108 PROF. F. CRACE-CALVERT OX THE 



into contact with large quantities of carbonic acid during 

 twenty-four hours. 



These results appeared so interesting, that I decided to 

 institute several series of experiments. 



First Series. — Perfectly cleaned blades of iron placed in 

 bottles filled with ordinary Manchester water were rapidly 

 covered with rust, whilst similar blades, placed in the same 

 water previously deprived of ah' and carbonic acid by boil- 

 ing, remained free from rust for a period of four weeks — 

 thus proving that oxygen and carbonic acid are necessary 

 for the production of oxide of iron in presence of water. 



Second Series. — Into bottles filled with some pure dis- 

 tilled water (which had been boiled and then allowed to 

 cool in corked flasks) blades of iron were introduced, and 

 a part of the water in the bottles was displaced by common 

 air, pure oxygen, or carbonic-acid gas ; but the results were 

 unsatisfactory. I therefore decided to keep the upper part 

 of the blades dry j to effect this, cleaned blades of crinoline- 

 wire were introduced into bottles containing pure oxygen, 

 and then boiled, and cooled distilled water was introduced 

 by means of an aspirator until only half the blades were 

 immersed in the water. By this method I was enabled to 

 ascertain the comparative degree of oxidation of that part 

 of the blades dipping in the water ; . and the results observed 

 were as follows : — 



The section of the blades out of the water remained 

 bright for several days, whilst that in the water became 

 attacked in about six or twelve hours j and the deposit in- 

 creased so quickly that, after two or three days, the blade 

 was entirely covered with an ochre deposit of the hydrated 

 sesquioxide of iron. This rapid oxidation of iron under 

 these circumstances appeared to me to be entirely due to 

 a galvanic current ; for the oxide was deposited in two 

 separate columns, which left the outside edges of the blade 

 perfectly bright, as well as the centre of it, each separate 



