Anomalies in some properties of powder mixtures.

Mixtures of lactose and paracetamol and of lactose and oxytetracycline exhibit anomalous properties. The mean particle sizes, tensile strengths and flow properties of the mixtures are not proportionally intermediate between those of the constituents. The results are ascribed to changes that occur in the packing arrangements of the particles. These changes could have practical consequences in monitoring the progress of a mixing operation by measuring apparent particle size and in controlling the properties of granules, capsules and tablets prepared from the mixtures.