A. Silicate

IN a previous publication the solubility of silicate and zinc phosphate cements in dilute organic acids, of varying pH, has been reported. ' This research has been continued to include certain materials not previously studied and to determine the effect of additional variables on the solubility of silicate cement. The procedure was the same as that employed in the earlier investigation.' Discs of the particular material were suspended in distilled water and buffered dilute acids for varying periods of time. Generally only those media were used which had been found previously to be the most deleterious: acetic acid, pH 4.0; citric acid, pH 4.0; and lactic acid, pH 4.0. Distilled water, pH 6.0, was also included since this is the common laboratory test medium employed.in cement solubility tests. As in the former study, the organic acids were 0.001 M solutions buffered with their sodium salts. The storage times were 24 hours and 1 week in the same solution and 1 week with the solutions being changed daily, although some tests were also run with silicate over a 28-day period. A minimum of four specimens were used for each set of conditions and the mean values are presented. The solubility of individual specimen