254 EIGHTH REPORT — 1838. 



of the chemical actions, under vai-ious modifications, of air and 

 water upon iron ; 2nd, a statement of the experiments upon 

 the large scale which have already been instituted at the re- 

 quest of the British Association ; 3rd, a refutation of some fal- 

 lacies as to supposed methods of protection of iron from the 

 action of air and water ; 4th, the suggestion of a proposed new 

 method of protection of cast and wrought iron from tliese ac- 

 tions, now in progress of experiment ; and, lastly, the state- 

 ment and consideration of such questions upon this subject as 

 still stand in need of experimental answers, and are desiderata 

 to chemical science and to civil engineering. 



3. There has been much discussion as to the number and 

 composition of the oxides of iron, arising partly from the diffi- 

 culty of procuring iron free from foreign matter for experiment, 

 and partly from its oxides combining with each other. They 

 are now reduced to two, viz. 



The Protoxide = F e O 

 The Sesqui-oxide = F Cg O3. 



The hydrate of the first is not permanent, and its water has not 

 been precisely determined ; it is highly probable from analogy 

 that it has the composition F e O + 2 H O. 



There are two hydrates of the sesqui-oxide, one of which 

 occurs native = 2 F Cg O3 + 3 H O, and the other formed arti- 

 ficially = F Cg O3 4- 3 H O, and others probably exist. These 

 two oxides are capable of combining and forming 



Magnetic oxide (native) = F Cg O3 -j- F e O, 

 Forge scales (battitures) = Fe^O^ + 6FeO. 



Other less distinctly ascertained combinations have been de- 

 scribed. It is dubious whether forge scales are a chemical com- 

 bination at all, but I'ather a mixture of the protoxide and sesqui- 

 oxide in progress of cliange by cementation into the latter. 



4. And first of our chemical knowledge of the action of air 

 and water upon iron. 



Of the Action of Pure Water upon Iron. 



" Pure water deprived of air does not act on iron at any tem- 

 perature below 80° Reaum. = 212° Fahr., and at that but slowly. 

 The water was freed from any air bj^ Hall, by boiling, and by 

 the action of the iron itself." — (Marshall Hall, Phil. Trans. 

 1818; Karsten, Chim. du Fer.) 



." At a red heat, and above it, iron is instantly oxidized by 

 decomposition of vapour of water, producing, according to Ro- 

 biquet and othei's, (Fe^Og + FeO)." — {Journal de Pliarm. 

 1818.) 



