The condenso-purifier consists of three perforated diaphragms, placed one over the other in rectilinear cast-iron boxes. These diaphragms are movable, and slide on projections running round the interior of the boxes. In each of the latter there is an overflow pipe, g, that runs to the box or compartment below, and an unperforated plate, f, that slides over the diaphragm so as to cover or uncover as many of the holes as may be necessary. A stream of common water runs in through the funnel, e, over the upper diaphragm, while the gas enters the apparatus through the pipe, a, and afterward takes the direction shown by the arrows. Reaching the level of the overflow, the water escapes, fills the lower compartment, covers the middle diaphragm, then passes through the second overflow-pipe to cover the lower diaphragm, next runs through the overflow-pipe of the third diaphragm on to the bottom of the purifier, and lastly makes its exit, through a siphon. A pressure gauge, having an inlet for the gas above and below, serves for regulating the pressure absorbed for each diaphragm, and which should vary between 0.01 and 0.012 of a meter. The effect of this purifier is visible when the operation is performed with an apparatus made externally of glass. The gas is observed to enter in the form of smoke under the first diaphragm, and the water to become discolored and tarry. When the gas traverses the second diaphragm, it is observed to issue from the water entirely colorless, while the latter becomes slightly discolored, and finally, when it traverses the third diaphragm, the water is left perfectly limpid. Two diaphragms have been found sufficient to completely remove the solid particles carried along by the gas, the third producing only a chemical effect. This apparatus may replace two of the systems employed in gas works: (1) mechanical condensers, such as the systems of Pelouze & Audouin, and of Servier; and (2) scrubbers of different kinds and coke columns. Nevertheless, it is well to retain the last named, if the gas works have them, but to modify their work. [Illustration: FIG. 2.--PLAN VIEW WITH BY-PASS.] This purifier should always be placed directly after the condensers, and is to be supplied with a stream of pure water at the rate of 50 liters of water per 1,000 cubic meters of gas. Such water passes only once into the purifier, and issues therefrom sufficiently rich in ammonia to be treated. If there are coke columns in the works, they are placed after the purifier, filled with wood shavings or well washed gravel, and then supplied with pure cold water in the proportion stated above. The water that flows from the columns passes afterward into the condenso-purifier, where it becomes charged with ammonia, and removes from the gas the tar that the latter has carried along, and then makes its exit and goes to the decanting cistern.