Artificial Lithographic Stone.—

An important German invention is thus described in the Photographic News: The plates employed by Messrs Wezel & Naumann, of Leipzig, are prepared as follows: Lithographic stone is partly dissolved and partly reduced to a pulp by digestion in hydrochloric and sulphuric acids. To this pulp is added a mixture of solution of asphaltum and resin and a small quantity of oil. By this means a mixture of fatty or resinous salts of lime and sulphate of lime is formed. After evaporating the excess of acid a dilute solution of soda is added, and warm zinc plates are covered with a fine spray of the mixture. The plate thus coated with a film of artificial litho-stone, is afterwards treated in the same way as an ordinary lithographic stone, except that in place of nitric or hydrochloric acid, phosphoric acid mixed with dilute gum arabic is employed. Plates thus prepared have yielded as many as six thousand impressions, and the process is used to the almost entire exclusion of other processes by Messrs Wezel & Naumann, who have over thirty steam-presses doing various kinds of lithographic work.