EFFECT OF WIRE GAUZE; SAFETY LAMPS. 277 



of the pipe the issuing explosive mixture will be fired, and the 

 flame will pass through the pipe into the bladder, causing its 

 contents to explode ; just as a train of gunpowder would allow the 

 flame of burning powder to pass along it from one end to the 

 other, or as a piece of burning touch paper (Expt. 258) will allow 

 the smouldering combustion to go on, gradually but regularly, till 

 the whole is consumed. 



If, however, the piece of touch paper be placed between two thick 

 flat copper plates with a portion projecting, on lighting the part 

 sticking out it will burn as usual ; but the combustion will not 

 penetrate far between the copper plates, the conducting power of 

 these being great enough to cool down the burning paper so as to 

 extinguish it. 



In much the same way, by employing a long fine metal tube, 

 instead of a comparatively short wide piece, in the mouth of a 

 bladder of mixed oxygen and hydrogen, it is possible to prevent 

 the flame passing back through the tube and firing the contents of 

 the bladder ; the sides of the tube act here as the copper plates 

 with the touch paper, conducting heat away so rapidly that the 

 flame cannot pass along, the chemical action of burning being 

 stopped by the cooling. What is termed a safety jet based on this 

 principle is sometimes used to produce an oxyhydrogen flame 

 (Expt. 211), the two gases being mixed and made to pass through 

 a tube filled full of pieces of wire, packed longitudinally in the 

 tube as close as possible ; the interstices between the wires allow 

 the gases to pass to the jet at the end, where they are burnt 

 together, but act as the long narrow tube with the bladder, pre- 

 venting the flame from passing back by the cooling action exerted 

 in virtue of conduction. 



When the tubes are fine enough, a very short length suffices to 

 enable this cooling action to be sufficiently 

 rapid to prevent an ordinary candle or oil 

 lamp flame from passing ; so that a piece of 

 fine wire gauze may be pressed down on the 

 flame almost to the base without allowing 

 the inflammable gases and vapours that pass 

 through to take fire ; or, conversely, if a gas 

 jet be turned on, and a piece of wire gauze 

 held over it, the gas that passes through the 

 gauze may be lit (fig. 130), but the flame will 

 not pass downwards through the wire meshes. Fig. 13 - Wire Gauze 

 This property of wire gauze is utilised in and Flame - 



the construction of various forms of gas burner, where air and 

 gas are mixed and burnt together so as to produce a blue 



