But the most interesting and most promising of all is the complete inorganic synthesis that dispenses with the aid of vegetation and starts with coal and lime.  These heated together in the electric furnace form calcium carbide and this, as every automobilist knows, gives acetylene by contact with water.  From this gas isoprene can be made and the isoprene converted into rubber by sodium, or acid or alkali or simple heating.  Acetone, which is also made from acetylene, can be converted directly into rubber by fuming sulfuric acid.  This seems to have been the process chiefly used by the Germans during the war.  Several carbide factories were devoted to it.  But the intermediate and by-products of the process, such as alcohol, acetic acid and acetone, were in as much demand for war purposes as rubber.  The Germans made some rubber from pitch imported from Sweden.  They also found a useful substitute in aluminum naphthenate made from Baku petroleum, for it is elastic and plastic and can be vulcanized.

So although rubber can be made in many different ways it is not profitable to make it in any of them.  We have to rely still upon the natural product, but we can greatly improve upon the way nature produces it.  When the call came for more rubber for the electrical and automobile industries the first attempt to increase the supply was to put pressure upon the natives to bring in more of the latex.  As a consequence the trees were bled to death and sometimes also the natives.  The Belgian atrocities in the Congo shocked the civilized world and at Putumayo on the upper Amazon the same cause produced the same horrible effects.  But no matter what cruelty was practiced the tropical forests could not be made to yield a sufficient increase, so the cultivation of the rubber was begun by far-sighted men in Dutch Java, Sumatra and Borneo and in British Malaya and Ceylon.

Brazil, feeling secure in the possession of a natural monopoly, made no effort to compete with these parvenus.  It cost about as much to gather rubber from the Amazon forests as it did to raise it on a Malay plantation, that is, 25 cents a pound.  The Brazilian Government clapped on another 25 cents export duty and spent the money lavishly.  In 1911 the treasury of Para took in $2,000,000 from the rubber tax and a good share of the money was spent on a magnificent new theater at Manaos—­not on setting out rubber trees.  The result of this rivalry between the collector and the cultivator is shown by the fact that in the decade 1907-1917 the world’s output of plantation rubber increased from 1000 to 204,000 tons, while the output of wild rubber decreased from 68,000 to 53,000.  Besides this the plantation rubber is a cleaner and more even product, carefully coagulated by acetic acid instead of being smoked over a forest fire.  It comes in pale yellow sheets instead of big black balls loaded with the dirt or sticks and stones that the honest Indian sometimes adds to make a bigger lump.  What’s better, the man who milks the rubber trees on a plantation may live at home where he can be decently looked after.  The agriculturist and the chemist may do what the philanthropist and statesman could not accomplish:  put an end to the cruelties involved in the international struggle for “black gold.”