Summary Results are reported on the action of 5% solutions of ammonium salts on a Portland, a Portland-pozzolana, and a high alumina cement concrete. Ammonium chloride and nitrate solutions had a strong leaching action, acting as dilute acids owing to loss of ammonia by reaction with lime. Strengths of concrete cubes with all three cements fell by at least a half in four years without outward signs of deterioration. Analysis of the specimens showed large reductions in the lime content of the cements. In the action of ammonium sulphate on Portland cement, the expansion caused by formation of calcium sulpho-aluminate is dominant. High alumina cement was unaffected by ammonium sulphate.

Existing data on the conductivity of calcium hydroxide solutions a t 25" show dish'ew data are given which confirm ccrtain of the previously published Values of p , for calcium hydroxidc solutions a t 25" are also given and com-crepancies. results. pared with the only other available data, those of Flint and Wells a t 30".

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