ABOUT forty years ago two young chemist; announced that they had succeeded in making enough indigo to be pretty sure they had it. The method used by them was entirely independent of the indigo plants. The yield was extremely small and there seemed to be no promise in the method of future commercial success. A quarter of a century later or thereabout the manufacturer was supplying the world with artificial indigo and the occupation of the indigo planter, if not gone. was going. And now the chemical world is all agog over rubber. Last year a specimen of artificial rubber was exhibited at Berlin identical in all its properties with the natural substance. At present there appears, to be sure. to be little prospect of early commercial success along the line suggested, but the results already reached are of such interest as to incite to many efforts to solve the problem. First a few words concerning rubber. This substance is obtained mainly from South and Central America, though. of late years, owing to the great increase in the demand for it, plantations have been started, espetially in Ceylon and the .Malay Peninsula and Archipelago, and these are now contributing to the world's supply. In 1909 the production of rubber is stated to lia\'e been 70,000 tons. It is obtained from various trees as RC1Jra lrasiliensis, Manihat GlaziovU, Oastilloa elastica, Juntumia clast1ca, F!CU8 elustica, Hancornia speroso, etc. Deep incisions are made near the base of the tree. The liquid aowing from these incisions :s heated to drive off most of the water anll the residue is tile impure rubber of the market. The valuable constituent is caoutchouc, a colorless, elastic, amorphous substance. This has long been known but little has bfen learned in regard to its chemical nature until recently. fn general terms it may be stated that chemists do uoi lil«' to 10rk with gummy substances, but prefer things that crystallize, or that boil without decomposition, or that form definite c:rystallizable products. “ow taoutchouc does not crystallize, it does not boil without decomposition, and until a few years ago it was not lmown to be capable of yielding definite crystallizablp products. Great impetus was given to its study by the discovery of Harries that it forms a well-defined j.rodllct when treated with ozone, and that the ozonide t Iws obtained decompose' when boiled with water and yields levulinic aldehyde, a substan(e that can easily bp identified. It haK also ' been shown that caoutchouc forms a so-called nitrosite when treated with nitrous acid, and this nitrosite can also easily be identified. Tit!;” facts make it pOHsiblp for the chemist to tell whether he has caoutchou(, in hand or not and the scientific study of the substance has been materially advanced in consequence, Before the discovery of these fads a product had been obtained artificially that was deseribed as “like rubber,” but the question whether it was identical with caoutchouc or not could not be definitely answpred. :ow it is possible to determine with cprtainty whether a substance is or is not caouttnouc. To identify caoutchouc after you get it is one thing, to determine what it is is quite another. The first ;tep towards the solution of this problem was taken a number of years ago when GreviUe Williams showed that when rubber is heated to decomposition a very volatile substance is formed which he called “isoprene.” This boils at 36 deg. C. and is a hydrocarbon of the formula C)!,. Later Harries found that this same hydrocarbon is formed by the action of moderate heat upon oil of turpentine anll (J th"r terpenes. This isoprene has come to be the chief factor in the artificial jJreparation of rubber, for it is this substance which when exposed to eertain conditions is eonvnrted at least partly into eaoutchouc. That isoprene readily undergoes change wal observed by Tilden who announced in 1892 that one of the products is caoutchouc, Later he stated that contact with strong acids as, for example, aqueous hydrochloric acid, causes the change of isoprene into caoutchouc, at least to a small extent. Still later he claims to have discovered that isoprene is changed to caoutchouc spontaneously. He says: “Sper:imens of isoprene were made from several tel' penes tn the course of my work, and some of them I have preserved, I was surprised a few weeks ago at finding the contents of the bottle containing isoprene from turpentine entirely' changed in appearance. In place of a limpid, colorless liquid, the bottle contained a dense syrup in which were floating several large masses of a solid of a yellowish color. Upon examination, this turned out to be India rubber." Harries tried to repeat Tilden's work, but although he kept at it for seven years he was unable to confirm his results. He says: “Tilden must therefore accidentally have hit upon conditions which caused the polymerization of the isoprene, but, and this is the main point, he did not furnish the proof that he really had produced caoutchouc.” Klages had previously publicly stated that it is impossible to produce caoutchouc by the method suggested by Tilden. This was the state of affairs as far as the chemical public was concerned until the summer of 1909. Then Harries received from an English fnn a specimen of a substance which it was claimed had been made artificially by a proceSB patented by Dr. Heinemann in England. Harries foulli that the substance was in fact caoutchOUC, but he did not believe that it had been made artificially. Heine· mann's method consisted in passing acetylene, ethylene, and methyl chloride together through a tube heated to redness. Harries could not make this work and others WilD tried i also failed. Up to this time the experiences of Harries had been anything but encouraging. In November, 1909, he ,'eceived from the Elberfeld Color Factory some specimens of artificial rubber whieh had been made from isoprene by a secret process devised by Dr. Fritz Hof-mann. This led Harries to tal{e up his own experiments On the subject again, and toward the end of January, 1910, he was in a position to apply for a patent. The method devised by him consists in heating isoprene with strong aeetil acid in a closed tube. The product thus obtained is unquestionably caoutChouc. jWI the seielltific point of view the problem of the artificial preparation of caoutchouc is thus solved, but it is a far cry frOltl this to commercial success. Given iso]rene in sufficient quantity and at a sufficiently low price and the commercial problem will be solved. At present artificial rubber is almost as precious as the diamond, but, on the whole, the problem is in a more hopeful state tilan the indigo problem was for years after the start was made. The manufacturers and those who are carrying on chemieal investigations for them are plainly of the opinion that the work is worth while. That great frm, the Baden Aniline and Soda Faetory (generally called the “Badische") has taken out a number of patents in this field, and this is most significant. It is this firm that worked out the indigo problem and is now supplying the world with artificial indigo, having expended in the preliminary work millions of dollars! It is this firm that is placing the llanufaeture of artificial nitrates upon a firm scientific basis—probably the most important problem before the world as it involves ultimately the food supply. It may safely be predicted that before many' years have passed rubber will be artificially prepared in quantity sufficient to supply the great and increasing demand for it. lean t ime then: is no danger of a famine as plantations are springing up to supplement the supply of wild rubber. As has been pointed out the first tiling to be done is to get enough eheap isoprene. The only way to do this that appears to be in the least promising is to make it from oil of turpentine. The thief constituent of this oil is a terpene of the eomposition C,0H". while isoprene has the composition C,H,. The immed:ate problem, therefore, is to break down the molecule of the terpene, C,uH,., into simpler molecules of the cOmposition, C:,H,. If this could be done easily and cheaply the rubber problem would be solved. In thh connection it is of interest to note that, acccrding to an article that has just come to hand, Staudinger and Kleven have succeeded in increasing the yield of isoprene obtained from the terpene, dipentene, by heating to a high temperature the vapor of the terpene under diminished pressure. When the pressure is sufficiently low the yield is about 60 per cent. ' This is a very important observation for the purpose in view. Dipentene itself does not, to be sure, occur in nature in very large quantity, but the chief constituent of American oil of turpentine is pinene, a substance of the same eomposition as dipentene, and pinene is converted into dipentene by heating it to 2i0 to 270 deg. C. The way out may therefore be through turpentine. To recapitulate, turpentine eontains pinene. Pinene is converted into dipentene by moderate heat. Dipentene when heated to a high temperature under diminished pressure yields isoprene. Isoprene can be converted into caoutchouc by heating it with concentrated acetic acid and by other methods that need not be described here_ There are other hydrocarbons similar to isoprene that undergo changes similar to that by which isoprene is converted into caoutchouc, and there is therefore a prospect of the ultimate preparation of a number of products similar to rubber but differing from it in some respects. The commercial instinct has already led to the patenting of some of the processes involved. This aspect of the subject is, however, or it appears to be, of much less importance than the main problem briefly presented in this article. In the chemical laboratories connected with the great factories, especially in Germany, where several hundred well trained chemists are frequently engaged in a single factory, no doubt much work is now in progress. which has for its object the solution of the artificial rubber problem. This is also true of laboratories not connected with the factories. From time to time an article will appear in a scientific journal or a patent will be announced giving some result of the work. As usual, of the failures and disappointments, which always far outnumber the successes, we shall hear very little. But some day we shall wake up to learn that artificial rubber is on the market and then we shall be told truly that scientific research has scored another brilliant success. In the eyes of the world success will mean commercial success. But it must not be forgotten that this, if and when attained, will be based upon innumerable results that have absolutely no commercial significance. Greville Williams heated rubber and obtained isoprene many years ago. No one dreamed at the time that this simple fact might ultimately become the basis of a great industry. Harries treated caout(:houc with ozone and founded a method for indentify-ing caoutchouc which has proved of fundamental value in all subsequent work on this subject. Y Ve want to know what caoutchouc is, whether any one ever devises a method for making it artificially or not, and in the highest sense the knowledge will be just as valuable whether such a method results or not. But that is another story.