LEWIS. — AUTOCATALYTIC DECOMPOSITION OF SILVER OXIDE. 725 



complete and satisfactory for further discvission. These were made at 



327.0° C, 332.5° C, 352.2° C, and 353.3° C, and may be designated 



A, B, C, and D, respectively. 



The results are represented in Figure 2, the reaction velocity being 



plotted vertically and the time horizontally. Instead of the time when 



the experiment began, the time of maximum velocity was taken as zero. 



Thus, the maxima of all the curves fall on the same vertical line. The 



velocity is expressed as the fraction of the whole quantity of oxide which 



is decomposed per second. This can, of course, be readily found from 



(he rate of evolution of oxygen when the temperature and pressure are 



known. If x represents the fraction of the original oxide that has been 



dx 

 decomposed, the velocity is — . 



An inspection of these curves shows, as was to be expected, that the 

 maximum velocity is greater and the whole time of the decomposition 

 less the higher the temperature of the experiment. Further, we are 

 struck by the great regularity of the curves and by their very evident 

 similarity to one another. They appear to belong to a single family of 

 curves, such as may be represented algebraically by a single equation 

 with one variable parameter. It seemed likely that if these curves were 

 reduced to the same scale they might almost coincide. 



This was attempted by plotting each experiment with a different unit 

 of time, so chosen as to make each maximum velocity equal to unity ; 

 that is to say, the unit of time in each case is the time which would be 

 required for complete decomposition if the whole reaction progressed at 

 a uniform rate ecjual to the maximum velocity. In other words, the 

 units of time chosen are inversely proportional to the maximum velocities, 

 which therefore, in the new scale, become numerically equal and fall on a 

 single point. 



The four curves thus plotted in Figure 3 come astonishingly near to coin- 

 cidence; in fact, they do coincide within the limits of experimental error. 



Among all the cases in which reaction velocity has been studied, the 

 present phenomenon occupies a wholly unique position. Exceedingly 

 few autocatalytic reactions have been quantitatively studied. In a homo- 

 geneous system the study of the reaction of oxalic acid and permanganate 

 by Schilow * may be mentioned, and in heterogeneous systems the study 

 of the action of acids on sodium thiosulphate by Foussereau,t and the 



* Ber. d. deutsch. Cliem. Ges., 36, 2735 (1903). 

 t Ann. Chim. Phys. (6), 15, 533 (1888). 



