of Danger in Torpedo Experiments. 75 



Total resistance of circuit ... ... ... -752 Ohm 



Resistance of fuse when cold ... ... '325 ,, 



Leaving for resistance of the conducting wire -427 „ 

 which resistance = about 54 yards. 



This is the greatest length of wire through which the cur- 

 rent would fire the charge, on the supposition that the resist- 

 ance of the wire is constant. 



Through that distance the charge might not be expected 

 to explode, but I could not assert that it would not explode. 

 The current would probably heat the wire, though perhaps 

 but slowly ; the resistance of the wire would increase with 

 the temperature, and this increase would most probably 

 reduce the current to a strength at which it would not tire 

 the charge. It is in the first rush of the current through the 



ill r> 



conductor that the danger would lie, for that first rush might 

 raise the wire to a temperature considerably higher than that 

 at which it could maintain it, and that higher temperature 

 might be dangerous. 



From Bloxom's Chemistry, third edition, page 503, I find 

 that gun-cotton, which is the material in a properly made 

 fuse which is in contact with the platinum wire, and is first 

 fired by it, " is more easily exploded than gunpowder. The 

 latter requires a temperature of at least 600° F., whilst 

 gun-cotton may explode at 277° F., and must explode at 

 400° F." It further appears that the average tempera- 

 ture at which gun-cotton explodes when in the condition 

 most favourable to its rapid heating is about 300° F. ; 

 and this, it is important to note, is a temperature much 

 nearer the lower than the higher of the two limits given. 



According to the Chatham Instructions in Military 

 Engineering, the resistance of the platinum wire increases 

 •07 per cent, per degree F. As its resistance at 60° F. is 

 •325, at 277° F. it would be— 



. 325 + J25 x W X 217 = .^ ^ 



And at 400° F. it would be— 



•325 + ' 325 X 2 X 34 ° = -402 Ohm 



For the lower of these resistances we have — 



Total resistance of circuit ... -752 Ohm 



Resistance of fuse at 277° F. ... -374 „ 



Resistance of wire ... *378 



