tan. Both were economical devices. The New England tanners had long been accustomed to dry their spent tan during the summer and store it for winter use. It was then brought into service to heat liquors, and in some cases to generate steam for general tanning purposes. It was found, however, that nearly a half of it was lost in drying. The result was, that attention began to be given to the problem of utilizing it to greater advantage. In 1852 Joseph B. Hoyt conceived the idea that the wet spent tan might be burned in a detached brick furnace. He made the experiment at his tannery in Woodstock, Ulster County, N. Y. After several trials he was successful, and got from the utilization of this hitherto useless product enough power to drive his whole machinery. Since the success of Mr. Hoyt a number of furnaces have been devised for burning this wet tan. That of Mr. Hoyt, as perfected by him, consisted of two pairs of ovens, each pair being connected with three horizontal flue boilers. Each oven, with its boiler, was independent of the other, and each had a separate feed-pipe, steam-pipe, and water-tank. The only things in common between the ovens were the fire-room and the chimney. The ash-pits were the entire width of the grate, and the distance from the under side of the grate-bars to the bottom of the ash-pit was nearly five feet. This permitted a double current of air to. form in the ash-pit, the cold one entering at the front near the bottom, passing toward the back end, becoming gradually warmed by the intense heat from the grate, a part entering the oven through the grate, and the rest finally passing out of the ash-pit at the front at a temperature of 300°. By closing the furnace so as to prevent the return current, the temperature of the ash-pit could be raised to 500°. The success of these furnaces worked an immediate change in the whole tannery economy. Hitherto tanneries had been limited to the banks of streams, where they could get good water-power. Now such power was not necessary. Tanneries could be located in the open flats, where access was easy, and where the inconveniences and expenses of elevations could be avoided. Fuel was no longer an item of importance. Tanners, therefore, were not obliged to confine themselves to one great building, but they could spread out into as many smaller ones as their convenience and business demanded. They, furthermore, were no longer obliged to consider the cost of generating steam, and as a result labor-saving machinery commended itself to all. The discovery of this method of burning wet spent tan has been the determining element in the construction of the modern tannery. At the same time it has been one of the most important factors in reducing the cost of the production of leather.
From the definition of leather already given—a chemical or
