Sidney Morgan

“ We are concerned only with the necessity for supplying a demand for smoke-cured sheet rubber. Broadly, the process is akin to the smoke-curing of herrings, and the objects are much the same—viz., (1) drying, (2) preservation—except that while herrings are only dried partially, rubber should be dried perfectly.
On a small scale a primitive smoke-house could be built easily and cheaply, and such a building might be fully as efficacious as the most elaborate and expensive installation. ”

“ The writers cannot give a number, but have no hesitation in stating that if a factory cannot complete its whole day’s work before dark, it is inadequately equipped. No work should be done after dark, if possible, as it cannot receive the supervision which crepe-making demands. To make comparison between the number of machines in any two factories and their respective outputs is not sound argument, as the out-turn of two similar machines will depend upon the speed at which the rolls travel—i.e., the gearing between the machines and the engines. ”

“ Clean Weeding.—Intimately connected with the growth and development of the rubber tree one has to consider the conditions under which it is allowed to mature. The argument has been used that, since the habitat of Hevea Brasiliensis is in the jungle, we should be proceeding against nature by introducing conditions unlike those under which the “wild” rubber tree grows. It is difficult to treat such an argument seriously, as by quoting parallel instances in arboriculture it could be shown that growth, development, and yields are improved by cultivation of “wild” plants. ”

“ It should be premised that a factory in which rubber is to be prepared should be as light and airy as possible. In this respect quite a number of the older factories are lacking, and they seem to have been designed to exclude as much air and light as possible. Under these circumstances, the building is always dark, there is always an air of dampness, dirt may accumulate, and there is usually a bad smell. Rubber prepared under these conditions is always liable to be below the high standard which should be attained, and the general tone of the factory is depressing. ”

“ Much can be learned from an inspection of the coolies’ buckets, and the cause of small defects in the finished rubber can often be thus traced. Leaves, stems, bark-shavings, and dirt appear in the buckets, and it is a source of constant surprise to imagine how even unintelligent coolies can allow such things to happen. These objects are removed before or during straining, but still they ought not to be there in the first place, and the fact that such a state of things exists is evidence of neglect on the part of the coolies or lack of supervision. ”

“ Owing to the existing differences in equipment and speed of drive, etc., the regular practice of any one estate may be unsuitable for another. It remains, therefore, a matter of study for each estate to discover the minimum number of times which rubber should pass through the machines, consistent with the factors indicated above. In any case it may be assumed that if any factory cannot prepare a good crepe by passing the rubber, say, twelve times through the rolls, there is some deficiency in the machines, or of speed; the coagulum may be too hard, or the rolls may be badly worn. ”

“ Attention has been drawn to the fact that there may be exceptional cases, when the determining factors lie beyond the control of factory processes—e.g., heavy rains causing over-dilution of latex, the yielding of “yellow” latex from newly opened areas, etc. But on the whole there is now no reason why the general average product from any estate should not be uniform in colour and appearance. Furthermore, it should be possible for large groups of estates, by the adoption of uniform methods, to produce similar rubber from all the plantations. ”

“ Surface Moulds or Mildew.—During the last two years, complaints regarding the incidence of “mouldy rubber” (i.e., relating chiefly to the presence of mildews on the surface) have become increasingly common.
To judge by the comments of producers, who as a rule never again see their rubber after it leaves the estate, one would infer that the defect is imaginary, and that the complaints are made solely with a view to repudiation of contracts or the general cheapening of an article of commerce. ”

“ The possibility of obtaining the ideal knife, which will go to sufficient depth into barks of varying thickness to yield the maximum quantity of latex without wounding, is quite as remote at the present time as it was some years ago. Meanwhile the search for that ideal knife continues, and occasionally one learns of the alleged merits of some new instrument which, it is said, fulfils all requirements. It is only to be regretted, both for the sake of the inventor and for the expectant buyers, that the claims always fail in some one or more particulars. ”

“ Hence it should be remembered that a formula which suits the needs of one field or one estate will not necessarily prove suitable in the case of another field or estate. Unless this point is appreciated trouble may ensue. On some estates it has been the custom to give equal quantities of sodium sulphite solution to all coolies irrespective of the ages of the trees in the fields to be tapped. Thus it happened that the latex from one field was found to have insufficient anti-coagulant present, while that from another field could only be coagulated by the addition of an excess of acid. ”

“ The better grades of wild rubber, such as Fine Para, were more difficult to break down, but not so difficult as most plantation rubber, because they had already received a preliminary “working” in the process of washing and crepeing, and we have already explained that such treatment takes more power than the crepeing of the soft moist coagulum on the plantations. The amount of “working” or “plasticising” produced in the rubber is connected with the power expended; the greater the expenditure of power, caeteris paribus, the greater the working effect on the rubber. ”

“ Suction-gas plants are now made, in which a wonderful variety of refuse can be consumed in the production of gas, whereas ordinarily estates are restricted to the use of either charcoal or anthracite coal. Both oil and gas driven engines are eminently suitable for the purpose of a rubber factory, and the results obtained on different estates with either are often discussed in favour of one or the other. The selection ultimately narrows itself down to one of cost of running, in which availability of supplies becomes an essential feature. ”

“ To those accustomed only to the preparation of crepe rubber, where coagulation can be effected in large batches, the preparation of sheet rubber always seems to demand much more labour. As a matter of fact, although the preliminary operations certainly do demand more care and labour than in crepe-making, there are compensating advantages in the machining stage. For the preparation of sheet of the highest quality on any but the largest scale, elaborate installations of machinery [90] are quite superfluous, as equal results can be obtained with pairs of rolls worked by hand. ”

“ Making a Solution.—The making of a solution of the chemical would seem to be a simple matter, but to judge by the ill-effects sometimes observed in the dry rubber the simplicity of the operation appears to have been overrated. Great care must be exercised in preparing the solution, and the work should not be left to the few minutes preceding its actual requirement; such has been found to be the case in several factories, so that it is not surprising if the rubber is defective. ”

“ Indeed, no investigation or analysis of the raw rubber can enable one to foresee exactly how the rubber will behave on vulcanisation. This illustrates the deficiency in our knowledge of vulcanisation. When dealing with soft, resinous, or decomposed rubbers, it is safe to anticipate a weak vulcanised product; but when we come to deal with a number of samples of “standard” crepe or sheet—i.e., sheet or crepe passing a certain standard of appearance—it is found that differences in vulcanising properties cannot be foreseen. ”

“ For imperative reasons it may be sometimes found necessary to smoke rubber when the only available building is a single-storey one. As a temporary measure, the building may be converted into a smoke-house by placing the fires in pits sunk deeply into the ground, and effectively screened above by iron baffle plates. But it is not advisable that smoking be continued in such a single-storey building, as the best effects are not obtained, and the risk of fire is far too great. ”

“ There can be no doubt that, on the whole, the number of cases of “spot” disease is on the decline; but equally it is certain that a very few estates will always be liable to outbreaks as long as drying is attempted in existing houses. For these reasons it is a poor policy to temporise, and the only sound policy in extreme cases would be to give up ordinary air-drying in favour of some method of artificial drying. As regards the majority of estates preparing pale crepe for various reasons, it is not expected that any will instal artificial driers. ”

“ But it is essential for the best results that there should be running water, so that the substance in solution is carried away. If the sheets are merely washed in a large vessel, which has been filled with clean water, it must be obvious that, by the time some scores of sheets have been washed, the protein matter in solution on the surface of the sheets has been transferred to the washing water, so that the later sheets of the batch are liable to show the defect again on drying. ”

“ The recognition of these principles as applied to the planting of H. Brasiliensis has focussed recent attention upon the desirability of planting nurseries with seeds obtained from those trees which are known to be good producers of latex of normal consistency. It does not follow that the tree of most rapid growth and development is necessarily the best yielder; such is often not the case. In the matter of selection, therefore, one has to take other standards than that of size; and the issue is narrowed chiefly to a consideration of the yields of latex given by individual trees. ”

“ Lubrication of Machines.—It must always appear to those inexperienced in engineering matters that existing methods for lubricating rubber machinery are distinctly crude, when [167] one considers the delicacy of the material to be prepared. Many existing machines are still lubricated with oil, which has to be administered in generous quantities. Generally, such machines have been so designed that the excess of oil may find an easy passage into the tray which receives the rubber. If not, it drops just outside the tray to the floor, and is washed away in great gouts. ”

“ The sympathy of the writers is certainly on the side of the producers, inasmuch as they realise how extremely difficult, and even impossible at times, it is for the most careful individual to prepare sheet-rubber free from this blemish. ”

“ The accommodation over the factory may be restricted to the purpose of receiving lower grade rubber which is not so liable to “spot” diseases, and possibly does not take so long to dry as first-grade rubbers of equal thickness. It is evident, therefore, that the erection of double-storey factories is false economy, as separate drying-houses have to be built eventually. This conclusion does not apply with the same [175] force to factories worked in conjunction with smoke-houses for preparing sheet rubber, but, nevertheless, such a factory should not have another floor above the work-room. ”

“ At night such a building would reek with a moisture-laden atmosphere, and little drying could be expected to take place in that interval. From actual experience it has been shown that rubber hung to dry in such a room, situated over a damp factory, is very liable to attacks of “spot” diseases, since the presence of perpetual moisture is favourable to the development of these diseases. If a double-storey building has to be worked, it will be readily seen that no first-grade rubber should be allowed to dry in it. ”

“ More often than not, also, the actual clear space is very limited, and rubber trees grow close up to the walls of the buildings. Under such circumstances, it is difficult to see how these buildings can be anything but dark and damp, and it is not difficult to understand the slow rate of drying. In a few cases the sites chosen proved to be so unsuitable that the estates were confronted with a very serious problem, the solution to which was, either the erection of another complete set of buildings in a more suitable spot or the installation of artificial driers. ”

“ Considering the importance attached to colour in the dry rubber by brokers and consumers, and knowing how extremely trivial are the causes which may mar the colour, it is rather surprising that better provision is not made for the reception and handling of latex in factories. Too often the receiving vessels are placed on the floor of the store close to the entrance. Coolies bringing in latex cannot avoid bringing with them quite a considerable amount of dirt. ”

“ As a matter of fact, up to certain limits of added water, the reverse is actually the case—i.e., the more water in the latex the less acid must be added, assuming that for pure latex the proportion of pure acid to latex is taken as 1 part to 1,000 parts. This was found to be the case up to dilutions of three or four times the volume of latex. To take concrete examples which will perhaps make the truth more clear:
Assuming we commence by making up our stock solution of acid by adding 100 parts of water to 1 part of pure acid, this gives us a mixture of 1 to 100. ”

“ Stickiness is only temporary, and may be remedied. As a general rule, it is due to packing sheets, which have not a good raised “ribbing,” and which may have been coated with light tarry deposits (see Glaze) . This surface film may be removed by washing the sheets, or scrubbing them, with cold water. Usually a further two days’ air-drying will make the rubber fit for packing; and if the smoke-curing has been efficient, there should be no need to anticipate trouble from mildew. Some estates adopt this practice daily with success, as a form of insurance against complaints of surface deposits. ”

“ In favourable weather the rubber dries well, but in a long period of wet weather rubber may accumulate at an alarming rate, and the accommodation is sometimes severely taxed. Of course, the rate of drying under the best conditions is mainly dependent on the thickness of the crepe, and every endeavour should be made to maintain a thin style of preparation. If this precaution is not taken, the rubber is liable to recurrent attacks of “spot” disease, and one’s troubles are very much augmented. This is a disability to which rubber treated in artificial driers is not liable. ”

“ The appearance of the partially dry slabs is unattractive, but that does not signify if the quality of the vulcanised product satisfies requirements.
For the average producer, the difficulty lies in having to meet the demands of the general market. Even, therefore, if one assumes that the intrinsic qualities of slab rubber are all that the claims advance, it would be necessary for the producer to be assured of definite and regular sales. ”

“ Colour of Smoked Sheets.—It may be of interest to note that the effect known as oxidation is attributed to the presence of micro-organisms called enzymes (ferments) in the latex. It can also be produced artificially in various ways—e.g., by the use of the crude product of wood-distillation (pyroligneous acid) as a coagulant, or by the addition to the latex of small quantities of a phenol such as carbolic acid. It is thus possible to prepare in sheet form a rubber which has the appearance of having been smoke-cured, although it may never have been in a smoke-house. ”

“ It is an elementary point in the study of ventilation problems that the best system of natural ventilation is obtained by admitting cool air near or through the floor and providing an exit for the warmer air at the highest point in the building. It is not often that such a rule is infringed in the ventilation of rubber drying-houses, but several of the older buildings erred in this respect. In a good modern house there is a space (about 2 feet in height) all round the base of the walls merely closed with expanded metal ”

“ The amount of earth-scrap collected on any estate will depend, all other things being equal, upon the labour expended in its collection. Certainly on well-organised estates, having ample labour, the amounts collected are huge in comparison with other estates. The ground at the base of the tree below the latex-spout is systematically turned over with pointed sticks and large clots of rubber are often picked up. Here, again, it is advised that the collected earth-scrap should not be allowed to remain in heaps upon the floor of the factory. ”

“ One can hardly imagine a modern factory in full working being equipped with only one engine, which might possibly have an excess of power necessary to drive all the machines. In the case of breakdown, which sometimes happens in the best supervised factories, it would be small consolation to know that this excess of power was present theoretically. ”