1888.] A Case of gradual Chemical Change. 125 



ratio to the amount of each present ; the composition of the mixture 

 thus remains practically unchanged, and the rate of decomposition 

 in each mixture is constant. Each experiment then is brought to an 

 arbitrary close as soon as the constant velocity has been determined 

 by the observation of a few intervals. The subjects of investigation 

 were : the comparison of the velocities in different mixtures, and thus 

 the establishment of laws connecting variation in velocity with varia- 

 tion of each of the ingredients. 



In a large number of experiments hydrogen chlorate was used. Mix- 

 tures of dilute solutions of the two acids, chloric and hydrochloric, were 

 made in various proportions ; being arranged in several series in each 

 of which the amount of one of the acids present was varied in arith- 

 metical progression, and the effect upon the rate investigated. Then 

 the effect of the presence of certain quantities of potassium chloride 

 upon the rate was observed, for the purpose of connexion with a new 

 series of experiments. In these potassium chlorate and hydrogen 

 chloride were used, and series for variation of one of the ingredients 

 taken as before. The effect of varying the quantity of potassium 

 iodide present and that of varying the temperatures were also 

 observed. 



The results may be thus briefly summarised : 



Variation in Hydrogen Chlorate. The rate varies with the amount 

 of hydrogen chlorate, in the first place, directly, as a substance 

 taking part in the chemical reaction ; and in the second place with a 

 small acceleration proportional to the quantity present, so that the 

 substance has a coefficient of action independent of its being a parti- 

 cipant in the reaction. Thus 



B = aQ (1 + 6Q), 



where Q represents quantity, B rate, a and 6 constants. 



Variation in Hydrogen Chloride. The variation of the rate with 

 that of hydrogen chloride is not of this simple nature. It would 

 seem to be (1) an effect of the secondary order above mentioned 

 (accelerative) on the decomposition of hydrogen chlorate by itself, 

 and in addition to this (2) an effect of both primary and secondary 

 order on the decomposition of hydrogen chlorate with hydrogen 

 chloride. 



Variation in Potassium Chloride. The addition of this salt has a 

 small accelerative effect on the normal rate proportional to its quan- 

 tity. It thus appears to be a neutral salt not taking part in the 

 reaction. 



If a mixture of solutions of potassium chlorate and hydrogen 

 chloride in molecular proportion between 1 : 2 and 1 : 12 is made, 

 complete double decomposition ensues, the hydrogen chlorate formed, 

 in presence of the hydrogen chloride remaining, liberates oxidising 



