Determination of phosphate was performed with lanthanum nitrate in an aqueous medium in the presence of a haematoxylin indicator. Following processing of the organic phosphorus compound in a Schoniger flask the mixture was acidified and boiled off and then the pH was adjusted to 6.1–6.3 with hexamethylene tetramine. The hot solution was titrated with lanthanum nitrate. The orange colour of haematoxylin changed to violet-blue at the point of equivalence, while precipitation of lanthanum phosphate was observed.