378 ^Ir. J. J. Hood on flu- Laws of Chemical Change. 



Since A and wA arc the values of the active bodies before 

 tlio action begins, tliey cannot be taken as the initial values 

 when / = 0, as the equation only applies when the change is 

 actually going on, and the solutions require to stand a few 

 minutes after mixing to allow the action to get into a normal 

 state before the first observation can be made, when t is to be 

 taken as =0. Putting y = A — oc, or amount remaining at 

 time t y the equation becomes 



j = _^((»-l)A+y), (6) 



the solution of which is 



, ^ , A log, , ^-r =C-fcvt. . (7) 



(n— 1)A Se (n — l)A+ f y 



Let a be the value ofy when £ = 0, 



(n-l)A * e (n-l)A + a s 

 and inserting this value, the final equation becomes 



-•-^MfeX 4 ^)}' . < 8 > 



where 



q/ == log«10 

 tcv{n — 1)A* 



This equation is established on the same supposition as (4), 

 and that the compounds formed during the action have little 

 influence on the change either as retarding or accelerating 

 agents, as indeed the experiments indicate. 



Experiments. — As yet I have not been able to try very ex- 

 treme values for n ; in the experiments made it only ranged 

 from *5 to 5 ; above this latter value the action proceeded so 

 rapidly that large errors occurred, rendering the results worth- 

 less : still I think the following experiments may be of in- 

 terest as showing the truth of the formula. 



The method of making the experiments was exactly the 

 same as for those given in the first part of this paper. 



Experiment (a). — The solutions employed were 25 cubic 

 centims. ferrous sulphate (equal to '4923 grin, iron), 10 cubic 

 centims. potassic chlorate containing '3593 grm., and 2G0 

 cubic centims. water — total volume 295 cubic centims, — this 

 quantity of potassic chlorate being able to oxidize twice the 

 amount of iron present, or n = 2. The number of cubic cen- 

 tims. of permanganate required for 10 cubic centims. of this 

 solution before the action commenced, or the value of A, was 



