178 Dr. J. BOTTOMLEV on 



found in connection with the subject of this paper are 

 contained in a memoir by Spring and Van Aubel in the 

 Annales de Chiviie et de Physique [6], 1 1. They there give 

 the details of experiments to determine the velocity of 

 dissolution of spheres of zinc containing a minute amount of 

 lead in Hydrochloric, Hydrobromic, and Hydriodic acids of 

 different degrees of concentration, and at different tem- 

 peratures. They found that the maximum velocity, 

 measured by the volume of Hydrogen evolved, did not 

 occur at the commencement of the reaction ; they first 

 noted an increase and then a decrease. The period during 

 which the velocity is increasing they term the period of 

 induction ; this is most noticeable when the acids are 

 dilute ; with concentrated acids, the maximum velocity is 

 almost simultaneous with the commencement of solution. 

 Unfortunately their results are not strictly comparable with 

 the results of the theory announced in this paper ; I have 

 supposed that the mass of the solvent is kept in such a state 

 of disturbance that at any instant the whole mass may be 

 considered homogeneous. This condition does not seem to 

 have been fulfilled in their experiments ; the evolution of 

 Hydrogen when brisk would no doubt tend to mix the 

 different parts of the solution, but when the evolution was 

 slow this agency might not be sufficient to secure the 

 supposed condition. Hence we might expect, on comparing 

 results of experiments with calculations founded on the 

 above theory, that the times found b}- experiment would 

 depart further and further from the calculated times as the 

 solution approached completion. The calculation applies 

 of course only to that portion of the observations which 

 commences at the completion of the period of induction. 



The numbers in the following table are taken from the 

 memoir above cited ; they show the results of the action of 

 a 10 per cent solution of hydrochloric acid at the tem- 

 perature 15° C. on a sphere of zinc. Complete solution 



