interest. Dr. Gerlach, of Hanover, a practical manufacturer, thinks it may be twenty years before artificial, or, as it is sometimes called, synthetic rubber can compete with the natural. He points to the fact that it took at least as long a time for synthetic indigo to reach the commercial stage after it had been first produced in the laboratory. Millions of dollars were expended in the investigations by one firm alone. But as we have had the romance of the alizarine industry, by which a product of coal tar replaced the extract of the madder root and ended its cultivation in France, and the romance of the indigo industry which has so largely affected the growth of the indigo plant in India, so we may have the romance of the synthetic rubber industry, but many a long and weary investigation must be carried on, many patents will be abandoned and much money will be spent, apparently in vain, for no process can be considered commercial unless it can produce rubber not only more cheaply than it can now be obtained from the plantations, but more cheaply than there is any likelihood of its ever being produced from natural sources. Probably twenty cents a pound should be considered the maximum cost of a commercial process for synthetic rubber.
Rubber was found to yield on heating the substance isoprene among others. This substance has the same percentage composition as rubber, but its molecular structure is considered to be simpler and to be represented by the formula
Isoprene was accidentally found to change into rubber apparently upon long standing, and efforts were made to produce rubber from isoprene at will. It was found that by heating at a high temperature with acetic acid in closed tubes the change takes place and later a small amount of sodium was found to produce a similar effect at a lower temperature.
The problem of synthetic rubber is then two-fold: first, to get cheap isoprene; second, to convert isoprene cheaply into rubber. The most natural source of isoprene seems to be oil of turpentine, which has the same percentage composition, but it has not proved satisfactory and its formation from isoamyl alcohol gives greater promise. Isoamyl alcohol is one constituent in fusel oil, whose presence in raw spirits renders them so injurious. It is obtained to a small extent in the ordinary fermentation of potatoes and other starchy substances. Professor Fernbach, of the Pasteur Institute, has discovered a method of fermenting starch which, instead of yielding a large amount of ordinary alcohol and a small amount of fusel oil, produces fusel oil with practically no ordinary alcohol. This fusel oil, however, instead of having a large quantity of isoamyl alcohol consists chiefly of butyl alcohol, from which butadiene,
