EXPRESSION OF CONTENT

In defining content, the expression "per cent" is used according to circumstances with one of two meanings:
per cent m/m (percentage, mass in mass) expresses the number of grams of substance in 100 grams of final product.
per cent V/V (percentage, volume in volume) expresses the number of millilitres of substance in 100 millilitres of final product.
The expression "parts per million (ppm)" refers to mass in mass, unless otherwise specified.