536 The Architectural Review and American Builders' Journal. [Feb., deterioration, in the material wherewith it is covered. The water may pass around ; and so, finally, underneath ; but will not soak through it. There- fore, if persons using, design it to be a fire and weather-proof coating for the roof, or any other part of the building, they must be sure it actually covers what they wish to protect. Plastic Slate can be applied, with the same good effect, to a roof of any angle, or to the perpendicular sides of a house. For the latter very important purpose it is put on with a brush as a paint, until it reaches the thickness of about 3 3 5 of an inch. Its color is dark brown ; although, of course, any color can be painted over it when set. Its weight is about one-fourth that of tin. It is smooth, and sheds snow easily. Plastic Slate is perfectly fire-proof. Slate itself is strictly non-combustible ; but the Coal-tar is combustible. If a fire is kindled upon a new roof, the oil will ignite and burn out; the slate, in the unctuous semi-fluid, is consolidated and petrified, and then remains intact. Nothing can be ignited through the slate, unless the latter grows red-hot. The oil being already volatilized by the heat, there is nothing left to burn ; there- fore, an old roof is fire-proof. But the new mastic will not burn, nor the oil burn out of it, unless in close contact with other combustible matter, which is already fired and giving off intense heat, so that if a wood or coal fire is kindled upon any part of a new roof, it will neither spread, nor burn the boards beneath. It is a great renovator for old shingle or metal roofs. Plastic Slate is the invention of Wil- liam L. Potter, a plain farmer and mil- ler, of Clifton Park, New York. " After suffering many partial failures, in com- pounds of lime in all its various forms, in sand, granite, plaster, mineral coal clay of various kinds, red and blue shale, marble dust, soap-stone, cement, coal- tar, vegetable tar, asphaltum, &c, in all the proportions and combinations that an intelligent and inventive mind could suggest, for fourteen years, he tried slate also, in many combinations, and found that the mixture of ground slate and coal-tar alone possessed the properties, and gave the results he desired." Not caring to have the reputation of intro- ducing any thing of no intrinsic value to mankind, Mr. Potter devoted much time to testing his theory and final pro- duct by severe, private, practical experi- ments upon his own premises. Con- vinced finally of the great value of his discovery, he applied for letters patent, which were granted by the United States, in February, 1865, and by Great Britain soon after. Plastic Slate was first brought into public notice, at a meeting of the Far- mers' Club of the American Institute of New York, held, June 20th, 1865, reported in the New York Tribune of July 1st, same year. The matter was called up by Mr. Solon Robinson, and discussed by Professor Tillman and Mr. James M.Allen, of Fredericktown, Ohio. The latter exhibited laths and shingles, mementoes of Mr. Pottex's first experi- ments, which had the mastic firmly ad- hering ; and almost incorporated with the very fibre of the wood. About the thickness of pasteboard, on the outside, had become indurated to the original hardness of slate. The interior retained a degree of toughness, imparted by the coal tar. At this rate, it would require about ten years, to harden a coating an eighth of an inch thick. Whether mixed thin, and spread upon the sides of a house, with a brush, or mixed thick, and spread over the roof, with a trowel, this composition is imme- diately adhesive and impervious Sur- faces exposed for hours, in a coal fire, show no change. For this information, we are indebted to the Philadelphia Agents, Messrs. J. S. Ciiahoon & Co., of No 102 South Fourth street.
