ON THE VELOCITY OF CHEMICAL REACTIONS 



William Duane 



In investigating the laws of physical chemistry it is expedient 

 for the physicist to devise and develop the methods of measurement, 

 and for the chemist to apply them. In the following pages are de- 

 scribed two methods of measuring the velocity of chemical reactions. 

 The velocity of a chemical reaction is the rate at which a chemical 

 compound appears or disappears during that reaction. The changes 

 in the quantity of this compound present during successive intervals 

 of time are measured by the changes in some property of the chem- 

 ical system during the intervals. This property is usually either a 

 chemical or a physical one. 



Fig. 1. 



In the first of the followincr methods the basis of the measure- 



o 



ment is the change in the index of refraction of the system, and in 

 the second the change in its volume. 



The first method is applicable to those chemical systems only 

 that are transparent. It is substantially the following : Rays of 

 light from an illuminated slit S (Fig. 1) passing through a long focus 

 lens L and the tube a h c d form a distant image S, of S. The slit 

 S is perpendicular to the plane of the diagram which represents a 

 horizontal section of the apparatus. The tube ah c d has plane glass 

 ends a h and c d; and a plane glass plate a c divides it into two 



Originally printed in The American Journal of Science, Vol. XI, May, 1901. Reprinted 

 through the courtesy of the Editor of that Journal. 



