scope:

This method of test is applicable only to asphaltic products derived from petroleum and should not be applied to natural asphalts containing nonbituminous matter insoluble in xylene.

Materials, which by use of standard solvent are classed as positive, may be further tested to determine their degree of positiveness by means of their "xylene equivalent." The xylene equivalent shall be the lowest percentage by volume of xylene in a solvent composed of xylene and standard naphtha or xylene and normal heptane, as specified, that produces a "negative spot" for the material in question. These shall be known as the "naphtha-xylene equivalent" and "heptane-xylene equivalent," respectively. The percentage of xylene in the solvents shall be stated in even 5.0 percent increments. When neither xylene equivalent is specified, the standard naphtha only shall be used as the solvent.

The values stated in SI units are to be regarded as the standard.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

The quality of the results produced by this standard are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of R 18 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with R 18 alone does not completely assure reliable results. Reliable results depend on many factors; following the suggestions of R 18 or some similar acceptable guideline provides a means of evaluating and controlling some of those factors.