The extensive proJHBHf carburetted hy drogen gas from coal or roMrrar, or other like substances, has been thought by many good chemist8tobe quite impracticable, one of the difficulties to be overcome is that of obtaining a retort so constructed that the coal tar, which is made to enter it in fluid form, will not coo it sufficiently to destroy the product, and cause an incrustation of the tar upon the sides of the retort. This difficulty has been obviated by Stephen Meredith, of Erie, Pa. Mr. Meredith has constructed a novel retort for the accomplishment of the object above stated. It is so formed that a heated surface is constantly presented to the fluid tar. This is effected by placing within the retoit, longitu dinally, a cylinder which may be made to revolve in bearings, working in stuffing boxes, to prevent the escape of the gas lrom the retort. A pipe or tube passes longitudinally into the retort and over the entire length of the cylinder, the portion of the tube within the retort being perforated to permit the fluid tar, which enters the retort through the pipe to fall upon the cylinder. As the cylinder revolves it constantly presents a new surface to the heated retort, thus the tar is prevented from forming incrustations and burning on the sides ot the retort,but is readily converted into gas. Measures have been taken by the inventor to obtain a patent.