The interior walls of the gate-houses of the Croton Reservoir in Central Park, New York, have been successfully treated according to the Sylvester process, which is fully described in a paper read by Mr. Dearborn before the American Society of Civil Engineers, May 4, 1870.

The process consists in using two washes or solutions. The first, composed of three quarters of a pound of castile soap dissolved in one gallon of water, laid on at a boiling heat with a flat brush. When this has dried, twenty-four hours later apply in like manner the second wash of half a pound of alum dissolved in four gallons of water. The temperature of this when applied should be 60 to 70 deg. Fah. After twenty-four hours apply another soap wash, and so on alternately until four coats of each have been put on. Experiments showed that this was sufficient to make the wall water-tight under forty feet head of water.

At the time of application the walls had been saturated, and the weather was cold. The gate-chambers were covered over and heated thoroughly with large stoves. The drying, cleaning the walls with wire brushes, and applying the mixture, took ninety-six days. Twenty-seven tons of coal were used for the drying, and one ton for heating the soap solution. Eighteen thousand eight hundred and thirty square feet of wall were washed with four coats. The drying and cleaning of the walls cost 6 1/2 cents per square foot, and the plant, materials, and labor of applying the wash cost 3 3/8 cents per square foot.