e rather dark in colour owing to the natural oxidation which followed. Then it was discovered that by diluting the latex the degree of oxidation was diminished, and later it

hat the pale biscuits were not in any way superior to the

e reverse of pleasant. Even when dry the sheets had to be continually brushed free from moulds, and by the time the rubber reached the market it was again usually mouldy. Such are, eve

matter of fact, although the preliminary operations certainly do demand more care and labour than in crepe-making, there are compensating advantages in the machining stage. For the preparatio

nd latex in each individual dish, and in some small or non-progressive factories that is still the procedure. Quite apart from the question of labour entailed, the process is quite unnecessary. Even if comparatively small volumes of latex are handled, stand

actice with the employment of shallow coagulating tanks has simplified working and reduced the cost of labour. It is not intended to enter into any lengthy discussion relative to the merits of sheets made in pans as against those made in tanks. It is granted that it is po

coagulating tanks must be regarded as merely temporary devic

he result of experience the size of units has now been

oagulating Ta

glazed tiles. Note slots incorporated in side ti

keep clean and in "sweet" condition. The glazed tiles, unless extremely well laid, allow the acid serum (from which the rubber is removed) to percolate between the interst

Tanks, with Dilut

he R

cks, chute, and

ate and side-pieces necessary in the lining of a tank. If such adjuncts could be secured, the disabilities indicated above wo

t could measure (internally) 6 feet by 4 feet by 1 foot deep, with slots 11?2 inches apart, and 3?8 inch in width. The tanks might be reinforced with iron bars, so that they could either be used alone or emb

iew of F

position and coag

enerally employed in smaller factories, or where future large increases of crop preclude the present installati

on of coagulating tanks, we can do no better than offer r

the construction of coagulating tanks, wooden partitions are employed. In the few exceptional cases the partitions are either of glass or of aluminium. The f

ks, but the necessary slots were very ingeniously created by means of aluminium "distance-pieces," the two long edges of which were turned at right angles to the face of each piece to a depth of about 1?4 inch. The ends of the thin aluminium partition moved in the slot thus formed between t

hence various measures have been tried with that object in view. When new the boards have been surface-waxed or varnished, and the treatment has been repeated on occasions. But in course of time the surface film of waterproof material has disappeared, partially or wholl

Tanks, without Dilu

itating

en partitions should receive the same treatment, and once a week at least (or every day if possible) they should be placed in the sun for an hour or two, car

the matter out of the question, but it is possible now that such a material would be worthy of extended trial. Except in the matter of cost, it would appear to have

containing Coa

arat

x is standardized. Note vent, to the left, through wh

ted daily to a level of dry rubber content. Whatever may be the practice elsewhere, it is now fairly general on estates in Malaya to reduce all

s taken difficulties arise, such as (1) unsatisfactory and uneven coagulation, (2) too thick a coagulum for easy workin

heeting Tanks (P

ks, Raised,

ickness of coagulum is prepared. Furthermore, over-dilution means an increase in the number of tanks required for any original volume of latex. This involves an increase in floor are

s. dry rubber per gallon. Primarily this standard has a direct connection and interdependence with the distance between the partitions (or between the slots) in coagulating tanks. The distance found mos

e have two possible ma

ons, causing visible differe

ing differences in the density (e.g.,

latex of a standard of 11?2 lbs. per gallon is employed

t is found in the experience of some estates that their requirements are satisfied by a slightly lower standard than 11?2 lbs. per gallon. Thus it is not uncommon to note the adoption of a standard equivalent to 1 lb. 4 ozs. or

sitive to indicate fairly small differences in density of latex, and has one mark on its aerial portion accurately indicating a density corresponding to the required standard. On scientific groun

Archief voor de

y consist of a submersible bulb with a projecting stem which is graduated. The "Metrolac" differs from others in that the bulb is of torpedo form (thus re

lly delicate and require careful manipulation, they are of considerable practical value and satisfy a definite requirement. Until an instr

of which may be in daily use, while the other is kept in safe custody and only employed, say, once a week for purposes of checking the accuracy or degree of inaccuracy of the other. This can be done with reasonable approximity by placing both instruments in a tall vessel containin

ubber Growers' Association are now introducing glass instruments. These are neces

instrument employed for that purpose only. This need was well recognised by many estates when, during the War and the consequent shortage of supply of "Metrolacs," a demand arose which was met in some degree by crude ins

aration. In point of fact, such calculations are not strictly necessary, as the operation of standardising the latex can be done quite simply and skilfully by a trained native. Latex as it reaches the store in average weather from any particular division or field does not vary greatly in density. The trained coolie or foreman, basing his practice on experience, adds to the latex a quantity of water, and then makes a first test wi

est removed by means of a thin board of a width slightly less than the breadth of the tank. The skimmings are sometimes placed in pans and subsequently made into a second grade of sheet rubber, or the

h this the latex percolates, while the froth is retained on a small area. The froth is removed prior to the addition of the acid. After stirring in the acid solution most estates again skim the surface of the latex; but if the stirring has been perfor

old which will do all the work required. It will be evident to anyone acquainted with rubber preparation that in the matter of actual quality of rubber the question of smoothness or a pattern can have no bearing on the result. One advantage claimed for ribbed sheet which may entirely justify the preference exhibited by consumers, relates to the question of packing. When rubber arrives at home it is frequently found to be in an almost solid block, due to

robable that the market value of the rubber is slightly increased. It is not our duty to attempt to reason why this simple operation should increase the market value of sheet rubber; it is sufficient to recognise that it is s

ern of mark, one cannot do better by way of introduction tha

of Rubber," Rubber Growers' A

x it is found that strips of coagulum 11?2 inches in thickness

g with a heavy hand-roller made of hard wood. The roller is p

he rolls fairly open, and once with a narrower space. It is not found advi

attern on the rubber. The surface of the sheet is raised in well-defined ridges, which appear to present the maximum drying surface exposed to the atmosphere of the smoke-house. Thus, not only is the appearance of the sheet rendered attractive, but also the period of dr

rubber to remain over night, and the coagulum receives attention early next morning. During the interval (averaging about eighteen hours), the coagulum consolidates, leaving an almost clear serum if the correct quantity of acid has been added to the latex. Any but the very slightest trace of m

dled next morning without any marked stretching, and in some estates the rubber is put direct thr

le the coagulum while rathe

er to work, and sheets of imp

s greater freedo

cidence of "rus

rd, it only holds provided that the rubber can be finished and placed

e working of the rubber is then commenced. As a general rule this means that the operations of rolling and marking must be completed, a short

any case it remains true that night work should be avoided if possible. If, however, it can be arranged without increasi

strips of coagulum any preliminary hand-rolling, as the rubber is con

cted on a specially constructed table. This consists essentially of an inch-thick hard-wood plank about 2 inches wider, and 4 or 5 feet longer, than the strip of coagulum. Along the edges of the pl

n the plank, they prevent the coagulu

being squashed too wide, and t

bout 6 inches long, of the same width as the table (between the edge-strips), and with the sharp end of the wedge pointing

but as long as rubber is valued on such grounds w

rocedure is to reduce the thickness of the coagulum gradually. The same could be effected, of course, on one machine; but obviously the distance between the rolls would have to be readjusted at each operation

erroneous to imagine that heavy machines (such as those used in crepe preparation) are required. Light machinery only is nece

n sheet rubber. If the rubber has been properly prepared a light pair of rolls

ogether. The last has the greatest vogue at present, while the first has almost gone out of favour. An objection lodged against the second design is that the edges of the grooves sometimes cut through the rubber, so that the dried sheet divides in strips. It would appear

varying measurements, but the usual design has groove

this is done it is advised that the main grooving of the rolls be carried into the "branding" strip; othe

are running "free," experience generally decides that the deficiency in the appearance of the rubber should be attributed to faulty previous preparation rather than to the marking rolls. Sets of rolls have been changed often without justification or an improved result. It would always be well to be certa

f the coagulum would be normal, but owing to the abnormal rubber-content the effect of passing through the smooth rolls would be the production of a strip thicker and firmer than ordinary. If

eet rubber should be at least 18 inches wide, in order to

e procedure indicated in the foregoing paragraphs, the dry sheet should

dead moulds could be seen, if not over the whole sheet, at least in the corners of each diamond mark. It has been demonstrated in practice that there is no advantage in allowing sheets to air-dry partially before smoking. In fact, t

smoke-house and subsequent to rolling. These will be enlarged upon in a subsequent section of the book, and a

e perpendicular distance between the supports in the smoke-house. It is necessary to remark that the piles of sheets should not be allowed to accumulate, but should be dealt with in subsequent treatment progressively. If for some re

ible, and given a thoroughly good swilling. The caution must be given that the hot water sho

r, but there is no reason why they should not be placed in the open air without cover or shade. From continued experience of this pr

on the surface, when exposed for, say, two hours, is nil; and the safety of the process

f "Dripping" Fre

the F

ys it would be advisable to light the fires earlier than usual, consistent with the work required to be done in the house-e.g., in the removal of dry rubber. There wou

eception of the wet rubber. The sheets are taken directly from the marking rolls and placed in the chamber, beneath which a fire is started. The sheets thus drip in a

ory to smoking the whole process should be continuous, and de

od of Hanging

on of certain patent processes. Air-dried sheets are generally made on small-holdings, and are bought in the market chiefly for the purpose of macerating and making into blanket crepe. We have no intention, therefor