Brouardel's manometer, represented herewith, is designed for showing graphically variations in the pressure of gas, either at the works during the course of manufacture, or at any point whatever in the system of piping.

For this purpose water manometers have hitherto been employed; but, although the indications given by these are very accurate, their form and weight are such as to render them not easily transportable; and then, again, considerable care is necessary in putting them in place.

Mr. Brouardel's registering manometer does not give so accurate indications, perhaps, but it possesses, as an offset, the merit of being very portable and easily put in place; and, besides, it inscribes the hour at which the pressure is exerted.

The apparatus consists of a metallic cylinder, A B, which carries a circular shoulder, C, that rests on a plate, D--the latter being put in motion by a clock which is wound up by means of a button under the base, E, of the apparatus. The two standards, F F, carry a crosspiece which supports a disk that closes freely the aperture of the drum, A B, in such a manner as not to impede its rotation.

In the interior of the cylinder there is a metallic cup which is connected with the central reservoir by an impermeable membrane, I. These three parts form a closed chamber, into which the pressure comes through a tube, F, provided with a cock. A spring, M, which counteracts the pressure, is arranged between the crosspiece, G, and the bottom of the reservoir. The latter carries also a small rod, K, which is provided with a cord made of braided silk. This cord runs over a pulley, N, whose axle carries at its other end a still larger pulley, O. Toward the middle of the latter is fixed a silken cord which hangs down on each side, after making several turns around the pulley. To the front cord is attached a slide, Q, moving in a vertical direction, and to which is fixed an inscribing style, R. The other extremity of the thread enters the hollow upright, and carries a weight which is greater than the combined weights of the slide, the membrane, and the internal reservoir. The upright serves as a guide to this counterpoise.

In order to use the apparatus there is affixed to the cylinder, A B, a sheet of paper divided in a vertical direction into as many parts as the cylinder takes hours to make one revolution. The divisions running horizontally represent centimeters of water or of mercury, according to the strength of the spring, M, which should be so constructed as to be in relation with the pressure. The operation of the apparatus may be readily understood.

GAS INDICATOR OF MANOMETER.

GAS INDICATOR OF MANOMETER.

When the gas reaches the pressure chamber, the spring, M, contracts, and consequently the counterpoise descends, and causes the cord, O, which carries the slide and writing style, to wind around the pulley. When the pressure diminishes, the movement takes place in an opposite direction.

The tracing is done by means of a special form of style giving indelible curves through the medium of colored glycerine. The position of the point is determined in such a way as to annul the friction of the pen, and consequently to give it greater sensitiveness.

It should be remarked that the course of the rod, K, is amplified in the tracing of the ordinates of the pressure according to the ratio of the diameters of the pulleys, N and O.

The apparatus may be carried by hand by means of the handle, S, either in or out of its case. To put it in operation, it is only necessary to connect the apparatus with a gas burner (located near the place where the variations of pressure are to be observed) by means of rubber tubing. The apparatus may be employed under the same circumstances as glass and U-shaped water manometers, with the further advantage that the results are registered, and consequently can be more easily compared.