312 PRINCIPLES OF CHEMISTRY 



marsh gas, CH 4 , and chlorine, C1 2 , according to the equation CH 4 + C1 2 

 = CH 3 C1 -t- HC1. A great number of similar- cases are met with 

 amongst organic that is, carbon compounds. Gerhardt was led to 

 the discovery of his law by investigating many such reactions, and 

 by observing that in them the reaction of equal volumes precedes 

 all others. 



But if nitrogen or hydrogen give several compounds with oxygen, 

 the question proposed above cannot be answered with complete clear- 

 ness, because the successive formations of the different combinations 

 cannot be so strictly defined. It may be supposed, but neither 

 definitely affirmed nor experimentally confirmed, that nitrogen and 

 oxygen first give nitric oxide, NO, and only subsequently the brown 

 vapours N 2 O 3 and N0 2 . Such a sequence in the combination of nitro- 

 gen with oxygen can only be supposed on the basis of the fact that NO 

 forms N 2 O 3 and NO 2 directly with oxygen. If it be admitted that NQ 

 (and not N 2 or N0 2 ) be first formed, then this instance would also 

 confirm the law of Avogadro-Gerhardt, because nitric oxide contains 

 equal volumes of nitrogen and oxygen. So, also, it may be admitted 

 that, in the combination of hydrogen with oxygen, hydrogen peroxide 

 is first formed (equal volumes of hydrogen and oxygen), which is de- 

 composed by the heat evolved into water and oxygen. This explains 

 the presence of traces of hydrogen peroxide (Chapter IV.) in almost 

 all cases of the combustion 6r oxidation of hydrogenous substances ; for 

 it cannot be supposed that water is first formed and then the per- 

 oxide of hydrogen, because up to now such a reaction has not been 

 observed, whilst the formation of H 2 from H 2 2 is very easily re- 

 produced. 10 



Thus a whole series of phenomena show that the chemical reaction 

 of substances actually takes place, as a rule, between equal volumes, 

 but this does not preclude the possibility of the frequent reaction of un- 



10 This opinion which I have always held (since the first editions of this work), as to the 

 primary origin of hydrogen .peroxide and of the formation of water by means of its 

 decomposition, has in latter days become more generally accepted, thanks more especially 

 to the work of Traube. Probably it explains most simply the necessity for the presence 

 of traces of water in many reactions, as, for instance, in the explosion of carbonic oxide 

 with oxygen, and perhaps the theory of the explosion of detonating gas itself and of the 

 combustion of hydrogen will gain in clearness and truth if we take into consideration the 

 preliminary formation of hydrogen peroxide and its decomposition. We may here point 

 out the fact that Ettingen (at Dorpat, 1888) observed the existence of currents and 

 waves in the explosion of detonating gaS by taking photographs, which showed the 

 periods of combustion and the waves of explosion, which should be taken into con- 

 eideration in the theory of this subject. As the formation of H 2 O 2 from O 2 and H 2 

 corresponds with a less amount of heat than the formation of water from H 2 and O, it 

 may be that the temperature of the flame of detonating gas depends on the pre-focmation 

 of hydrogen peroxide. 



