Abstract
The factors influencing the hydrolysis of condensed phosphates to ortho‐phosphates in waste waters are considered. If accurate estimations of the relative concentrations of orthophosphate and condensed phosphates are required the samples must be analysed immediately, unless they can be stored without further hydrolysis. The use of mercuric chloride and formaldehyde as preservatives at normal pH and pH 10 in filtered and unfiltered samples has been examined. Mercuric chloride, in filtered samples, without adjustment of the pH was found to be the most satisfactory treatment.