394 Royal Society ■.•-— 



aqueous solution of chlorine in the acid solution of peroxide of 

 barium, but more slowly. I have elsewhere shown that the action 

 of iodine is expressed by the equation 



I 2 +Ba 2 2 =2BaI + 2 . 



(4) The decomposition of chromic acid is of special interest. In 

 this case there are two distinct reactions, the first of which takes 

 place when chromic acid is in excess, according to the equation 



2Cr 2 3 + 3H 2 2 =Cr 4 3 + 3H 2 + 30 2 ; 



the second, which occurs when a large excess of peroxide of hydrogen 

 is present, and in which the peroxide of hydrogen loses exactly 

 double the amount of oxygen lost by the chromic acid, so that the 

 final result is expressed by the equation 



2Cr 2 3 + 6H 2 2 = Cr 4 3 + 6H 2 + 9 . 



In the interval between these reactions the ratio of the loss of 

 oxygen from the peroxide to the loss from* the chromic acid varies 

 between the limits 1 and 2 according to a definite law, being pro- 

 portional to the ratio of the masses of the substances employed. I 

 am able to show, by direct experiment, that the reaction between 

 the extreme limits is the sum of two distinct and simple atomic de- 

 compositions. 



The alkaline peroxides which produce these peculiar effects of 

 reduction, under other conditions act as powerful oxidizing agents ; 

 thus an acid solution of ferrocyanide of potassium is oxidized by 

 peroxide of hydrogen to ferricyanide. Hydrated protoxide of man- 

 ganese is oxidized by peroxide of barium to the condition of peroxide 

 of manganese. A concentrated solution of hydrochloric acid evolves 

 chlorine from peroxide of barium. 



This last reaction I have made the subject of a special investiga- 

 tion, with the view of determining the conditions under which the 

 two reactions, 



4HCl+Ba 2 2 =2BaCl+2H 2 + Cl 2 , 



and 2HCl+Ba 2 2 = 2BaCl + H 2 2 , 



respectively take place ; and I find that when a solution of hydro- 

 chloric acid is boiled with peroxide of barium, if the solution be con- 

 centrated, chlorine, if the solution be dilute, oxygen, exclusively is 

 evolved ; and that for each intermediate degree of dilution chlorine 

 and oxygen together are evolved in a constant ratio. 



It is thus seen that those differences in the behaviour of the 

 different classes of peroxides, from which an imaginary distinction 

 has been drawn between the oxygen respectively contained in them 

 as positive or negative, are not fundamental and characteristic 

 differences. The oxygen in the peroxide of barium is the same as 

 that in the peroxide of manganese, according to the only test of 

 identity which we can apply, for we can produce with it the same 

 effects. Nor are the peculiarities in the reactions of the oxygen of 

 the alkaline peroxides of such a nature as to need any special hypo- 

 thesis to account for them ; for in no case are the combining proper- 

 ties of the particles of matter, like their atomic weights, constant for 



