An Investigation of a Case of gradual Chemical Change. 401 



effect is to produce a slight addition to the rate, proportional to the 

 amount of iodide added. A similar result has been obtained with 

 potassium chloride, and in view of these results we conclude that 

 potassium iodide acts only as an indifferent salt, and does not imme- 

 diately promote the reduction of the potassium chlorate, but only 

 serves to prevent the accumulation in the liquid of chlorine or chlo- 

 rine oxides precisely as the presence of thiosulphate serves to prevent 

 the accumulation of iodine. 



FIG. 1. 



The apparatus employed in all our experiments was the same as 

 that used by Messrs. Harcourt and Esson, and consisted of a cylinder 

 of white glass 310 mm. high and 64 mm. in diameter ; at a distance 

 of 213 mm. from the base a fine line was etched round the cylinder 

 marking a volume of 792 c.c. The cylinder was closed with an india- 

 rubber stopper perforated with three openings, through which passed 

 a thermometer and an inverted funnel tube. The third hole was 

 ordinarily closed with a cork, and served to give access to the con- 

 tents of the cylinder. The inverted funnel tube was connected with 

 an apparatus for the generation of carbon dioxide. 



The method of proceeding was as follows : Into the cylinder pre- 

 viously filled with carbon dioxide was brought the weighed quantity 

 of potassium chlorate to be employed, with sufficient water to dissolve 

 it. To this was added a measured volume of hydrogen chloride of 



