Certain few estates, however, have continued its use, and no trouble is claimed to ensue. The following formula is stated to give satisfactory results in the preparation of sheet rubber, when applied as in the preceding paragraphs bearing on the employment of sodium sulphite:
Formula for Use of Formalin (Formaldehyde).
(a) 1 pint of formalin is diluted with 5 gallons of water.
(b) Of this solution 1 gallon is required for 50 gallons of standardised latex.
In noting this formula the writer gives no recommendation regarding its use. Whatever may be the actual facts regarding the effect of formalin upon the vulcanisation of rubber, when used in minimum proportions, there can be no question concerning its injurious effect if used in excess. Beyond this the factors of cost and loss militate against its wider employment.
CHAPTER IX
PREPARATION OF SHEET RUBBER
Pale Sheet.—The first form in which plantation rubber was prepared was as “biscuits” or sheets. This form remained in favour for some years. The first biscuits or sheets were rather dark in colour owing to the natural oxidation which followed. Then it was discovered that by diluting the latex the degree of oxidation was diminished, and later it was found that if the soft coagulum were placed in almost boiling water for a short time the resulting rubber was pale. Thus there arose gradually a demand for pale sheet. With our present knowledge we are in a position to state that the pale biscuits were not in any way superior to the darker ones, and they were in most cases actually inferior.