The following procedure shall be used to determine the concentration of magnetic particles and to check for
the accumulation of dirt or other contaminants in a suspension. The equipment required is a 100 cubic
centimeter (cc) or 100 milliliter (ml) pear-shaped, graduated centrifuge tube and stand (see Figure 3-33).
Filling Centrifuge Tube from Hose
Thoroughly agitate the suspension.
Run suspension through the hose and nozzle for at least 1 minute. This is to assure the suspension in
the hose is fresh and agitated.
Fill the 100 cc (100 ml) centrifuge tube with agitated suspension using the hose.
Demagnetize the suspension in the tube to reduce clumping.
Place the centrifuge tube in its nonferromagnetic stand and allow settling on a vibration free surface
for 1 hour for oil baths and 30 minutes for water baths. Inspections or Process Control Inspections
CANNOT BE ACCOMPLISHED prior to the full 1 hour time limit. The suspension concentration
must be within T.O. limits prior to use.
Observe the total level of settled particles at the end of the settling period. The graduated cylinder
reads directly in milliliters. The level of contaminants must be subtracted from the total level to
obtain the concentration of particles (see paragraph 18.104.22.168.3).