The grand ABC of rubber (part I) -- K Trade Fair

The grand ABC of rubber (part 1)


The westernmost state of -> Brazil, bordering the Amazon, four times as big as Switzerland with an area of 164,000 square kilometres and an abundance of rubber trees (-> Hevea brasiliensis). Originally Bolivian territory before Brazil started to obtain -> Rubber there at the end of the 19th century and immigrants to all intents and purposes established a separate state within the state (“Republic of Acre”). This triggered armed conflicts with Bolivia that lasted for several years and were ended by the Peace Treaty of Petrópolis that was signed on 17. September 1903, when Acre was finally assigned to Brazil.
Sources: Zischka 1936, 148; Jünger 1942, 79



A city on the Ohio and Erie Canal in the US state of Ohio. What was originally a provincial village (1827: 200 inhabitants; today: more than 200,000) developed into the “Rubber Capital of the World” and the main customer for -> Rubber when the rubber manufacturing companies Goodrich, Goodyear, Firestone and General Tire settled there. Firestone, for example, started with twelve employees; fifty years later, the Firestone Tire & Rubber Company employed 72,000 people.
Sources: Zischka 1936, 161; Fischer 1938, 27; Klemm 1960, 20



The longest river in South America; its banks and those of its tributaries have a total length of 60,000 kilometres. The drainage basin of the Amazon is almost twice as big as the Indian sub-continent at almost six million square kilometres. It became the main area for the exploitation of wild rubber once the industrialisation process started to accelerate in Europe and the United States. In 1900, Chapman C. Todd (1848 – 1929), captain of the “USS Wilmington” determined that the river has an average depth of 36 metres between its mouth and the city of -> Iquitos. Ocean steamers can travel about 1,000 miles inland on it; its bed is so wide as far as -> Manaus that it looks like the sea while flowing like a river, which led it to being called “Rio Mar”. In his book “Paradiese des Teufels”, which appeared in 1933, the author Balder Olden (1882 – 1949) drew comparisons to the Congo River in Africa: “The Congo and the Amazon! ... Both of them cut deep into their part of the world along the Equator, both of them are navigable, both of them provide natural access from Europe and its culture to the tropical jungle. Rubber forests grew in the Congo and Brazil, while Europe ate its way into the tranquillity of both the Congo and the Amazon to harvest the rubber and ravaged the indigenous population.” – The name “Amazon” is, incidentally, associated with tribes of militant women known as Amazons, who are supposed to have lived on the Rio Jamunda, a tributary, under their Queen Conori. This, at any rate, is what a report from 1541 and 1542 says that Gaspar de Carvajal (1500 – 1584), a Spanish Dominican monk and Archbishop of Lima, wrote after he had explored the South American continent from Peru as a missionary and follower of Francisco de -> Orellana. Carvajal quotes Orellana as saying: “Que rio mar! I will give it the name ‘River of the Amazons’”. Alexander von Humboldt (1769 - 1859) questioned this report, however, claiming that the writers of the 16th century were “inclined to emphasise the miraculous and had a tendency to glamorise descriptions of the New World on occasions by borrowing from classical antiquity”. By the way: a potential source of the name apart from the legendary Amazons is the Indian word “Amaçunu”, which means “noise of water clouds”. Carvajal reported that there were enormous flood waves which left devastation in their wake and for which the Indians made a “water dragon” responsible.
Sources: Carvajal o. J., 267 – 276; Butze 1954, 90, 96, 116 – 121; Fischer 1938, 24; Jünger 1942, 19, 80 and 90; Olden 1933, 99 – 102 and 1977, 139 – 141; Hoppenhaus 2013, 36



The original home of the rubber tree, the -> Hevea brasiliensis. At the beginning of the 20th century, there was only wild rubber; plantations had not been introduced yet. 50,000 tonnes of the 54,000 tonnes of natural rubber tapped all over the world by -> Seringueiros around 1900 came from Brazil, while the rest came from the Congo area. Brazil quickly lost its rubber monopoly to Great Britain, that grew rubber trees on high-performance plantations in its colonies in tropical Asia, particularly Ceylon and British Malaya. The share of global natural rubber production accounted for by Brazil dropped from 80 per cent to 3 per cent in just a few decades – and it amounts to only 1.2 per cent today.
Sources: Zischka 1936, 155 – 156; Hoppenhaus 2013, 37



The name of the city of Bogor on the Indonesian island of -> Java from 1746 – 1942 (1895: 25,000 inhabitants; today: 950,000). What was at the time the biggest botanical garden in the world (“Kebun Raya Bogor”) was created here as of 1744 under Dutch colonial rule. The first seedlings of the -> Hevea brasiliensis reached Buitenzorg in 1876, where they thrived. Starting in 1910, botanists headed by W. M. van Helten started to increase the yield of rubber trees with the help of grafting techniques. The experiment was successful: Buitenzorg’s eight-year-old trees produced 650 kilos of rubber per hectare, whereas the trees in British Malaya only produced 300 kilos. This was because the latex vessel system underneath the bark of the newly cultivated Hevea was denser than in the tree’s wild form, while the Buitenzorg trees were less demanding where climatic conditions were concerned too and managed with less water. So it is quite appropriate that the literal meaning of the word Buitenzorg is “without a care” or “sans souci” – the French phrase that is sometimes used in English too.
Sources: Zischka 1936, 163 and 168; Jünger 1942, 67; Helbig 1949, 261



Synthetic rubber, a polymer made from butadiene as the basic component (isomer). When chemists looked for ways to manufacture rubber synthetically at the beginning of the 20th century, they only had one single raw material at their disposal, although it was a promising one: -> Isoprene, the isomer of natural rubber. The German chemist Fritz Hofmann (1866 – 1956) from Elberfelder Farbenfabriken, previously known as Friedrich Bayer & Co., produced the isoprene synthetically from derivatives of coal tar and converted it into synthetic rubber via heat polymerisation with the application of high pressure. The Imperial Patent Office granted him Patent No. 250 690 for this on 12. September 1909. The science of synthetic rubber developed rapidly above and beyond isoprene, however: Hofmann discovered that isoprene belonged to a wide-ranging family of hydrocarbons known as butadienes. Butadiene is a liquid gas with molecules that tend to bond in chains, i.e. they polymerise easily. The formation of chains can be accelerated by using chemical additives that will be outlined below, as a result of which substances with extremely different physical properties are created, e.g. liquid with an oily character or solid – and the long series of possible end products includes ones with characteristics that are similar to rubber.
In contrast to isoprene, butadiene is comparatively inexpensive to produce. Elberfelder Farbenfabriken (Hofmann und Coutelle) made dimethyl butadiene from acetone and aluminium around 1910 and obtained methyl rubber from it by heat polymerisation too. The quality of the methyl rubber was considerably inferior to natural rubber, however, and did not match synthetic rubber made from isoprene either. Since an inferior substitute for rubber did not promise to be a good business proposition, dimethyl butadiene was abandoned in favour of “pure” butadiene. Cheap raw materials that were in plentiful supply in Germany (lime and coal) were available to produce it. The two materials were melted together at about 3,000°C to produce calcium carbide. Acetylene was obtained from carbide and water and was converted into acetaldehyde with the help of mercury salt, sulphuric acid and water. The chemists then applied their skills to turn this intermediate product into aldol by adding sodium hydroxide solution. This viscous substance reacted with hydrogen under pressure in the presence of nickel to form butylene glycol, known as butol for short. This was heated and water was removed from the vapours produced – and what was left was, finally, butadiene gas as the desired end product.
The actual research process only started now: the aim was to find out under what conditions butadiene is converted into high-quality rubber. Two of the countless experiments finally produced satisfactory results:
• Polymerisation of butadiene with the help of sodium as a catalyst, i.e. as a substance that initiates and/or accelerates polymerisation without changing itself in the process. In other words: all that sodium does in synthesis of rubber is facilitate the process. The synthetic rubber produced in this way was given the name “Buna”, a word formed from the first two letters of “bu-tadiene” and “na-trium” (= sodium).
• Polymerisation of butadiene in emulsion, a process that converts butadiene into -> Latex, as nature does, instead of directly into rubber. If butadiene and water are shaken into an emulsion – using ammonium as the emulsion agent – and this is allowed to polymerise by adding hydrogen superoxide as a catalyst, what is produced is synthetic latex that can be processed in exactly the same way as natural latex (-> Latex, -> Vulcanisation).
Whichever alternative was chosen, care had to be taken in synthesis of the rubber to make sure that growth of the molecular chains was interrupted before the material became “too solid”, i.e. lost its elasticity. The chemists used what are known as polymerisation stoppers for this purpose.
Emulsion polymerisation was preferred in the manufacturing of synthetic rubber on a large industrial scale, initially at the Buna plant in Schkopau near Merseburg from 1937 onwards, whereas sodium rubber was only manufactured in small quantities.
Sources: Fischer 1938, 161, 163 and 168 – 169; Jünger 1942, 187 – 195; Kropf 1949, 26, 28 – 29 and 35 – 36



A word used by the Mainas Indians who lived on the Amazon that means “weeping wood” (“cao” = tree, “ochu” = tear), as the French mathematician and world traveller Charles Marie de La Condamine (1701 – 1774) reported after his trip to the Amazon in a memorandum that appeared in 1745 (“Relation abrégée d’un voyage fait dans l’intérieur de l’Amérique méridionale”). What was being referred to was the sap of the rubber tree. La Condamine writes: “If an incision is made in its bark, a milky white sap runs out that slowly darkens and hardens in contact with air”. “Kautschuk”, the German word for -> Rubber, is taken from “cahuchu”. The Austrian author Vicki Baum (1880 – 1960) wrote the novel “Cahuchu – Strom der Tränen” in 1943 and it is still available today.
Sources: Jünger 1942, 20 – 23; Klemm 1960, 10 –11


German Congo League

An organisation modelled on the British Congo Reform Association, which championed humanitarian reforms in the form of a native-friendly colonial policy following the -> Congo atrocities during the reign of the Belgian King Léopold II (1835 – 1909). The German Congo League was established in Hanover on 31. March 1910. The main initiators were Protestant missionaries and merchants; the Chairman was Karl Vietor (1861 – 1934), the Africa merchant from Bremen. What brought the various interest groups together was a number of competing ethical, religious and economic motives. The main aim of the merchants, for example, was to open up the Congo for trade from German East Africa. The Protestants allied themselves with the British against the Belgian Catholics, while German foreign policy involved the maintenance of some distance from England without alienating the country’s Belgian neighbours. The German Congo League therefore had to align its humanitarian commitment with the “national interests”, which had definite priority. Consideration was taken of Belgium, for instance, to the extent that a public call to join the German Congo League was not made until after the first visit to Berlin by the new King Albert I on 30. May 1910, following the death of Léopold II. The reformers were accused of being half-hearted as a result; it was also alleged that the League had taken too long to get established, since the Belgian government had already approved an initial Congo reform package. The German Congo League did not at any rate have much impact; one year after it was established, it had only 500 members. On 5. December 1913, it was disbanded and made a fresh start as the “German Association for the Protection of Natives”, which then received greater support.
Source: Kaiser 1994, 144 – 147



The name given to hard rubber (based on the word “ebony”); tough, non-elastic material that was used as a substitute for leather, wood, metal and horn. The level of hardness increases with the temperature and the amount of sulphur that is added to the raw rubber for the purposes of -> Vulcanisation, the inventor of which is considered to be Charles Nelson Goodyear (1800 – 1860), a mechanic and hardware dealer from Philadelphia. Goodyear succeeded in manufacturing ebonite in 1851, while his brother Nelson (1811 – 1857) improved and marketed the process. In 1851, Charles Goodyear presented a room at the Great Exhibition in London in which all the objects, including the furniture, were made from ebonite. Like vulcanisation, ebonite has several different fathers, as Goodyear’s endless patent disputes demonstrate; historians primarily mention the British chemist Thomas Hancock (1786 – 1865) in this context. The first hard rubber plant in the world was established as a subsidiary of the German company Meyer & Poppenhusen, Harburg near Hamburg, in New York in 1853. Technical exploitation of hard rubber on a larger scale then began roughly around the year 1860; it was used mainly to produce telegraph insulators, stick handles and combs.
Sources: Fischer 1938, 152; Jünger 1942, 40 – 42; Klemm 1960, 16



A polymer that deforms when subjected to external forces (pressure, tension) but returns to its original shape as soon as these forces decrease or stop. The most well-known elastomer is -> Rubber. Its elasticity (physical property) is an expression of the tremendous length of its molecules and their specific arrangement (chemical property), which can be compared to entangled spaghetti. If the entwined macromolecules are pulled apart, they disentangle and arrange themselves in parallel, like a string of pearls; if they are released, they return to their original, entangled configuration (static-dynamic balance). The elasticity increases as the temperature rises. Frost, on the other hand, causes elastomers to solidify like glass, because the molecules become immobile without heat energy from the surroundings.
Sources: Hoppenhaus 2013, 36; Wikipedia


Ficus elastica

A fig plant that is native to South and South-East Asia and is also known as the rubber tree. During the colonial era in the middle of the 19th century, the British and Dutch grew the plant on trial plantations in such places as -> Java, in order to obtain rubber from its sap in an attempt to weaken the Brazilian rubber monopoly. The product was unable to compete with the -> Hevea brasiliensis in either quality or quantity, however, particularly in view of the fact that it takes 25 years until the Ficus elastica can be tapped and it can still only be harvested every three years even then.
Source: Jünger 1942, 57 – 58



The word “rubber” comes from “rub”, because the fact that it can be used to remove pencil marks from paper was one of the first properties that Europeans discovered and appreciated about rubber. The English optician and mechanic Edward Nairne (1726 – 1806) stumbled on this by chance in his London workshop in 1770. In his book “Familiar Introduction to the Theory and Practice of Perspective”, the English chemist Joseph Priestley (1733 – 1804) then drew public attention to the erasing quality of rubber the same year. This explains why rubber was chosen as the name for the material. The fact that the British sometimes use the phrase “Indian rubber” too does not of course have anything to do with current-day India; it refers instead to America – due to the mistaken plan made by Christopher Columbus (1451 – 1506) to reach India by sailing west, in order to avoid the circuitous route around the Cape of Good Hope when sailing east.
Rubber is an -> Elastomer that occurs naturally and is a constituent of the sap of the rubber tree (-> Latex). In its solidified form, it is also known as “raw rubber” (-> Plancha, -> Vulcanisation).
Before it is vulcanised (-> Vulcanisation), i.e. is made durable with the help of heat and sulphur, there are restrictions on the use of rubber, as the first rubber coats (“Mackintosh”) demonstrated in the 19th century: in hot summers and cold winters, the material turns sticky and/or brittle and crumbly, while it in particular loses the property that was considered magical in ancient Europe: its elasticity.
One of the German words for rubber (“Gummi”) has its roots in Ancient Egyptian. In the 17th century, it was a colloquial word used for adhesive. The English term “Gum arabic” is in turn the word used for a medical substance and cosmetic that can be applied internally and externally, while “gum elastic” is a term used for the rubber obtained from liquid latex.
Sources: Fischer 1938, 10 and 151; Zischka 1936, 139; Jünger 1942, 23 and 27, 30 – 31; Kropf 1949, 8; Klemm 1960, 12 and 40


Hevea brasiliensis

The botanical name for the rubber tree that is native to tropical South America and is not related in any way to the tree colloquially given the same name (-> Ficus elastica) which is a familiar fixture in offices or living rooms. Hevea does not have any thick, fleshy leaves or creeping, aerial roots; in rainforests, it is quite a large, deciduous tree up to 30 metres tall, with vegetation reminiscent of maple or lime trees. The crown of the rubber tree forms glossy, three-fingered leaves, which it sheds completely in the dry season. The three-lobed seed capsules burst open as soon as they are ripe and catapult three gumdrop-sized seeds into the surrounding area.
Hevea brasiliensis is found in five million square kilometres of South American territory, from the jungles south of the Amazon to the western slopes of the Peruvian Andes. About three quarters of this area are in Brazil. Since Hevea trees are loners, only about eight of them are found in one hectare of rainforest.
The French globetrotter Charles Marie de La Condamine (-> Cahuchu) was the first European to discover the tree, when he travelled from -> Quito to -> Pará in 1743. The French engineer François Fresneau de la Gataudière (1703 – 1770), who met La Condamine (-> Cahuchu) in South America and corresponded with him, penned the first scientific description of the Hevea tree in 1747.
There are several hundred plants with sap that contains rubber (-> Latex) around the world, including lianas in Congo. The Hevea brasiliensis is by far the most productive, however, and it provides the highest-quality raw rubber too. For decades now, practically all the natural rubber in the world has therefore been obtained from this single tree, which has been optimised on plantations to increase the yield even more. (-> Buitenzorg). It takes five to ten years to grow Hevea trees before -> Tapping can begin. Plantation rubber can be tapped all year round, whereas the harvesting of wild rubber in the jungle is restricted to the period between May and September due to floods during the rainy season.
Sources: Zischka 1936, 142; Fischer 1938, 76 and 128; Helbig 1949, 266 – 267; Jünger 1942, 52, 56, 71, 75 and 78; Klemm 1960, 36; Hoppenhaus 2013, 36



Peruvian city (400,000 inhabitants) located on the -> Amazon close to where Peru, Brazil and Ecuador meet, only 400 kilometres from the -> Putumayo. Although it is 3,700 kilometres from the Atlantic mouth of the Amazon, it can still be reached by ocean-going vessels weighing up to 3,000 tonnes (ocean shipping ends here). Iquitos was originally a jungle backwater, but it became the rubber centre of Peru when the rubber boom developed. While it had fewer than 400 inhabitants in 1860, it had grown to more than 4,000 by 1887 and reached 10,000 inhabitants as early as 1900. Poor crop farmers became rich merchants who dealt with amounts their ancestors never even imagined. A luxurious life similar to -> Manaus was not, however, possible in this remote jungle location far away from where big money was based. Although the champagne flowed at exhilarating night-time parties here too, the supply of goods was limited. What became a luxury, i.e. unaffordable, to the Indians were such basic foodstuffs as flour, which cost at least ten times as much here as in Lima, the capital, or in distant Rio. The people who became rich in Iquitos did not run out of money even so – until the provincial governor started to pressurise them by the arbitrary imposition of taxes. Every governor did everything in his power to get rich as quickly as possible, because revolutions were a common occurrence back then, so that it was not unusual for a new official to replace his predecessor from one month to the next. The government in Lima was unable to do much about the abuse of power by the provincial rulers, since they had hardly any influence from such a long distance away. Because anyone who wanted to reach Iquitos had to struggle through 1,000 kilometres of practically impassable jungle. The only alternative was to make a detour via Panama and Barbados to -> Pará and then to travel the above-mentioned 3,700 kilometres up the Amazon by boat. This meant that Iquitos was further away from Lima than it was from Europe or the United States as far as travelling time was concerned. Due to its peripheral geographical location, Iquitos had very little involvement in Peruvian governmental life too; instead of this, Iquitos leaned more towards -> Brazil, particularly at the economic level. Quite apart from the fact that not much of any benefit could be expected of the government in Lima, because the country’s capital exploited the rubber trade in Iquitos by imposing customs duty amounting to millions that had to be paid to the local customs authority. So anyone who filled his pockets in Iquitos was well advised to get away as soon as possible – which was not as easy as it might sound, because there was no paper money in Iquitos; larger amounts were transported around in wheelbarrows ... When -> Brazil finally lost its rubber monopoly, so that rubber and share prices plummeted, the glamorous life that had been standard in the rubber towns ended almost overnight – the hustle and bustle soon died down in Iquitos too and the tranquillity of the jungle returned.
Sources: Fischer 1938, 47, 60 – 62, 114 and 121; Zischka 1936, 146; Jünger 1942, 80 and 90 – 91; Klemm 1960, 24, 26; Olden 1977, 142



Unsaturated hydrocarbon gas. Basic component (isomer) of natural rubber; can be obtained synthetically from turpentine and cresol. The chemical formula is: C5H8, a compound in which there is a 5:8 ratio of carbon atoms to hydrogen atoms.
Isoprene was discovered in 1860 by the English chemist Charles Greville Williams (1829 – 1910), who obtained it via rubber distillation. Isoprene was identified as the basic component of rubber. However, since it was not identical to rubber, the research scientists had to solve the problem of what exactly the difference was. The hypothesis was developed that rubber consisted of a multiple number of the basic component; in other words, the rubber molecule represented an aggregation of dozens, perhaps thousands, of isoprene molecules to form a macromolecule, in a nutshell: a polymer product of isoprene. What remained to be settled was how many isoprene molecules needed to bond so that the hydrocarbon turned into rubber and how they must be arranged (in a ring, in chains, entangled etc.).
In rubber, isoprene has already completed the polymerisation process. This process, which was completed in nature, had to be imitated at the laboratory level in order to verify the macromolecule hypothesis and thus obtain the key to the synthesis of artificial rubber (-> Buna). The assignment was therefore to polymerise isoprene obtained by harvesting rubber trees into rubber, i.e. to convert it back into rubber. The French chemist Gustave Bouchardat (1842 – 1918) had already considered this to be possible, but he had been sneered at by his learned colleagues. In 1879, Bouchardat then produced a rubber-like substance from isoprene and hydrochloric acid. It was, finally, Fritz Hofmann (1866 – 1956), a chemist from Elberfelder Farbenfabriken, who was the first to polymerise isoprene successfully into synthetic rubber, for which he was granted a patent in 1909 (-> Buna).
Sources: Zischka 1936, 170 – 173; Fischer 1938, 152 and 155 – 156; Jünger 1942, 185 – 186 and 188; Klemm 1960, 38



An Indonesian island that was one of the Dutch Indian colonial territories until 1949 and is about three times as large as its “mother country” at about 127,000 square kilometres. Whereas Java had 50 million inhabitants in 1947, 130 million people live there now, 9,6 million of them in the capital of Jakarta (formerly known as Batavia) alone.
The Dutch fleet reached South-East Asia as early as the end of the 16th century via the Cape of Good Hope. Following the establishment of the Dutch East India Company in 1602 and an armistice in the Eighty Years’ War between the Netherlands and Spain, which lasted from 1609 to 1621, overseas trade flourished.
The Dutch already endeavoured to enter the rubber business and end -> Brazil’s monopoly in the 19th century before the British tried (-> Wickham). After rather disappointing attempts to produce rubber on Java using the -> Ficus elastica that was native to the island, they equipped an expedition to Peru, which succeeded in buying several hundred rubber trees (-> Hevea brasiliensis), a small proportion of which reached Java in good condition. A plantation was set up with them on -> Buitenzorg, where Hevea grew and flourished. Due to its successful plantation economy, Dutch India was soon considered to be a “model colony”. In the 20th century, rubber even replaced sugar cane as the most important product grown so far. After the First World War, more and more native producers grew Hevea in their own gardens too, processed the -> Latex into raw rubber (“smoked sheets”) themselves and eventually participated in rubber export to the same extent as the colonial rulers. In view of the ongoing strength of the demand experienced from the car and electrical engineering industry, the geographer and Indonesia expert Karl Helbig (1903 – 1991) forecast in 1947 that “rubber farming in Indonesia would be expanding steadily”, due in particular to the fact that the Hevea – optimised in -> Buitenzorg – “appears to grow just as well on any soil and with any amount of rain above a certain minimum”. Indonesia now supplies an impressive 21.7 per cent of global natural rubber production and has only Thailand ahead of it (36,6 per cent).
Sources: Jünger 1942, 57 – 58, 61; Helbig 1947, 28 – 32, 71, 73 - 74; Hoppenhaus 2013, 37



natürliches →Elastomer, Bestandteil des Milchsafts des Kautschukbaums (→Latex), in geronnenem Zustand auch als „Rohgummi“ bezeichnet (→Plancha, →Vulkanisation).



The growth area of the tree, separating the bark and bast from the wood of the trunk. It is a tissue of divisible cells that forms bark on the outside and wood on the inside. Any damage done to the cambium does serious damage to the tree as a whole too. The rubber tappers (-> Seringueiros) knew nothing about the cambium – but they knew that the latex yield was greatest when they used their knives to cut right through the bark and then peeled it off in wide strips. Rubber trees that are wounded in this way again and again bleed to death eventually. If the cut made is too shallow, on the other hand, too little latex is obtained. What is involved here is precise work, so that it is not unusual for rubber tappers to be compared with precision mechanics.
Sources: Jünger 1940, 69; Helbig 1949, 267; Kropf 1949, 10; Klemm 1960, 23


Congo atrocities

In 1900, reports reached European magazines from missionaries operating in the state of Congo, which was still independent and the rubber resources of which the Belgian King Léopold II (1835 – 1909) was having exploited by private companies, about atrocities committed against the natives. There was talk of forced labour, corporal punishment, mutilation and murder. In response, the British government sent their Consul Roger Casement (1864 – 1916), who was personally familiar with the country and its people, to the Congo. His report appeared in 1904 and confirmed the truth of the what had been downplayed as alleged atrocities. It is estimated now that this brutal system of exploitation led to the loss of ten million lives. Europe protested strongly about this, while there was a sense of shame too. The Belgian King was in the international crossfire and was made personally responsible for the violence and killing in Congo (“Leopoldine system”). Public opinion in England was headed by the journalist Edmund Dene Morel (1873 – 1924), who wrote shocking books about the Congo atrocities (main work: “Red Rubber”, London 1906). An English Congo Reform Association was established, which was copied in Germany too (-> German Congo League). All the investigations, debates and appeals produced little in the way of results, however, until Belgium annexed the independent state of Congo as a colony on 15. November 1908, after which it was known as “Belgian Congo”. It was now ruled by the Parliamentary government rather than by the King. The difference between the two regimes was not as large as many reformers had hoped, however. Although excessive violence came to an end, forced labour continued. What international commissions and philanthropic movements had failed to achieve was finally achieved by the triumphant success of plantation rubber in Asia and the price slump on the global rubber market: demand for wild rubber plummeted and Congo’s share of world production dropped from eleven per cent in 1900 to two per cent in 1914.
Sources: Fischer 1938, 107 – 110; Jünger 1942, 108 – 109; Klemm 1960, 31 – 32; Olden 1977, 130; Kaiser 1994, 137; Hochschild 2000, 366, 384 – 385 and 390 – 391



The milky sap of the rubber tree (-> Hevea brasiliensis), also known as “rubber milk”, which is composed of the rubber itself (25 to 35 per cent) and water (65 to 75 per cent) and otherwise contains proteins, carbohydrates, salts and fatty acids. What is involved here is, in other words, an emulsion, i.e. the consistent distribution of a substance, here a natural elastomer (-> Isoprene), in a liquid medium. A state of limbo, as it were, in which negatively charged, mutually repellent protein membranes make sure that the rubber substance cannot isolate itself from the liquid.
It goes without saying that the rubber tree does not produce latex so that human beings can tap it; the aims are instead to ward off parasites, to act as the tree’s own antibiotic and to heal wounds. Prussic acid has a similar purpose, which is to protect the leaves of the Hevea against insect damage.
During -> Tapping, the latex flows into small cups or bowls that are attached to the tree. When they are full, the collection containers are emptied into buckets and are later processed into raw rubber via coagulation. To do this, the wild rubber collectors started a smoky fire, over which they smoked the rubber milk as it rotated on a stick, as a result of which it coagulated immediately. Balls that weighed up to 25 kilograms were formed by the coagulation of more and more layers and were then dried in the sun. The denser this elastic rubber “cake” (-> Plancha) was and the fewer bubbles it contained, the higher the quality and thus the price. In order to increase and standardise quality, the raw rubber manufacturing process was intensified considerably on rubber plantations. Alum, diluted formic or acetic acid, was added to the latex so that it coagulated. The lumps of coagulated latex were then kneaded mechanically and rolled out into sheets. After being smoked for twenty-four hours, the standard product of the rubber plantations was complete – ribbed smoked sheets, one metre long and 30 centimetres wide. The raw rubber was, finally, prepared for export by being packed in plywood crates and was then transported to rubber factories in -> Akron, Birmingham or Hanover.
Sources: Zischka 1936, 171; Fischer 1938, 153 – 154; Jünger 1942, 69, 76; Kropf 1949, 10; Klemm 1960, 37 – 38; Hoppenhaus 2013, 37



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