OXIDATION OF IRON. 109 



column apparently representing the poles of a battery. In 

 fact, the production of this precipitate was 

 so rapid that, after a short time, a consider- 

 able amount was found as a deposit in the 

 bottle. 



To be certain that the oxidation of the 

 immersed portion of the blade was not due 

 to the fixation of oxygen dissolved in the fluid, but to the 

 decomposition of water through a galvanic current, I exa- 

 mined the gaseous mixtures existing in the upper part of the 

 bottle, and found hydrogen in large quantities, thus proving 

 that the water had been decomposed, its oxygen being fixed 

 by the iron, whilst the hydrogen was liberated. 



Action of Oxygen and Carbonic Acid on Iron in pre- 

 sence of Water. 



To ascertain the influence which carbonic acid exerts on 

 the oxidation of iron, I prepared mixtures of oxygen and 

 carbonic acid in the following proportions : — 



25 of oxygen to 75 of carbonic acid. 



75 » 2 5 



84 „ 16 „ 



88 „ 12 



Having introduced iron blades and the above gaseous mix- 

 tures into bottles, they were inverted over water so that 

 their necks dipped into this fluid. When half the gaseous 

 mixture had been displaced by aspiration, as in the previous 

 experiments, the following results were obtained; viz., whilst 

 that portion of the blade standing out of the water in the 

 previous experiments remained for weeks unoxidized, in 

 this series the same section of the blade assumed rapidly a 

 dark colour, which became afterwards of a dark brown. 

 This change of colour was no doubt due, first, to the for- 



