b. These processes have already been discussed and will not be reviewed here.
Besides, the use of heat to separate substances, precipitation, filtration, and collation
may also be used.
Precipitation is the process of separating, by physical or chemical change, solid
particles from a previously clear liquid. The separated solid is called the precipitate; the
causative agent, the precipitant; and the liquid that remains in the vessel above the
precipitate, the supernatant liquid. A precipitate may, because it is less dense, float to
the top instead of settling to the bottom. Crystallization is a type of precipitation in that
the precipitate takes on a crystalline structure. That is to say, the solid formed has
definite structure. Granulation, or the production of fine crystals, is a disturbed or
interrupted crystallization. Large crystals are prevented from forming by constant
agitation during the cooling. Instead of a single mass being formed, a fine granular
a. Filtration is a process for separating suspended or sedimental solid material.
A porous barrier made of paper, sand, charcoal, or other insoluble material allows the
liquid to pass, but prevents the solid from moving with the liquid. Medications must be
filtered before dispensing under the following circumstances:
Undissolved material is present in the solution.
The solution to be dispensed is cloudy.
Sometimes the active ingredients in a solution will hasten or "fall-out" of
solution. Thus, filtering the solution will remove the undissolved material or
cloudiness; however, that material is the drug the physician wanted the
patient to receive. When you see undissolved material in a solution that has
been supplied to you, you should seek the assistance of someone (that is, a
pharmacy officer to determine the wisdom of using a particular solution.
b. The usual filtering apparatus in the pharmacy consists of filter paper and a
glass funnel. The funnel may be either smooth or ribbed glass. The ribbed funnel
hastens the filtration process by providing a passageway for the liquid.