148 AXIMAL CHEMISTRY LECTURE VI. 



Sulphurous Hydric perox. Sulphuric "Water 



H a S0 3 H 2 0.0 = H 2 S0 4 + H a O, 



The second half of the liquid I now pour into this bottle, 

 charged, as you see, with brown fumes of peroxide of nitrogen, 

 and agitate the whole for an instant or so ; when the rapid oxida- 

 tion of the sulphurous acid is rendered evident, in this as in the 

 former experiment, by an abundant precipitation of sulphate of 

 barium, while the brown peroxide is simultaneously reduced to 

 the state of colourless oxide of nitrogen, thus : 



Sulphurous Nitric perox. Sulphuric Nitric oxide 



H a S0 3 + NO.O = H 2 S0 4 + NO. 



(156.) The peroxides of hydrogen and nitrogen, therefore, are 

 deoxidised by sulphurous acid in a precisely similar manner ; but 

 we shall find a great diiference of behaviour in the protoxides re- 

 sulting from their respective deoxidations. Thus the protoxide of 

 hydrogen, or water, is a far more difficult substance to peroxidisethan 

 sulphurous acid itself. It is only, indeed, by a series of indirect 

 processes that we are able to fasten on to its molecule an additional 

 atom of oxygen, so as to convert it into the peroxide; and this 

 added atom of oxygen is retained with such a feeble force, that it 

 is frequently thrown off in the gaseous state, and constantly 

 given up with the greatest readiness to any oxidisable substance, 

 such as sulphurous acid. Although, therefore, it seems strange 

 that sulphurous acid should not readily absorb oxygen from the 

 air, there is nothing strange in its taking away the additional 

 loosely combined oxygen existing in peroxide of hydrogen. But 

 the oxide of nitrogen resulting from the deoxidation of its per- 

 oxide is a very different kind of body. Of all compounds known 

 to chemists it is the one which absorbs free oxygen with the 

 greatest avidity. No sooner, for instance, do I open the stopper 

 of this bottle than the contained nitric oxide which we reduced 

 from the peroxide a few minutes ago, combines at once with fresh 

 oxygen from the air to become reconverted into the brown per- 

 oxide ; and, on now closing the bottle and agitating its contents, 



