[3] “The Employment of Sodium Bisulphite in the Preparation of Plantation Rubber,” Beadle, Stevens, and Morgan, India-rubber Journal, August 2, 1913.
As long as such conditions prevail estates must continue to adopt any device of proved harmlessness, in order to obtain the best possible price for their product, and not because we desire to continue a practice which some assure us to be unnecessary, and which, moreover, adds somewhat to the cost of production.
Quantities of Sodium Bisulphite.—It must be premised that, although sodium bisulphite is employed on some few estates in the preparation of sheet rubber, we do not advise the practice. It is unnecessary, and may lead to some little trouble and delay in drying. In any case, sodium sulphite gives the results desired for sheet rubber (see [following]). It must be understood, therefore, that we are concerned here, in the case of sodium bisulphite, with its employment in the preparation of fine pale crepe only.
As the dry rubber contents of latices vary with the age of the trees, the general health of the trees, the seasons and general climatic conditions, the relative strain imposed by depletion of reserves through tapping, etc., it will be clear that the effect produced by a definite quantity of sodium bisulphite in any given volume of latex will also vary—i.e., the effect depends upon the potential amount of rubber present. A dilute latex needs less sodium bisulphite than a richer latex to produce the same effect in colour.[4]
[4] Incidentally there are certain occasions, as in the opening of areas of bark rested for long periods, when the latex is of a rich yellow colour. Sodium bisulphite will not “bleach” this colour, and it is well to remark again at this stage that the action of the chemical is only to avoid or arrest oxidation (darkening).
Hence it follows that if in any factory uniform quantities of the solution are used for any given volume of undiluted latices from different areas of the estate, the effect upon the dry rubbers will vary. This explains why some estates obtain different shades of rubber in their fine pale crepes.
The remedy obviously is to reduce the variation in latices by diluting them all to a standard rubber content as is done in sheet preparation. One is thus assured that the prescribed quantities of sodium bisulphite will meet requirements in every case, and that waste will be avoided.
Working with a standard of 11⁄2 lbs. dry rubber per gallon the following formula should serve as a maximum:
Formula for Use of Sodium Bisulphite.
(a) Dissolve sodium bisulphite in water at the rate of 1 lb. to 10 gallons.