MT 42 - Particle size of copper and sulphur products
Content Handbook F
Outline of method
The method is based on the rate of settling of particles in suspension in a liquid of known viscosity. A suspension of the sample is successively decanted into a series of beakers. A cumulative curve of particle size is constructed.
42.1 Formulations without carriers
The sample is made into a suspension of unit particles. This is then successively decanted into a series of beakers.
42.2 Formulations containing carriers
A suspension is successively decanted as in MT 42.1. Separate determinations of the total weight (active ingredient plus carrier) and the active ingredient for each successive deposit are made.
These determinations give the particle size of the active ingredient and also that of the carrier.
The method is intended for determining the particle size of water insoluble copper compounds and 'micronized' sulphur products.
For the method to give correct results, a number of conditions must be fulfilled.
(i) All determinations must be carried out at the same temperature or, if this is not possible, the results should be corrected to a common temperature, ± 2°C, unless otherwise specified.
(ii) The particles must be in discrete form. The suspension, therefore, must be prepared in such a manner that neither agglomeration nor coagulation occurs.
(iii) The procedure is only valid for samples containing particles of the same nature and density.
(iv) The particles must be totally insoluble in the dispersing fluid.
(v) The particles must be nearly spherical, that is to say, there must not be a disproportionate difference in their three dimensions. It is assumed that this condition is fulfilled for simple inorganic copper compounds and sulphur powders.
(vi) The concentration of particles in the liquid must be small, so that their rate of fall is not affected by neighbouring particles.