TRANSACTIONS OF THE SECTIONS. 29 



separate, that is, the base from the acid, then the hydrate of manganese thus dis- 



E laced woidd absorb free oxygen, and the sulphurous acid at once reduce again the 

 inoxide formed. At any rate, without insisting on so definite a hj^pothesis, it is 

 probable that this action of the manganese salt is in some way related to the fact 

 that the protohydrate of this metal has the property of absorbing oxygen from 

 water, and parting with this oxygen to sulphurous acid. Similarly this proto- 

 hydrate is readily oxidized by chromic or permanganic acid, and the resulting bin- 

 oxide is readily reduced by oxalic acid. 



Of these actions the author has selected for study that of permanganic upon 

 oxalic acid. 



AVhen the four following substances, permanganate of potassium, sulphuric acid, 

 oxalic acid, and sulphate of manganese, are brought together m aqueous solution, 

 a chemical change takes place, resulting in the formation of sulphate of potassium, 

 sulphate of manganese, carbonic acid, and water. The amount of change depends 

 upon the amount of each of the first-named four substances, upon the dilution and 

 temperatm-e of the solution, and upon the time during which the substances are left 

 in contact. As far as can be observed, these are all the conditions which affect the 

 amount of chemical change in this case ; it is not affected by light, nor by the agita- 

 tion of the solution. The amount of change is greater, within certain limits, in 

 proportion as the quantities of permanganate of potassium, sulphuric acid, and 

 sulphate of manganese are greater, and the quantity of water less ; in proportion 

 also as the temperature is higher, and the time of mutual contact longer. It is 

 gTeater, the larger the quantity of oxalic acid, up to that point at which the oxalic 

 and pemiangauic acids are present in the proportions in which they act one upon 

 the other ; after that point, an increase in the quantity of oxalic acid diminishes 

 the amount of chemical change. The author has made many series of experi- 

 ments, in each of which all of these conditions, except one, were kept invariable, 

 and that one was varied according to a regular progression. He hoped thus 

 to determine what function of each of these variable quantities the chemical 

 change is, and so to obtain a true expression of the reaction. He made, for ex- 

 ample, a series of experiments, in all of which he took the same quantities of per- 

 manganic acid, oxalic acid, sulphate of manganese, and water, maintaining always 

 a temperatm'e of 16° C, and allowing each experiment to proceed for exactly five 

 minutes ; but in the second experiment he took twice the quantity of sulphuric 

 acid used in the first, thrice the quantity in the third, four times the quantity in 

 the fourth, and so on. When five minutes from the moment of mixing had expired, 

 the action was stopped, and the amount of permanganate still remaining deter- 

 mined. A series of nimibers was thus obtained, presenting a regidar decrease, 

 which should bear an ascertainable relation to the corresponding quantities of sul- 

 phuric acid, taken in arithmetical progression. This relation, however, the author 

 has not yet succeeded in detennining ; but in this, as in other series, the numbers 

 exhibit the most perfect regularity. This is best seen by representing the results 

 graphically. Along the axis of x is mea- 

 sured that quantity, which is varied in 

 each successive experiment; along that of 

 y the quantity of changing substance which 

 remains still unchanged at the close of the 

 experiment. This quantity, it will be seen, 

 varies rapidly at first, the difterences be- 

 coming le.ss and less as the total quantity of „ 

 residual substance diminishes. The series 

 of experiments which appeared most inter- 

 esting was that in which, all other condi- 

 tions being kept constant, the time during 

 which the experiment lasted was varied. 

 Such a series jdelds a cmwe similar to that 



which represents the effect of varying the 0123456 

 amount ot sulphuric acid. The curve above ^ 



serves, therefore, as a general representation 

 of such a series. It may be regarded in this case as exhibiting the course of a 



