BETWEEN THE CONDITIONS OF A CHEMICAL CHANGE AND ITS AMOUNT. 221 



(4) y<a. The fraction of v decomposed in a unit of time greater than the fraction 

 of u decomposed in a unit of time. 



In this case the last equation of the system is of the form 



The experimental cases corresponding to this are recorded on pages 210, 215, «:=4, 6, 

 8,10. 



It is thus possible to have all these four cases in succession in a set of experiments 

 in which only one condition is progressively varied, provided that the variation of 

 y and « is such that y is at first greater than a, but increases in a less ratio than a. 

 Several attempts have been made to calculate equations of the form y=aie~'''''+aie~''^ 

 vphich should give the experimental numbers within the eiTors of experiment, and at the 

 same time yield values of the fractions a, |8, y from which the law of their variation with 

 a variable quantity of sulphuric acid could be discovered. Some of these equations are 

 recorded on page 214. The number and exactness of the experimental results are, how- 

 ever, not sufficient to enable us to extract from the complicated equation 



trustworthy values of a, (3, y, and this inexactness precludes the possibility of investi- 

 gating the law of their variation when the conditions of the experiment are varied. 

 What we can state with certainty is, that the numbers are all satisfied by equations of 

 the forms 



y=zae~", 



and that successive sets of numbers, obtained by varying one condition progressively, are 

 satisfied by these successive forms of equations. These forms, and the order of their 

 succession, are accounted for by a hypothesis for which there is considerable experi- 

 mental evidence, and it is thus highly probable that the results arrived at in the above 

 discussion give a true account of the progress of the reaction. 



The law of variation of a, j3, y with the conditions of the system will probably be 

 detected when the case in which (3, y both vanish for all conditions of the system, has 

 been fully discussed. 



A complete investigation of this case is reserved for a future communication. 



