A Critical Study of the Determination of Total Dissolved Solids and Loss on Ignition in Water Analysis

The determination of total solids is one of the oldest determinations made in water analysis and has apparently always been taken to represent the amount of material in the water. In a great many analyses this determination includes both suspended and dissolved materials while in others the sample was first filtered so that the results give only the material in solution. The "loss on ignition" has frequently been taken as a measure of the organic matter in water, and the residue after ignition, or fixed residue, as a measure of the mineral matter in solution.Comparison of reported determinations of total solids and "loss on ignition" with the results of analysis of the actual mineral content indicates that in many the figures for total solids and for "loss on ignition" have no real significance. This paper presents the results of a study based on analyses made in the Water Resources Laboratory of the United States Geological Survey of about 850 natural waters, to determine the reasons for the differences reported. In addition, residues from about 300 of these waters were heated at different temperatures and for varied time periods.