text: The volume concentration  (not to be confused with volume fraction) is defined as the volume of a constituent  divided by the volume of the mixture :
  Being dimensionless, it is expressed as a number, e.g., 0.18 or 18%; its unit is 1.
  There seems to be no standard notation in the English literature.
  The letter  used here is normative in German literature (see Volumenkonzentration).