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 arrangement 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 (Fe2O3), 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 (Fe2O3), and then it was subjected to a reducing action for a definite shorter period. In this way it was obtained covered with the magnetic 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 (Fe2O3),
2 Fe O3 Fe2O3;
but, this being in contact with red-hot iron, its lower surface is reduced to magnetic oxide, as shown in the following reaction:
4 Fe2O3 Fe 3 Fe3O4.
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 (Fe2O3).
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 Fe2O3 CO 2 Fe3O4 CO2.
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 H2O Fe3O4 H8.
We will now pass to a description of the different processes, as carried 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 (CO2), it is only allowed to take up one atom of oxygen, and thus forms carbonic oxide (CO). The latter,
