1865.] Laws of Connexion, fyc. 471 



not well adapted to the purpose in view. It is not chemically simple. 

 More than one change occurs under the circumstances of the experiment, 

 and the equation above written represents only a net result. But the ex- 

 amination of a second and simpler reaction in which the authors are at 

 present engaged, has confirmed an explanation which had already suggested 

 itself to them of the results of this series of experiments, and thus they are 

 now enabled to present these results together with a theory which explains 

 and is supported by them. 



The effect of varying the amount of each of the reagents and the dura- 

 tion of the action was successively investigated. The remaining condition 

 of temperature was not made the subject of experiment, owing to the dis- 

 covery of the complex nature of the chemical change. A series of Tables 

 contain the numerical results of these experiments. The principal com- 

 plication arises from a secondary reaction which takes place between per- 

 manganic acid and the manganous salt formed by its reduction. It became 

 necessary, in consequence of this action, to include manganous sulphate 

 among the reagents the effect of whose variation was to be determined. 



The general method of experimenting was briefly as follows : Measured 

 quantities of the standard solutions of oxalic acid, sulphuric acid, and man- 

 ganous sulphate were mixed with a measured quantity of water and the 

 whole brought to a temperature of 16 C. A measured quantity of a stan- 

 dard solution of potassic permanganate was added, and the time of the 

 addition noted. Throughout the course of the action the temperature, 

 observed by means of a thermometer passing into the fluid, was kept rigo- 

 rously constant. When the required interval had elapsed, an excess of 

 potassic iodide was thrown in, and the liberated iodine, which furnishes an 

 exact measure of the residual permanganic acid or manganic oxide, esti- 

 mated by means of a standard solution of sodic hyposulphite. The amount 

 of chemical change occurring in any given time with any given amounts of 

 the several reagents can thus be determined. 



1 . Variation of Sulphuric Acid. Each experiment of this series was 

 allowed to proceed for four minutes. Oxalic acid and potassic permanga- 

 nate were employed in the proportions in which they act one upon another. 

 The quantity of sulphuric acid was varied from the proportional quantity 

 up to seven times that amount. A regular increase in the amount of che- 

 mical change within the allotted time occurs with each increment of sul- 

 phuric acid. The relation of these quantities, which formed the subject 

 of many series of experiments, is, however, of a complex character. Two 

 or three reactions, it is shown, occur simultaneously, and each of these is 

 influenced by the acidity of the solution. 



2. Variation of Manganous Sulphate. At the ordinary temperature in 

 a dilute and feebly acid solution, permanganic acid acts very slowly upon 

 oxalic acid, but the presence of a manganous salt, formed by its reduction 

 or previously added, causes a great acceleration. This acceleration is shown 

 to reach a maximum when three molecules of manganous sulphate are 

 taken to one of permanganate. By the reaction of these quantities man- 



