It was found also as time progressed that sheet rubber, on air-drying, became covered with external surface moulds, and that, more often than not, the smell of the drying rubber was the 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, even now, the handicaps under which those who prepare pale sheets have to labour. Few, however, are the estates making pale sheets, and they are confined almost entirely to native holdings.

To those accustomed only to the preparation of crepe rubber, where coagulation can be effected in large batches, the preparation of sheet rubber always seems to demand much more labour. As a 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 preparation of sheet of the highest quality on any but the largest scale, elaborate installations of machinery are quite superfluous, as equal results can be obtained with pairs of rolls worked by hand.

Uniformity of Product.—There will be no need to enter again into a discussion of the preliminary operations of receiving and straining latex for sheet-making. They have been fully dealt with in [Chapter VII]. It used to be the general custom to mix the acid and 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, standardisation by dilution should be the rule, and the acid solution should be added to the bulk. It is possible to stir in the acid and to ladle out uniform quantities in each pan or dish from a bulk volume of up to 40 gallons if the organisation is efficient.

On any but a small scale the labour entailed in the handling and cleaning of pans is excessive, and shallow tanks are now employed on most estates. The reception and standardisation of latex by dilution has already been discussed in [Chapter VII]. The combination of this practice 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 possible to make a “pan” sheet superior in appearance to the general average of “tank” sheets; but from an economic standpoint the introduction of the use of tanks into all but the smallest factories is only a matter of time, if the demand for this class of rubber persists.

The Ideal Tank.—Even the most modern installations of sheet-coagulating tanks must be regarded as merely temporary devices, as, given facilities, the room for improvement is so wide.

The first tanks made erred in being too large, and as the result of experience the size of units has now been reduced to a maximum of 12 feet by 4 feet by 1 foot deep.

Unit Modern Coagulating Tank (Two Views).
Construction of brick and cement with lining of glazed tiles. Noteslots incorporated in side tiles. Partition boards in piles in thebackground.

Tanks are at present constructed either of hard timber or of brick and cement faced with glazed tiles; both types have inherent drawbacks. The wooden tanks are difficult to 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 interstices. Thus “pockets” of liquid collect beneath the tiles, and in process of the decomposition of certain constituents dissolved in the serum evil-smelling gases are set free.