The Preparation of Plantation Rubber Part 6

CHAPTER VII

_PRELIMINARY TREATMENT OF LATEX_

RECEPTION OF LATEX AT THE STORE.--Bearing in mind the remarks in Chapter VI. on the conditions under which latex is transported, it follows that nothing but the very best and most suitable vessels should be used in the store. A point to which adequate attention is not given in many factories might be mentioned here. 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. Presuming that a hose-pipe has been installed, and that the floor is constantly being sluiced down with water, no great harm will result. But would it not be ever so much better if the dirt were kept out? In how many factories is provision made for this? Such an arrangement is not difficult to make, and is already in practice on a few estates. A verandah is built outside the wall of the factory and all latex is received there. In another place open chutes are provided which terminate in the straining sieves. The coolie thus stands on the verandah where he removes coagulated lump and impurities from the latex, which is then poured down the chute, pa.s.sing through the sieve into large coagulating jars or tanks.

Too often it would appear, from the writers' observation, there is a lack of adequate supervision on the arrival of latex at the store. 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. Efforts are made in a large number of cases to cope with these troubles, but on some estates things are allowed to proceed in the same slipshod way, and too much responsibility is thrown on the straining process.

[Ill.u.s.tration: RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER COOLIE" BY SAMPLING OF LATEX.]

It is suggested that it should be the business of a European to supervise the reception of latex every day. This is at present quite impossible on some estates, but it does not alter the fact that this supervision should be provided, and is extremely necessary.

It is surprising how the point is overlooked in many factories--not that they are in a dirty state, but they fall short of being cla.s.sed as clean factories for want of the little that makes the difference. Possibly those in charge do not believe that all this fuss need be made, but the writers can a.s.sure them, from a practical knowledge of a very large number of factories, that cleanliness does pay.

It might not be credited to Tamil coolies, but yet it is probably true, that the moral effect of working under the cleanest and best conditions has an influence upon the store coolies, and that their work is better in consequence. Everything which will tend to simplify the cleansing of the factory should therefore be installed. Hose-pipes, glazed tiles, clean floors, plenty of light and air are not fads or fancies, but considerable factors in determining the final quality of the rubber. There is considerable truth in the suggestion that the coagulating room and machine room should be as "spick and span" as a modern home dairy.

STRAINING OF LATEX.--This is a most necessary process, and one which usually entails much trouble and time which one could wish avoided. It will be admitted that the trouble could be reduced greatly if the regulation of field processes could be made more stringent. In spite of knowledge that impurities must not be allowed to enter the cups, coolies will ignore the rule that the cup must not be placed in position until the bark shaving has been cut. The result is that pieces of bark fall into the cups, and coolies are generally too careless or too hurried to remove them.

Again, when cups are placed on the ground, it is easy to see that dirt may adhere to them. In the collection of latex some of this dirt may fall into the bucket. Since the introduction of cup-holders on many estates the trouble from this source has decreased considerably, but, nevertheless, it may be taken for granted that even under the best of conditions all latex requires straining.

The best type of strainer has yet to be evolved. Usually it consists in principle of a piece of fine bra.s.s mesh contained in some form of holder.

Theoretically such a strainer should work well, but in actual practice nearly all strainers are a source of continual worry. Undiluted latex, as received at the factory, is of a rich consistency, containing very fine particles of dirt and often minute particles of prematurely coagulated rubber. The latter soon clog a fine mesh strainer, while the former may pa.s.s through. When the flow through the strainer becomes slow, the coolie in charge generally rubs the top surface of the sieve with a piece of coagulum, thus forcing material through the mesh. He then rubs the under-surface, with the result that undesirable matter falls into the strained latex. In theory it seems a simple matter to have a number of sieves ready so that a clean one may be subst.i.tuted for a clogged one, which should be cleansed at once with water. In practice the factory coolie will probably only carry out instructions when the eye of the superintendent is alert. As a result of the rubbing and consequent strain, the bra.s.s mesh usually breaks away from its support and the fracture may not be detected for some time, during which irreparable damage may have been done to the resultant rubber.

In view of the presence of the fine particles of dirt, to which allusion has been made, fine sieving of the latex appears to be essential, especially when sheet-rubber is to be prepared. The fine sieves are generally of the type known as "60 mesh," and they do not usually give thoroughly satisfactory results even when the gauze is supported and strengthened by means of cross-wires placed underneath. The general fault with these strainers is that a sufficiently wide "selvage" is not allowed in the clamped edges of the gauze, or that the edges of the support are so sharp and abrupt that the strands of the gauze are soon severed by the strain imposed in vigorous cleaning.

Many estates use two strainers; the first a more robust one containing "30 mesh" gauze, and the second the fine "60 mesh." Even this device does not bring about the desired immunity from trouble. Relief could be obtained if the latex were always in a more freely fluid form. Estates employing anti-coagulants in the field benefit in this respect. Other estates, although finally using the finest of mesh, experience far less trouble than most estates by reason of a difference in method of working. This can be explained by an outline of the system adopted on a particular estate:

(_a_) On arrival of the rich latex at the store, all visible coagulated lumps and other extraneous matter are removed by the tapper.

(_b_) Each tapper's latex is diluted with a quant.i.ty of water.

(_c_) The diluted latex pa.s.ses through two sieves, one above the other. The top sieve is of stout perforated zinc sheet, with 10 circular holes to the inch. This removes all large particles. The lower is of "30 mesh" bra.s.s gauze, and practically no rubbing is required. The latex is now in glazed-tile tanks, in which it is further diluted to the required standard by means of a recording instrument.

(_d_) The latex flows by means of a chute into the coagulating tanks, pa.s.sing through a large "60 mesh" sieve.

It is not guaranteed that this method will furnish a complete absence of very fine particles of dirt in sheet rubber, as the human element enters so largely into the question; but it can be stated that no complaints have been received on the point of "specks of dirt" since this system was inaugurated.

On the same estate fine sieving in the preparation of pale crepe has been abandoned as an unnecessary refinement. The two coa.r.s.e sieves mentioned above are employed only, and it is to be acknowledged that the results justify the procedure.

BULKING OF LATEX.--Not long ago advanced estates used to combine all latex before coagulation, in order to obtain uniformity of product. Previously it had been the custom to deal only with comparatively small separate volumes of latex, with obviously great disadvantage.

Since the introduction of instruments such as the "Metrolac," by means of which any volume and all volumes of latex may be reduced to a common standard of dry rubber content, the necessity for "bulking" has pa.s.sed. It is not now necessary to keep latex standing, perhaps for two hours, awaiting the arrival of other latex from distant fields.

STANDARDISATION OF LATEX.--In modern practice, as already pointed out, it is possible now to handle any volume of latex with a view to its reduction to any required standard of dilution for the purpose of obtaining a uniform product. For the reception and subsequent handling of the latex various schemes have been devised, and they are usually planned in connection with coagulating tanks used in the preparation chiefly of sheet rubber.

[Ill.u.s.tration: END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD FOR RECEIVING LATEX AND FILLING TANK.

T, Sheet coagulation tank; C, cylinder for reception and dilution of latex; GG, gutter; PP, raised platform on verandah; SS, steps leading to platform; W, dwarf wall; EE, expanded metal part.i.tion; OO, open.]

In the successful working of a tank it is necessary, in order to obtain the best results, to standardise all latex. This cannot be effected properly in the tank itself, and hence it is the practice to dilute each lot of latex to standard before it is run into the tank. In the ordinary way this would entail a great deal of labour in handling the diluted latex. To obviate this, the scheme outlined in the accompanying sketch has been suggested on several occasions and in various quarters. Such a scheme or modification of it has been put into successful practice on several estates. Although the drawing was made some considerable time ago when estates were not then prepared to go so far in this direction, subsequent modifications show only minor differences which, while leaving the original principle intact, testify to a fertility of resource in adapting the idea to existing circ.u.mstances and buildings. The drawing is _in toto_ almost a replica of the original installation now in successful use on the Kinrara Estate of the Ledbury Rubber Company. On this company's Ledbury Estate likewise a similar system is employed, except that the reception verandah is part of a natural formation and needed no such direct raising. Several other estates have now adopted the scheme, which has been proved to be of practical value. The writers make no claim to originality in the idea, which might have occurred to many independently on the introduction of coagulating tanks.

[Ill.u.s.tration: RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX.]

VERANDAH.--In reproducing the drawing it is believed that the sketch will convey practically all the information required. It may be explained that the coolies are allowed to enter only the outer part of the verandah. The buckets are handed across the low wall into the care of factory coolies, who strain the latex through gauze sieves into the latex cylinders.

LATEX RECEPTION VESSELS.--These cylinders may be similar to the tanks commonly used for transport of latex from distant fields to the factory. An 80-gallon cylinder is easily mounted by its trunnions on a suitable iron framework which is superimposed on a skeleton truck.

[Ill.u.s.tration: ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH.]

The latex is diluted down to standard in the cylinders, the truck is moved opposite the compartment to be filled, and a light movable gutter is placed beneath the vent of the outlet pipe. This pipe is fixed in the bottom of the cylinder, and is provided with a large stop-c.o.c.k which is operated by a spanner key. The stop-c.o.c.k should be of the simplest type, capable of being taken apart and a.s.sembled in a minute or so. The orifices should be large enough for a coolie to insert at least two or three fingers so as to facilitate cleaning, and the pipe should have no right-angle bends.

On the inside of the cylinder a scale of gallons may be painted, so that one may possess a knowledge of the quant.i.ties run into, or required for the completion of, any compartment.

A SCREW PLUG UNSATISFACTORY.--It may be of benefit to managers who contemplate such an installation to know that the adoption of a stop-c.o.c.k in the vent pipe of the cylinder is the outcome of experience. In one instance the vent pipe as designed was fitted with a screw plug at the end.

Unfortunately with this arrangement the flow could not be regulated, and owing to the "head" of the latex it dashed violently down the gutter, struck the bottom of the coagulating tank, and thence was scattered over the factory.

ANOTHER INSTALLATION.--In another type of installation, in place of the vessels travelling upon a raised verandah platform, the standardised latex is conveyed to the coagulating tanks by means of drums supported by hooks to a chain-block and pulley which travels on an overhead gantry. This method is practicable, but may be regarded as less satisfactory in general working than the verandah method of treatment.

A MODERN INSTALLATION.--In the most recent scheme for dealing with the reception of latex, its standardisation, and conveyance to the coagulating tank, the main principle of the first system outlined is retained; but the receptacles are not mobile. Glazed-tile tanks are employed, the capacity of each being approximately equivalent to that of each unit coagulating tank.

The accompanying ill.u.s.trations show the general arrangement and some details of the system of reception tanks employed on the well-known Pataling Estate.

CHAPTER VIII

_COAGULATION_

Whether it is necessary to employ any coagulant, or whether latex should be allowed to coagulate naturally, will not be discussed at this stage.

Neither will mention be made of any patent processes of coagulation which employ other than acid mediums. These subjects will be treated in a subsequent section of the book.

CHOICE OF COAGULANTS.--It is not proposed here to enter into a discussion as to the merits of the dozens of known coagulants. Suffice it to state that acetic acid, although the oldest general coagulant, still remains the best and safest at the present time. There is a deal to be said in favour of the use of another organic acid, formic acid. It is equally as safe as acetic acid, and quite efficacious; the only drawback is that, taking all things into consideration, it is very slightly more expensive. Acetic acid, therefore, will always be implied in this chapter when the word "acid" is used.

STRENGTH OF ACID SOLUTION.--In the old days it was the rule rather than the exception to find pure, undiluted acid used in coagulation. In many cases no harm resulted, for the simple reason that, owing to the large proportion of water in the latex, the acid was thereby very much diluted. The estates had to thank the over-dilution of the latex for the non-injury of the resulting rubber.

Some estates make up a stock solution of 1 part acid to 20 of water, and use this with success because of the fair amount of added water present in the latex.

It must be understood that what is being referred to now is not the absolute quant.i.ty necessary for coagulation, but the proportions--_i.e._, the respective volumes of acid and water in the solution of acid made up every day. That the strength of the acid solution, as well as the quant.i.ty used, has an effect upon coagulation can be easily demonstrated in the following way:

Take separate and equal lots of the same latex, and to each add the same quant.i.ty of pure acid, but in each case diluted with varying quant.i.ties of water. It will be found that coagulation is quickest where pure acid is employed, and slowest where the acid is most dilute. It will also be found that, providing the quant.i.ty of acid employed was sufficient for coagulation, the best and most uniform coagulation is obtained from the use of the most dilute acid, within limits. It will often be found that where pure acid has been employed coagulation is local--_i.e._, we have lumpy coagulation, and often a very milky remaining liquor. This is due to the fact that, as coagulation is immediate upon the spot which is first touched by the pure acid, a deal of the acid is enclosed within the rubber at that spot, and hence other portions of the latex are deprived of acid. It is in such cases that most air-bubbles are enclosed.

As the dilution of the acid solution is increased the mixing is more thorough and uniform. Coagulation is slower, and air-bubbles can escape to the surface.

METHOD OF MAKING STOCK SOLUTION.--Experiments have been repeatedly made in the laboratory with acid solutions of varying dilution, from pure acid down to 1 part of acid in 500 parts of water. While it has been found that a 1 in 5 solution can be used where the latex is very dilute (say, 1 part of latex to 5 parts of water), and a 1 in 20 solution may be used in fairly dilute latex (for crepe-making), it is undoubtedly a fact that for latex as generally "standardised" on estates a much more dilute solution of acid should be used--_e.g._, 1 in 100, or even 1 in 200, of water. It must be borne in mind that the quant.i.ty of acid necessary for coagulation is not changed, but merely the dilution. Let us take a concrete case to ill.u.s.trate the point: