The grand ABC of rubber (part 2)


Spelled differently in Spanish as Manaos; the capital of the Brazilian state of Amazonas that is located on the Rio Negro river. There was already an Indian settlement here on the hilly left bank of the river in the 16th century. A Portuguese fort was built in 1669. The number of inhabitants increased ten times over from 3,000 to 30,000 during the rubber boom at the end of the 19th century. Although Manaus was one thousand miles away from the Atlantic mouth of the Amazon, it could be reached by ocean steamers; this meant that it was possible to travel from Europe or the United States right into the heart of Brazil without having to change ship a single time during the trip. The town developed into the biggest rubber shipping centre in the world with one of the most modern ports (floating docks). Raw rubber from Peru (-> Iquitos) and Bolivia (-> Acre) was shipped from here too. Tall buildings for banks and palatial villas for the directors of the rubber companies, the rubber traders and the leaders of their private armies were constructed on land taken from the rainforest. Headlines were made when an opera house was built that was larger, more magnificent and more expensive than its counterpart in Paris. The rainforest opera house just below the Equator attracted performers by paying fees that were paid nowhere else. Such global stars as the Italian tenor Enrico Caruso (1873 – 1921) sang in Manaus and the idolised French actress Sarah Bernhardt (1844 – 1923) performed in The Lady of the Camellias here. Cars reached Manaus for the first time eventually too – the vehicles with rubber tyres to which the rubber barons owed their tremendous wealth and which caused rubber collectors (-> Seringueiros) immense suffering (-> Putumayo). At the time, observers described the town as similar to the kind of vivid fantasies one is susceptible to when running a high fever, but all the luxury came to an end when the rubber fever died down. The development of Asian plantation rubber from the British colonies cut demand for wild rubber and led to a severe slump in the rubber price on the world market. Not least of all, the high transport costs now became a competitive disadvantage: to ship one tonne of rubber just from Manaus to the sea, to -> Pará, it cost the same as the competition had to pay for the entire voyage from Singapore to Liverpool. The palaces in Manaus went to rack and ruin and no more European guests came to see operas. The gloomy predictions that Manaus would become depopulated and disappear under rainforest vegetation proved to be inaccurate, however: the rubber that Brazil lost was replaced by coffee and, thanks to its port, Manaus remained the trading centre for the entire upper basin of the Amazon. At the beginning of the 1940s, the town had about 90,000 inhabitants and now Manaus is a city of almost two million people. Incidentally: Manaus is attracting international attention in 2014 as one of the venues for the Football World Cup (four games in the first round, including the one between England and Italy).
Sources: Carvajal o. J., 263 – 264; Fischer 1938, 60, 115 and 121; Jünger 1942, 70, 80, 87, 90 and 115; Klemm 1960, 24; Olden 1977, 141



Wild rubber collectors in South American rainforests (-> Seringueiros).
Sources: Zischka 1936, 145; Kropf 1949, 10; Klemm 1960, 23



In 1879, the French chemist Gustave Bouchardat (1842 – 1918) succeeded in polymerising -> Isoprene into rubber-like substances using hydrogen chloride gas (HCl). In 1930, the US chemists Arnold Collins and Wallace Hume Carothers (1896 – 1937) from the DuPont de Nemours Group in Wilmington / Delaware obtained chloroprene – which is related to isoprene – from sodium chloride. It was polymerised and vulcanised into synthetic rubber (trade names: Duprene, Neopren), which was insensitive to oxygen, mineral oil and UV radiation. At the time, the Soviet Union produced a kind of rubber known as Sowpren from butadiene. It was based on a process developed by the Russian chemist Sergei Vasilyevich Lebedev (1874 – 1934), who manufactured butadiene from potato spirit (ethyl alcohol) and managed to polymerise it with metallic sodium (-> Buna). The Communist Party newspaper “Pravda” (which in English means “truth”), however, concluded that Sowpren was of inferior quality, an assessment that was to be confirmed by practical experience with Russian tanks equipped with Sowpren tyres in the Spanish Civil War (1936 – 1939).
Sources: Fischer 1938, 174 – 175; Jünger 1942, 194 – 195; Kropf 1949, 35; Klemm 1960, 47


Orellana, Francisco de (1511-1546)

Spanish Vice-Governor of -> Quito, lieutenant of Gonzalo Pizarro (1502 – 1548), half-brother of the infamous conquistador Francisco Pizarro (1476 – 1541). On 12. February 1542, Orellana was the first European to discover the -> Amazon. Gonzalo Pizarro and Orellana left Peru at the end of 1540 with an army of 2,000 men to explore the land that was unfamiliar to them the other side of the Andes and to look for cinnamon trees – searching at the same time for the legendary “gold country” known as Curicuri. After marching through the wet and rainy tropical forest on foot for months, the men were at the end of their tether when they reached a huge river on which they thought the gold country might be located. It was the Rio Napo. They continued to find it difficult to work their way through the jungle along its banks. Omágua Indians, whose villages they came across, finally helped them to build a ship. Gaspar de Carvajal (-> Amazon), the monk who was accompanying them, wrote:

“When construction of the ship was coming to an end, we suddenly realised with horror that we were lacking a substance that could not be replaced and that no-one had thought of. We did not have any pitch to caulk the joints. There was no way to make the ship float without pitch. We tried to explain to the Indians what we needed, but they did not understand us, because they did not need pitch to build their canoes. Since they were helpful people, they brought us all sorts of things, but none of them was able to replace pitch. [...] A coincidence saved us. One of us watched an Indian as he made a slit in the grey bark of a tree with his stone knife, with the outcome that thick, white sap flowed out immediately. We asked the Indian what was done with this sap and the answer was that blankets were made with it that provided protection against moisture and cold. This was what we were looking for! Wherever possible, we collected the white sap in coconut shells and smoked it over a fire. The elastic yellow substance that was produced in this way was a worthy substitute for pitch.”

Orellana encountered this rubber – for that is what we are talking about here – later on again with the Machiparo Indians, incidentally – “they played with balls that bounced when they were thrown on the ground”. The ship was launched on 10. December 1541, when it was given the name “Victoria”. Pizarro formed a crew of 51 soldiers and officers, appointed Orellana to be captain – and did not go on board himself. Their paths separated: while the group under Pizarro’s leadership battled its way back to Peru – only eighty men arrived there alive – the crew of the “Victoria” reached the -> Amazon on 12. February 1542, on which they stayed all the way to its Atlantic mouth. Orellana and his companions took eight months to get from the Rio Napo to the sea, covering a distance of four thousand kilometres. In completing this trip, he demonstrated that there was a waterway that could be travelled by ship across the South American continent. He did not find the gold country, however, much to the disappointment of his henchmen, who suspected that the Indians had led them off the track and now set their villages on fire, tortured men and raped women. Carjaval complained: “Orellana tried in vain to stop this senseless and dangerous hunt and I myself reminded the furious, manic men – unsuccessfully – that they were Christians. That is what they were, the conquerors of Mexico and Peru, and now their showed their true faces.”

Back in Europe, the Spanish crown appointed Orellana to be governor of the Amazon territory he had discovered, which was given the name of “New Andalusia”. In May 1545, Orellana left for South America again – encouraged by the Casa de las Indias, the Spanish colonial authorities – to search for the gold country, which he suspected to be on the Rio Negro. He never came back; he went missing in the rainforest, so that he was finally declared dead; 1546 is considered to be the year he probably died. The Casa de las Indias soon lost interest in New Andalusia. The Portuguese crown benefitted from this: Captain Francesco Caldeira Castelo Blanco (1566 – 1619) established the settlement of Feliz Lusitânia, which later became -> Pará, at the mouth of the Amazon on 12. January 1616. The Portuguese made their way up the river into the heart of the country, established settlements on the banks and took possession of Brazil – although they did not find the gold country either.
Sources: Carvajal o. J., 241 – 242, 247, 260 and 279 – 282; Jünger 1942, 19 – 20; Butze 1954, 89 – 97 and 116 – 121



Name today: Belém (Portuguese for Bethlehem); capital of the Brazilian state of Pará, sea port where the Amazon flows into the Atlantic Ocean, the most important Brazilian port for exporting wild rubber to North America and Europe for a time during the rubber boom. Between 1890 and 1913, the number of inhabitants increased from 50,000 to 275,000 (the city has 1.4 million inhabitants today). This means that Pará was the biggest of the South American rubber towns, full of life and proud of being known as “Paris on the Equator”. However, when the rubber traders and collectors penetrated further and further into the heart of the country, Pará soon lost its position as the main trading location to -> Manaus.
Sources: Zischka 1936, 146; Fischer 1938, 60 and 115; Jünger 1942, 70, 80 and 90; Olden 1977, 141



Elastic rubber “cake”, basic product made from coagulated -> Latex. All that has to be done to coagulate rubber milk (flocculation of solid rubber substance) is to neutralise the electric charges that are typical of emulsions, e.g. by smoking it above a fire or by adding acids. A process that can be compared with the way butter is made from milk – with the difference that what is involved here is a fat/water emulsion.
Sources: Fischer 1938, 154; Klemm 1960, 22 and 38; Kropf 1949, 10



A tributary of the upper Amazon that starts in the Colombian Andes, is 1,800 kilometres long and forms the border between Colombia, Ecuador and Peru. Due to its remote location and inaccessibility, the Putumayo region was considered to be a lawless no man’s land by adventurers of all kinds, over which the flag of no nation was raised and in which the principle of the survival of the fittest ruled (“devil’s paradise”). During the wild rubber boom, the Putumayo was exploited primarily by Colombians, who used the Indian population as forced labour and initiated a bloody, eleven-year reign of terror that cost about 45,000 Indios their lives. The outcome of this murderous regime that is summarised by historians as the “Putumayo atrocities”: eleven dead Indios per tonne of rubber! The British Consul General Sir Roger Casement (1864 – 1916), who travelled the Putumayo in 1910, was the key witness – after he had informed the world about the -> Congo atrocities only a few years before.
Sources: Zischka 1936, 146 – 148; Klemm 1960, 26 – 27; Olden 1977, 138, 140 – 141, 143 and 147 – 148



Former province of the Viceroyalty of Peru in the territory of what is now Ecuador, the capital of which is also called Quito. La Condamine (-> Cahuchu) went to Quito in 1735 to determine the shape of the earth on behalf of the French government. It had been observed that a pendulum oscillates to different extents according to the latitude at which the measurements are taken. The conclusion drawn from this was that the latitudes shorten from the Equator to the Poles and that the earth is therefore a ball which flattens at the Poles. A hypothesis that Newton had already postulated – and La Condamine now succeeded in providing the empirical evidence in a seven-year project together with the academics Louis Godin (1704 – 1760) and Pierre Bouguer (1698 – 1758). On an unrelated note, La Condamine also informed Europe about the Indian arrow poison curare, the cinchona tree (its bark contains the alkaloid quinine, with which pain, fever and malaria are treated) and, not least of all, the rubber tree (-> Hevea brasiliensis). La Condamine reported that the Indios who lived in Quito coated cotton fabric with the milky, white sap of this tree (-> Latex), making it impermeable to water as a result. The Mainas Indians from the upper reaches of the Amazon even made boots from it, in which their feet did not get wet when they waded through swamps.
Sources: Jünger 1942, 20 – 21; Klemm 1960, 10 – 11



The Portuguese word used for wild rubber collectors in Brazil; in Portuguese, the rubber tree is called “seringueira”, which is based on the word for “syringe”. The puzzling etymology is attributable to the use that the Indian native population made of rubber milk. The report that La Condamine (-> Cahuchu) wrote about his travels in 1745 includes the following passage about the Omágua tribe: “Pear-shaped bottles are made from it, at the neck of which a wooden tube is attached. If the bottle is squeezed, a jet of the liquid it contains comes out of the tube. So it would be accurate to describe these bottles as syringes”. A different explanation given is that the word “syringe” was applied to the rubber tree due to the narrow tubes that extend throughout the bark to collect the -> Latex and that the Indios used to inhale intoxicants.

The following was reported about the seringueiros’ everyday work: the “aviado” (contractor) took on a number of workers for the harvesting months and sent some dependable natives into the territory he had leased to search it. The detailed report provided by these particularly trustworthy workers included information about the number of tappable trees and a conclusion about whether it was worthwhile covering the area in question. If there were five trees in one hectare, it was considered to be definite that operating there would be profitable. On the basis of the reports presented by the scouts who had searched the forest, the seringueiros were taken to the area where they were supposed to work – which generally involved long boat trips – and were spread around the designated area. Each of the rubber collectors started off by building a hut covered with palm leaves, which acted as his home during the harvesting season. Once the hut had been built, he began to cut a path through the rain forest that connected all the rubber trees in the area allocated to him. It was a strenuous job to create this pathway, which normally linked 90 to 120 Hevea trees, through the maze of roots, ferns and ginger plants. Each of the workers was given one or two of these forest pathways that started outside his hut and eventually returned to where it began after covering a long distance. Once all these preparations had been made, milking proper could begin. For this purpose, the seringueiro went round his territory early in the morning, cut the trunk at a height of about three metres using a special knife and attached a tinplate container underneath the V-shaped, fishbone-shaped or spiral scar, out of which the rubber milk (-> Latex) flowed. This -> Tapping operation had to be done before sunrise, because rapid evaporation caused the flow of latex to stop prematurely later on in the day.
Sources: Jünger 1942, 22 – 23 and 75 – 76; Klemm 1960, 36 – 37; Hoppenhaus 2013, 36



Tributary of the -> Amazon that starts at the confluence of the Juruena and Teles Pires and is 810 kilometres long; it can be negotiated by ocean steamers as far as the rapids that are 330 kilometres from the mouth near Santarém. Travellers described their journey on the Tapajós as follows: “It makes its way through walls of towering vegetation” (including numerous rubber trees -> Hevea brasiliensis). “The sound of the gurgling water carries soothingly to the banks with their dense vegetation, under the gloomy cover of which an endless variety of flora and fauna flourishes unseen”. Itaituba is located 240 kilometres upstream from Santarém, on the right bank of the river. At the end of the 19th century, it was a village with a few hundred Indian inhabitants, who made their living as fishermen, hunters and farmers (growing corn, yucca, sugar cane and bananas). In May 1876, Henry -> Wickham took 70,000 rubber seeds on board her in Itaituba that he had collected with the help of the Indians and smuggled them to England – a coup that made it possible to start plantations in Britain’s Asian colonies. “The name Itaituba cannot be found in any English history book, although Great Britain owes a fortune amounting to hundreds of billions to this long-forgotten Brazilian village”: this sentence comes from the book “Battle for Rubber”: The Rio Tapajós river is, however, also where ambitious economic plans failed: the US car magnate Henry Ford (1863 – 1947) tried to establish Hevea brasiliensis plantations on its banks. In 1927, Ford acquired the concession rights to 12,000 square kilometres of land, an area the size of the Austrian state of Tyrol, from the government of the Brazilian state of Pará with the aim of clearing it and planting rubber trees. Due to a land swap, two different areas were involved from 1934 onwards: Fordlândia, 200 kilometres south of Santarém, covering an area of 9,500 square kilometres, and Belterra, 50 kilometres from the place where the Tapajós joins the Amazon, covering an area of 2,500 square kilometres. Tapping of the oldest trees started in the spring of 1937. The stand increase to ten million Hevea trees by 1940. Ford’s jungle experiment ended in disaster even so: a fungus attacked the rubber trees – that were planted too close together – on several occasions, so that they died and Ford had to start again from scratch. The sales outlets decreased too, because synthetic rubber started to conquer the market – Fordlândia generated losses on an ongoing basis. The grandson of the car pioneer, Henry Ford II (1917 – 1987) wanted to end the Brazilian adventure as quickly as possible. In 1945, he sold the sites – in which his grandfather had invested more than USD 25 million – back to the Brazilian state for the symbolic price of USD 244,200. In the meantime, Fordlândia, which once provided a living for 8,000 people, is a ghost town with just 800 inhabitants.
Sources: Zischka 1936, 165 – 166; Fischer 1938, 144 and 167; Jünger 1942, 63 – 67, 169, 173 and 179; Hoppenhaus 2013, 37



Obtainment of -> Latex from the -> Hevea brasiliensis by making cuts in the tree’s bark on a daily basis. The tappers (-> Seringueiros) have to operate very conscientiously when they are doing this: because too deep a cut with the tapping knife harms the -> Cambium, bark deformation occurs, which leads to a reduction in the amount of latex the tree produces. The bark takes time to recover, so the entire tree needs to be used carefully when tapping. If all the precautions are taken, the Hevea can be tapped for about three years, before the first tapping point has recovered completely and can be tapped again. During the roughly five-month harvesting period outside the rainy season, about three to four kilograms of rubber can be obtained per tree in this way. In view of this relatively small yield, the protracted tapping method was practically never used in the forests on the -> Amazon. Instead of a knife, the rubber collectors frequently used an axe. Although more milk flowed as a result, the rubber tree always died without recovery periods of several years. All of the bark of some trees was removed or the trees were even felled in order to obtain as much latex as possible at one go. This overexploitation was so far advanced as early as the end of the 19th century that the more easily accessible areas of the forests were not suitable for regular rubber harvesting any more. Such wastage of natural resources – or as we would say nowadays: the lack of sustainability – drove up the rubber price; the gap between supply and demand on the world market became larger and larger. This was to change as the amount of plantation rubber increased – but there was a time delay, because cultivated Hevea trees cannot be tapped until at least five years after they are planted.
Sources: Zischka 1936, 142 and 145; Jünger 1942, 57, 69 and 76 – 78; Helbig 1949, 260 and 267; Kropf 1949; 10; Klemm 1960, 36 – 37


United States Rubber Company

The “United States Rubber Company”, known in short as US Rubber, was established in 1892 in Naugatuck in the state of Connecticut, which was a stronghold of the American rubber industry at the time. It was a merger, initially of nine companies, which primarily manufactured shoes and boots from rubber, particularly Hayward’s “Colchester Rubber Company” and Goodyear’s “Metallic Rubber Shoe Company” (-> Vulcanisation). Establishment of the company was initiated by Charles Ranlett Flint (1850 – 1934), a businessman who was involved in rubber trading between -> Brazil and the USA and was known as the “father of trusts”. Flint’s biggest accomplishment apart from US Rubber is considered to be the “Computing-Tabulating-Recording Company” (CTR), which was founded in 1911 and was later to spawn IBM.

Rubber shoes were a growing market at the time, which more and more companies were entering and which experienced fierce price wars as a result. US Rubber held 50 per cent of the market, which was a clear competitive edge for the companies involved. The rubber trust subsequently acquired two of the biggest rivals and increased its market share to 75 per cent. Around the turn of the century, the core business of the rubber manufacturing companies switched to the production of car tyres. In 1905, US Rubber – which had focussed entirely on rubber boots until then – entered the tyre business by buying Rubber Goods Manufacturing (RGM). As the treasurer of US Rubber, Flint went to Brussels in 1906 to secure the rubber from Congo from King Léopold II (1835 – 1909) (-> Congo atrocities). DuPont assumed control of US Rubber in 1927. Tyre sales in the USA slumped by two thirds in 1929, when the Great Depression began. US Rubber’s business flourished even so, with the company increasing its market share from just under seven per cent to 30 per cent within just one year by reducing prices; the main customers included General Motors and Ford.

As long as the USA did not produce any rubber of its own, the US rubber industry – which was the largest rubber consumer in the world – remained completely dependent on supplies of raw materials from the British and Dutch colonies in Asia – and they were forced to pay the prices that the monopoly demanded. The US President Calvin Coolidge (1872 – 1933, term of office: 1923 – 1929) reacted to US Rubber’s complaints about this. As a result, the American Congress approved the equivalent of two million Marks to have the potential for growing rubber trees on the Philippines and in South America investigated – without any major success. Representatives of US Rubber had no luck in London with Winston Churchill (1874 – 1965), on the other hand: the British Chancellor of the Exchequer (Minister of Economics and Finance) continued to do everything in his power to limit the quantity of rubber available, so that the price remained stable at the highest possible level. Downing Street still had large debts with Uncle Sam from the Great War – the fact that the government was particularly keen to pay them back with American money from the rubber business was a rumour that hardly anyone denied ....
Sources: Fischer 1938, 142 – 145; Gale Encyclopedia of U. S. Economic History



Process to make natural or synthetic -> Rubber resistant at high temperatures with the help of sulphur. While the sulphur bonds with -> Isoprene (natural rubber) and butadiene (synthetic rubber -> Buna), the molecular chains lengthen and are at the same time linked to form a network via interconnections (sulphur bridges). This makes the material more stable, without it losing its elasticity. In other words, the chemical operation changes the physical properties of the rubber, making it more resistant to heat and cold, for example, thus increasing its practical value and broadening the range of technical applications.

Vulcanisation was invented not by a chemist but by Charles Nelson Goodyear (1800 – 1860), a hardware dealer from Philadelphia, who kept on experimenting with the relationships between rubber and other substances until his trial-and-error method produced success. Although Goodyear made his discovery in 1839, the history of vulcanisation goes back much further: it is alleged that the Indians on the Amazon were already familiar with the sulphurisation of rubber in the pre-Columbus era. Reliable records indicate that the Berlin chemist Friedrich Wilhelm Lüdersdorff (1801 – 1886) observed that sulphur powder eliminated the stickiness of a rubber/turpentine solution. Lüdersdorff published a scientific paper about this in 1832 (“Dissolving and restoring Indian rubber, known as gummi elasticum”), the significance of which was not recognised, however, so that it was soon forgotten. It is probably around the same time that Nathaniel Hayward (1808 – 1865), a manufacturer in Colchester / Connecticut (USA), succeeded in making a viable material from sticky rubber via “solarisation” (1838: US Patent 1090). Hayward reported that his attention had been drawn in a dream to the idea of blending rubber with sulphur and then letting it dry in the sun, after he had carried out experiments with unsuccessful results. Goodyear realised the development potential of the process, which he acquired for the equivalent of 12,000 Marks. After a number of setbacks and lengthy attempts to find out what was the right temperature, Goodyear succeeded in producing a marketable vulcanised material in the winter of 1839. He called it “metallised rubber” or “elastic metal”. He did, however, fail to apply for patent protection. When he at long last decided to do this almost five years later, it turned out that the British chemist Thomas Hancock (1786 – 1865) had developed a similar process that had already been patented in Great Britain in 1843. The businessman Horace H. Day (1813 – 1878) had, in addition, secured the rights for North America from Hancock and was being generous in granting licences. Goodyear, on the other hand, now had the US Patent 3633 for the “vulcanisation of rubber” that had been granted to him on 15. June 1844. The court in Trenton / New Jersey took a decision in favour of Goodyear in the legal patent and priority dispute against Day in 1852. Goodyear had commissioned Daniel Webster (1782 – 1852), who was the US Secretary of State at the time, to act as his lawyer and he demonstrated persuasively that Hancock could only have developed his own method if he had known about the “metallised rubber”. The word “vulcanisation” is not attributable to Goodyear, however: it was created by the artist and inventor William Brockedon (1787 – 1854), a friend of Thomas Hancock, who based it on Vulcanus, the Roman god of fire and blacksmithery.
Sources: Jünger 1942, 31, 34, 36 – 41, 188 – 189, 193; Klemm 1960, 13 – 15; Hoppenhaus 2013, 36


Wickham, Henry (1846-1928)

British explorer in the “gold rush” town of Santarém on the Rio -> Tapajós river, a tributary of the -> Amazon; in May 1876, he smuggled 70,000 seed capsules of the Hevea brasiliensis, on which there was a strict export ban, to England by ship. After starting to grow trees from them successfully at Kew Gardens, the royal botanical gardens in London, the young rubber trees were shipped to the British colonies in tropical Asia, where they were planted successfully in Ceylon (Sri Lanka) first – the plantation rubber era had begun.
Sources: Zischka 1936, 152 – 155; Fischer 1938, 67 – 87; Jünger 1942, 63 – 70; Kropf 1949, 22 – 23; Klemm 1960, 34 – 36; Hoppenhaus 2013, 37



Uncertainty factor in polymerisation. Example -> Rubber: the hydrocarbon -> Isoprene is the basic component (monomer) of this natural polymer. In other words, the rubber molecule is a combination of numerous isoprene molecules. Initially, research scientists had to leave it open exactly how many of them are needed to form a rubber molecule: the chemical formula was “(C5H8) x times”, i.e. the isoprene molecule perhaps ten, a hundred or possibly even a thousand times. The “x” therefore stood for an unknown – or for a variable, as far as the quality and the physical properties of the rubber in question were concerned. In the 1930s, for example, it was assumed that the “x” was somewhere in the 1,000 to 2,000 range in high-quality plantation rubber.
Sources: Zischka 1936, 170 and 173; Kropf 1949, 34



Plantation for rubber trees in French Indochina (now Vietnam), 40 kilometres north of Saigon (now Ho Chi Min City), that was established by the French botanist Perrin, who was trained in -> Buitenzorg. 200 years after La Condamine’s journey to the Amazon (-> Cahuchu), France now had natural rubber of its own and was as a result at least in a position itself to cover a fifth of its industry’s needs at the time.
Source: Zischka 1936, 168

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References used

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