Percolation

It is the slow movement of the menstruum through the drug to be extracted.

It is downward displacement of the saturated solution formed in maceration and extraction of the
remaining active constituents present in the drug by the slow passage of menstruum through the
column of drug.
Percolators.

Three types of percolators are generally used,

i) Conical percolator
ii) Cylindrical percolator
iii) Steam jacketed percolator

i) Conical percolator:
This is made of glass or of metal, usually copper, which is tinned inside.
It is conical in shape having lower diameter not less than half of the upper
diameter.
Advantage: there are less chances of choking of conical percolator in case the
drug swells up, because a drug can slope against the wall of percolator.
Disadvantage: There is undue loss of menstruum due to evaporation because of its
bigger upper diameter.

ii) Cylindrical percolator

The percolator is cylindrical in shape i.e. upper and lower diameters are same.
These are used in case of those drugs which are difficult to get exhausted and
when there are less chances of swelling of drug after Imbibition.
When a higher concentration of alcohol or any other volatile solvents are used as
menstruum, cylindrical percolator is preferred.

iii) Steam jacketed percolator

This is used when percolation is to be carried at higher temperature, in order to
increase the solvent action of menstruum.
Here percolator is maintained at high temperature by jacketing it with steam.

Different types of Percolation Processes.

The various percolation processes used for extraction of drugs are:

1. Simple percolation or Percolation for tinctures
2. Percolation processes for concentrated preparations such as:
a. Reserve percolation process
b. Modified Percolation process
3. Continuous hot percolation or soxhelation
Various steps involved in the percolation process are:

Size reduction:
The drug to be extracted is subjected to suitable degree of size reduction, usually from
coarse powder to fine powder.

REASONS:
i) to increase the surface area of the drug exposed to the menstruum,
ii) for uniform packing of the percolator,
iii) to slow down the movement of the menstruum and
iv) to ensure complete exhaustion of the drug.
Imbibition:
During Imbibition the powdered drug is moistened with a suitable amount of menstruum and
allowed to stand for four hours in a closed vessel. During this period the drug swells up as the
menstruum penetrates the cell walls.

This is done in order-

1. to allow swelling of tissues of drug before packing in percolator. If the drug is packed in
dry state subsequent swelling will choke the percolator,
2. to allow entrapped air to escape which will otherwise disturb the packing of the
percolator
3. Uniform packing of percolator. If dry drug is packed it may cause the fine particles to be
washed out of the percolator during percolation.
The quaintly of menstruum to be used for moistening of drug depends upon swelling
power of the drug. Generally, half the number of mls of the menstruum is used as the
number of grams of the drugs to be extracted.
The best way to check the proper moistening of drug is to press the drug lightly and see if
it can retain impression or not.
Packing:
After Imbibition the moistened drug is evenly packed into the percolator.
• Before packing, the imbibed drug is passed through sieve to break any lump or masses.
• Glass wool previously moistened with menstruum is placed on the bottom of the
percolator. This is done to prevent blockage of the outlet or tap.
• The moistened drug is then added, a little at a time into the percolator and pressed lightly
after each addition till whole of the drug is packed into the percolator.
The packing should not be too tight, it will lead to slow extraction rate. Similarly, loose
packing will allow the menstruum to pass through quickly resulting in incomplete contact
with the drug.
The drug should occupy 2/3rd capacity of the percolator.
• After packing, a piece of filter paper is placed over top of the packed drug bed. Washed
sand is placed on the filter paper.
• This is done to prevent disturbance of the top layer of packed material when menstruum
is added into the percolator.
Maceration:
After packing sufficient menstruum is added to saturate the material. When the liquid begins to
drip from the bottom of the percolator, the tap fitted at its bottom is closed. More menstruum is
added if required, so that a shallow layer of menstruum is maintained over the drug bed.
The percolator is allowed to stand for 24 hours to macerate the drug.

During this 24 hrs period of maceration, the menstruum penetrates into tissues of drugs and
dissolves the active constituents.
A short maceration before percolation enables the extraction of active constituents of the drug
with a considerably less quantity of menstruum.

Percolation:
After 24 hours maceration, the lower tap is opened and liquid collected therein is allowed to drip
slowly at a controlled rate until 3/4th volume of the finished product is obtained. The rate of
collection of percolate is 10-30 drops per minute.
Sufficient amount of menstruum is simultaneously added over the drug because at no time
packed material should be allowed to become dry.
After collecting 3/4th volume, the percolate is tested for complete exhaustion of the drug by
various tests.
Tests to check complete exhaustion of the drug:
i) Take a few ml of the last percolate and evaporate to dryness, it no residue remains - it shows
that the drug is completely exhausted.
ii) The specific gravity of last few ml of percolate is measured. If it is equal to the specific
gravity of the fresh menstruum the exhaustion is taken to be complete.
iii) Specific chemical tests may be performed on the percolate for the drugs containing alkaloids,
glycosides, tannins, resins or bitter constituents.

The marc is then pressed and the expressed liquid is added to the already collected percolate.
More menstruum is added to produce the required volume.
The liquid is then allowed to stand to settle the suspended particles, decanted or clarified by
filtration.

Examples:
i) Tincture of belladonna
ii) Compound tincture of cardamom
iii) Strong tincture of ginger etc.