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X. On the Laws of Connexion between the Conditions of a Chemical Change and its 

 Amount. By A. Vernon Hakcourt, M.A., Student of Christ Church., and Bermm- 

 strator of Chemistry in the University of Oxford; and William Esson, M.A., Fellow 

 of Merton College, Oxford*. Communicated by Sir B. C. Brodie, Bart, F.R.S., 

 Professor of Chemistry in the University of Oxford. 



Received September 5, — Read November 16, 1865. 



I. On the Reaction of Permanganic and Oxalic Acids. 



When any substances are brought together under circumstances under which they act 

 chemically one upon another, a change takes place which consists in the disappearance 

 of a part of the original substances and the appearance of an equal weight of other sub- 

 stances in their place. This change continues, if the circumstances remain the same, until 

 the whole of one of the substances taking part in it has disappeared. Its total amount 

 is therefore ultimately determined by the amount of that substance which was originally 

 present in the smallest proportional quantity. The attainment of this limit, as will be 

 shown, requires theoretically an infinite time, but the velocity of chemical change is so 

 great that the practical limit of an inappreciable residue is in most cases speedily reached. 

 Owing perhaps to this fact, chemists have been led to bestow their chief attention upon 

 the result, and not upon the course of these changes. Occupied in investigating the 

 relation between the reagents and the ultimate products of a reaction, and studying the 

 chemical and physical properties of the thousand diflFerent substances thus produced, they 

 are accustomed to regard the various conditions under which every chemical change takes 

 place, and by which its amount is determined, chiefly as means to an end, as points to be 

 attended to in a receipt for preparing one substance from another. 



The object of the investigation which the authors have the honour of laying before 

 the Royal Society in the following pages, has been to estimate quantitatively the relation 

 of chemical change to some of these conditions. With this view they have selected for 

 examination cases in which the change appeared to be of a simple character, and the 

 conditions affecting it few in number, and capable of being defined. 



Although unquestionably every chemical reaction is governed by certain general laws 

 relating to the quantity of the substances partaking in it, their temperature and physical 

 state, and the time during which they are in contact, yet the number of cases in which 

 the investigation of these is practicable is extremely limited. In the first place, it must 



* The experimental inquiries recorded in this paper were chiefly Mr. Hakcoubt's, the mathematical discus- 

 sion is Mr. Esson's. 



MDCCCLXVI. 2 E * 



