(56 



DIVING BELL 



usefully employed in a steam-boiler, or is allowed to run off. The air and a small 

 quantity of water is forced up from the cylinder D, by the stroke of the piston c, into 

 the chamber F, which is thereby filled with water, and thus the air is expelled there- 

 from, a small quantity of the water passing with it and covering the valves, by which 

 means they are kept tight and wet. The air and water thus discharged, after passing 

 around the small tubes in the valve chamber and being cooled, are forced outward 

 and conveyed to the condenser. On the return stroke of the piston, the other chamber 

 F is filled, and air and water expelled from it in like manner through its valve into 

 the valve chamber. There is always a sufficient quantity of watet in the cylinder 

 and chamber F to fill the latter when the water is all expelled from the cylinder, by 

 the piston c having been driven to one end of it, and when the piston returns to the 

 opposite end of the cylinder the water flows in behind it, and draws in its equivalent 

 in bulk of air and water through the valve H. On its return, this is forced out through 

 the valve k into the chamber i, as mentioned above. The water being non-elastic, if 

 the parts are kept cool enough to avoid raising steam, this process may be continued 

 for any length of time. A transverse section of this apparatus is shown in Jig. 633. 



Figs. 634 and 635 represent the speaking tube and alarm bell above referred to. 

 The construction of this mechanism is as follows : There is a hollow casting, one portion 



634 



of which is triangular in form, from one end of which a short tube a projects. This tube a 

 has a screw cut on it, and a projecting flange at its junction with the triangle. This is 

 screwed into the top of the diving vessel or armour from the inside, and projects through 

 it to allow the coupling of a flexible or other hose to be attached to it. At the opposite 

 angle, and in a line with a, there is a tubular projection b, provided with a screw to 

 receive a cap/, to which is to be attached a piece of hose. Within the tube/, and at 

 its junction with b, is placed a thin diaphragm of metal or other suitable material c, 

 for which purpose, however, a thin silver plate that just fits the bore of the cap / is 

 preferred. This diaphragm closes all communication between the diving vessel and 



635 



the external air. By this means it is easy to converse through any required length of 

 tubing. It may be desirable to fit a stop-cock into the tubular projection b, as a pre- 

 cautionary means of preventing the escape of air in the event of a rupture of tho 

 diaphragm. The upper part of the triangular enlargement of tho speaking tube is 

 tapped for a stuffing box at g, within which there is an axis h, which runs from side to 

 side of tho said enlargement, and through tho stuffing box at one aide. On this axis 

 h is fixed a lever i within the said enlargement, which lover communicates with the 

 surface of the water by means of a wire fixed at its reversed end, and running through 

 the whole length of pipe. On tho outer extremity of the axis h is affixed a hammer, 

 which strikes on a bell k connected to the tube, as shown in the drawing. By this 



