Reasoning by a.n.a.logy, it would appear that no apparent harm would result to sheet rubber from sun-drying for periods up to four or five hours. From experience (see Chapter IX.), not the slightest ill-effect is found to result from the short interval of preliminary drying or dripping practised on many estates preparatory to smoke-curing.

ARTIFICIAL DRIERS FOR SHEET RUBBER.--It is understood that when vacuum driers were first applied to the drying of rubber it was thought possible to dry sheet rubber in this way. The practice was found to be impossible, as the length of time required and the temperature were responsible for the destruction of the form of the rubber; it became tacky and semi-liquid.

THE "CHULA" DRIER.--Although several suggestions of devices for artificially drying sheet have been made, only one is known to be in use at the present time. In the original form this was used for drying other tropical products. It consists of a large iron chamber, in which are several compartments divided by means of baffle-plates. At one end there is a small furnace and, by means of a fan, smoke and hot air are drawn through the compartments. Owing to the temperature attained (140 to 160 F.) sheet rubber cannot be completely dried in the chambers, and is, as a rule, only treated in this manner for one or two days. Drying is then completed in an ordinary air-drying house. It is claimed that drying is expedited, and that the rubber can be packed in ten days.

In the more recent modification, the smoke and hot air which leave the Chula drier pa.s.s through a large room in which may be hung either sheet or crepe rubber. It would seem that all sources of danger have not been eliminated from the process, as on one estate a wooden room containing rubber was ignited by a spark which pa.s.sed through the drier.

Yet another form exists in which the furnace is outside the main building, and in the ordinary course of working only heats a series of open pipes through which air is drawn by a powerful fan. By means of a valve it is possible to allow smoke from the furnace to pa.s.s into the room with the hot air for the preparation of smoked rubber. The hot air or smoke is distributed in the lower room by means of main and branch pipes, and pa.s.ses through an open floor to the room above. With such an arrangement it is possible, therefore, to prepare either air-dried or smoke-cured rubber. If the method could be successfully applied to the drying of crepe it would be of great a.s.sistance on some estates. There would seem to be a difficulty in working it for the drying of sheer rubber and crepe together, as the temperature suitable for the one is excessive for the other. Given an efficient control over the temperature of the hot air, the house should be successful in the drying of crepe, provided the rubber is not hung in folds of too great length. For smoke-curing sheet rubber the period is said to be reduced by several days in comparison with the time occupied in an ordinary smoke-house, but it is not clear that such a system would have any advantage over a modern smoke-house, in types of which rubber can be fully cured in periods ranging from five to ten days.

CHAPTER XII

_SORTING, GRADING, AND PACKING_

The question of standardising the output of our plantations is one which has occupied attention for some years, with a not inconsiderable degree of success.

Meanwhile opinion is growing in favour of proceeding along the line of reducing the number of plantation grades to a minimum. At present some confusion exists. Some estates make up tree-sc.r.a.p and bark-shavings together; one estate puts tree-sc.r.a.p, earth-sc.r.a.p, and bark-shavings into one uniform crepe; other estates have three or more separate sc.r.a.p grades--_e.g._, lump-rubber and "washings," tree-sc.r.a.p, earth-sc.r.a.p, and bark-shavings sc.r.a.p. There is a movement on foot at present to try to restrict plantation rubber to three grades:

CREPES--1. _First Quality Latex._--_I.e._, crepe made from the true coagulum obtained from the regulated coagulation of strained latex. This is a pale rubber, and may be prepared satisfactorily if the directions given in preceding chapters are followed. Naturally there must be, in all factories, some defective rubber of this grade. For various reasons the crepe may be of inferior colour, or is slightly contaminated with dirt or traces of oil and grease, etc. This defective rubber should be placed aside most rigorously and plainly marked as "off-quality."

If a proper scheme of standardisation of latex and chemicals is followed, there should not be any such variety in shades of colour, such as was common in No. 1 crepe in the past.

Comparatively few estates in Malaya now prepare thick (or blanket) crepes in the No. 1 grade, but in such cases the same rules must be applied as govern the sorting of thin fine pale crepes.

2. _Compound Crepe, No. 1._--In this it is proposed to include cup-coagulated lumps, coagulated lumps from transport vessels, skimmings, bucket rinsings, cup-washings, and tree-sc.r.a.p. It has been shown in Chapter X. that strict care is necessary to eliminate all oxidised (dark) sc.r.a.ps.

These are relegated to a lower grade. The possession of a "sc.r.a.p-washer" is necessary if the best results are to be obtained.

On some estates the ingredients of this compound crepe, while fresh, are placed in a common jar or tank to which a quant.i.ty of sodium bisulphite (1 per cent. solution) and acid are added. The resulting conglomerate ma.s.s is cut up for working.

3. _Compound Crepe, No. 2._--This grade would include the remaining lower grades--viz., bark-shavings, sc.r.a.p, and earth-rubber sc.r.a.p.

REDUCTION CARRIED TOO FAR.--However desirable it may be to diminish the number of grades, it must be pointed out that diminution and simplification are not necessarily synonymous terms in this matter. It is well known that on estates where the earth-rubber is only brought in at lengthy intervals, say of a week, the resulting crepe is sometimes very tacky. This is only natural, and is due to the prolonged exposure to the sun's rays. With the improved machinery now at our disposal, and with the increasing attention which will be given to the lower grades in the future, it is possible to prepare from average bark-shavings crepe free from bark, and of quite a good colour. Where trees are not "sc.r.a.pped" before tapping, there would seem to be no objection to amalgamating the rubber obtained from the bark-shavings with the No. 1 Compound crepe; and it would be a distinct danger and possible loss if this good rubber were to be mixed with earth rubber. The liability of the latter to become tacky is well recognised; and if possible it should be maintained as a separate grade, in which it would be permissible to mix only rubber obtained from actually dry shavings from "sc.r.a.pped" trees, or heavily-oxidised sc.r.a.ps which have been rejected from other grades.

SHEETS.--Broadly there are no fine distinctions to be made at present in the grading of smoked-sheet rubber; it is either No. 1, or if any so-called defect is visible the sheets must be rejected and plainly marked as "off-quality."

Clippings (tr.i.m.m.i.n.gs) may either be made into crepe or shipped under their own description.

RUBBER GROWERS' a.s.sOCIATION'S RECOMMENDATIONS.--Taking the foregoing arguments into full consideration, it would seem that, strictly speaking, the number of grades cannot be reduced to less than four at present without producing some amount of confusion.

In its handbook,[15] the Rubber Growers' a.s.sociation remarks:

[15] "Preparation of Plantation Rubber," 1917.

"The fewer grades the better, and regularity of each grade is most important.

"The grading should be as follows:

"(No. 1) Fine crepe (or No. 1 sheet), made from the free or liquid latex.

"(No. 2) Clean light brown crepe, made from lumps and skimmings.

"(No. 3) Sc.r.a.p crepe, made from tree-sc.r.a.p.

"(No. 4) Dark crepe, made from bark-shavings, earth rubber, and the lower quality of sc.r.a.p.

"Tacky rubber should be packed separately.

"_Compound Sc.r.a.p Crepe._--Estates using sc.r.a.p-washers should make a compound crepe of grades Nos. 2 and 3, which will make one compound free from bark and specks. All rubber intended for No. 4 should be most thoroughly washed."

Concerning these recommendations the remarks in preceding paragraphs should be studied.

CARE IN SORTING.--Whether dealing with smoked-sheet, pale crepe, or lower grades, the strictest care is necessary in sorting and grading. This work must of necessity be relegated to coolies, and they should be trained men.

Instructions must be definite, and doubtful specimens of rubber should always be placed aside for the decision of the European superintendent. Any pieces showing unmistakable signs of what are regarded as defects should be stringently rejected. In the case of pale crepe, when the defect is confined only to a small area it is permissible to cut out the affected portion. Similarly there can be no objection, in the case of smoked sheets, to an occasional sheet being treated in this manner. On the majority of estates these rules are observed carefully, but some estates yet have to learn that defective pieces of rubber may not be concealed in a bulk of otherwise good quality. Samplers have often an uncanny knack of hitting upon the defective specimens, and it is entirely the fault of the estate's sorters if these pieces are submitted as being representative of the ma.s.s.

CHOICE OF CASES.--Consumers complain justly of the presence of chips, splinters, and wood-dust. It will be evident, therefore, that whatever the type of case employed the interior surfaces should be smooth, there should be no cracks or gaps in the timber, and the cases should be cleaned out before using. There remains great room for improvement in the means and method of packing, and in spite of suggested alternatives we are at present restricted to the use of wooden cases.

From comparisons of actual quality and fulfilment of the requirements indicated above, there can be no question that cases made of three-ply wood, such as the "Venesta," are in every respect superior to the ordinary wooden cases of "Momi" type. The consideration of cost and available supplies, of course, enters largely into the question, and three-ply cases are not at present so largely employed as they deserve to be.

A new type of case was recently exhibited in Singapore. It emanates from the U.S.A. and is made of a fibrous material, resembling in appearance a very stout cardboard. The complete case when a.s.sembled consists really of two boxes, one of which is inverted and slides down over the other. Packing is completed by means of stout wire, which is strained by a simple ratchet arrangement. It is claimed that from 225 to 250 lbs. of rubber can be contained. Other claims made amount to the statement that the case is practically indestructible under normal conditions of handling and shipping. A demonstration given certainly appeared to substantiate the statement fully. Rubber packed in cases of various and average type was allowed to fall from a height of about twenty feet. In all instances the wooden cases of every type were either smashed or badly burst, whereas the fibre cases were merely dented. These cases are obtained in flat sections, which, in a.s.sembling, are folded and clamped by means of copper rivets in a special but simple machine. It was pointed out that objection might be lodged against the use of copper for this purpose.

More recently there is announced a new packing case which is stated to be made from low-grade rubbers, but information is rather vague.

BAGS.--There are in local use stout canvas bags which have the advantage of being used many times, as long as they are waterproof and kept in good dry condition. Their employment for the conveyance of smoked-sheets would appear to be permitted, but crepe rubbers sent in them are often reported upon as being "ma.s.sed" at the edges, and hence difficult to "sample."

BALES.--Attempts to bale rubber for the market have been frequent, but no success seems to have attended the efforts. In some quarters the failure has been ascribed to prejudice on the part of buyers, but it is the opinion of the writers that the objections to baling are, or could be, well-founded. Ma.s.sed rubber often cannot be inspected properly, and hence is always open to suspicion that internally there may be unsuitable portions.

There have been several schemes put forward for winding crepe rubber on spindles so as to form a cylindrical package complete in itself. We have seen the process, and certainly the method had much which appeared commendable. Apart from other objections which might be raised, there is always the one prominent objection mentioned in the preceding paragraph.

While baling of rubber is thus not likely to suit the general market, there is no reason why, as in one or two instances, it should not be practised by agreement between producer and consumer. It is believed that "slab" rubber is shipped in bales from Sumatra to the U.S.A.

Quite recently a proposal has been put forward to revert to a simple form of baling for ordinary plantation rubber. Under this scheme wooden cases are discarded, the packing material being composed of sc.r.a.p-grade crepe rubber which, it is claimed, could be put to use by the manufacturer. An obvious drawback would be evident if these bales happened to be exposed to direct sunlight or a continuous high temperature. The tackiness which might supervene would make the handling of such bales unpleasant, even if it did not affect the internal rubber.

FOLDING FOR PACKING.--In the packing of smoked sheets it would appear to be advisable to avoid, if possible, the folding of any pieces, as the objection is made that such rubber is difficult to "sample" on arrival, especially in cold weather. Sheets should be prepared or cut to such length that they occupy the full superficial area of the box, either singly or side by side.

[Ill.u.s.tration: A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT.]

The same remark applies to the packing of crepe rubbers, except that here we deal with units of folded rubber. Crepes are generally folded by hand, and coolies usually work to a certain dimension by means of a standard stick. The work is slow, but often gives employment, at a cheap rate of pay, to women and weak coolies.

Several machines have been invented to replace this labour. The best of these yet seen has a simple device by means of which the length of the fold is adjustable to suit the size of any packing case. It is called the "Senang" folder, and is made by the General Engineering Company (Radcliffe) Ltd., Radcliffe, near Manchester.

CARE IN a.s.sEMBLING.--Whatever the type of case employed, great care must be given to the a.s.sembling of parts and the final fastening. It is not uncommon to find in the operation of putting on the "strapping" that nails have been driven into the rubber. Extra bands of strapping are sometimes advised, and where these bands pa.s.s over the sides (not edges) of the case only specially short nails should be used.

All wood should be planed, and in cases other than three-ply should be of stout wood, not less than 5/8 inch in thickness. All timber used should be of uniform type and thickness.

METHODS OF PACKING.--The usual method of packing crepe is to fold the lengths to some measure of the dimensions of the case. This is done in a haphazard fashion on some estates, with the result that either s.p.a.ce is lost or the packing is badly arranged.