400 



Mr. W. H. Pendlebury and Miss M. Seward. 

 Table A. 



In this table are given the rates, representing the number of 

 hundred millionths of a gram of potassium chlorate decomposed 

 per minute in each .cubic centimetre of the liquid. The mixture con- 

 tained in each cubic centimetre 



{0'03789 gram potassium chlorate. 

 0'02496 gram hydrogen chloride. 



The potassium iodide present during successive intensities was 

 nX 0-000001978 gram, and n varied from 1 to 12. 



It will be noticed that there is at first a slight acceleration with 

 increase of potassium iodide, but very far from proportional to the 

 increase, as would be the case if the reaction depended primarily on 

 the amount of iodide present. After n = 5 the further multiplication 

 of the small quantity produced little if any charge in the rate. Per- 

 haps the minute amount of iodide present during the first few obser- 

 vations was insufficient for the immediate amount of the chlorine and 

 chlorous oxides formed. 



In fact the above numbers, besides showing that the liberation of 

 iodine is a separate reaction, not the primary one, seem also to indi- 

 cate that though with the quantity of potassium iodide usually taken 

 this secondary reaction is instantaneous compared with the primary 

 one, if the quantity is much decreased the former does take up a 

 time which is comparable with that of the latter, and so may produce 

 an appreciable retardation. 



We shall return to the consideration of variation of potassium 

 iodide later on, but have pointed this out to emphasise further the 

 observation already made, that time must be a factor in all changes, 

 but in very few does the connexion come within our powers of obser- 

 vation, so that other changes compared with these few are called 

 instantaneous. 



The amount of potassium iodide generally used in our experiments 

 corresponds to n = 60 in this series. In other sets of observations 

 some of which are recorded in Tables XI, XII, and XIII, p. 417419, 

 the effect of adding larger amounts of potassium iodide was tried. The 



