1820.] Impermeahility of Wire Gauze to Flame. 425 



sufficiently enlarged, the water passes through in the form of 

 minute spheres. Hence perhaps the increased energy of the 

 common blow-pipe, the film, or successive films, being directed 

 to a focal point and becoming solid. 



When the temperature of the tissue of the safety lamp is suffi- 

 ciently exalted, the gaseous matters in contact with its external 

 surface are kindled, and this high temperature is soon acquired 

 by the continued inflammation of the explosive medium encaged. 

 The iron or other metallic wire of the meshes radiates caloric 

 indeed, but receives much more than it yields from the flaming^ 

 cone ; and by such repeated accessions it soon rises to ignition, 

 ■which is accelerated when the explosive flame amounts to a max- 

 imum, and it plays in impotent fury against the bars of its prison, 

 the walls of that enclosure which impose a limit to its sphere of 

 action. 



Thus, when wire gauze is acted upon by a continued jet of 

 inflamed gas, the barrier is soon made sufficiently red-hot to 

 kindle the- gas which is propelled through unconsumed, and 

 which, therefore, exhibits a prolongation of the inflamed jet on 

 the other side. Thus gunpowder placed on a piece of fine wire 

 gauze resting on flame will not explode, until the wire gauze is 

 sufficiently ignited. But if the phenomenon of safety in the 

 wire gauze is to be ascribed to cooling influence, then I presume 

 to contend that alcohol, ether, or other inflammable matters 

 should not flame or continue to burn in contact with cooling sur- 

 faces, yet alcohol, &c. may be kindled, and will continue to 

 inflame on a plane of copper, &c. the best conductors of caloric 

 among the metals. 



In the occasional retrogression of the flame into the reservoir 

 of the oxyhydrogen blow-pipe, as the probabilities are that this 

 flame is a solid, an idea first suggested by Mr. George Oswald 

 Sym, from the very nature of the materials employed, so it can- 

 not be subject to the restriction presumed, as it is no longer a 

 film. But the retreat of flame into the reservoir through so 

 many centinels over its safety, seems to me, on the principle of 

 the supposed cooling influence, a problem which admits of no 

 solution. It has to encounter no less than four safety appen- 

 dages, and finally brave the portal of a safety valve before it can 

 penetrate the recipient ; and yet it must enter this meatus inter- 

 ims in the character of flame to do its mischief. Now really one 

 would thmk that it might be sufficiently cooled before it came 

 this length. 



Thus do we find a very simple expression of the facts, and I 

 think a satisfactory one in the structure and constitution of flame 

 itself; while, upon the other supposition, when we consider that 

 wire gauze, even at a dull red heat, maintains its character of 

 safety until it becomes of a temperature equal to that required to 

 explode fire damp ; and reflect also that meshes of paper, hair- 

 cloth, &c. nonconductors of caloric, whose cooling influences are 



