November ijth, igoo.] PROCEEDINGS. v 



wave on a very rapidly moving film, Professor Dixon has shown 

 that the wave is reflected back from the end of the tube, this 

 reflected wave being of great luminosity. The phenomenon 

 observed by Professors Liveing and Dt A^ar may therefore be due 

 to the light of the retreating wave passing through (and suffering 

 absorption in) the cooler gas in the rear of that wave. This is 

 made probable by the fact that photographs of the advancing 

 wave do not show any reversals of the calcium and other lines, 

 zvhen the end of the tube next the slit is open, and when therefore 

 no reflected wave is sent back. All the photographs of the 

 explosion-wave show that the front of the wave is exceedingly 

 sharp, and that the maximum brightness is '•cached immediately. 

 Professor Dixon further referred to the formation of hydrogen 

 peroxide in several cases of combustion, and discussed the 

 bearing of the facts on Mendeleefs theory as to the nature of 

 the action which takes place when hydrogen and oxygen combine. 

 Mendeleefs idea is that gases combine primarily in equal 

 volumes, so that in the case of hydrogen and oxygen the reaction 

 first gives rise to HoO.,, thus : — 



H2+Oo=H20o 



and subsequently the hydrogen and oxygen peroxide interact : — 



Ho+n20, = 2HoO. 

 If the gaseous products are quickly cooled by making the 

 hydrogen flame play on to water or ice, then some of the peroxide 

 escapes reduction and is found in the water. A second view is 

 that the hydrogen molecules break up the oxygen molecules, 

 liberating atoms of oxygen, some of which may combine with 

 the steam forming hydrogen peroxide : — 



H. +02 = H2O + O 



HoO + O = HP2. 

 Professor Dixon made some suggestions for an experimental 

 investigation of the question, and stated that he had begun some 

 experiments with a view of deciding, if possible, between the two 

 hypotheses. 



