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as much that is untrue and misleading has appeared in the press during the last few weeks.

But first, a few words about natural rubber. The Old World owes its knowledge of this substance to the New. This wonderful product became known in Europe shortly after Columbus discovered America. If I, coming from across the ocean, now bring you this colloid prepared there synthetically, I merely repay part of the debt which we owe America.

Hardly a generation ago, the southern part of this great American continent furnished the whole supply of the different kinds of rubber. Since then extensive plantations of rubber trees have been established in various tropical countries, and their yield has grown so enormously that the old home of wild rubber will soon be thrust into the background. This is a matter which involves many millions; consequently a very serious economical problem confronts South America.

You all know that caoutchouc is made from the milky sap of numerous species of trees and shrubs and the grotesquely formed lianas by various coagulation processes, and that this product, on being suitably treated with sulphur or sulphur compounds, i. e., by vulcanization, acquires its valuable and characteristic properties. The synthetic method took quite a different route. By breaking up the very complex molecule which rubber doubtless possesses, by pyrogenetic processes, i. e., by dry distillation, a veritable maze of all kinds of gases, oils, and resins was obtained, as well as a colorless fluid resembling benzine, to which the investigators gave the name "isoprene." It was Bouchardat who first expressed the belief that this isoprene, which is obtained in very small quantities and in an impure form by the dry distillation of caoutchouc, might be closely and intimately related to caoutchouc itself. This important question was then eagerly discussed for several decades by the scientists of all countries, and opinions were sharply divided.

As far back as the eighties, Tilden claimed to have prepared artificial rubber from isoprene by treatment with hydrochloric acid and nitrous acid. But neither Tilden nor his assistants, though they worked strenuously for years, succeeded in repeating the experiments. Moreover, numerous other investigators, among them our chemists, were unable to confirm the results. In 1894 Tilden found, however, that that isoprene which he had prepared about 10 years before, on standing, had partially polymerized into rubber. In this way Tilden, in fact, was the first discoverer of synthetic rubber. But this method which time has not yet permitted to repeat is obviously not a commercial one. Dr. Fritz Hofmann of the Farbenfabriken vorm. Friedr. Bayer & Co. is to be regarded as the real inventor of synthetic rubber, for, by the application of heat, he succeeded, as the first, in August, 1909, in polymerizing the isoprene molecules com

pletely into the complex rubber molecule on a technical scale. Somewhat later Harries invented independently another method of arriving at the same result. Everyone is now in a position to repeat this exceedingly simple experiment himself, but in order to confirm Hofmann's results, it is necessary to employ pure isoprene.

The practical value of this rubber, of which many samples are among the exhibits, has been tested by the highest authorities in this branch of the industry, whilst Prof. Karl Harries, whose unremitting labors extending over many years, prepared the soil for Hofmann's synthesis, has carefully examined the chemical constitution of the substance.

Isoprene belongs to the butadienes. It was therefore to be assumed at the start that betamethylbutadiene would not hold a peculiar and isolated position amongst the butadienes in general. It was argued that other members of this interesting group of hydrocarbons would yield analogous and homologous rubbers on being heated. In the synthesis of products occurring in nature, there is always a possibility of producing such variations, and our endeavors to find out whether this was true in the case of rubber were crowned with success, for to-day several representatives of the new class of caoutchoucs possessing different properties are known and are being submitted to technical tests. Exact proof of the existence of the class of isomeric and homologous caoutchoucs was also first presented by Elberfeld.

To you who hear this account and see these beautiful specimens, the matter appears very simple, intelligible, and clear. In reality, however, it was not so. The difficulties which have been overcome were great indeed and those which still remain to be surmounted, in order to produce a substance equal to para caoutchouc in quality and capable of competing with cheap plantation rubber costing only 2 marks per kilo, are still greater. But such difficulties do not intimidate the chemist and manufacturer; on the contrary, they spur them on to further efforts. The stone is rolling, and we will see to it that it reaches its destination. The end in view is this, that artificial rubber may soon play as important a rôle in the markets of the world as does natural rubber. The consumption of rubber is simply enormous. Finished articles to the value of 3 milliard marks ($750,000,000) are manufactured every year, and the raw material from which they are made, calculated at the present market price of 12 marks ($3) per kilo, costs 1 milliard marks ($250,000,000). Other tasks which the chemist has on hand shrink into insignificance compared with this gigantic problem. The laurel wreath will not adorn the brow of the wild dreamer but that of the scientist who, cool and persevering, pursues his way. The seed he sows ripens

slowly, and though according to the statements in the press, all this is mere child's play and the problem has been solved, I leave it to your judgment whether this is true or not, like much that printer's ink patiently transfers to paper. I am right in the midst of this excitement. I have employed articles made of synthetic rubber, and for some time I have used automobile tires made of this material. Yet, if you ask me to answer you honestly and truly when synthetic rubber will bring the millions which prophets see in its exploitation, I must reply that I do not know. Surely not in the immediate future, although synthetic rubber will certainly appear on the market in a very short time. But I hope to live long enough to see art triumph also here over nature.

We are now at the end of our journey. We have flown not only over the field of Germany, but also over all other countries where the chemical industry is cultivated. We have taken a passing glance at the untiring striving for advance, the restless search for the hidden and unknown, the ceaseless efforts to acquire more technical knowledge as witnessed in the great laboratories and factories of our mighty and ever-growing industry. We will now guide our airship into the haven whence we set out and land where our coworkers have gathered from all the countries of the earth to recount whatever progress each has achieved, and to discuss, in public and private, the problems which have been solved and those which still await solution. This is the purpose and aim of the congresses of applied chemistry, and in this way they promote directly and indirectly the interests of our industry. But they also serve another purpose-to spread far and wide knowledge of our great deeds. It is thus that they impress the importance of our science and the arts founded on it upon the public in general and especially upon those who have influence in social or official positions, so that our profession may advance equally with others, and so that the importance of the chemical industry and of those connected with it from an economic, hygienic, and social standpoint may become better and better known.

That the effulgent light of this knowledge will also be diffused by the Eighth International Congress of Applied Chemistry is assured by the magnificent organization which our friends, the American chemists, have provided, the skillful manner in which the affair has been conducted, the hospitable reception which has been extended to us, not only by our colleagues but by the people at large, and which is still awaiting us in our tours of inspection of the flourishing industry of America, in so many respects a model for others. For chemical science and the chemical industry the following words of Schiller are beautifully descriptive:

"Only the serious mind, undaunted by obstacles, can hear the murmuring of the hidden spring of truth."

HOLES IN THE AIR.

By W. J. HUMPHREYS, Ph. D.,

Professor of Meteorological Physics, United States Weather Bureau, Washington, D. C.

[With 3 plates.]

The bucking and balking, the rearing, plunging, and other evidences of the mulish nature of the modern Pegasus soon inspired aerial jockeys to invent picturesque terms descriptive of their steeds and of the conditions under which their laurels were won or lost. One of the best of these expressions, one that is very generally used and seems to be a permanent acquisition, is "holes in the air." There are, of course, no holes in the ordinary sense of the term in the atmosphere— no vacuous regions-but the phrase "holes in the air" is brief and elegantly expressive of the fact that occasionally at various places in the atmosphere there are conditions which, so far as flying is concerned, are mighty like unto holes. Such conditions are indeed real, and it is the purpose of this paper to point out what some of them are, when and where they are most likely to occur, and how best to avoid them.

Suppose for a moment that there was a big hole in the atmosphere, a place devoid of air and of all pressure. The surrounding air would rush in to fill this space with the velocity pertaining to free particles of the atmosphere at the prevailing temperature; that is to say, at the velocity of sound in air at the same temperature, and therefore at ordinary temperatures of about 1,100 feet per second, or 750 miles per hour. Even, therefore, if such a hole existed, it would be impossible for an aeronaut to get into it-he could not catch up with it.

But, according to the claims of some, if there are no complete holes in the atmosphere there are, at any rate, places where the density is much less than that of the surrounding air; so much less indeed that when an aeroplane runs into one of them it drops quite as though it was in a place devoid of all air and without support of any kind.

This, too, like the actual hole, is a pure fiction that has no support in barometric records. Indeed, such a condition, as every scientific man knows, could be established and maintained only by a gyration

or whirl of the atmosphere, such that the "centrifugal force" would be sufficient to equal the difference in pressure, at the same level, between the regions of high and low density.

Appropriate equations can be written to express the balance between pressure gradient and deflective force in any sort of winds, and at any part of the world (it depends slightly upon latitude). Therefore it is possible with certain conditions given to compute the wind velocity, or with other conditions given to compute the pressure gradient. But in the present case numerical calculations are not necessary. We know that an ascent of half a mile, easily made by an aeroplane, produces roughly a 10 per cent decrease in pressure, and we know too that a greater pressure difference than this seldom exists even between center and circumference of violent tornadoes. Hence a drop in density, or pressure, to which the density is directly proportional, sufficient to cause an aeroplane to fall, would require a tronadic whirl of the most destructive violence. Now there were no whirlwinds of importance in the air, certainly none that could be called tornadoes, at the times and places where aeronauts have reported holes, and therefore even half holes, in the sense of places sufficiently vacuous to cause a fall, must also be discarded as unreal, if not impossible.

Along with these two impossibles, the hole and the half hole, the vacuum and the half vacuum, should be consigned to oblivion that other picturesque fiction, the "pocket of noxious gas." Probably no other gases, certainly very few, have at ordinary temperatures and pressures, the same density as atmospheric air. Therefore a pocket of foreign gas in the atmosphere would almost certainly either bob up like a balloon, or sink like a stone in water; it could not float in mid air. It is possible, of course, as will be discussed a little later, to run into columns of rising air that may contain objectionable gases and odors, but these columns are quite different from anything likely to be suggested by the expression "pockets of gas.'

The above are some of the things that, fortunately alike for those who walk the earth and those who fly the air, do not exist. We will now consider some of the things that do exist and produce effects such as actual holes and half holes would produce-sudden drops and occasional disastrous falls.

AERIAL FOUNTAINS.

A mass of air rises or falls according as its density is less or greater, respectively, than that of the surrounding atmosphere, just as and for the same reason that a cork bobs up in water and a stone goes down. Hence warm and therefore expanded and light air is buoyed up whenever the surrounding air at the same level is colder; and as

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