The method pursued by Ozouf, in France, is a considerable improvement on Thénard’s process. Pure carbonic acid is used for the precipitation, and white lead of similar composition to that produced by the Dutch process is obtained, since the introduction of the carbonic acid can be regulated according to the volume and strength of the lead solution, and thus white lead of any desired composition can be produced. The most elaborate precautions for the health of the work-people are taken. The preparation of pure carbonic acid gas is based upon the absorption of this gas from a mixture of gases by a solution of sodium carbonate, and its evolution on heating the solution. The apparatus is shown in Figs. 18 and 19. The products of combustion obtained from the stove, _A_, are drawn by the air pump, _E_, through the pipe, _C_, into the cooler, _B_, which is regularly fed with cold water by _D_. The gases compressed in the receiver, _E´_, deposit moisture there, and then proceed through 3 horizontal cylinders, _F_, of sheet-iron, provided with agitators, in which the carbonic acid is absorbed by a cold solution of sodium carbonate of 9° B. The unabsorbed gases escape into the atmosphere through _G_ (Fig. 19). The sodium bicarbonate solution is received in the wooden tank, _H_, after passing through the 3 cylinders, _F_. The pump, _I_, of the alternating pump, _I I´_, lifts the sodium bicarbonate solution out of _H_ and sends it through the pipe, _K_, into the tubular cylinder, _J_, which stands upon a cylinder of larger diameter, _J´_, communicating with it only by the vertical tubes. The bicarbonate solution rises between the tubes in _J_, passes through the pipe, _L_, drops in a fine spray through the rose forming its mouth, and by means of the vertical tubes passes into _J´_ and thence into _M_, where it is heated by means of a steam coil to 100° C. Carbonic acid is then evolved, and the residual solution of neutral sodium carbonate, after cooling in the vessel, _R_, by means of the cold coil, is drawn off by the pump, _I´_, again to enter the cylinders, _F_, by means of the pipe, _K_. The carbonic acid evolved in _M_, together with steam, enters _J´_ through _N_, and in rising in the tubes of the cylinder, _J_, is cooled by the falling spray of bicarbonate solution. The cooling is completed in the coil, _O_, surrounded by water; the vessel, _P_, separates the condensed water and passes the gas on into the holder, _Q_. The pipe, _S_, connecting _P_ with the suction pipe of the pump, _J´_, serves to restore to the solution of sodium carbonate the water it has lost, thus maintaining the proper concentration. The cost of 1 cubic metre of carbonic acid is 10 centimes, of 1 kilogramme 5 centimes. [Illustration: FIG. 19.]