Agency of Carbonic Acid. 265 



with calcined magnesia, in the first place ; and of water im- 

 pregnated with carbonic acid gas, in the second. 



In two experiments, I placed a quantity of iron in contact 

 with hme water, and with water and hme-water mixed in the 

 proportion of four-fifths of the former and one fifth of the 

 latter. There was not, in either case, after the lapse of a very 

 long time indeed, any oxidation of the iron or evolution of gas. 



In another experiment, I placed the iron in water in which 

 I had mixed some freshly-calcined magnesia. There was, in 

 this case, as in the former ones, no apparent chemical change. 



I now contrasted with these experiments, one in which I 

 placed portions of iron in water impregnated with carbonic 

 acid gas. There was a very speedy and rapid disengage- 

 ment of gas, which was proved to be hydrogen by being 

 exploded with a mixture of atmospheric air. A small portion 

 of lime being dropped into the retort, the disengagement of gas 

 immediately ceased. » . 



It cannot be uninteresting to find, that the carbonic acid 

 coincides in the same law and mode of action with iron, and 

 probably several other metals, as the sulphuric and the 

 muriatic, in co-operating to induce the decomposition of water 

 placed in contact with them. Whatever establishes and 

 extends any law in science, may be truly said to advance our 

 knowledge far more than the discovery of the mere fact alone. 

 It is on this ground that I trust the preceding part of this 

 Memoir may not be deemed uninteresting. 



The second object of this Memoir is to discuss the question 

 of the mutual action of iron and water, under more ordinary 

 circumstances than those which have been described. 



It has been already stated that when pure iron is placed in 

 contact with distilled water, which has been freed as much as 

 possible from its gases by long boiling, the decomposition of the 

 water has been effected extremely slowly. So tardily, indeed, 

 is this effect produced, that M. Thenard has suggested that it 

 may be an effect of the chemical agency of light*. This au- 

 thor has also suggested that this decomposition of the water by 

 iron, may, in some instances, be connected with the evolution 



* Traile de Chlmie, ed. V. torn. 1; p. 361. 



