The material to be examined should be a pulp.
Procedure for use:
Mix a small quantity with water until the solids of the diluted pulp are between 8.37% and 9.37%. This corresponds to an Abbe refractometer reading at 20°C of 1.3460.
Spread a small drop of the well‐mixed sample with the end of a glass rod over the counting chamber.
Place the cover glass on to the counting chamber and carefully press down the shoulder of the chamber until Newton's rings are visible.
Note: Prepared samples containing air bubbles beneath the cover glass or an over‐full moat should be discarded.
If using a compound microscope, examine using the X10 eyepiece and the X10 objective.
Systematically examine all 25 fields and note those with a presence or absence of mould filaments (hyphae).
A field is regarded as positive if the aggregate length of not more than three filaments present exceed one sixth of the diameter of the field.
This is a general description of how a Howard Cell is used. The results are interpreted as a percentage of positive fields observed in all the fields examined.
Precise interpretation of the results is made by a statistical analysis of the sample and should be carried out in accordance with your own internal or published procedures.
