1902.] 



of the Flame in the Explosion of Gases. 



483 



The evidence against Le Chatelier's view may thus be sum- 

 marised : — 



1 . Its supposed effect is only seen when the contrasts are strong, and 

 not on photographs of the same phenomena in which the contrasts are 

 not brought out. 



2. It can be initiated in various ways by means of contrasts. 



3. The same effect is seen in the collision of two detonation- waves, 

 but Le Chatelier does not suppose that the "invisible wave " can pre- 

 cede the detonation. 



2. Repetition of v. Oettingen and v. Gernet's Experiments. 



The very short time required for the explosion in electrolytic gas to 

 raise the Welsbach oxides to incandescence was strong evidence against 

 the view held by v. Oettingen and v. Gernet, viz., that the detonation 

 of electrolytic gas is invisible^ and that the salts present in their ex- 

 periments only became luminous after the combustion had been for 

 some time complete. Our previous experiments had also shown con- 

 clusively that the detonation is not set up at once, but only after the 

 flame has run some distance which varies with the nature of the mix- 

 ture and the position of the spark. But to place the matter beyond 

 all doubt we have repeated their experiments, using a tube of the same 

 size and construction as theirs filled with electrolytic gas, but without 

 the addition of any salts. By careful development the course of the 

 flame can be seen on the negatives from the firing wire. In all cases 

 the explosion begins slowly and has slight luminosity until the retona- 

 tion-waves are started by reflection from the ends of the tube. Some 

 of our photographs closely resemble in detail those published by Oettin- 

 gen and Gernet, but they show the initial movements of the flame which 

 are lacking in their photographs. The reflections of the two waves 

 often run nearly parallel, but the stronger wave usually catches the 

 weaker and coalesces with it. The photographs thus make clear how 

 "secondary" waves running parallel with "primary" waves maybe 

 produced from a single explosion in a short tube. 



