274 



MR. V. H. VELEY ON THE CONDITIONS OF THE 



compound abed decomposes initially into ab and cd, which in their turn form ac and 



bd, thus 



(i.) abed = ab -\- cd 



(ii.) ab + cd = ac + bd, 



then, if neither of these changes is instantaneous, the rate at which bd, the measured 

 compound, is produced would gradually increase until the velocity of change (ii.) is 

 equal to that of change (i.). The reverse case of (i.) may also occur, in which ab and 

 cd combine to form abed, which is again decomposed thus 



(i.) ab + cd = abed 

 (ii.) abed = ac -\-bd. 



The experiments illustrative of this phenomenon are given below for a variety of 

 chemical changes. In Part I. the intervals of time observed before the maximum and 

 constant rate was reached have in all cases been omitted in order to shorten the 

 tables. To make the results the more comparable, all the observations are reduced on 

 the supposition that the mass of the substances undergoing decomposition remained 

 constant. 



Decomposition of Formic Acid into Carbonic Oxide and Water. 



Constant mass of sodium formate = 5 grams, corresponding to 3'384 grams of 

 formic acid, and yielding a sufficient volume of carbonic oxide for 160 observations of 

 10 c.c. each. Temperature 80'8 to 80'9. The observations are given up to the 

 point of maximum and constant rate. 



To determine the effect produced by a temporary lowering of temperature, at the 

 conclusion of the observations recorded in the first column the mixture was cooled by 

 being placed into water at 20, which caused the temperature to fall to 70. The flask 

 was then restored to its position and quickly heated up to the former temperature, 

 80'8 to 80 0> 9, when observations were again made ; but, as the loss of gas in the 

 interval was not determined, the times recorded in the second part of the table are 

 not reduced. They show, however, that the phenomenon of initial acceleration 

 repeats itself, 



