452 THE POPULAR SCIENCE MONTHLY 



interest. Dr. Gerlach, of Hanover, a practical manufacturer, thinks it 

 may be twenty years before artificial, or, as it is sometimes called, syn- 

 thetic 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 commer- 

 cial 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 culti- 

 vation 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 con- 

 sidered 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. 



Eubber 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 repre- 

 sented by the formula 



OH 2 = C — CH = CH 2 



I 

 CH 8 



Isoprene was accidentally found to change into rubber apparently 

 upon long standing, and efforts were made to produce rubber from iso- 

 prene 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 tem- 

 perature. 



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 fermenta- 

 tion 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 alco- 

 hol. This fusel oil, however, instead of having a large quantity of iso- 

 amyl alcohol consists chiefly of butyl alcohol, from which butadiene, 



