Mix the red phosphorus thoroughly and
weigh a 5 gram sample into a 250 ml. beaker.
Add approximately 200 ml.
of dispersing solution and mix with a stirring rod for 2 minutes.
to the cylinder of the Andreasen pipet apparatus and wash all the
material from the beaker into the cylinder with dispersing solution
contained in a wash bottle.
Add sufficient dispersing solution to the
cylinder so that the level is at the 20 cm. mark when the pipet is in
Close the vent hole of the apparatus and shake thoroughly for 5
Place in a constant temperature bath at
and record the
At the end of 46 minutes, open the vent hole, and draw up
10 ml, of liquid into the pipet by applying gentle suction.
Turn the 3-way stopcock and
stopcock when the 10 ml. mark is reached.
drain off the solution from the pipet into a tared 15 ml. sintered glass
Rinse the pipet with dispersing solution
crucible of fine porosity.
contained in a wash bottle and collect the rinsings in the crucible.
Place the crucible in a suction apparatus, turn on the suction, allow
to drain, and wash several times with water.
Dry in a vacuum oven at
for 3 hours, cool, and weigh.
Calculate the percent of particles
of less than 10 microns as follows:
P = percent of particles of less than 10 microns
R = grams of residue in crucible
V = volume of cylinder (to 20 cm. mark) in ml.
W = grams of red phosphorus in cylinder