RUSTLESS IRON. 395 



in which only the oxidizing gas, either air or carbonic acid, was allowed 

 to come in contact with the iron ; but this was found to be costly as 

 well as unnecessary. Now the furnaces are built so that the products 

 of combustion of the coal, used to heat the furnace, come directly in 

 contact with the iron undergoing treatment, and by a suitable ar- 

 rangement of dampers, etc., the same furnace can be used for the 

 Barff or steam process. In his experiments the inventor found that, 

 if he admitted a large excess of air, the article came out covered with 

 the red oxide of iron (Fe 2 3 ), and that below this red coating was a 

 thin film of the magnetic oxide. For some time he was at a loss how 

 to regulate the quantity of air added, so as to prevent the formation 

 of this red oxide, but finally hit upon the following plan : During a 

 certain time the iron was oxidized in excess, that is, to sesquioxide 

 (Fe 2 3 ), and then it was subjected to a reducing action for a definite 

 shorter period. In this way it was obtained covered with the mag- 

 netic oxide only. The chemical reactions that take place are given by 

 Mr. Bower as follows : the excess of air during the first part of the 

 reaction causes the formation of sesquioxide of iron (Fe 2 3 ), 



2 Fe + 3 = Fe 2 3 ; 

 but, this being in contact with red-hot iron, its lower surface is re- 

 duced to magnetic oxide, as shown in the following reaction : 



4 FeA + Fe = 3 Fe 3 4 . 



It would seem from this reaction that no reduction period would 

 be necessary : theoretically it would not, but practically it is required, 

 as there is always an excess of the red oxide (Fe 2 3 ). 



This excess of the red oxide is then reduced to magnetic oxide by 

 the reducing gases, consisting chiefly of carbonic oxide (CO), which 

 is converted into carbonic acid as follows : 



3 FeA + CO = 2 Fe 3 4 + C0 2 . 



When steam is used instead of air, the steam coming in contact 

 with red-hot iron is decomposed, giving up its oxygen to the iron, and 

 forming the black oxide, its hydrogen being at the same time set free 

 as gas. The following shows the reaction : 



3 Fe + 4 H 2 == Fe A + H 8 . 



We will now pass to a description of the different processes, as car- 

 ried out on the large scale. The furnaces in use vary somewhat in 

 construction, but the principle is the same in all. The iron to be 

 treated is placed in a large fire-brick chamber, known as the oxidizing 

 chamber, into which the gases from the producers pass after having 

 been through a combustion-chamber. In the latter the gases can be 

 mixed with air, and burned, when necessary, the amount of air being 

 regulated as required. The producers are simply very deep fireplaces, 

 the bed of coal being three to four feet deep, so arranged that only 

 sufficient air is admitted to burn the coal partially ; that is, instead of 

 being converted into carbonic acid (C0 2 ), it is only allowed to take up 

 one atom of oxygen, and thus forms carbonic oxide (CO). The latter, 



