o/n NE AND HYDROGEN PEROXIDE DALTnN'S LAW 207 



it leaves H 2 or O 2 , which do not act so sharply, although they still 

 contain oxygen. 17 Both contain the oxygen in a compressed state, so 

 to speak, and when freed from pressure by the forces (internal) of the 

 elements in another substance, this oxygen is easily evolved, and there- 

 fore acts like oxygen at the moment of its liberation. Both substances 

 in decomposing, with the separation of a portion of their oxygen, evolve 

 heat, while an absorption of heat is usually required for decomposi- 

 tion. 



Hydrogen peroxide is formed under many circumstances by com- 

 bustion and oxidation, but in very limited quantities ; thus, for instance, 

 it is sufficient to shake up zinc with sulphuric acid, or even with water, 

 to remark the formation of a certain quantity of hydrogen peroxide in 

 the water. 18 From this cause, probably, a series of diverse oxidation 

 processes are accomplished in nature, and, according to Prof. Schone, of 

 Moscow, hydrogen peroxide occurs in the atmosphere, although in vari- 

 able and small quantities, and probably its formation is connected with 

 ozone, with which it has much in common. The usual case of the 

 formation of hydrogen peroxide, and the means by which it may be in- 



17 It is evident that there is a want of words here for distinguishing oxygen, O, as an 

 ultimate element, from oxygen, Oo, as & free element. It should be called oxygen gas, did 

 not habit and the length of the expression render it inconvenient. 



18 Schiinbein states that the formation of hydrogen peroxide is to be remarked in every 

 oxidation in water or in the presence of aqueous vapour. According to Struve, hydrogen 

 peroxide is contained in snow and in rain-water, arid its formation, together with ozone 

 and ammonium nitrate, is even probable in the processes of respiration and combustion. 

 A solution of tin in mercury, or liquid tin amalgam, when shaken up in water containing 

 sulphuric acid gives rise to the formation of hydrogen peroxide, whilst iron under the 

 same circumstances does not give rise to its formation. The presence of small quantities 

 of hydrogen peroxide in these and similar cases is recognised by many reactions 

 Amongst them, its action on chromic acid in the presence of ether is very characteristic. 

 Hydrogen peroxide converts the chromic acid into a higher oxide, Cr 2 O 7 , which is of a 

 dark-blue colour, and dissolves in ether. This ethereal solution is to a certain degree 

 stable, and therefore the presence of hydrogen peroxide may be recognised by mixing 

 the liquid to be tested with ether and adding several drops of a solution of chromic acid. 

 On shaking the mixture the ether dissolves the higher oxide of chromium which is 

 formed, and acquires a blue colour. The formation of hydrogen peroxide in the combus- 

 tion and oxidation of substances containing or evolving hydrogen must be understood in 

 the sense of the conception, to be considered later, of molecules occupying equal volumes 

 in a gaseous state. At the moment of its evolution a molecule H.> combines with a mole- 

 cule O 2 and gives H 3 O 2 . As this substance is unstable, a large proportion of it is 

 decomposed, a small amount only remaining unchanged. If it is obtained, water is easily 

 formed from it ; this reaction evolves heat, and the reverse action is not very pro- 

 bable. Direct determinations show that the reaction H 2 O 2 = H 2 O + O evolves 22000 heat 

 units. From this it will be understood how easy is the decomposition of hydrogen 

 peroxide, as well as the fact that a number of substances which are not directly 

 oxidised by oxygen are oxidised by hydrogen peroxide and by ozone, which also evolves 

 heat on decomposition. Such a representation of the origin of hydrogen peroxide has 

 been developed by me since 1870. In recent times Traube has pronounced a similar 

 opinion. 



