November, 1926
INDUSTRIAL AND ENGINEERING CHEMI$TRY
1129
Developments in the Netherlands Indies Rusber-Planting Industry’ By 0. de Vries BUITENZORG, JAVA
UBBER is one of the youngest of tropical plantation products. Especially in the Netherlands Indies, where planters had large experience with other crops, such as sugar and tobacco, coffee, tea, cacao and cinchona, much attention has been paid from the very beginning to technical and scientific developments and to the establishment of rubber experimental stations, as these had already proved of such value with other crops. Hevea was introduced into the East in 1876, exactly half a century ago. Java received its first seedlings at the same time as Ceylon and Malaya, and Hevea was grown in Java on a small scale from the beginning. But the Setherlands Indies were slow in starting on a large scale, and at first had to seek much information on tapping, preparation, etc., in the older rubber districts, Ceylon and RIalaya. Technical developments, however, were rapid, and in recent years the Ketherlands Indies have tried to contribute their share to the general scientific development of the industry. We may pass the different historical stages and only mention here that a t present there is one central experimental station a t Buitenzorg, the “Proefstation voor Rubber,” which does the testing and general research work on preparation for the whole of the Netherlands Indies, and is the central institute for research on planting problems and for the advisory service for the whole of Java and South Sumatra. It has local officers stationed in different outlying districts, some of them forming part of the staff of the experimental stations for the other large crops situated elsewhere. The East Coast of Sumatra, where in a relatively small area about half of the Netherlands Indies European rubber plantations are situated, has a strong local experimental station for rubber as well as for other crops. The total budget for the current year amounts to about $150,000; the total staff consists of about twenty scientific and advisory officers for rubber alone.
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Native Industry
Besides the European plantation industry, the rapidly rising native rubber production has attracted much attention during recent years. The native crop already nearly equals that from European plantations and perhaps will surpass it in the near future. Native rubber cultivai.ion, however, is still extensive in character and shows only the beginning of intensification and technical development. The Government Department of Agriculture has a central agricultural experiment station a t Buitenzorg which not only does work of a general nature-introduction of new types, general research on budding, etc.-but also has started seed gardens for the native rubber growers. The Government Advisory Service has officers in the principal native rubber districts, who promote the use of better seed, the planting of green manures, better methods of cultivation and tapping, etc. In former years not much could be accomplished, because plenty orgood land was available and rubber-planting cost the native almost nothing as the seedlings were interplanted between the rice crop and the costs of clearing and upkeep came on the account of the rice. A plot of mature rubber represented to the native no capital value; tapping was drastic, and as soon as the trees were finished, fresh plots from younger clearings were available. At present, however, the best land has been taken in most of the districts, and the Presented under the title “Developments on the Dutch Rubber Plantations.”
rubber fields near the kampong or the river begin to represent a certain capital value; a change to more intensive exploita-
tion methods is due to come. Undoubtedly, Hevea is eminently suitable as a native crop; the limiting factors have not yet been reached and native rubber still presents large possibilities. Technical development, however, will be necessarily slow in the near future. Planting and Cultivation
Planting problems, of course, take the largest place in the work of the experimental stations. Hevea as a European crop is only twenty years old, and as it takes seven to ten years after planting before the productive capacity of a Hevea plot can be judged, progress is necessarily very slow. Diseases have to be studied and combated; methods of planting and thinning have to be tested; cultivation, soil upkeep, and manuring require much attention, not only to develop the best methods, but also to remedy the errors made in the past and to restore as much as possible the older plantations, which were the test plots for the whole industry. Selection of seed and development of budding may be important in giving us better yielding strains in the future. Our present Hevea has often been called a weed, so amazing is its regenerating power. 9 fallen tree or a branch stuck into the ground as a fence post will form new shoots which are not easy to kill; Hevea will grow and produce latex even in very adverse circumstances. Undoubtedly, the innate strength of our present Hevea has been of incalculable value in making possible the rapid and successful extension of both European and native plantations; but a t the same time this suggests that our present Hevea is only a very rough material, which may be refined and developed to much higher stages without becoming too sensitive a crop for large-scale planting. It will be clear that big problems await solution. Progress, as has been said above, is necessarily slow. An experiment with a new strain of seed or buds started now may only lead to a conclusion seven to ten years hence. Before that time, new experiments will have been started on experience gained in the meantime, and year after year the results will follow each other like waves on the beach, each next result effacing the high-tide mark made by its forerunner practically before its significance can be realized and turned into actual practice. Practically every new planting is done on new lines and based on a larger experience, but meanwhile the bulk of the old plantations remains and continues to produce its share, and the better results of newer plantings, which we hopefully expect, will only very gradually increase the general average yield. Let us hope that rubber prices will remain stable a t such a level that capital may be available for new plantings, so that the technical development of the planting industry can continue. Preparation and Properties
From the beginning rubber planters have been very keen to improve their methods of preparation and the properties of their rubber. They have felt that only in this way could plantation rubber gain a sound footing in competition with Brazilian and wild rubbers. Systematic testing of the output of a number of estates and a systematic study of methods of preparation were started on a scale unknown in any of the other big European tropical crops.
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vulcanization difficulties were the first 40 draw attention, and one of the causes of variability in rate of cure was discovered to be a bacterial decomposition of serum substances, chiefly proteins. Differences in the by-substances originally present in the latex were also found of great importance; different factors such as age of the trees, heavy or light tapping, etc., have a considerable influence, and in the last few years more variability than from any other source has probably been caused by slow-curing rubber obtained from trees that have had a prolonged rest, either because of tapping with alternating periods of two to four months or because of resting large areas in connection with restriction of output. The chief features of the problem of rate of cure are now well known. The question has been pushed to a practical issue and a rubber of guaranteed uniformity in rate of cure has now been put on the market by a number of estates by way of large-scale experiment. For such well-equipped estates as are willing and able to follow strictly standardized methods of preparation formulas have been drawn up that give practical certainty of a product very uniform in rate of cure. After the necessary preliminary arrangements and after regular testing of the output a minutely detailed formula is drawn up for each estate, and for lots prepared according to this formula a certificate is issued based on samples drawn by a wharf or other neutral body. The testing report not only certifies that the samples from the lot in question fall within the required limits of variability, but also that the methods of preparation on the estate are known and in accordance with the formulas for the production of a uniform rubber of prime quality. This report, therefore, is a t the same time a certificate of origin; rubber covered by such a certificate is sure to come from one of the best estates. The principal difficulties caused by the rate-of-cure problem may now be regarded as solved, and the work done on it has led to the development of a “special type” of rubber in the form of certificate rubber of guaranteed uniformity in rate of cure. Rubber, however, is a complex substance and from the beginning it was considered necessary to extend the tests to as many different properties as was compatible with daily routine testing of a large number of samples. Tensile strength and slope were among the first properties to be added to the list; but they have not gained much practical importance. Tensile strength is practically always satisfactory in the first grades; slope is very valuable to distinguish between the lower grades, but is always normal in the first grades. Viscosity is a very valuable test to check the results of the rate-of-cure determination and allow one to detect the factor that caused a deviation; but it is a kind of internal control between testing station and plantation, and its complex nature makes it too bewildering for the manufacturer who does not know the history of the sample. Viscosity in acidified benzene, added to the list in recent years, is a valuable test on real inner quality, but as such it is more a distinction between first and lower grades, or a check on beginning tackiness and decay. In first-grade rubber it is always good. Tests made regularly in the daily routine, such as liability to moldiness of smoked sheet, stickiness in both crepe and sheet, etc., give important information to producers, but are not of much interest to manufacturers. Plasticity determinations, however, are still of general interest and in recent years much time has been devoted to a systematic study of this subject. The plan, broadly, was the same as with the rate-of-cure problem. First, a method of testing was developed which was simple enough to be used in mass testing
Vol. 18,No. I1
with native helpers. Ira Williams had the great kindness to put his then unpublished results at the writer’s disposal in. 1921 and a modified Williams test for crude, unmasticated rubber could be worked out. The second step was a survey of the plastic properties of plantation rubber, as produced at present on European estates, so as to learn the existing variability and the possibilities of improvement. The third step was a systematic study of the influence on plasticity of all factors influencing the composition of the latex (physiological factors) and during preparation (chemical and physical factors, bacterial decomposition of by-substances). The results of these extensive investigations have already been published in part; other communicatioqs on this subject are in course of preparation. I t has been prophesied that in the plasticity problem history will repeat itself. With rate of cure,. plantations have learned to avoid many causes of variability and manufacturers have learned to control vulcanization much more accurately than in former years and to overcome variability by the use of accelerators. The two parties have met halfway and variability in rate of cure now seldom causes trouble. Shall we see the same thing repeated with plasticity? Will plantations learn to produce a rubber more uniform in this respect? Will manufacturers learn to control mastication and the plasticity of the dough as systematically as they now control vulcanization? And will the addition of softeners take away many of the present difficulties? The writer is of the opinion that a better, more systematic control of mastication in the factories is highly desirable and due to come. About softeners, others more competent than the present author will have to say a word; but from the plantation side the problem will not be so easily solved as the rate-of-cure problem. The rate-of-cure problem was a chemical one-content of certain accelerators-while the plasticity problem is a colloidal one and therefore much more complicated. The conclusion from the first series of investigations is that plantation rubber, tested fresh in the tropics, is reasonably uniform in plasticity. Of the principal factors in preparation and in the composition of the latex only a very few have a notable influence on plasticity, and the plasticity of fresh plantation rubber is very far from showing the large variability that was encountered in former years in respect to rate of cure. This simple and gratifying state of affairs seems, however, completely to be n u M e d by another factor. During transport and keeping the plasticity of crude rubber seems to change considerably and in very different ways. The study of the factors that cause a later hardening, and of the methods of preparation that may keep the rubber of constant plasticity until it is consumed, is necessarily very tedious and complicated. Extensive investigations, not only in the tropics but also in the factories, will be necessary’ to throw light on this side of the question. The plasticity problem is far from solved and it is by no means yet clear how much of the difficulties will have to be overcome on the plantation side, how much will have to be done by improvements in the control of manufacturing processes. Special Types
*
So much for the general problems; a few words may be added about developments along special lines. After visiting American and European rubber factories the writer has concluded that our present plantation rubber is too good for 80 per cent of the applications, and not good enough for certain special articles. In other words, most producers w i l l have to work in the direction of a cheap, uniform mass product of good inherent properties, while a certain number will have to cater for “special types.” Native rubber producers,
INDUSTRIAL AND ENlXNEERINC CHEMISTRY
November, 1Y26
large estates or groups, and estates in less favorable conditions will have to go in for mass production; the special types will have to be the aim of eertain well-equipped estates that specialize in this direction. As special types may be regarded especially clean rubber, very pale crepe, crepe of very even and smooth texture, certificate rubber (especially uniform in rate of cure); other types, that may be developed on the basis of further research, are special rubber for solutions, and a specially plastic rubber. The development of such special types is necessarily slow, because the middleman has only the commercial side in view and does not take an interest in technical developments. The progresa made with certificate rubber has already been described. It has not yet been possible to develop a specially plastic rubber, owing to difficulties with too great stickiness and with changes in plasticity during keeping. Large-scale experiments lave
1131
also been made with rubber containing a minimum of serum substances (prepared from strongly diluted latex) for insulation purposes; a demand for specially clean rubber from certain manufacturers is always present. Future of Industry
The near future, we hope, will bring us an enormous technical progress on the manufacturing side, so that manufacturing chemists will be able to draw up more detailed specifications and tell us exactly what they want. There is no doubt that there is still a great future in the improve ment of a raw product with such remarkable properties as rubber, and it is gratifying to see that cooperation between technical men on the consuming and the producing sides is steadily on t,he increase. The present symposium will doubtless be a milestone on this road.
X-Ray Contributions to the Analysis of the Structure of Rubber and Allied Materials By George L. Clark DBPAATMBNT 011 CXEMICU.E~omssariio,M A S S A C X U I~srrTura ~~~ OB TacsmmeY. C ~ M B ~ D O BM*s% ,
ITH the discovery that x-rays may be used in the study of the fundamental ultimate structure of rubber and allied substances, a new chapter is being written in the science of this most complex, useful, and interesting material. For more than two years the writer has been using x-ray methods in the investigation of rubber, balata, gutta-percha, proteins, and resins,' although the detailed results have not been published. Within the past year and a half, however, several papers by Katz2 have appeared which report the resulta of eompre liensive experiments on the structure of rubber as revealed by x-ray diffraction photographs. Althougli details differ considerably, the essential phenomena described by Katz have been confirmed both in the writer's laboratory, in the masterly rcscarclies of Hauser and Mark,s and in a single experiment by Ott.' X-Rays
The nature and production of x-rays and their utilization in the analysis of crystalline structure are now generally familiar. X-rays are electromagnetic vibrations in the ether, differing from ordinary light only in the wave lengths. A beam of x-rays, such as are used for studies of rubber, has an average wave length about as great as yellow light. The whole range of the electromagnetic spectrum covers, in order, the shortest and most penetrating cosmic rays, lately measured by Millikan, the y-rays from radium, x-rays, ultra-violet rays, visible light, infra-red rays, Hertzian and radio waves, and electric waves. Ordinary light is diffracted by a grating consisting of finely ruled linea on dass or metal. Under ordinary circumstances such a g r a t i n i d o a not diffract x-rays (except a t extremely small grazing angles) because these rays are too short. Nature has provided excellent diffraction gratings for x-rays in the form of crystals. The outer symmetrical form of I Clark, A ~ J .. R ~ ~ia, 558 ~ (1928); I Pouth ~ c ~ ~ Sym. ~ ~ posium Mononapb, 1926. 2 Chrm.-Re.. (9, 353 (1925); Nolumisrcnsdoftm, $0. 410 (1926); 2. nngrw. Ckrm., 38, 439, 545 (1925); Kolloid-Z., 86, 300;3 5 19 (1925). Knulsckrk'. December, 1825, p. 10; Kolloidchrm. Beikrfir, SP, 63 (1926) and AmLronn-Festschrift, p. 64; Gummi-Zlg.. 40, 2090 (IS%>. 4 Nolunuirrmsrhoftcn. 14, 320 (1926).
crystals indicates a definite orderly interior arrangement of structural units. It is very definitely known now that the atoms (or ions since they are charged and -) in a rocksalt crystal, for example, are arranged on a cubic lattice, as shown in Figure 1. In this crystal, therefore, there are atom-bearing planes, which are parallel, alike, and equidistant from each other. These distances are of the same order of magnitude as the x-ray waye length (1 A. or O.OoOooW1 em.). Consequently the crystal may act as a grating for x-rays. The simple fundamental equation governing diffraction or reflection of x-rays by a crystal is
+
nh = 2d sin B
where n is the order of the reflection (1, 2, 3, ete.), X is the wave length of the x-ray, d is the distance between the parallel identical planes, and @ is the angle of incidence (or 28 the angle of reflection) of the x-ray beam upon t.his set of parallel planes. It is obvious that an experiment w i t h x-rays will a t o n c e disclose w h e t h e r or not a substance is crystalline and may thus act a s a g r a t i n g . Furthermore if it is c r y s t a l l i n e , i t is possible to ascertain the value of d for this set of planes, provided that the wave length X is known. bv a sinzle experimental measWgure I-Model ofa Qgstal, Showfng u r e m e n t of t h e Regd-lfY of A-ngemenf of Atoms in Space angle 28 at which reflection may take place. On the other hand, if the plane the ~distance i ~ ~ d is ~ ~known, ~ ~ then ~ , crystal may be used to analyze a beam of x-rays whose wave lengths are unknown.
_ _
Single Crystals
When a beam of x-rays passes through a single crystal, each of the sets of parallel planes with its own particular value
