[25] See also “Preparation and Vulcanisation of Plantation Rubber” (Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture, April, 1918.
With this provision the crude pyroligneous acid which can be produced on estates, could be employed as a coagulant until such time as the price of glacial acetic acid was so low as to make the production of the crude acid non-profitable. This point would be determined from a knowledge of the cost of production per gallon, and the percentage of acetic acid per unit. For example, if the cost of production (including cost of timber for distillation, cost of fuel for heating the retort, cost of labour, etc.) was 60 cents per gallon of crude acid containing 9 per cent. of acetic acid, that would be equivalent approximately to buying glacial acetic acid at $30 per demijohn of 44 lbs.
Smoked Water.—A weak solution of pyroligneous acid may also be obtained by passing smoke through water. With this object in view, a machine was designed by the Federated Engineering Company of Kuala Lumpur. In this the principle of retorting was not employed. Smoke was produced by ordinary combustion in a compartment of the apparatus, and was drawn through water by the action of a high-speed fan worked by hand. A solution, equivalent in effect to a 2 per cent. solution of acetic acid, could be obtained at a comparatively cheaper cost than crude pyroligneous acid produced by dry distillation as it was then being practised. This was chiefly because of the wasteful methods of fuel combustion, in the latter process, in the heating of the retort.
Chinese Vinegar.—This agent was found to be a satisfactory coagulant, and, a priori, there is no reason why it should not be suitable, as it is essentially a dilute solution of acetic acid.
The qualities sold were generally colourless, and were probably the result of acetic fermentation of rice.
Samples tested showed a varying content of acetic acid, ranging roughly from 3 per cent. to 8 per cent.; but on this basis of valuation it was found generally that the price bore no relation to the degree of efficiency.
It was advanced not only that the vinegar was an efficient substitute for glacial acetic acid, but that it was also cheaper. This latter claim was proved to have no foundation in fact, even at the high price of acetic acid prevailing during the period of stress. It is not likely, therefore, that vinegar can displace acetic acid, except as an expedient.
Sulphurous Acid.—The anti-oxidant effect of sodium bisulphite and sodium sulphite is due to the liberation of the gas, sulphur dioxide. This gas dissolves easily in water, forming an acid solution called sulphurous acid.
This acid solution is an effective coagulant in fairly small quantity. Not only so, but it produces, in addition, the anti-oxidant effect noted in the employment of sodium bisulphite. It is thus possible to produce rubber varying in shade of paleness by means of a single solution.