1. INTRODUCTION

Nephelometry and turbidimetry are based on the direct (nephelometry) or indirect (turbidimetry) measurement of the scattered light intensity of an incident light beam from a monochromatic light source. In the rate nephelometry technique, the change of the scattered light intensity is measured as a function of time. Turbidimetry or nephelometry may be useful for the measurement of precipitates formed by the interaction of highly dilute solutions of reagents or other particulate matter such as suspensions of bacterial cells. All variables must be carefully controlled to achieve consistent results. Where such control is possible, extremely dilute suspensions may be measured.