On mixing indices

The current efforts at the National Bureau of Standards to produce a standard reference material (SRM)_for accurate size and concentration measurements in fine particle technology are discussed. Two batches of latex spheres are being characterized as calibration materials for “flow-through” particle counters. The criteria for selecting these materials, and the choice of the packaging techniques are described. The methods of measuring the size of the particles, which will be furnished in aqueous suspension, are discussed along with the measurement data.