Standardisation of Latex.—The question of the standardisation of latex has been dealt with in a general way in [Chapter VII.], and the reader is now familiar with the trend of the argument in its favour. It will be recognised that the necessity for standardisation exists to the same degree in the correct preparation of pale crepe as in the case of smoked sheet. Unless the dry rubber content is invariable, and the quantities of chemicals fixed, the colour of the crepe may vary appreciably.
It may be pointed out that it is not essential to adopt the same standard of dilution as for sheet preparation. Given that latices from all fields or divisions are fairly uniform, and of high rubber content, the standard may be taken at a figure equivalent, for example, to 2 lbs., or 21⁄2 lbs., or even 3 lbs. per gallon. It is wise, nevertheless, to take a lower standard for several reasons. For instance:
(a) The average dry rubber content varies with climatic conditions, position of the cut on the tree, general health of the tree, etc. On a rainy day the dry rubber content may be lowered too greatly by adventitious circumstances.
(b) Recording instruments often fail to give even approximately correct readings in rich latex. Errors may thus be made easily.
(c) A fairly soft coagulum means easier working on the machines, less labour, and proportionately cheaper costs.
Three Grades of Crepe Rubber.
Left to right: fine pale crepe; second quality pale crepe; compound crepe.
It is advised, therefore, that for general purposes the same standard as that found suitable for sheet rubber should be taken—viz., 11⁄2 lbs. dry rubber per gallon. At all events the standard should not exceed 2 lbs. per gallon.