272 Dr. V. H. Veley on Initial 



zinc is placed in dilute .sulphuric acid ; the acceleration was 

 noticed simultaneously by Spring- and Aubin ^ in measure- 

 ments of zinc dissolved per unit area per unit time (-—\ 

 and by myself in measurements of hydrogen gas evolved per 

 unit volume per unit time -^ t- This case is so far analogous 



to the one cited above in that if the zinc is cast into spheres 

 and rolled about in the acid continually kept in agitation the 

 reaction proceeds uniformly per diminution area per time, 

 namely, 



— -^- = const (1) 



or in relation to the concentration of acid C supposed in 

 ^lere 



dsO 



excess and volume of sphere 



4/3Mr3 + C 



= -OT (2j 



Case 2. The formation of one of the products of the 

 reaction which acts as an accelerator. 



(1) The production of manganese sulphate J in the reaction 

 between potassium permanganate and oxalic acid, which was 

 first investigated by Harcourt and Esson many years ao-o, 

 but not fully dealt with as being of a too complicated type. 



(2) The formation of mono-symmetric sulphur § in the 

 conversion of rhombic sulphur into that modification. 



(3) The formation of cyamelide in the polymerization of 

 cyanic acid || . 



In examples of Case (1) Ostwald gives the difFerential 

 equation 



|^=(/.i + /.-,C)(A-C)(B-C), . . . (3) 

 and for those of Case (2) 



^=Z'i + >t,(A-C)'-(B-C), ... (4) 



but it does not appear that at present any series of observa- 

 tions on the rate of chemical change of this type have been 

 subjected to mathematical analysis. 



* Ann. Chim. Fliys. [6] xi. p. 505. 



+ Phil. Traus. A. p. 257 (1888). 



X Ibid. p. 201 fa 860). 



§ Eeiclier, Incmt/vral Dissertation, Amsterdam, 1888. 



II Van't Hoft'; loc, cit. supra. 



