Alum.—This substance has been used for years by native rubber producers as a coagulant. It fulfils the desired purpose, and its popularity was maintained because of the ease with which it could be stored and handled. Unfortunately, this facility often led to the use of an excess, and native sheets were often criticised as being brittle. Investigations have shown that alum, even in minimum proportions, has an appreciably harmful effect upon the quality of the rubber prepared by its use as a coagulating agent. Its employment by native rubber producers has now been largely superseded by acetic acid in some form.
Pyroligneous Acid.—This is otherwise known under the names of “crude acetic acid” and “crude wood vinegar.” Owing to the shortage of acetic acid during the War, attention was directed towards the possibility of making an effective coagulant locally by what is termed the “dry distillation of wood“—i.e., the wood is not burned but heated in a retort. The enquiries could be placed in two classes:
1. Those which aimed at making the pure, strong acid of commerce.
2. Those which sought information concerning a crude coagulant (pyroligneous acid) on estates.
Regarding the first class, we can do no better than reproduce our remarks published in the April local report of the Rubber Growers’ Association for 1916—with the reservation that, on account of a threatened shortage of timber, a local scheme might not now be feasible:
“Probably the most common enquiry encountered since the rise in the price of acetic acid is concerned with the possibility of making acetic acid in this country. It may be stated that the proposition is a feasible one, even on a fairly large scale. We have the essentials necessary for such a scheme in:
“1. A good supply of suitable timbers, the most valuable of which, possibly, is mangrove timber, locally known as ’bakau.’ Other suitable timbers are known, but as far as preliminary experiments show mangrove timber gives the best yield. At present this timber is in great demand as a fuel for steam plants, but with the extension of the local coal industry the timber may become cheaper.
“2. There would appear to be less valuable timber which would be suitable for heating the retorts. Or, local coal might be used.
“3. Supplies of lime at reasonable rates are available, as the limestone formation in the peninsula is quite considerable in extent.
“4. Supplies of sulphuric acid are available from Japan, Australia, Burma, etc., even at the present time, although naturally rates are higher than normal. Under ordinary conditions, supplies from England and parts of Europe would be much cheaper than at current rates.