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XLIII. Reply to Prof. Wilhelm Ostwald's criticism on my 

 paper " On the Chemical Combination of Gases." 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



PROFESSOR WILHELM OSTWALD, in a work en- 

 titled Lehrbuch der Allgemeinen Chemie (Bd. ii. 

 p. 745), has criticised my paper on the Chemical Combina- 

 tion of Grases published in the Philosophical Magazine, Octo- 

 ber 1884, in which I applied the Williamson-Clausius theory 

 of dissociation to the solution of several problems in the theory 

 of the combination of gases. I wish in this letter to answer 

 this criticism, and, in order to make my meaning clear, I 

 must recapitulate one part of the paper. According to the 

 Williamson-Clausius hypothesis, the molecules of a gas are 

 continually splitting up into atoms, so that the atoms are 

 continually changing partners. I denned the " paired " time 

 of an atom to be the average time an atom remained in part- 

 nership with another atom, and the " free time " the average 

 time which elapses between the termination of one partner- 

 ship and the beginning of the next. Now the free time will 

 evidently depend upon the number of free atoms in the unit 

 volume, for before an atom can be paired again, it must come 

 into collision with another atom ; and though it need not get 

 paired at the first collision, yet it is evident that the time it 

 remains " free " will be proportional to the time between two 

 collisions, and, therefore, inversely proportional to the number 

 of free atoms in unit volume. But after the atom has got 

 paired with another, there is no reason why the time they 

 remain together should depend upon the number of molecules, 

 unless we assume that the atoms are knocked apart by colli- 

 sion with other molecules. 



As one of my reasons for undertaking the investigation 

 was, that an eminent spectroscopist had mentioned to me that 

 there was spectroscopic evidence to show that the molecules 

 got split up independently of the collisions, and as I wished 

 to see if I could get any evidence of this from the phenomena 

 of dissociation, it would have been absurd on my part to beg 

 the question by assuming that the paired time was inversely 

 proportional to the number of atoms. I therefore made no 

 supposition as to the dependence of the paired time on the 

 number of atoms, except when the dissociation was produced 

 by an external agency, such as the electric discharge, but left it 

 to be determined from the experiments. 



The above reasoning seems to me to be clear enough, but 

 as it is substantially the same as that in my paper, and Prof. 

 Ostwald says it is difficult to conceive how it is that I have 



