110 PROF. F. CRACE-CALVERT ON THE 



matiori of carbonate of the protoxide of iron, mixed with 

 carbon existing in the iron ; and then the excess of oxygen 

 in the mixture converted the carbonate into magnetic or 

 saline oxide of iron, with a little sesquioxide of iron. Whilst 

 these phenomena were proceeding with that portion of the 

 blade exposed to the gaseous atmosphere, the one dipping 

 into the aqueous solution was observed to loose its bril- 

 liant and metallic lustre in a few minutes, presenting a 

 black appearance, which became, at the end of three hours, 

 of a dark greenish hue, due to the formation of similar 

 compounds as those above described. 



In all these experiments the water became not only 

 turbid after a short time, but on the surface of the same 

 floated a considerable amount of magnetic oxide and car- 

 bonate of the protoxide of iron, and which varied in quan- 

 tity according to the relative proportions of oxygen and 

 carbonic acid employed. This series of experiments con- 

 firms the result of the previous ones, that carbonic acid is 

 a most active agent in determining the oxidation of iron*. 



Action of Carbonic Acid on Iron in presence of Water. 



Having studied the action of oxygen and of carbonic 

 acid and oxygen on iron in the presence of water, I was 

 desirous of ascertaining what would be the action of car- 

 bonic acid and water. I operated in a similar manner as 

 in the previous experiments, and obseiwed that the blades 

 in the gaseous mixtures had assumed a dark grey appear- 

 ance ; in the liquid they were black, the carbon having been 

 rendered perceptible by the iron having been dissolved as 

 carbonate of protoxide of iron, soluble in the excess of 

 the carbonic acid. After a few days, a perfectly white 

 deposit was formed on the edge of the water, which gra- 

 dually increased and became so abundant that some fell to 



* The composition of the various deposits above described was not 

 assumed, but was determined by careful analysis. 



