DESCRIPTION OF THE PLATES

359

Fig. 4 is a flask for weighing gases. Its orifice is furnish-ed with a brass cap and stop-cock. The flask is connected witha bell-glass in the manner stated before. If this flask has beenpreviously exhausted by means of an exhausting syringe, and acommunication be then mads with the bell-glass by opening bothcocks, the gas contained in the bell-glass may be transferredinto the flask, by pressing down the bell-giass into the water ofthe pneumatic trough ; the gas will then be forced up into theflask, the cocks being then shut, the flask may be removed, andits weight ascertained by means of a delicate ballance. The dif-ference between the weights of the flask when exhausted, andwhen filled, give the weight of the gas in the flask, which may,by the same method, be compared to that of common air, See.

In a similar manner a bladder may be filled with gas by tyingits mouth to a stop-cock, and screwing it on that of the bell-glass,by means of the connecting piece, and proceeding as just de-scribed.

Fig. 5 is a perspective view of a pneumatic cistern of whicha description has been given already, page ]7S, vol. i.

PLATE. V.

Represents Burkitt’s, and Pepys's distillatory apparatus for im-pregnating fluids with gases, See.

Fig. 1...A. is a tubulated retort, joined to a tubulated receiver,b. From this a bent tube proceeds to the bottom of a second re-ceiver, g. from the upper tubulature of which a communicationis made, by means of a tube twice bent at right angles, with thetwo necked bottle, i. The principal advantage of this apparatusconsists in a valve, constructed by placing a plano-convex lensupon the mouth of the small tube, accurately fitted by grinding,and inserted into the lower aperture of the receiver, g. and similarto the valve in the well known apparatus of Nooth, but with more