This Company’s retorts--they are patented--are in use at the various works of the Pumpherston Company, and are an interesting feature to visitors. The shale is fed by gravitation into cylindrical-shaped retorts, and built vertically in ovens of four, each oven having four chambers. The upper portion is of cast-iron, 11 feet long by 2 feet in diameter at the top, and slightly enlarged toward the bottom. Heat is applied externally from the incondensable gases obtained from the distillation of the shale, and this heat is made to circulate round the retort. In the case of the poorer qualities of the shale, however, the heat is assisted by producer-gas. The heating gas enters near the bottom portion of the retort, which is of fire-brick, along with a certain quantity of air, and a high temperature--from 1,200°F. to 1,600°F.--is maintained, in this portion converting the nitrogen of the shale into ammonia, which is preserved by a continuous supply of steam delivered at a slight pressure at the bottom of the hopper. The oil gases are distilled from the shale in the cast-iron portion of the retort at a temperature of about 900° F., and, along with the ammonia gas, are drawn off by the exhausters through a branch pipe at the top of the retort, through the atmospheric condensers, from which the condensed liquid oil and water containing ammonia flow into a small separator tank. It is here that, owing to their different specific gravities--for one is lighter than the other--they assume different levels, and are thus drawn off into separate tanks. The gases then pass through ammonia scrubbers, in which they are washed for ammonia, and then through the naphtha scrubbers, where the lighter gases, which could not be caught in the atmospheric condensers, are washed with oil and a good quality of light oil or naphtha is recovered. The incondensable portion passing from these scrubbers is burned in the retorts as previously mentioned. With a shale of average yield, the retort can be heated by these incondensable gases from the distillation, and a surplus obtained for burning under steam boilers.