M, Devine, C: 436) (9) (10)
German scientists in the late 1800’s started to hone in on the particular bacteria responsible for converting nitrate to nitrite. This is becoming very important to us because generally, nitrate exist because of the action of bacteria, but particularly, as Dr Ed Polenski speculated in 1891, it is the action of bacteria that turns nitrate from saltpetre into nitrite in curing brines and meat that is being cured.
The question we have been asking is if this was a fair assumption for him to make and the answer is an overwhelming “yes!”
From 1868 it has been known that bacteria in soil is responsible for the exact same reduction. It was known for 23 years before Dr Ed’s 1891 experiments on curing brine and the meat being cured.
The reduction of nitrate in soil to nitrite or ammonia was brought about by various forms of microorganisms. The person who demonstrated this in 1868 was the German scientist C F Schonbein. Many others, including Gayon and Dupetit confirmed this. (Waksman, SA, 1927 : 181)
“The presence of carbohydrates gryserol and organic acids, in addition to peptone was found to stimulate the reduction of nitrate to nitrite, while an abundance of oxygen hindered it.” (Waksman, SA, 1927 : 181)
Frankland showed that particular bacteria are concerned in the process. If there were peptone in the solution, it would help the process. They also made the following very important observation namely that the lack of aeration greatly favoured the process.
Maassen tested 109 different bacteria and found that 85 were capable of reducing nitrate to nitrite, especially Bact. Pyocyaneum. Similar results were found by other researchers.
Not only did they find that many of the bacteria responsible for the reduction were anaerobic, but that many strict aerobic bacteria were found to act anaerobically in the presence of nitrates. (Waksman, SA, 1927 : 181)
This was true of soil and certainly it should be true in meat and brine systems also!
Andreas and I have been discussing these results and the implication to the meat processing industry at length at nights after the customary “reading” by his father.
We were bent on designing our own brine that would incorporate the latest technology and scientific evidence.
We wanted to stand on the shoulders of the men and women of ages past and apply everything that is known in the fields of science and technology to the meat industry. What was of the greatest interest to me was the realisation that back home, David Graaff has been applying his mind to a different form of technology. I have been fascinated by the micro world and the new emergence of the science of micro biology, chemistry and food science.
David has been fascinated by a different form of technology that effectively addresses the same core concern namely the preservation of meat, but through the science of refrigeration. You guys all know Uncle David well, but I will give you a glimpse in how he is approaching the same problem in a future letter.
I am excited about the weeks to come! Every day I get out of bed, excited and almost unable to wait for the next discovery. Even though these things have been known for years, to me, it is as if I have not only stepped onto a different physical land, but I have entered an entire new world that I knew nothing about. Introduced to me by Jeppe and Andreas.
I cant wait to get back and see you guys. I cant wait to see and hold Ava! I cant wait for tomorrow to be back at work with Andreas and Jeppe! I cant wait to start applying everything that I have learned with Oscar, back in Cape Town and to translate this into a proper bacon factory. I cant wait to report back to the rest of the great team who will help us build the dreams into a company. James and Willem and Anton and the rest of our friends!
Its late. A strong wind is blowing. Its cold. Maybe it will be a bit difficult to get out of my warm bed tomorrow!
Lots of love and send my regards to Uncle David when you see him. Tell my dad and my mom that I miss them.
(c) eben van tonder
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(1) Nitrite is the essential curing agent and in salpeter is coupled with potassium.
(2) Sodium Nitrite is converted to potassium nitrite by reacting with potassium chloride. The saltpetre was obtained as it precipitated as the solution cooled. (Myers, RL. 2007: 229)
(3) These are ionic compounds, consisting of positive ions (cations) and negative ions (anions); hence ionic compounds often consist of a metal and a non-metal. (Myers, RL. 2007: xxi)
(4) Potassium nitrate (PNO3); Sodium Nitrate (NaNO3); Calsium Nitraten (Ca(NO3)2) The ammonia compounds in urea and fecal waste underwent nitrification to produce nitrates, with combined with potassium in the soil to form saltpetre. Nitrification involves the conversion of ammonia (NH3) and ammonium (NH4+) compounds into nitrite (NO2-) and nitrate (NO3-).
NH3 + O2 -> NO2- + 3H+
NO2- + H2O -> NO3- + 2H+
The dirt was mixed with ash in order to keep the pH neutral. After this, the saltpetre was refined.
(Myers, RL. 2007: 228)
(5) In 1858, a summary was published of all recent advances in agricultural chemistry, and the use of mineral, vegetable and animal manure in the American Farmers Encyclopaedia.
They detail the following procedure for curing bacon: “The flesh of the hog, after it has been salted and dried, and it is either smoked or kept without smoking, when it is called green bacon. . . .
In order to have good bacon, the hair should be swealed off, not scalded, the flesh will be more solid and firm. The best method of doing this is to cover the hog thinly with straw , and to set light to it in the direction of the wind. As the straw is burnt off, it should be renewed, taking care, however, not to burn or parch the skin. After both sides have been treated in this way, the hog is to be scraped quite clean, but water must not be used. After the hog has been properly cut up, the inside or flesh-side of each flitch is to be well rubbed with salt, and placed above each other in a tray, which should have a gutter round its edge to drain off the brine.
Once in four of five days, the salt should be changed , and the flitches frequently moved, putting the bottom one at the top, and then again at the bottom. Some persons, in curing bacon, add for each hog, half a pound of bay salt, and a quarter of a pound of saltpetre, and one pound of very course sugar, or treacle. Very excellent bacon may be made with common salt alone, provided it is well rubbed in, and changed sufficiently often. Six weeks in moderate weather, will be sufficient for the curing of a hog of 12 score.
Smoking of bacon is much better than just drying it.
(Gouverneur Emerson . 1858: 131)
(6) The best English methods for curing bacon has been described as follows in 1858: “The sides of the hogs are laid in large wooden throughs, sprinkled with bay salt, and left unmoved for 24 hours, to drain off the blood and the juices. Then they are taken out, and wiped quite dry, and some bay salt, previously heated in an iron frying pan, is rubbed into the flesh till it enough of it is absorbed. This is done for four successive days during which the flitches are turned every day.
With large hogs, the flitches must be kept in the brine for 3 weeks, and must be turned every other day, after which they are dried as usual. In these methods, the hide or skin is left on; but in some countries there is a different practice, which has been recommended abroad as preferable, because it affords an opportunity of converting the skin into leather. . . When the consumption of bacon is very rapid, the last mentioned practice may be adopted; but it is certain that bacon will in a short time become rusty and consequently loss be incurred if it be not cured with the rind and kept in a dry room” (Gouverneur Emerson . 1858: 1031)
(7) An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. (Wikipedia. Anaerobic_organism)
(8) Processed meats many times contain bacteria, many of which are responsible for changing nitrate to nitrite. “This conversion proceed more rapidly in unpacked bacon than in the vacuum packed variety, a difference which has been ascribed somewhat surprisingly to the low reducing activity of anaerobic bacteria. (Hill, MJ. 1991: 96)
(9) The nitrate and nitrite in salts are primarily responsible for the curing activity in meat. “The reduction of nitrate (NO3-) salts to nitrite (NO2-) and then to gaseous NO and its subsequent reaction with myoglobin to form the nitrosyl-myoglobin complex forms the basis forms the basis for cured meat flavour and colour.
It was also later realized that it is bacteria that first converts nitrate into nitrite, which is the mechanism underlying in the preservation of food. Nitrite in meat is responsible for inhibiting for the growth in aerobic bacteria (especially the spores of Clostridium botulinum), retard the development of rancidity during storage, develop and preserving the meat flavour and colour, stabilizing the oxidative state of lipids in meat products.” (Dikeman, M, Devine, C, 2014: 436)
(10) Prof. D. R. Hoagland, professor of plant nutrition, University of California (www.nature.com) suggested in 1908 that the “reduction of nitrate to nitrite, nitrous acid and nitric oxide was by either bacterial or enzymatic action, or a combination of the two and was essential for NOHb formation. The scientific knowledge led to the direct use of nitrite instead of nitrate, mostly because lower addition levels were needed to achieve the same degree of cure.” (Pegg, RB, Shahidi, F. 2000)
In keeping with our interest in the person and his discovery, the following notice was published at the death of Prof. Hoagland by the University of California.
Dennis Robert Hoagland, Professor Emeritus of Plant Nutrition, died September 5, 1949. His life had been fruitful in achievement and stimulating in quality.
Professor Hoagland was born in Golden, Colorado, April 2, 1884. He attended the Denver public schools and in 1903 entered Stanford University, graduating with an A.B. degree in the Chemistry major in 1907. After a fall semester of graduate work he accepted a position at the University of California in January 1908 as Instructor in Animal Nutrition. From that time until his retirement June 30, 1949, with the exception of the period 1910 to 1913, his academic life was associated with the Berkeley campus.
About 1910 the U. S. Department of Agriculture became concerned with the alleged injurious effects of food preservatives on humans. A consulting board of scientific experts was set up and Professor Hoagland became a member of its staff. This assignment took him to the University of Pennsylvania where in addition to his research he found opportunity to continue his graduate studies in chemistry. It is evident that this early experience introduced him to the intriguing problems of biochemistry and this interest once developed became his major scientific concern the remainder of his career. In 1912 he accepted a graduate scholarship at the University of Wisconsin in the field of Animal Biochemistry, a field there cultivated with distinction by E. V. McCollum and E. B. Hart, and he was awarded the M.A. degree in 1913.
In the fall of 1913 he returned to California as Assistant Professor of Agricultural Chemistry. This area of knowledge, through the stimulating domination of Professor Hilgard, concerned itself with the soil and crop problems confronting California agriculture. Professor Hoagland found no difficulty in adapting himself to this new emphasis. It was probably his diversified early experience that made it possible for him later to develop on this campus a world center for the study of interrelated plant and soil problems. His broad interest did not lead him to scatter his efforts however. He early demonstrated an ability to clearly outline a segment of the field and vigorously attack it, without restricting his vision of the entire complex problem. It was this quality which enabled him to achieve so significantly.
Professor Hoagland became head of the newly created Division of Plant Nutrition in 1922. Under his guidance and stimulation, this became more than a “Division” in the College of Agriculture: it was in effect what the Germans might have termed an “Institut für Pflanzen und Boden Wissenschaft.” It was a dynamic research center in which both basic and practical problems of plantsoil interrelationships were studied with enthusiasm and insight; the laboratory was a magnet which drew students and mature investigators from all parts of the world. His own contributions to the research center’s activities were many and important. It was the early disclosure by himself and associates of the phenomenon of so-called “active absorption” of salts by living cells, both plant and animal, that compelled a complete reappraisal of salt absorption processes. His own research and that of his students led to new discoveries on the need and function of “trace” chemical elements–elements required by living cells in such minute amounts as to escape detection except by the use of the most refined techniques. These and other revelations constituted the leaven which activated investigations in many associated fields. His laboratory was a center with a radiating influence which reached out and touched other great scientific centers, and also the lone worker at an isolated post.
Professor Hoagland entered fully into the academic life of the University. He served as a member, then as chairman, of the Budget Committee and as a member of many other Senate and administrative committees. He was a member of numerous scientific organizations, including the National Academy of Science, and served on important national scientific boards. Many honors came to him. The American Society of Plant Physiologists presented him with the Stephen Hales Award in 1929; the annual $1,000 prize of the American Association for the Advancement of Science was given to him and an associate jointly in 1940. He was selected as Faculty Research Lecturer at Berkeley in 1942 and the same year delivered the John M. Prather Lectures at Harvard. In 1946 he was awarded the Barnes Life Membership in the American Society of Physiologists.
Professor Hoagland was married to Jessie A. Smiley in 1920. She died in 1933 leaving three sons, all of whom are graduates of this University. He did not possess a rugged constitution and the last few years of his life were marred by illness. But almost to the last he kept a faculty for keen appraisal of scientific and social situations and an interest in human events of the most diverse sort. He was a man of judgment, of tolerance, and of discernment, one who abhorred hypocrisy and admired honesty. He was the quality out of which great human structures are built.
W. P. Kelley D. I. Arnon A. R. Davis” (CDLIB)
Binkerd, E. F.; Kolari, O. E. 1975. The history and use of nitrate and nitrite in the curing of meat. Food and Cosmetics Toxicology
McCarty, M, et al. 1981. The Health Effects of Nitrate, Nitrite, and N- Nitroso Compounds. National Academy Press
Dikeman, M, Devine, C. 2014. Encyclopedia of Meat Sciences. Academic Press.
Gest, H. 2004. The discovery of microorganisms by Robert Hooke and Antoni van Leeuwenhoek, Fellows of The Royal Society. Notes and Records. The royal society journal of the history of science.
Gouverneur Emerson . 1858. The American Farmer’s Encyclopedia. A O Moore.
Hill, MJ. 1991. Nitrates and Nitrites in Food and Water. Ellis Horwood Ltd.
Mauskopf, MSH. 1995. Lavoisier and the improvement of gunpowder production/Lavoisier et l’amélioration de la production de poudre. Revue d’histoire des sciences
Myers, RL. 2007. The 100 Most Important Chemical Compounds: A Reference Guide. Greenwood Publishing Group.
Pegg, RB, Shahidi, F. 2000. Nitrite Curing of Meat: The N-Nitrosamine Problem and Nitrite Alternatives. Food & Nutrition Press, Inc.
Waksman, SA. 1927. PRINCIPLES OF SOIL MICROBIOLOGY. The Williams and Wilkins Company.
Wisniak, J. The rise and fall of salitre. Indian Journal of Chemical Technology. Vol 8, 2001.
Whittaker, CW, et al. July 1932. A Review of the Patents and Literature on the Manufacture of Potassium Nitrate with notes on its occurance and uses. United Stated Department of Agriculture. Miscellaneous Publications Number 192.
Figure 1: http://www.denstoredanske.dk/Danmarks_geografi_og_historie/Danmarks_geografi/K%C3%B8benhavn/K%C3%B8benhavns_Havn
Figure 2: http://www.rugusavay.com/antonie-van-leeuwenhoek-quotes/
Figure 3: http://www.rugusavay.com/antonie-van-leeuwenhoek-quotes/
Figure 4: http://en.wikipedia.org/wiki/Talk%3AHistory_of_the_periodic_table