COMMUNICATION OF THE GENERAL EXPERIMENT STATION OF THE A.V.R.O.S
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RUBBER SERIES No. 31
ON THE URGENCY OF WASHING
FRESHLY PREPARED SHEETS IN STREAMING WATER
by
IR. JHR. F. C. VAN HEURN.
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When rubber prices fall brokers and traders in rubber become more discriminating. Minimal defects in the appearance of rubber, small deviations from the normal, to which no attention is paid under ordinary circumstances are now enlarged to serious grievances. If the planter wishes to suffer no loss he has to redouble his activity in order to be sure that nothing might be claimed against his rubber.
An example may be seen in the following:
When looking over a collection of sheet samples and cutting them, some of the thicker ones will be found to have a white or a light coloured stripe in the cross sectional area. This phenomenon is very common and known in the rubbertrade. Though many judged it to be of no significance and it was often overlooked, sometimes it was observed, especially since it is associated with a lack of transparency of the sheets. This phenomenon was characterized, often in trade, by more or less phantastic names such as "immature" or "undercured". To more initiated persons it is known to be due to the presence of moisture in the rubber. The development of this stripe can be described as follows:
The drying process of sheets takes place in the smoke houses. The outer surfaces of the sheets will dry first and become transparent.
In the middle a nontransparent water containing area remains and if sheets in that state are cut they show the white stripe in a high degree. Gradually the water will evaporate until in normal cases no water will remain. The stripe gets smaller and fainter and finally disappears.
Microscopical examination shows no condensation drops in the stripe. It is evident that when such samples were sent to the Proofstation the diagnosis was: "Insufficiently dried, either by working off the sheets too thick or due to the inefficiency dried, either by working off the sheets too thick or due to the inefficiency of the smoke house". From what follows it has appeared to us that this judgement cannot have been always reasonable. In order to prove the statement mentioned above we returned a part of the original sample, that had been fully dried by us in a stove and in which the stripe had disappeared.
Nevertheless some time ago Mr. VAN ALTENA, Secretary of the S. I. P. E. F. drew our attention to the fact that the stripe, which had disappeared by heating the rubber in a stove, came back within a few days and that the same phenomenon had been observed on one of the
