General Style of Finish.—Broadly, there is no single and definite style of finish, but on the whole it may be stated that the greater proportion of crepe rubbers are prepared in a thin form and with a close-knit texture or finish.

Very little thick or blanket crepe is now made on estates in Malaya, so that beyond the mention of that type little need be written. A fair amount of blanket crepe is sold in the Singapore market, but it should generally be regarded as re-made rubber—i.e., it may have been prepared from thin crepes, or from native pale sheets, in local rubber-washing factories. In appearance these crepes have a rough finish, and vary in colour according to the crude material employed.

The general preference of the market at present is for a thin, smooth-finished crepe, with a close-knitted surface—i.e., free from what is described as “laciness.” What effect this looseness of finish can possibly have upon the quality of the rubber is not understood, but the standard type set up by the market must be comparatively free from small holes.

Under existing conditions governing the sale and purchase of rubber, various “standards” are set up. These really have no bearing upon the intrinsic qualities of the rubber, and are concerned almost entirely with superficial attributes. They are necessary in the absence of any proper scheme of evaluation for the establishment of certain standards of comparison, which imply that the rubber is apparently clean, free from certain recognised defects, and has been carefully prepared—as far as can be determined by a superficial examination. Thus the question of “finish” has attained disproportionate importance, but must be respected when preparing rubber for sale.

Under ordinary conditions, thin crepe rubber, as it leaves the finishing machines, has what may be termed “deckled” edges. On many estates, in order to comply with market conditions, the edges of the wet crepe are trimmed, and the trimmings re-made into lengths of crepe. This is done under the impression that the market price is influenced by the evenness of the edges of crepe rubbers.

Again, it sometimes happens that, owing to “wear” of the rolls, the finished dry crepe may show a faint but distinct pattern of mark—a diamond or a horizontal bar. Since these are not accepted under the “standard” comparisons, rubber exhibiting these characteristics does not obtain the top market price. In other words, these innocent and innocuous marks are regarded as defects and penalised accordingly.

Enough has been written to show how very important becomes the question of finish. It will be acknowledged that the superficial qualities demanded in the “standard” market type can be reproduced by any estate having adequate machinery and ample facilities for drying and handling the rubber.

Methods of preparation and formulÆ for the employment of chemicals are so well laid down that, up to the stage of machining, no difficulty need be encountered. But the standard type of finish in the dry crepes cannot be obtained unless the estate factory is fully equipped with the three types of rolls necessary—i.e., macerators, intermediate crepers, and smooth finishing-rolls. This subject has received full discussion in Chapter XIII., and is here only mentioned with the view of emphasising the point that no estate can be blamed for a lack of “finish” in crepe rubbers if the equipment of machinery is inadequate or in poor condition.

If, on the other hand, the factory has ample machinery for requirements, and a good finish cannot be obtained on the thin crepe, then it is time the rolls were attended to and changed, or that the ratios of the driving pinions were altered.Dirty Edges.—It seems to be almost impossible to keep old machines clean, and it is equally difficult to keep the edges of crepe free from oil and dirt. Usually these dark edges are to be found on crepe which is rather wide, and it will be noticed that where wide crepe is made, unless special precautions are taken, the edges of the rubber often pass under the edges of the hopper and so pick up dirt and oil. On most machines it is a great mistake to attempt the preparation of wide crepe; nothing but narrow crepe must be made. To obtain this it is necessary to decrease the width of the hopper placed above the rolls. This can easily be effected by blocks of heavy hard wood, cut to shape and fastened in position.

Sometimes the dark edges of crepe are due to another cause. Rolls may be gradually worn in the middle, so that to obtain a good finish it becomes increasingly necessary to tighten up the screws which regulate the distance between the rolls. It thus happens that just at, and beyond, the edges of the rubber the rolls grind upon each other, and fine particles of iron and graphite are transferred to the rubber. In such a case it is evident that either the rolls must be “turned” or that a new pair of rolls must be substituted.Iron-Stains.—One of the causes of iron-stain on rubber has been mentioned in the preceding paragraph. This particular kind of iron-stain must not be confounded with rust-stain, and gives a dark dirty colour. It results from the grinding together of the rolls, and is usually noticed in the finishing of fine pale crepe. For this operation it is necessary to screw up the rolls tightly, and it will be plain that, whenever the rolls are vacant of rubber, there is a tendency for them to grind upon each other, thus setting free fine particles of iron and graphite. In order to avoid this, one must be careful to see that between the working of each length of fine crepe the rolls should be occupied with another piece of rubber, which may be kept for the purpose. In some factories this trouble apparently does not exist, while in others the amount of wear on the rolls is surprisingly great, and the damage done to the rubber is excessive. The only way in which this difference can be accounted for is that there must be a great difference in the quality of the roll material. Some rolls seem to be excessively soft, and from these contamination by iron-stain is great. For this reason rolls are sometimes rejected, and there would appear to be an objection to any but chilled steel rolls for the final stage of finishing crepe rubbers.Rust-Stains.—Rust-stains, on the other hand, throw the responsibility entirely upon the labour and supervision of the factory. Rust is formed upon the rolls when they are at rest, and any one passing pale rubber between the rolls before they have been thoroughly cleaned is guilty of culpable negligence. Even when apparently clean, a piece of lower grade rubber should be passed through the rolls several times so as to remove any slight trace of rust remaining.

Rust-stains have also been caused in a few cases by the large knives which are used to cut up lumps of coagulum, or by allowing freshly coagulated rubber to come into contact with iron vessels in the factory.

A similar appearance has been traced in a few instances to contamination of the coagulum in transit by the dust of the reddish rock (laterite) employed in localities for road-making.Oil-Marks.—The origin of oil-marks in crepe has already been described in Chapter XIII. The whole question resolves itself into one of cleanliness, moderation in lubrication, and supervision. The machines should be inspected every day, and once a week rolls may be swabbed down with a 10 per cent. solution of caustic soda applied by means of a piece of cloth fastened round the end of a stick. Immediately after this operation water should be turned on and the rolls set in motion, so that all traces of caustic soda are thoroughly removed. If possible, lubrication by oil should be substituted by grease lubrication through screw caps.

Particular attention should be paid to the back of the machines. None but the individual in charge of engines should be allowed to lubricate the machines, and he should be held responsible for any excess of lubricant.As a rule oil-marks are restricted to the edges or the proximity of the edges of crepe, but sometimes the streak is to be found in the middle of the length. In such a case it is almost certain that the oil or grease has been picked up by the rubber in the tray. It sometimes happens, if the “liners” of the bearings are eccentrically worn, that a few drops of dirty oil or a particle of grease are squirted out to some distance. These usually find a resting-place in the tray, and the contamination may then appear in any part of the rubber.

It will be clear, therefore, that all trays beneath machines should be examined as the probable source of danger from contamination by oil and dirt. If the trays are as wide as or wider than the effective portion of the rolls, they should be discarded. In their place (except sometimes in the case of the macerating machine) all that is necessary is a movable piece of board, in width not less than from 4 to 6 inches shorter than the width of the rolls. Any oil or grease ejected from the bearings will thus be allowed to fall clear of the board; and defects due to oil streaks, etc., will be very much diminished, if not entirely obviated.

This point in connection with the damage possible by the existence of wide trays is commended to the notice of manufacturers of machines for plantations, as it is common to find that trays are made which contravene the rule prescribed by experience. In fact, trays on some machines have been so designed as to act as “traps” for all dirty matter exuding from the bearings. Not only so; they are sometimes made of such a shape and height that oil or grease lodging upon the edges act as a “wipe” to the rolls, thus increasing the possibility of contamination. Until this defect was investigated, it was common to note continued contamination of pale crepes in spite of all precautions taken in cleaning the rolls at frequent intervals. The trouble due to this cause is intensified when the same machines are employed for the preparation of scrap-rubber crepes and No. 1 crepe. Small pieces of scrap find their way towards the bearings and lodge on the edges of the trays. Unless a thorough inspection is made before proceeding with the working of the No. 1 (pale) grade, contamination may be continuous.Dirt.—Streaks due to the presence of dirt (as apart from oil or grease contamination, or that due to pieces of oxidised scrap) are unusual, and when they do appear their origin seems to be somewhat of a mystery. It could scarcely be advanced that the dirt was picked up on the machines, as it is difficult to imagine where such dirt could come from. In one or two instances there has been fairly clear evidence that the dirt was contained in the coagulum, and the only explanation fitting the case is that it fell into the latex after straining and during the course of coagulation. On cutting open lumps of coagulum brought in from the field division, it has sometimes been noticed that dirt is included, and the foregoing explanation is the only reasonable one. How it was possible for dirt to get into the latex must be left for explanation to those better acquainted with the conditions under which the latex was coagulated.Holes.—On some estates it would seem impossible, with the existing machines, to make really good crepe. The complaint is that, if thin crepe is attempted, it is invariably found to be “full of holes“; and as, apparently, the presence or absence of small holes in crepe rubber is a factor which influences buyers, this defect must be avoided at all costs. Why this matter of small holes in thin crepe should weigh so heavily with buyers is a matter which the writers are not in a position to explain. As a matter of fact, the presence of small holes is most generally an indication that the rubber has received the minimum amount of working on the rolls consistent with good washing. Further working would only be undertaken with the idea of so consolidating the rubber as to get rid of holes in order to meet the market scheme of valuation.

This is usually achieved by making a very thin crepe and rolling together two lengths when wet. The resulting crepe may be slightly thicker than ordinary, and the method employed may be usually detected by the appearance of the edges unless these are trimmed.Greenish and Tacky Streaks.—Occasionally one meets cases in which pale crepe exhibits streaks varying in colour from a decided green to an almost black in which the greenish tinge is scarcely perceptible. Experience indicates that these streaks are much more dangerous than they appear superficially, inasmuch as they contain traces of brass from the “liners” of the bearings. The presence of the copper in brass is responsible for a gradual disintegration of the rubber, commonly recognised as “tackiness.” In fact, copper may be said to be a “poison” to rubber, and every effort should be made to avoid possible sources of contamination. The effect may be proved easily and perceptibly by fastening together several pieces of crepe rubber by means of a brass “paper-fastener.” In course of time a salt of copper, green in colour, will be formed, and it will be found that the portions of rubber in contact with the fastener have “perished” and become tacky.

This contamination of crepe rubber may take place in two ways:

The inevitable effect, apart from the superficial defect, is incipient tackiness. The extent to which this may develop will depend upon the amount of the copper compound present, but it should be remembered that an exceedingly small trace is capable of causing a disproportionately large amount of damage. This effect is further magnified if the “tacky” piece of rubber is packed in close contact with previously unaffected rubber.

When the defect is discovered, the affected portions should be cut out, and the cuttings should be burned. To mix them with the lowest scrap grades, as may be done thoughtlessly, is only inviting further trouble.

Besides the source of danger already indicated, it may be found, but far less frequently, that contamination may arise from the presence in the rubber of small pieces of the brass mesh which is generally used for straining latex.The view appears to be held in some quarters that these tacky streaks and patches in crepe rubber may arise from contamination with oil or grease alone. This does not agree with our experience. An experiment was made to test the point using fresh oil and grease drawn from drums in stock, specimens of the same lubricants to which traces of a copper salt were added, and samples of lubricants taken from the bearings of several machines. The treated pieces of rubber were placed in contact with untreated pieces of crepe which served as “blanks.”

Notes were made at intervals extending over a period of two years. The conclusions arrived at were:

These observations regarding the possibility of damage to crepe rubbers from the existence of brass “liners” or “bushes” in the bearings of the machines lead to the natural query as to whether the use of brass is necessary. Experience shows that it is not necessary. Machines in use for years have been running with plain bearings of iron or other metallic substances. Satisfaction is obtained without the use of brass.Cotton and other Fibre.—One of the most frequent complaints made against low grade crepes is the presence of fibre—generally classed in a wholesale fashion as “cotton-waste.”

It is true that some years ago most of the complaints were genuine in referring the cause to cotton-waste. The defect arose chiefly owing to the careless use of this material in the factory. Lumps of waste when discarded were often thrown to the ground, and became mixed with the heaps of scrap rubber and bark-shavings awaiting attention. The fault was one of sheer negligence, and nothing can be advanced in extenuation. Even when the soiled waste was thrown into the external drains, it often returned to the factory mixed up with the scraps of rubber recovered by means of the drain-screens.

As far as the complaint concerns itself with cotton-waste only, the remedy is plain, and lies in the power of the management by reason of the ability to restrict the use of “waste” only to the engine-drivers and mechanics.

In the vast majority of cases, however, the defect arises from circumstances beyond the direct control of the factory, and under conditions which make it difficult to check the evil. Although against instructions, and for the purpose of fulfilling other orders, some coolies persist in using pieces of cloth for cleaning cups. In course of time, unless the practice is detected, this cloth becomes coated with rubber. Careless coolies throw it away, when it may be collected by the individuals who gather earth-scrap; or it may be brought into the factory in the tappers’ scrap-bag.

Cases have been known in which the fibrous matter observed in the dry crepe rubber was of such a nature as to indicate that the source might be attributed to leaf-stalks which had passed through the scrap-washer. It is an easy matter to condemn the sorting as being careless, but it is another matter to instil into the mind of factory coolies such a respect for easy and sane precautions that the practice of them will be continued when the eye of the supervisor is not fixed upon the workers.

It will be clear that contamination by fibrous matter should be limited practically to the lowest grades of rubber.The appearance of cotton-waste in high-grade crepes must be most unusual, and the writers have not yet seen a case in a drying-house. That it does occur, however, seems to be evident from brokers’ reports. It is extremely difficult to imagine how the waste enters the rubber. One possible explanation is that a coolie may have been cleaning the rolls surreptitiously with waste, which may have passed later into the rolls together with rubber. Another explanation was offered in one factory by the observed fact that coolies engaged in cutting up coagulum, ready for passing into the machines, kept a wad of waste for the purpose of keeping the knife-blade clean. This may have found its way into the rolls. It must be recorded that in the course of many years of experience no case has been seen in any drying-house of contamination of the higher grades of crepe by fibrous matter.Bark and Grit.—With ordinary machines and the usual process of working, it would seem impossible to wash and macerate some of the scrap rubbers sufficiently to free them entirely from bark. This applies specially to the grade of rubber prepared from bark-shavings. Specimens have been handled in which it was practically impossible to detect bark, but in such instances the amount of working necessary would be such as to interfere seriously with the regular working of the factory. Even with the employment of special scrap-washing machines, complaints of the presence of bark in dry crepe have been received, but it is certain that this mode of operation reduces the quantity of bark to a minimum. While fully realising that the amount of working it is possible to give in proportion to the existing machinery and the output per day is limited, it must be recognised that the working of lower grades of rubber is usually insufficient, and that where possible it is the duty of estates to pay more attention to these lower grades. A considerable improvement in this direction has been noticed of recent years. It is not uncommon to encounter managers who fail to appreciate that complaints regarding the presence of bark in the lower grades are founded on legitimate grounds, and that they are not frivolous objections put forward for the purpose of depressing the price of the article. The sooner such an idea is jettisoned the better. There would appear to be a good future demand for the lower grades, and it is only natural that consumers will be willing to pay the best price only for an article which is clean.The same arguments apply to the complaints regarding the presence of sand and grit. The quantity of the latter found in low-grade crepes from some estates is surprisingly high. Its presence can often be shown by the simple device of spreading a piece of crepe over the upturned and hollowed palm of one hand, while striking the rubber with the other hand.

The incidence of bark in higher grades of crepe may be due to inadvertence or to gross negligence. In the former class one might put those occasions on which pieces of bark are embedded in lumps of naturally coagulated rubber. A piece of bark-shaving may fall unnoticed into latex and be partially responsible for the coagulation which takes place. This piece of coagulated lump may be massed with others, and hence, unless each small piece is cut up, the bark is not perceived. Or again, by some unknown means, a piece of shaving may drop into a jar of latex, and so become embedded in the coagulum. Sometimes this becomes evident on cutting up the rubber, but it is quite as likely to pass unseen. On the whole, the presence of bark in first-grade rubber is most unusual, and should be seen before the rubber is packed.

In the class due to negligence may be included cases in which careless coolies place the cup upon the ground before tapping. Pieces of shavings fall into the cup, and coolies are too lazy to pick them out. More often than not coagulation in the cup is caused. As it is impossible for the European staff to supervise each individual tree tapped, some cases must continue to pass unheeded. Sometimes bark-shavings are brought in with the latex, and if a broken sieve is being used, these, with other impurities, pass into the jar, and are embedded in the coagulated rubber. This must be classified as negligence, for no manager would willingly allow the use of a broken sieve. Again, naturally coagulated lump rubber on arrival at the factory sometimes contains evident pieces of bark, leaves, and stems of leaves. For lack of supervision the average coolie would not think of picking out these obvious impurities, and would pass the whole mass into the machines.Oxidation Streaks.—Since the introduction of sodium bisulphite defects due to streaks, caused by portions of the coagulum becoming oxidised, have practically ceased to exist. In the usual course, and without the use of an antiseptic agent, the freshly coagulated rubber has a surface darkened by oxidation. Unless this dark surface were carefully cut off, there would result a crepe containing dark streaks caused by the mixture of the oxidised surface portion with the bulk of the paler coagulum. The presence of oxidation streaks in No. 1 crepes, now being made, would imply either that no anti-oxidant substance was in use, or that the quantity necessary to prevent this surface oxidation is exceedingly small. Although the price obtained would appear to be influenced by the presence of oxidation streaks, no evidence can be obtained that the actual quality of the rubber suffers to the same degree as does the appearance—i.e., there is no evidence to show that a pale rubber, in which surface oxidation has been inhibited, is intrinsically superior to one in which slight natural oxidation has been incident.“Yellow Latex” Streaks.—This appearance of “yellow-latex” streaks in not common, and may be accounted for by incomplete mixture of two different latices. It is a fact of common observation that, when a new portion of bark is being tapped for the first time, there is a distinct yellow tinge in the latex excluded. As tapping progresses, this colour vanishes; usually it may persist for a period varying from two weeks to more than a month. Should this latex be poured into ordinary latex without thorough mixing, it is sometimes found that, when the crepe rubber is dry, there are distinct yellow streaks. It should be remembered that, as the rubber content of the latex from first tappings is high, this latex is lighter than latex which is more dilute, so that the mixed latices must be well stirred with a broad paddle to obtain intimate mixture. It would be much better to keep yellow latex apart, and coagulate it separately, if at all possible. In such case the resultant crepe may be of a distinct canary yellow in tint.In scrap-crepes of the higher grade this distinct yellow colour is often visible in streaks which indicate the presence of tree-scrap, etc., obtained from recently opened tapping areas.Bisulphite Streaks.—These, again, arise from defective mixing. In the dry rubber it is seen that there are streaks of colourless rubber in a general mass, which may be of varying shades of yellow; or, a length of exceedingly pale rubber is apparently streaked in patches with a darker shade of colour. A solution of sodium bisulphite is heavier than latex, and there would be a tendency, therefore, for the chemical to sink in the large mixing jar. Unless stirring is thorough it is possible that portions of the latex would not be in contact with sodium bisulphite while others receive more than a fair share. Especially would this effect be seen where coagulation takes place quickly, and experience bears out the truth of the suggestion. Another factor which has some bearing on the point is the strength of solution in which sodium bisulphite is used. In the ordinary course of working, the acid coagulant is added immediately after sodium bisulphite has been stirred in. Should a strong solution of the bisulphite be used, and if coagulation takes place quickly, it is easy to see that the possibilities of obtaining a uniform and intimate mixture are small. Probably in no factory is the sodium bisulphite now added to latex in powder form, but it has been found that if care is not taken to see that all the bisulphite has dissolved before the solution is added to latex streaks may result in the dry rubber. The undissolved particles sink to the bottom of the coagulating jar or tank, and there slowly dissolve, forming local strong solutions. The effect upon the rubber in the vicinity of these strong solutions is much more marked than in the bulk of the coagulum, and hence lighter streaks or patches appear in the dry rubber. In spite of apparently complete mixture by good stirring, it will be seen that it is possible, therefore, to have failed in this direction if any undissolved powder remains in the solution of sodium bisulphite.“Spot” Disease.—Few managers of estates preparing pale crepe rubbers are unacquainted with this defect. It is manifested by the appearance of small coloured spots varying in density (i.e., number to a unit area) and differing in hue. The most common colours are black and orange, but “spots” of brick-red, yellow, violet and ruby and green tints have been noted, the last named very seldom. Sometimes in place of definite “spots,” or colonies, the colour is spread over practically the whole surface of the rubber as a “flush.”These coloured spots, or “flushes,” indicate infection by minute fungi, which are present in the latex prior to coagulation. The infection of the latex takes place in the field by means of spores, which are only visible with a microscope.It is not feasible to discuss any method of preventing this infection of latex by air-borne spores, as the eventual preventive measures are so simple. But it may be believed that under ordinary weather conditions most latices are infected before reaching the factory. It is likewise true that even fine pale crepes shipped in perfect condition may contain possibilities of trouble in the form of “dormant” spores, the development of which may commence and continue if favourable conditions arise.

The subject of “‘Spot’ Diseases” has been treated fully in previous publications,[19] and it is not proposed here to enter into any lengthy discussion.

If any reader is desirous of producing the defect experimentally, all that is necessary is to prepare a piece of crepe rubber of rather more than ordinary thickness, roll it up while wet, and place aside for some days.

This experiment reproduces the conditions favourable for the development of the spores, and spots of various colours may result. It will be clear that the chief factor influencing the result is the continued presence of plenty of moisture.

This condition may be created inadvertently in the course of factory practice, if piles of crepe rubber are allowed to remain for any appreciable period before hanging to dry. For this reason batches of wet crepe should always be placed on edge, to allow free drainage of surface moisture, if the rubber cannot be taken at once to the drying-sheds.

The condition also is provided if the thickness of the crepe is excessive. In some factories, having no smooth-roll finishing machines, the crepes may have a distinct raised pattern upon them. It is usual to note that if “spot” disease appears in such crepes, it is incident to much greater degree in the thicker portions of the rubber—i.e., upon the raised pattern.The direct connection between the rate of drying and the appearance of coloured spots or flushes is thus established, and it only remains to adopt precautionary measures which will lead to an avoidance of delay (1) between machining and hanging, (2) in drying.It is indicated, therefore, that, if spot disease is to be avoided, the prime consideration is the preparation of a thin crepe which will dry quickly under average conditions. It may sometimes happen that even very thin crepes will sometimes be found affected on some estates. In such instances, it will be found that the design or situation of the drying-house is at fault, and that specially favourable conditions for the development of the fungi have been created by excessively wet weather. Should the trouble persist in spite of the preparation of the thinnest crepe, it would be advisable either to abandon this form of No. 1 product or to consider the installation of artificial aids to drying.

We have not yet encountered any case in which it was found necessary to treat the latex with an antiseptic or disinfectant substance for the prevention of “spot” disease. There appears to be an idea held in some quarters that sodium bisulphite may be so employed as a fungicide. This does not agree with our experience, which is confirmed by Sharpies (Bulletin No. 19, F.M.S. Department of Agriculture).

In 1913 experiments with chinosol were undertaken at the Pataling Laboratory of the Rubber Growers’ Association, and an account of the method of treatment was given in a printed report issued to subscribers. Dr. P. Arens,[20] of the Malang Experimental Station (Java), has also recommended the use of chinosol. The substance is expensive, but is effective in very small quantity. On the whole, given average conditions in factory practice, such aids should not be necessary, and where keen supervision is not available may lead to other difficulties.

It has already been remarked that it is possible for “spot” disease to develop in dry rubber which previously gave no evidence of the presence of fungi. The condition necessary to such an occurrence is supplied by the presence of moisture. Thus, to state instances which are by no means uncommon, if a box of rubber is allowed to remain exposed to rain, or is damaged by flood-water, or by sea-water during transit, or (sometimes) if the rubber is packed in a damp case, the crepe on arrival at its destination may be found to be affected to a degree dependent upon the extent of wetting and the duration of the wetting period.

No means are known by which these coloured spots, due to the growth of chromogenic organisms, can be removed from the rubber. Naturally, although they may be present in the darker lower grades of crepe, they are not so easily visible as in pale crepe. It follows, therefore, that every possible precautionary measure must be taken when pale crepe has to be prepared.

We are often asked whether it is possible for an infected piece of rubber to affect sound rubber hanging in the same building; and whether, in case of “spot” disease appearing, it is necessary to disinfect the drying-house.In a general sense, the answer to both queries is in the negative. It has not been proved possible to transmit the disease from one piece of crepe to another, except by the closest possible contact and in the presence of an abundance of moisture.

A dry crepe, even when in close contact with an infected dry specimen, has not been found to be affected.

Unless, therefore, pieces of rubber are pressed together, under favourable conditions as to moisture, there has been observed no transfer of disease.

Similarly it has not been found that the presence of spotted rubber in one part of the drying-house has been responsible for an outbreak of disease in another part of the same building. Furthermore, after the removal of diseased rubber from the drying-shed, freshly prepared rubber may be hung on the same supports without becoming affected, and without any intermediate treatment of the wooden bars, providing the crepe is thin and weather conditions are good. In our experience, no case has been observed in which the disease has been communicated to freshly prepared rubber by reason of the previous presence of affected rubber. In our opinion, therefore, any scheme for disinfecting the interior of a drying-house, as a preventive measure against the spread of “spot” disease, is unnecessary.

All other things being equal, it is plain that much will depend, as to the incidence of coloured spots, upon the design and situation of the drying-house. Sufficient has been written in previous chapters to indicate the importance of these points as affecting the rate of drying, upon which hinges the possibility of the appearance of “spot” disease.In conclusion, the chief points in any discussion of this subject may be summarised thus:

1. No coagulum should be left without working for longer than the ordinary period. Otherwise, the prevailing conditions are very favourable for the development of the disease.

2. Thin crepe only should be made. The quicker the rate of drying the less possibility is there of the coloured spots appearing.

3. Crepe should never be allowed to remain folded overnight, and batches of folded wet crepe should be placed on edge to drain off surface moisture. The rubber should be hung to dry as soon as possible.

4. Several species of fungi causing coloured spots have been recognised, and it has been proved conclusively that it is possible to infect latex and also fresh coagulum.

5. As far as our present knowledge goes, it appears that infection takes place chiefly, if not entirely, by means of the latex in the field-vessels. It may take place during transport also, or even during coagulation.

6. While it is certain that infection can be caused by contact, it has not yet been shown that infection of the finished wet rubber takes place in the drying-houses by means of air-borne spores—at least, under ordinary drying conditions.7. There is reason to believe that no further infection takes place once the rubber is well into the drying stage, and that dry rubber is not infected even by contact. From this one might infer that, as long as rubber remains dry, infection cannot take place during the voyage to the port of consignment.

8. Coloured spots do not appear until the rubber is about half dry, because that period is necessary for the development of the fungus to that stage in its life-history when it excretes colouring matter. The fungus in its earlier and colourless stage may have been present from the time the latex entered the cup.

9. The natural habitat of the fungi would appear to be decaying vegetable matter in the field.

10. Finally, if it is found impossible to be rid of fungoid-spot disease after having exercised all care and observed all known precautions, nothing remains but to supersede the ordinary drying process by some system of quick drying, such as the vacuum-drying process or a hot-air draught system, in which the rubber dries so quickly that any possibility of appearance of “spots” is entirely removed.