1-11. METHODS OF COMMINUTION
Comminution is a broad term that includes several methods or processes of
accomplishing reduction in particle size. Pulverization is the reduction of a substance to
a powder. Several methods used to comminute solids follow:
a. Trituration. Trituration is the process of reducing the particle size of a
substance by rubbing it in a mortar with a pestle. Trituration is also a correct term for
the intimate mixing of two or more powders together, the rubbing of light, fluffy powders
into heavier, denser, and more compact composition. In either sense of its use,
trituration is more than a grinding or mixing. It is a technique widely used in pharmacy.
Trituration is a crushing-mixing process, accomplished with circular motion of the pestle
(1) Technique. To properly triturate a substance and ensure best
pulverization and intimate mixing, you should use the following technique:
(a) Place the substance to be comminuted, thoroughly mixed, or
defluffed in the mortar.
(b) Start at the center of the mortar, with downward pressure on the
pestle and a circular motion of very small diameter; rub the substance between the
pestle and the mortar. Gradually increase the diameter of the circles until you reach the
side of the mortar and then decrease the diameter of the circles gradually until the
center is again reached.
(c) Scrape the powder frequently with a spatula from the sides of the
mortar and from the bottom of the pestle.
(d) Continue the trituration until the desired comminution is attained or
until the powders are thoroughly mixed.
Types of mortars.
(a) Wedgewood mortars. Wedgewood mortars are most commonly
used for trituration because their rough surface aids in the rubbing. They are difficult to
keep clean, however, because of their porous surface. Dyes must never be triturated in
a wedgewood mortar as the color will become permanently affixed to the vessel and
threaten future powders.
(b) Glass mortars. Glass mortars are preferred for comminuting
substances that stain and for dissolving granular or crystalline substances that require
rubbing to aid in their solution.