1&39.] Memorandum of Experiments, tyc. H5 ( J 



A joint of bamboo, see fig. 9 b, about 5 inches long by 1^ in dia- 

 meter, capable of holding 21bs. of mercury, was fitted with a small 

 brass stopcock below, through which when opened the mercury might 

 escape. It was found by experiment, that when fully open 21bs. 

 escaped through the stopcock employed in a few seconds more than five 

 minutes. 



The bamboo joint was fixed on a wooden frame//, having a vessel 

 below to receive the mercury. A stout copper wire was led through 

 the diameter of the bamboo, one and a half inch from the bottom. 

 A similar wire was inserted three-fourths of an inch below, and in the 

 same direction with the first, and this second wire was divided into 

 two parts, as shewn in the drawing. The ends of the wires were turned 

 into a few loose spirals to allow of their being readily connected with 

 the battery on one side, and with the conductors to the mine on 

 the other. 



Suppose this joint filled with mercury, the stopcock shut, and the 

 battery wires connected with it at one side (say the right,) and the 

 mine conductors connected with it at the left — in this case metallic 

 contact being established in the conductors c, c, between the battery 

 and the mine, no ignition can possibly occur, because the electricity 

 returns to the battery by the first cross road it meets, if I may be per- 

 mitted to use this homely, but I think expressive, illustration. 



If we now open the stopcock and allow the mercury to trickle out 

 as soon as its level subsides below that of the highest copper wire, the 

 only path of the electric fluid now lies through the mine, the platinum 

 becomes ignited, and explosion ensues. 



But should any accident have occurred, so that no explosion takes 

 place at once, and should therefore the whole arrangement need inspec- 

 tion, the mercury still subsiding passes after two or three minutes 

 below the second wire, which having been previously cut, the circuit 

 is now completely interrupted, and the whole arrangement is perfectly 

 safe for inspection. 



In using this apparatus two things must be attentively borne in mind. 

 No accident can happen while it is full of mercury, but when once 

 emptied it must not be filled again while in connexion with the bat- 

 tery, otherwise an explosion may ensue. 



The whole arrangement is shewn in the accompanying diagram, in 



5 s 



