Appendix 2 



Magnetic Valves and Electro-magnets 



The ballast of the Trieste is composed of cast-iron peHets. It has the 

 appearance of small, rather regular balls of a diameter of xq iri-? ^nd is 

 obtained, in the same way as bird-shot, by the cooling of a shower of 

 molten metal (see Plate X). It is contained in two sheet-metal tubs with 

 funnel-shaped bases. The piping of this funnel is narrower at one place 

 and the lower tube is surrounded by a coil. Fig. 16 gives a diagram- 

 matic view of the valve, where the coil is represented simply by three 

 turns of a cable. Fig. 17 gives a cross-section of the valve in more 



Fig. 16. Diagram of the magnetic valve 



detail. As long as an electric current runs through the coil d, the iron- 

 shot is magnetized just where the tube narrows. In this way it is trans- 

 formed into a more or less rigid mass which acts as a plug. Thus the 

 pellets cannot flow away. As soon as the current is cut, the pellets are 

 demagnetized and flow like sand in an egg-timer. It is enough to switch 

 on the current to stop the flow at once. It is clear that the principle is 

 very simple. 



[152] 



