1866.] 



Lau's of Connexion, ^c. 



265 



the law of connexion between the condition thus varied and the amount of 

 change. 



Accordingly a series of sets of experiments was made, in which, all else 

 being kept constant, different quantities of potassic iodide were used in 

 different sets. It is shown that the values of a derived from the different 

 sets of experiments are proportional to the quantities of iodide used in each 

 case. In this series hydric sulphate was an ingredient of the solutions ; a 

 second series was made, in which an equivalent quantity of hydric chloride 

 was substituted. The result, as regards the effect of varying the amount of 

 iodide, was the same as in the previous series. The rate of chemical change, 

 that is to say the amount in a given time with a constant quantity of per- 

 oxide, was found to be directly proportional to the amount of iodide in the 

 solution. Thus the law of connexion is the same in this case as in that 

 already investigated of the variation of peroxide. 



The total amount of chemical change is a function of all the conditions 

 of the system in which it occurs. If we call this amount 2, the volume of 

 the solution v, its temperature h, the time during which the change pro- 

 ceeds t, and the amounts of the various ingredients, peroxide, iodide, &c. 

 in a unit of volume, p, i, a,b, c . . then 



^ b, c, . . . h,i, . , . . . t, . .V . . .). 



The form of this function is determinate in the case of two of these condi- 

 tions, viz. V, t, and has now been determined experimentally in the case of 

 p and i, so that the equation may be written in the form 



2=^^ t V ./(«, b, c . . , h , . 

 The number of ingredients, represented by a, b, c, &c., which may be in- 

 troduced into the system and affect the amount only, and not the nature of 

 the chemical change, and which m^ay therefore be regarded as so many con- 

 ditions of the reaction, is doubtless very large. The authors believe that 

 the investigation of the influence of some of these may prove of interest, it 

 being possible thus to compare various substances which may be sub- 

 stituted one for another in the system by a new standard. They find, for 

 example, that comparing equivalent quantities (in the ordinary chemical 

 sense) of hydric sulphate and hydric chloride, the effect of the latter is 

 nearly double that of the former. But the most important condition of 

 the change whose influence is still undetermined is that of temperature, for 

 this condition intervenes under all circumstances of the reaction, and indeed 

 in all chemical changes whatever. The authors have already made many 

 experiments on both these points. The results of this investigation, which 

 will complete the study of the reaction, may, they hope, form the subject 

 of a subsequent communication. 



