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I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
centration of 12 to 13 per cent of ammonia was reached. At 0" C. the absorption was almost quantitative; the very small amounts of carbon monoxide remaining in the hydrogen can be eliminated by using higher pressures. The solution absorbed carbon monoxide to the amount of twelve to fifteen times its own volume, and it was regenerated a t about 60" C. The temperature was kept comparatively low in order to avoid too rapid evaporation of the ammonia, which may be recovered as ammonium sulfate. The carbon monoxide had a purity of 97 to 99 per cent; impurities were hydrogen and nitrogen. The semi-plant scale apparatus ran for several weeks without any trouble; only the evaporated ammonia had to be replaced. The iron equipment was not attacked by the absorption solution and no copper was precipitated.
Vol. 22, No. 4
The same method was then successfully applied in a large plant installation where pure carbon monoxide was manufactured from water gas for the preparation of phosgene. Literature Cited (1) Badische Anilin und Soda Fabrik, German Patent 289,694 (April 3,
(2) (3) (4) (5)
(6) (7) (8) (9) (10)
1914). Berthelot, Bull. soc. ckirn., 121 6, 176 (1866). Condamine, Compt. rend., 179, 691 (1925). Damiens, Zbid., 178, 849, 2178 (1924). Gmelin-Kraut, "Handbuch der anorganischen Chemie," 7th ed., Vol. I, Pt. 3, pp. 564 and 585; Vol. V, P t . 1, pp. 735, 911, and 1033. Hainsworth and Titus, J . Am. Ckem. SOC.,43, 1 11921). Kanzner, French Patent 629,743 (February 24, 1927). Larson and Teitsworth, J . A m . Ckem. Soc., 44, 2878 (1922). Leblanc, Compt. rend., 30, 483 (1850). Moser and Hanika, Z . anal. Ckem., 67, 448 (1926).
Cultivation and Preparation of Rubber in the United States' D. Spencez AMERICAN RL-BBERPRODUCERS, INC.,SALIXAS, CALIF.
A solution of the important problem of finding a H E economic imporof these tires ran over 10,000 source of rubber in this country has been undertaken tance of p r o v i d i n g miles; and with material such in California in the cultivation and extraction of rubber some source of rubber a s will soon be available in from the Mexican guayule plant. This undertaking within the confines of this quantity sufficient for a d e was begun about eighteen years ago and the expericountry is well recognized. quate experimentation, tires mentation has now reached the stage where a factory Practically all the rubber conmade entirely from this rubfor the commercial extraction of the rubber from this sumed in the United States, ber will give a still better acplant is in sight. The problem of rubber cultivation estimated a t 485,000 tons for count of themselves. in the United States has been studied from various this year, now comes from I n seeking a solution to angles-botanical, chemical, agricultural, mechanical, one source, the Hevea brasilithe problem of rubber culand economic-and a brief outline of what has been acensis tree, growing under t i v a t i o n i n t h i s country, comdished along these lines is given. intensive cultivation in the what are the most important Far East. If, for any reaeconomic factors t o be conson, this source of supply should be cut off, or its output sidered? I n addition to the ability of a plant to produce curtailed, the far-reaching consequences on our situation here rubber in quantity, there is the larger question of its suitmay be easily estimated. With this in mind, and with nearly ability from the standpoint of intensive cultivation by 5000 acres of healthy rubber-producing plants coming into mechanical means. I n a country where labor is high it is bearing in this country and a factory for the commercial ex- inconceivable that any system can succeed which calls for an traction of this rubber well within sight, it may not be amiss, expenditure of manual labor such as is required in the protherefore, to outline briefly something of what has already duction of rubber from existing sources today. Therefore, been accomplished toward the practical solution of this all- aside from the problem of finding the richest possible source of rubber and of determining the adaptability of the material important problem. Considerable public attention has been directed to the ques- selected to the climatic and soil conditions available within tion through the medium of the press, and efforts have been, this country, there is the question as to how such material and are still being made, to solve the problem of rubber pro- can be produced on a large scale and the rubbgr therefrom duction by chemical means or by the development of a source recovered by means requiring a minimum of human effort. of crude rubber from some hitherto neglected weed or plant A study of any one of these fundamental questions without capable of intensive development within this country. So equal consideration being given to the others must leave the far as we are aware, none of these efforts, however, are even problem unsolved. Our task was, therefore, not only to find remotely successful in competition with present sources of a form of plant life a t once rich in rubber, but also one capable supply, nor have they advanced, in fact, beyond the labora- of adaptation to the agricultural and mechanical problems tory experimental stage. Furthermore, in the manufacture involved in its intensive exploitation in this country. We of rubber goods in the United States no attempt has been made have been confronted throughout, not only with botanical, to supplant the existing sources of raw rubber from Hevea biological, and chemical problems, but with problems of agribrasiliensis, except that in which a number of automobile cultural and mechanical engineering. tires made entirely from guayule rubber grown in California Cultivation of Guayule were first manufactured under the direction of the Continental Rubber Company of New York in 1927. On test cars several Scattered throughout the northern central portion of Address before t h e California Section 1 Received December 26, 1929. Mexico, over thousands of square miles of more or less desert of t h e American Chemical Society at San Francisco, Calif., December 13, country, is a shrub known to the natives as guayule, from 1929. which rubber has been extracted on a commercial scale for 1 Vice president. Intercontinental Rubber Company.
T
I
Ouayuls s t Four Yeam of Aae
the past twenty years. This shrub, known botanically as Parthenium argc?itatum, has been the basis of all our work, not merely iiecause of its capacity to produce rubber in extraordinary amount, but hecause investigations had shown that this plant, more than any other, seemed to meet the climatological, agricultural, and mechanical requirements essential to its successful development in the United States. There is nothing new, Iherefore, in the idea of extracting rubber from Lwaynle. The natives in Mexico were first found doing this by chewing the shrub, making play balls from the material which they thus obtained. But the ease with which'the rubher can be quantitatively separated from the bark and other tissue of the p h o t by mechanical means on a large scale was a matter for later denionstration and a fact of major im-
Genersi view
Of
Guayvlc Nursery, Salinas, calif,
means with assurance of a uniform stand of healthy plants. Many problems have had to 1~ inirestigatetl and solved. The net result, however, is to be seen in the 20-acre nursery at Salinas, Calif., where some 25 million healthy, uniform guayule plants are now growing from seed which was planted by machinery last spring, watered and otlierwise cared for by mechanical means, involving the supervision of one foreman with an average of five laborers to help him. Botanical Development
I n tlie botanical field of investigation i t soon became apparent that Mexican guayule seed was far from uniform, and similarly that the plants produced from the seed showed endless characteristic variations among themselves. The first problem, tlien, was to separate and segregate these various strains for individual study. From about a thousand strains of Guayule separated from tlie offspring of the Mexican seed and characterized by differences in rubber content; hy distinctive differences in size, color, leaf, and branch, and root a
Ixgging Guayule Planta from Nurmry Beds
portance in considering its exploitatian in this country. To the pioneer work of Doctor Lawrence in this connection a word of trii3ut.e is due. The first steps toward the cultivation of guayule in this country were taken in 1912, when a quantity of p a y n l e seed was collected by Doctor iclcCallum, in Mexico, for experimental purposes here. This seed was first sown a t San Diego County in 1913, and froin this small beginning sprang our present source of supply. At first the problem of germinating the seed in quantity was most difficult, and a 5 per cent germination was all that was obtained. But today, by suitably treating the seed by scieiitific methods before sowing, a 9G per cent germination test is secured at the start, and the seed so treated is now handled and sown in quantity by mechanical
Guayule Plana Packed Ready for Shipment to Fields
development; and last, but not least, by differencesineaseof propagation and hardiness in cnltivation, Doctor McCallum has been able to separate a few strains which form thebasis of all the present field plantings. These strains have heen selected, not merely for their high rubber content, but for their hardiness and ease of development, together with adaptability to varying conditions in this country. We cannot pay too high a tribute to the painstaking work of Wm. J. MeCallum in this connection, the record of which we hope will some day be made known.
386
I,VDCSTRIAL A-VD E-YGISEERISG CHEMISTRY Rubber Content of Guayule Plant
The pure rubber content of the plant varies with the different strains, all the way from a few per cent in the case of the characteristic h’lariola type to 14 or even 16 per cent in our special strains now under cultivation. Under normal conditions there is a progressive increase both in percentage and in total amount of rubber per plant with each year of growth. Recent investigations have shown that the young guayule plants grown from seed sown in our nursery at Salinas
Four-Row P l a n t i n g M a c h i n e
less than a year ago now contain 6.3 per cent of pure caoutchouc on a bone-dry, deleafed basis. On the basis of the number of these seedlings (by count) per acre actually growing in the nursery, the above represents a yield of 1164 pounds of pure caoutchouc per acre per year. This astounding iesult compares favorably with the average results of experiments to date with bud-grafted stock of Heceu brasiliensis after 7 years of waiting. We have encountered no particular difficulty in milling out the rubber from these young plants. We have set 4 years as the optimum period of growth before harvesting, although n.e have recently demonstrated the possibility of producing in 2 years as much rubber per plant or per acre as x e had figured on obtaining after 4 years. The significance of this is most important. From biochemical studies which have already been made, our knowledge regarding the rubber-forming habit of our plant has been considerably enlarged, so that we are in a pobition intelligently t o regulate and stimulate the synthesij of rubber by the plant and thereby t o augment still further the amount of rubber which can be obtained from a given area of land under guayule cultivation. Experiments on cross fertilization of different strains of guayule for rapidity of growth with maximum rubber content also offer encouraging possibilities. From what has already been demonstrated by biochemical studies of the past 2 years, we believe that we have oiily just begun to develop the latent possibilities of thi. shrub as an agency for the synthesis of caoutchouc on iucli a scale as has never yet been visualizecl. Mechanical Cultivation
The young seedlings are gathered and transplanted from the nursery to the field mechanically by a six-row planter, of our own design, capable of planting 150,000 plants in 8 hours. In the latest design of this planter, in use last spring for the first time, we were able to set the young plants in the field so accurately that we can now cultivate the fields by our four-row cultivator, working crosswise as well as lengthwise of the rows without difficulty or injury to the young plants,
vo1. 22, s o . 4
thus eliminating practically the only remaicing hand operation-namely. hand hoeing-in connection with field operations during the growth of the plants in the field. Extraction of Rubber
From field to factory for the extraction of the rubber the plants are pulled and chopped mechanically and transported in continuous operation. The extraction of the rubber from the shrub on a large scale is carried out in continuous-feed tube mills, such as are used in the grinding of ore, wood pulp, and the like. These mills are fed by belt conveyors with crushed shrub which has been previously subjected to a conditioning and drying process in order t o develop maximum quality and quantity of rubber. Experience has shown in this connection, as in the case of plantation rubber, that both quality and quantity of output are largely determined by the initial treatment of the raw material. In its passage through the revolving tube mill the crushed 3hrub is first thoroughly disintegrated by metallic grinding halls or flint pebbles. The discharge from this first mill is fed continuously through revolving screens, where it is drained and washed free from water-solubles t o a second mill of similar design but containing small, rubber-covered lead balls. In this second mill, in the presence of fresh water, the shrub is still further disintegrated, but the rubber is caused t o agglomerate into small particles, about the size of a pea or smaller, according t o conditions of milling. These small particles of rubber have come t o be known in the trade a5 “worms.” The discharge from this mill is then carried to settling tanks, where these rubber worms are mechanically separated from the fiber or bagasse by flotation. The worms are then cleaned prior t o drying and blocking of the dried rubber for shipment. Laboratory check analyses show that we can recover in this way within 0.25 per cent of the total rubber present in the shrub.
General View of G u a y u l e Field
Composition of Rubber from Guayule
TTe have frequently been asked TT-hether the material which n-e extract from guayule is “real” rubber and how it compares with plantation rubber from the Far East. The rubber from guayule has the same chemical composition as that from Herea. Combustions of the materials extracted daily from our field shrub in the course of routine analysis show that we are dealing with a pure hydrocarbon of the empirical formula CiH8, giving the same bromine and chromyl chloride derivatives as plantation rubber. The behavior of our mill product toward vulcanization, which is a matter of daily study in our laboratories a t Salinas, and the fact that tires have
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INDUSTRIAL AND ENGINEERING CHEillISTRY
April, 1930
already been successfully made from California-grown guayule rubber leave no doubt as to its true nature. Physical Quality of Rubber
Although the physical quality of guayule rubber has appeared to be different from that of Hevea, it is impossible, a t present, to state whether this difference is an inherent characteristic of the hydrocarbon itself or is merely due to methods of treatment, which largely determines the physical character of any rubber, whether from Hevea latex or from guayule shrub. U’e have already in operation a process of “retting” of guayule shrub similar to the retting of flax, by means of which we have succeeded in profoundly changing the physical character of the rubber from guayule, making it in all respects more like the product from Heuea brasiliensis. By this simple means, involving the exposure of the shrub for about a meek t o the action of microorganisms and air, we are enabled to mill out a rubber which in its vulcanized state has the tensile elongation and other physical. properties of plantation rubber to a very marked degree. By this same operation, if desirable, we can also remove as much as 7 5 per cent of the acetone-soluble materials characteristic of the
Silk-A
Mexican guayule rubber of the past, producing by this means a crude rubber from guayule shrub having an acetone extract of about 5 per cent, in this respect again closely resembling plantation rubber. In the past there has been no particular object to prepare material of this character, for with the limited output available Mexican guayule rubber, with nearly 25 per cent of acetone-soluble impurities, has found a ready market a t a price within 80 per cent of that of plantation rubber. Furthermore, with a uniform plant product to begin with and a uniform method of handling and treatment throughout, we shall be able, in commercial production in this country, to obtain a uniformity of quality of product from guayule hitherto unknown, and suitable for use in all kinds of rubber goods. In regard to the cost of production, we believe that guayule rubber will be successfully produced in this country in competition with present sources of supply from the Far East. I n this belief, which is based on our first-hand knowledge of the “all in” cost of rubber production from our own estates in the Far East, we have prepared and are going ahead to set out an additional 2500 acres of guayule this spring and annually thereafter.
Field for Research’
Elbert M. Shelton and Treat B. Johnson RESEARCH
LABORATORY OF C H E S E Y
VER four t h o u s a n d years of practical application in industry a n d approximately one hundred years of occasional scientific inve4gation have given 115 a fair genwal acquaintance with silk. Biochemical Processes of the Silkworm
B R O T H E R S , S O U T H A ~ A S C I I E S T E R , C O X N . , .AND T H E
Received February 27, 1930
UNIVERSITY,
NEWHAVEN,C O N N .
While s p i n n i n g its cocoon, t h e silkworm ejects the contents of its two silk glands through minute spinnerets, one on each side of its head, t o form two threads which a r e c e m e n t e d t o gether with a layer of socalled “sericin,” similar in its elementary chemical comp o s i t i o n but differing dist i n c t l y in physical properties and amino acid content f r o m t h e central filaments of fibroin. There have been many speculations as to the origin of sericin, none of which seem sufficient to account for its presence or t o explain its origin. One of the most promising explanations assumes that the fibroin is secreted by the long tail-like portion of the silk gland, while the walls of the enlarged reservoir secrete a slimy fluid which is the sericin. As the fibroin is accumulated in the reservoir of the silk gland, it assumes a position in the central portion of the reservoir in such a way that as the contents of the gland are later ejected there passes out a filament which is similar in cross section to the contents of the gland-that is, which might be pictured as a core of fibroin surrounded and possibly lubricated in its passage through the spinneret by a thin shell or tube of sericin. To confirm this or any other theory for the origin of the sericin, the support of the biologist is needed, and there is much room for careful correlation of the actual anatomy of the silkworm with the nature of the products secreted from its silk glands. A report of a preliminary investigation during 1929 from the Biology Department of Oberlin College commented very favorably upon the silkworm as a subject for study.
A study of the characteristic properties of natural silk reveals this substance as an organic compound whose chemistry is not well understood. Not only is our knowledge of its fundamental chemistry very limited, but we are also woefully ignorant of the biochemistry of the biological changes involved in its synthesis. On account of the great commercial irnportance of the natural silk industry, it is essential that an attempt be made to fill in these gaps in our knowledge of this textile material. The purpose of this paper is to point out some of the lines of investigation whose promotion promises to lead to new data of immediate commercial and scientific importance.
The si1ki\-oriii, regardleis of differing pel,sonal opilliolls as to the hand,omeness of its appearance, is a most attractive subject for study. Here, during that period of the life cycle of the moth when in its larval stage it is storing up materials and energy to carry it through the remaining stages of its existence, there occurs the only true organic chemical synthesis which takes place in the manufacture of silk. The transformation of the coinpoundb of vegetable growth to the viscous solution in a form t o be qpun by the worm into a silk fiber is a liiochemical proces. the understanding of which challenges the efforts of all n-ho are interested in the origin and composition of proteins. Although the silkworm has become so highly domesticated that it is extremely sensitive to adverse conditions during its larval stage and subject to more than its share of ills. yet with the information available regarding the care of the larvae, evrn a beginner with reasonable personal attention may expect to obtain a crop of healthy mature silkworms in the course of six weeks after the eggs are allov-ed to hatch. In other words, we have here a biological process which can easily he appropriated by a chemist for obtaining material in sufficient quantity for study by chemic7al technic. 1
DEPARTMENT OF C H E M I S T R Y , T A L E
