I 



[ 271 ] 



XXXiy. hutial Accelevatlon in Chemical Chanqe. 

 By y. H. Yeley, D.Sc, F.E.S.^ 



DURING the past forty years the phenomenon of so-caUed 

 initial acceleration has formed the subject of many 

 observations in cases of yery different types ; the literature 

 has been collated by yan't Hofff, as also by myself J. As 

 more attention has been paid of recent years to investigations 

 on the rate and conditions of chemical change and to the 

 mathematical analysis of observations, it appeared of interest 

 again to take up the subject from the stand-point of our more 

 advanced knowledge. Though in most^ if not all cases, the 

 phenomenon in question can be referred to secondary actions, 

 yet it does not appear possible to include all such cases in the 

 same category. At the outset it is evident that when a 

 chemical change starts slowly at first, then increases to a 

 maximum and subsequently decreases according to the law 

 of mass action, such a result might be the effect of two wholly 

 different causes, namely, on the one hand of the gradual 

 formation of some accelerating substance up to a constant 

 amount, and on the other of a delay occasioned either by the 

 formation of isome intermediate substance or some retention 

 up to a certain amount of one of the products of the reaction. 

 The former would be a case of true acceleration, the latter of 

 true retardation or reluctance. 



In the present communication it is desired briefly to discuss 

 examples of these two different categories, and more especially 

 to deal with a consideration of cases of the latter. 



First category, Case (1). The formation of an inter- 

 mediate accelerator from one of the substances initially 

 present. 



(1) Formation of nitrous acid when certain metals are 

 placed in dilute nitric acid, as first observed by Millon and 

 more recently by myself § . 



(2) Formation of (probably) some persulphuric acid when 



* Comniunicated by tlie Aiitlior. 



t Studies in Chemical DynaDiics (Eng. trans.) pp. 91-101 (1896). 



X Phil. Mag. [5] xxxvii. p. 165 (1894). Ostwald, in alluding to this 

 paper, T\aites {Lehrbuch, Band ii. p. 269) as foUows : — " In der That 

 sind sie " (Beispiele) "so hiiufig dass dadurch ein sonst ganz verdienst- 

 licher Forscher V. II. Yeley sicli zu der ganz nnhaltbaren Annahnie 

 verleiten liess^ der geschilderte Eealrtionsverlauf mit anfanglicher 

 Beschleunigung sei der typische Fall der chemischen ^^organge ..." 



Though I cannot but appreciate the compliment contained in the 

 former portion of the paragraph, yet I must demur to the latter portion. 

 It is true that in our present state of knowledge the assumption is 

 untenable, but it is equally true that I have never maintained it. 



§ Phil. Trans. A. p. 279 (1891). 



