In distilling shale or other carbonaceous substances to obtain oil, paraffin, ammonium salts, etc., sulfuric or other acid is added to the material, in the still or before treatment. The shale is first reduced to a fine powder. Acid tar from the treatment of oils may be used instead of acid. Hydrogen is sometimes passed into the still, or iron or other metal is mixed with the shale to generate hydrogen in the still. A figure is included which shows the condenser for paraffin and heavy oils, consisting of an iron cylinder connected with the still by a short pipe and surmounted by a long pipe communicating with other condensers. The pipe projects into the cylinder and perforated plates or baffles are fixed across the central portion of the cylinder. The condensed oils are drawn off by a pipe.