Section VI. PERCENTAGE SOLUTIONS
a. Variable Meaning of Percentage.
(1) The word percentage can have different meanings under different
circumstances. In solution, we are dealing with solids that are weighed and liquids that
can be weighed or measured; thus, it is necessary to define the expression of age
concentration of solutions. There are three different percentage solutions.
(a) Percentage weight in weight (w/w)--expresses the number of grams
of solute in 100 ml of solution.
(b) Percentage weight in volume (w/v)--expresses the number of grams
of solute in 100 ml of solution, regardless of whether water or another liquid is used as
the solvent. Table 1-11 is helpful in preparing weight-in-volume solutions.
(c) Percentage volume in volume (v/v)--expresses the number of
milliliters of solute in 100 ml of solution.
(2) The strength of a certain solution expressed in one of the ways is likely to
be different from the strength expressed another way. It is therefore important to know
whether a particular desired percentage strength for a prescription is w/w, w/v, or v/v.
Some helpful rules are given below.
b. Rules for Percentage Solutions.
(1) Unless specifically stipulated otherwise, the following rules hold true for
(a) Mixtures of solids are weight in weight (w/w).
(b) Solids in liquids are weight in volume (w/v).
(c) Liquids in liquids are volume in volume (v/v).
(d) Gases in liquids are weight in volume (w/v).
(2) For example, to make a 10 percent solution, dissolve 10 gm of a solid or
10 ml of a liquid in the amount of solvent necessary to make 100 ml of finished solution.
c. Ratio Strengths. Often the strength of a preparation, particularly the
strength of a weak solution, may be expressed in terms of a ratio. Ratio strengths are
also volume in volume (v/v), weight in weight (w/w), or weight in volume (w/v).