No. 1, or Fine Pale Crepe.—Considering first the preparation of the highest grade, fine pale crepe, it must be stated that the difficulties attached to the process are generally not sufficiently appreciated. In this pale rubber minor blemishes are so plainly apparent that their importance is highly exaggerated, and what would worthily escape notice in smoked rubber assumes disproportionate prominence in pale crepes. The very fact that such a delicate material as colourless coagulum has to be manipulated in coarse iron rollers, with the attendant oil and grease worries, should be sufficient to deter one from criticising too harshly the occasional lapses of an estate struggling to give of its best to the market. At the same time there can be no doubt that if precautions are taken to attend to all likely sources of contamination, defects in pale crepe may be avoided to a wonderful extent; and on some estates the observance of elementary rules enables the preparation of the finest pale crepe to be made almost mechanically.Standardisation of Latex.—The question of the standardisation of latex has been dealt with in a general way in Chapter VII., and the reader is now familiar with the trend of the argument in its favour. It will be recognised that the necessity for standardisation exists to the same degree in the correct preparation of pale crepe as in the case of smoked sheet. Unless the dry rubber content is invariable, and the quantities of chemicals fixed, the colour of the crepe may vary appreciably.

It may be pointed out that it is not essential to adopt the same standard of dilution as for sheet preparation. Given that latices from all fields or divisions are fairly uniform, and of high rubber content, the standard may be taken at a figure equivalent, for example, to 2 lbs., or 21/2 lbs., or even 3 lbs. per gallon. It is wise, nevertheless, to take a lower standard for several reasons. For instance:

It is advised, therefore, that for general purposes the same standard as that found suitable for sheet rubber should be taken—viz., 11/2 lbs. dry rubber per gallon. At all events the standard should not exceed 2 lbs. per gallon.Coagulation and Coagulant.—Coagulation may be undertaken without any special arrangement of tanks, and is usually effected in the ordinary “Shanghai” glazed earthenware jars containing about 45 gallons. Given reasonable care, and a fairly fool-proof system of calculation for the quantities of chemicals required, no difficulty need be experienced.

On a larger scale it is advised that proper reception tanks, in which standardisation can be effected, should be installed. Where both sheet rubber and fine crepe are being prepared, the whole system of sheet-coagulating tanks may be employed with considerable advantage, even to the insertion of the partitions.

If ordinary jars are used, and the coagulum is left until the following morning, the mass of rubber has to be cut up into pieces of a size suitable for the machines. The knives or saws are sometimes rusty, and the colour of the coagulum is affected. The coolies often feed into the machines lumps which are too large, with the result that portions are thrust under the cheek-blocks and become stained.

When a sheet-coagulating tank is used all labour of cutting the coagulum is obviated. The long strips are handled and fed into the rolls easily. It may be seen, likewise, that actual work is thus saved in machining.Quantity of Coagulant.—For a general discussion on the coagulant and quantities employed, the reader is referred to Chapter VIII. It is there recommended that for latex standardised to a level of 11/2 lbs. per gallon, the proportion of pure acetic acid should be in the ratio of 1:1,200. Directions are there given for the making of the solution, and the calculation of the quantity required for any given volume of latex.

It is pointed out that for average undiluted latex the basis of calculation, for quantities of acetic acid required, should be taken on the ratio 1:1,000. Where latex exceeds a dry rubber content of 3 lbs. per gallon, it may be necessary to increase the quantity of acid to 1:800.

If a standard of 2 lbs. per gallon is adopted, the formula given for the 11/2 lbs. standard will not give full satisfaction, and the quantity of acid solution must be increased slightly in order to obtain complete coagulation. Assuming that the original solution is prepared in 1 per cent. strength, the following difference would be noted:

It is not possible to lay down an exact figure governing all cases, as so much depends upon the treatment undergone by the latex before it reaches the store.

Some estates continue to use solutions of greater strength, generally 5 per cent., in crepe preparation. While such solutions may be effectively stirred in when the latex is dilute, it is advised that for intimate mixture the solution need not be stronger than 1 per cent.

In estimating the quantities of acetic acid required much depends upon the interval which is to elapse between the addition of acid and the time of working of the coagulum. If the rubber is to remain until next morning, the average formulÆ will be found suitable; but if it is required to work the coagulum with an interval of less than three hours, an excess of acid must be employed. The excess need be comparatively small, unless the interval is much reduced. For instance, it is the practice on some few estates to begin the machining of the coagulum about half an hour after coagulation commences; in which case it is usual to add from a quarter to a half of the normal quantity in excess. It need scarcely be pointed out that unless this procedure is strictly unavoidable it should be discouraged on account of the waste of coagulant involved. Incidentally, the use of strong solutions of acid under such circumstances may lead to increased deterioration of the rolls.Colour of Fine Crepe.—We are sometimes assured that manufacturers do not pay the attention to the question of colour which sale conditions would lead one to believe. As far as we are concerned, and as long as there is no direct traffic between producer and consumer, it must be recognised that in the vast majority of cases we are forced to concern ourselves only with the standards set up in the markets. This, in spite of the knowledge that, all other things being equal, the arbitrary distinctions in colour afford no indication of the intrinsic value of the rubber. Under present circumstances it is plain that if paleness is demanded it has to be supplied.

Probably without exception all estates employ sodium bisulphite as the agent for the prevention of that darkening (oxidation) which is natural in drying rubber.Sodium Bisulphite.—A formula for use of this chemical is given in Chapter VIII., and is applicable to latex standardised to 11/2 lbs. dry rubber per gallon. If a higher standard is chosen the quantity calculated as in (b) of that formula may be increased slightly, and the exact requirements found by experience. The caution must again be given that the employment of an excess of sodium bisulphite will lead to the production of an over-pale rubber, and a prolongation of the drying period. If thick crepes are made, an excess of the chemical is sometimes made visible by a greyish powder deposited on the edges of the strips of dry rubber.

It must be emphasised that the formula in Chapter VIII. indicates the maximum quantities required for use with standard latex. Many estates will find it expedient to use less of the chemical; and if it is found that the desired result is not obtained from normal proportions, attention should be directed to the points discussed in the following paragraph.Evaluation and Deterioration of Sodium Bisulphite and Sodium Sulphite.—Sodium bisulphite and sodium sulphite are both bought for our purpose in the form of a fine crystalline powder, and on analysis good specimens should contain over 90 per cent. pure substance, when packed in well-sealed vessels.

It has often happened that shippers or local sellers, by inadvertence, have supplied the one chemical in place of the other—to the detriment of the rubber and the discomfiture of managers of estates. The error, as a rule, has not been detected for some time, and then perhaps only as a result of complaints or enquiries reaching the laboratories. To the layman, and certainly to the native who usually has charge of these substances, it is not a simple matter to distinguish between them without special knowledge. There are certain elementary tests, however, which can be applied on all estates serving to make the distinction, but affording no information regarding the actual quality of the chemicals. They are given in a comparative form on page 116. Samples of doubtful specimens may be sent to the laboratories for analysis, but the bulk of the chemical should not be used.

During the War some very poor shipments were received, and much trouble was caused. Under normal conditions there can be no question that it is to the interests of chemical manufacturers to supply the best article; and it is anticipated that in future there should be no difficulty in procuring shipments of a high degree of purity.

It will be evident that, as sodium bisulphite under normal conditions gives off a gas when exposed to the atmosphere, it deteriorates in quality continuously. It is the potential presence of this gas which makes the powder effective as an anti-oxidant and disinfectant. It is within the experience of all accustomed to the handling of this chemical, that in addition to the loss of gas, the powder cakes into a hard mass on exposure. If only the top layer is caked, the remainder may be in fair condition; but no caked portions should be used, as they cannot be of good quality. They may, however, be used for the treatment of scrap rubber, to be discussed later.Care of Sodium Bisulphite.—The ready tendency of sodium bisulphite to deteriorate on exposure should give sufficient indication regarding its treatment in storage. It should be bought only in drums (or other air-tight containers), and should be stored in a dry place. No drum should be opened until required, and the common practice of keeping an open drum on the floor of the factory should be avoided.

Drums are of two sizes, generally containing 1/4 or 1/2 cwt. respectively. It will be obvious that, although the prime cost may be cheaper with the larger quantity, it would always be preferable to secure the smaller drums, as the loss on exposure will be less.

Most commonly the 56 lb. drum is purchased. It should not be difficult to calculate the period during which the contents will be consumed, on the basis of a maximum of 1 lb. per 100 gallons of latex. A 56 lb. drum, assuming no loss or waste, should be sufficient to treat at least 5,600 gallons of latex (say, 8,500 lbs. of rubber)—if the bisulphite is of first-class quality, and the use is applied only to the preparation of fine pale crepe.

Where the quantity used per diem is small, it is advised that precautions should be taken to preserve the quality of the chemical when a drum is opened. It might be of advantage to place the contents of the drum in smaller sealed tins, or to have made a special container (with a closely fitting lid) into which the powder can be placed as soon as the drum has been opened.Mixing Solution with Latex.—Emphasis has been laid, in Chapter VIII., upon the necessity for care in the preparation of the solution. Equal regard must be given to the mixture of the solution with the latex.

On a few estates it used to be the practice to add the powder to the solution of acid, with stirring. Obviously this led at least to a great loss of efficiency, owing to the rapid escape of the gas which was evolved.

The solution of sodium bisulphite should be poured into the latex in as uniform a distribution as possible. The mixture of solution and latex should be thoroughly stirred, and if only natives are in charge a minimum period of five minutes should be prescribed before the addition of the coagulant. A thorough stirring should again follow the advent of the acid.

If these elementary rules are not observed faithfully, the deficiency will most probably be manifested in the dry rubber in the shape of streaks of varying shades of colour.

Finally it may be insisted upon that deteriorated sodium bisulphite should not be used. In order to obtain an effect double the quantity may be required, and the residual salts left in the rubber on evaporation of the moisture will be responsible for prolonged drying, surface deposits, and possibly “spot disease.”Former Methods of Making Pale Rubber.—Merely as a matter of historic interest it may be mentioned that previous to the introduction of sodium bisulphite pale crepes were made in comparatively small quantity by various devices, among which the following might be quoted:

Working the Coagulum.—Description of the details of necessary machinery for crepe-making is relegated to Section III. of this book. Here we shall treat only of the matter in general.

In the preparation of crepe rubber heavy machinery is necessary, and ample engine-power must be available. The machines should comprise three types:

Without such equipment it is not possible to prepare the grade which is known as “fine pale crepe.” In the common acceptation of this term crepe of No. 1 quality generally connotes fineness and paleness with a thin crepe which has a good, smooth, and fairly well-knit texture.It is, of course, possible to make a thick pale crepe, using only the macerators and intermediates, but the “finish” will be that typical of the particular grooving of the intermediate rolls. For the preparation of crepe ordinarily, the possession of smooth rolls is a sine qua non.

For reasons which will be explained more fully in the chapter dealing with the defects of crepe rubber, the practice of preparing thick crepes direct from the coagulum is now very uncommon. Thick crepes are generally made by reworking dry rubber, either in the form of thin crepes or from air-dried sheets. The market for the latter in Malaya is confined almost entirely to Singapore, where factories buy native rubber and re-work it into thick crepe.

The bulk of the output of No. 1 crepe from estates is in the form of thin “fine pale crepe.” The artificial standard set up by buyers and brokers necessitates this thin crepe being of even texture and fairly free from small holes (“looseness”). What difference the small holes are to make in the vulcanising properties of the rubber is beyond our knowledge; but such being the standard, it must be attained if the full price is to be obtained.

In order to secure the desired effect the coagulum must be passed consecutively through the three types of rolls, and undergoes a varying degree of working in each.

Given the necessary equipment of machines, it is possible to make a good specimen of thin pale crepe if the coagulum passes through all the rolls a total of twelve times (or even less in exceptional cases). There is no intention of suggesting that this is possible on all estates. Clearly the number of times the rubber passes through the rolls will depend upon the total efficiency of the machines. This in turn involves such factors as (a) the size of the rolls, (b) the number of machines of each type, (c) the gearing of the pinions, (d) the speed of the drive, etc. Again, much depends upon the nature of the coagulum worked. A fairly soft coagulum will offer less resistance, and conversely a dense coagulum will require more machining.

It has been shown by the writers in previous publications that over-working of the coagulum has an effect on the vulcanisation of the rubber; and this has been confirmed by others.[10] Apart from this point, it should be recognised that over-working, beyond that necessary to produce a thin crepe of even texture, is to be deprecated, on the ground of economy, in working.

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.Lower Grades of Crepe Rubber.—Even a few years ago it was plain that the lower grades of crepe (i.e., all grades lower than first latex rubber) were not sufficiently appreciated in the market. There was often a marked difference in price between a first-grade crepe and crepe made from naturally coagulated lump. This arose chiefly from lack of knowledge. It has since been recognised in some measure that no reason exists for such a wide difference in price, and more recently the margin between even the first-grade rubber and the lowest grade of scrap rubber has been a gradually diminishing one. Providing sufficient care is exercised in the preparation of the lower grades, one would expect to see but very small difference in prices between any two grades. It is true that adequate attention has been given to the preparation of the scrap grades only in comparatively recent years, and it is acknowledged that when high prices were ruling for first-grade rubbers sufficient attention was not generally given to the subject of the preparation of the lower grades.Naturally Coagulated Lump Rubber.—The grade of rubber made from the naturally coagulated lump which forms in buckets and carts is usually of a mixed colour, due to the fact that the lumps oxidise very quickly. When they are allowed to remain overnight before being machined, it can be imagined that the colour of the dry crepe would be very dark, or would contain very dark streaks. Such is ordinarily the case, unless special precautions are taken.

Providing that the coagulated lump is free from bark, leaves, and leaf-stems, and certain other precautions taken, the difference in price between coagulated-lump crepes and first-grade crepes should be very slight. Too often, however, not sufficient supervision is given to the coagulated-lump rubber, and it is common to see it come into the factory containing leaves and bark. These should be picked out before the latex is strained, but obviously it would be better to ensure that they did not enter the buckets in the first place.

It would seem reasonable to suppose that if some means could be employed for preventing or checking the surface oxidation of naturally-coagulated lump rubber, there would be a corresponding improvement in the colour of the dry crepe. That such a method is practicable has been demonstrated on many estates. The lump when lifted out of the latex is allowed to drain for a few minutes, and is then (without squeezing) placed in a dilute solution of sodium bisulphite. A 1 per cent. solution is sufficiently powerful. It is not to be thought for a moment that by the use of sodium bisulphite any previous oxidation will be counteracted; all that is claimed for the treatment is that any further surface oxidation will be checked, and the rubber may be allowed to remain until the next day, for working, if it is so desired. It will probably be found that quite a quantity of latex has been expressed from the lumps by contraction, and acid may be added to obtain the rubber from this. On other estates the lump rubber is worked on the machines as it is received, and the resulting crepe is submerged in a weak solution of sodium bisulphite over-night. It is then rinsed in water and hung to drip before weighing and placing in the drying house. Under certain conditions some of the lump rubber darkens rapidly during transport to the store, and any such oxidised portions must be rejected if a uniform colour is to be expected in the crepe.Following the procedure indicated above, some estates find it possible to prepare from naturally coagulated lump rubber a crepe which can be classed as No. 1 grade.Skimmings and Washings.—The skimmings of tanks, as already shown, may be prepared sometimes as a second quality of smoked sheet; but generally they are amalgamated with the rinsings of cups and buckets, treated with sodium bisulphite and acid, and made into crepe form.

The cup-washings, as they arrive at the store, represent a very dilute latex, the rubber from which is generally of a greyish colour.

Bucket-washings should yield a good type of pale rubber if they are obtained properly. To obtain the maximum quantity of good rubber the buckets should first be rinsed. A gang should be taken, a small quantity (say a quart) of water poured into the first bucket, and this dilute latex used progressively in all the buckets of that gang of tappers. The result is a fair latex which can be added to the bulk of No. 1 latex, provided it is free from dirt. Where sheet rubber is being prepared, carefully strained cup-washings or bucket-washings may be utilised in the dilution of the latex to the required standard, thus increasing slightly the percentage of first-grade rubber.Tree-Scrap.—As tree-scrap is a naturally coagulated rubber, it should be expected to show up well in quality. This is usually the case; but from what has been said of the effect of sun-heat it will be understood that if trees are not regularly “scrapped,” there is a danger that the crepes may be found to contain tacky streaks due to the inclusion of old scrap which has been sun-baked. In hot dry weather, on widely planted areas tapped on alternate days, it has been noticed that scrap remaining for two days often exhibits a resinous appearance, and feels sticky to the touch.

If tree-scrap is to be made as a separate grade, as used to be the general custom, care should be taken to see that it is free from bark and dirt. On some estates where scrap-rubber is paid for per pound collected, it is usually the rule to insist that scrap shall be washed free from dirt and picked free of bark. This course is to be commended, but might probably prove impracticable to the majority of estates. Theoretically, of course, the operation of machining should rid the scrap of all traces of bark; but in practice it does not do so.

Some proportion of the tree-scrap is usually found to be heavily oxidised, and naturally if a crepe of uniform colour is to be obtained these dark scraps must be rejected, otherwise dark streaks will be formed. Coolies should be instructed to sort out the dark pieces before arriving at the store.Bark-Shavings.—It has been intimated in a previous section that the method of obtaining and collecting bark-shavings varies with the type of labour employed.

Where the scrap is removed from the edge of the bark on each occasion before tapping, the amount of rubber to be extracted from the dry shavings is very small—so small, in fact, that when the price of rubber is low, it is doubtful whether it pays to collect and work the material.

On the other hand, where trees are not “scrapped” before tapping, the bark-shavings and tree-scrap are collected together, and the amount of rubber derived from the mixture may be 30 to 40 per cent. upon the gross weight—depending chiefly upon the quality of the tapping (i.e., in this case, the thickness of the paring). Another factor influencing this figure would be the effect of using an anti-coagulant on the cuts.

Bark-shavings entail such wear upon the ordinary machines during working, especially if fairly free from rubber, that unless the factory is equipped with a special “scrap-washer” it is advised that this material should be sent for working to a factory having the necessary equipment. Whenever possible, bark-shavings should receive treatment on the day of collection.

It used to be quite common to see heaps of bark-shavings accumulating on the floor of a factory, and generating excessive heat. Yet these heaps were allowed to stand about for a day or days. Is it any wonder then that tackiness was found to develop when the rubber was dry? It is here definitely laid down that no heaps of bark-shavings should be accumulated even for half a day. Tanks should be provided in which the shavings should be submerged in water.Earth-Scrap.—Of all grades of crepe this is the one most liable to become tacky in transit. This tackiness to a large extent cannot be avoided, as old pieces of earth-scrap may be brought in amongst the bulk. Probably these old pieces have been exposed to the sun for days, and have become quite resinous. It would be practically impossible to go through all earth-scrap in order to find these odd pieces, but unless this were done one could not guarantee that the earth-rubber would always be free from tackiness. The difficulty does not appear, however, on estates where earth-rubber is collected systematically at very frequent intervals.Fibrous Matter in Low-Grade Rubbers.—It is sometimes found in this and other lower grade rubbers that pieces of cloth or cotton-waste are concealed. Coolies may have used them for cleaning cups, or the store coolies may have been at fault. Earth-scraps especially should be examined, before working, for such extraneous matter.Scrap-Washers.—These are heavy machines specially devised for the treatment of lower grade rubbers. In these the raw rubber is well masticated and freed from impurities, if the machine functions efficiently.

There are several types of these machines, all of which are efficient. That best known is the “Universal” washer, made by Joseph Baker, Sons, and Perkins, Ltd. (formerly Perkins Engineering Company). Coming into local favour during the War, the “U.E.” scrap-washer, made by the United Engineering Company (Singapore), gives very good service. The “C.C.C.” washer, made by the Colombo Commercial Company, is suitable for the purposes of an average estate. There are others, less well known. Most of these machines are made in varying sizes to meet the requirements of small, medium, or large estates; and if funds are available, a scrap-washer should be regarded as an essential item in the machinery of any estate employing engine power.

The rate of output of scrap-washers will depend mainly upon the speed at which they are driven, and when ordering the equipment it would be advisable to state the ordinary speed of the back-shaft, length of drive, etc. It does not follow that the larger the rate of output, the greater is the efficiency of the washer. The point is not as to what quantity of rubber can be taken out per hour, but what quantity is actually freed from impurities.

It is advisable for the superintendent to obtain a thorough knowledge of the general construction and principles of the particular scrap-washer employed. In the past it was not uncommon to find superintendents innocent of the fact that a certain type of washer possessed movable parts upon which the efficiency of the cleansing largely depended. It was often found that these parts, which were intended to be removed and cleaned at intervals, had become firmly fixed and could not be removed for inspection.

It must be recognised also that the machines are liable to considerable damage if extraneous substances are allowed to enter—for example, tapping-knives, stones, pieces of iron, spouts, etc., which are sometimes present in the loose scraps of rubber or shavings, owing to the carelessness of coolies. Under the best regulated-system, such accidents occasionally occur, but a great deal of trouble could be avoided by having it understood that each charge must be sorted over before entering the washer.

Again a deal of extra work, and much wear and tear, is caused by the abuse of the scrap-washer—e.g., in the cleansing of earth-scrap. As this reaches the factory it often contains a quantity of internal or adhering earth. Before entering the washer a good proportion of the external soil could be removed if the scraps were thrown into a tank and given a thorough soaking and stirring. In a similar manner dry bark-shavings, which have been allowed to accumulate, could be softened.

In the actual working of scrap-washers instructions are generally given by the makers. These sometimes advise the introduction of warm water (or of steam into the cold water supply) for an interval during the working of each charge. Where possible, such instructions should be followed, as by this means the individual pieces of rubber are massed together, in the final stage, into a “sausage” form which is easy to transport and to manipulate in the ordinary crepeing battery.Compound Crepes.—The attitude of both buyers and sellers with regard to the types of lower grade rubbers appears to be changing. In the past, from any one estate there might be obtained as many as six grades of crepe below No. I. These comprised:

(1) A pale rubber (often streaked) obtained from coagulation of cup washings and bucket rinsings.

(2) A pale rubber (often streaked) obtained by coagulation of the skimmings from the surface of the No. 1 latex.

(3) A streaked and dull rubber prepared from naturally-coagulated clots found in cups, buckets, and latex carts.

(4) A streaked rubber prepared from scrap which had coagulated upon the face of the cut bark.

(5) A brownish and streaked rubber made by maceration of bark-shavings to which pieces of tree-scrap adhered.

(6) A dark rubber, often tacky, prepared from scrap found in or on the ground near the base of the trees. As it is often a matter of weeks between any two regular collections, it is easy to understand why the dry rubber was more liable to be “tacky” than any other grade of crepe.