Page:Popular Science Monthly Volume 29.djvu/410

396 either alone or mixed with hydrocarbons, formed by the decomposition of naphtha, used during the reduction periods, is the gas that passes into the combustion-chamber to be there mixed with air or not, according to the result desired to be produced.

The fuel used in this country is anthracite coal, with the addition, during the reduction periods, of a little naphtha or crude petroleum. A small stream of the oil is led into the top of one of the gas-producers, where it is vaporized, and passes along with the other gases on their way to the oxidizing chamber.

Cast-iron before it can be treated requires to be "pickled," to remove any sand adhering to the casting. The "pickling" is done as follows: The iron is first placed in a bath of dilute sulphuric acid, and allowed to remain there for from ten to fifteen minutes, or even longer, if the casting is a very rough one. It is then removed and washed with boiling water, and when dry the sand which is now loosened is taken off with steel brushes. Now the article is ready for treatment in the furnace. The pieces to be treated are placed on the drag, a heavy iron plate, which is run into the furnace through a large door in one end. Before making the charge, the furnace must be heated to a white heat; having attained this temperature, the door is opened and the charge run in as quickly as possible, then closed and tightly luted, so as to exclude all air. The charge is heated with a slightly reducing flame, that is, one in which there is an excess of carbon, until it has reached a bright cherry red. During this heating of the charge only enough air is admitted to the combustion-chamber to partially burn the gases. When it has reached the proper temperature, the "gas" is turned on, that is, the supply of air is entirely cut off, a small stream of oil is allowed to flow into the producer, and the chimney-damper nearly closed. The flame in the furnace now becomes smoky. During this reduction or "gas" period, which usually lasts twenty minutes, the gases rich in carbon come in contact with the red-hot charge, and reduce any sesquioxide to magnetic oxide. At the end of this time the oil is shut off, the gas partially so, and the chimney-damper opened. When the furnace has become free from smoke, the air-valve is opened so as to let air enter the combustion-chamber in quantity only slightly in excess of that needed to burn the gases completely. This excess (of air), in conjunction probably with the carbonic acid formed by the combustion of the gases, oxidizes the iron to sesquioxide, which will be reduced by the next "gas" to magnetic oxide. When the oxidizing period, which lasts forty minutes, is over, the air-valve is closed, the gas turned full on, and the oil run into the producer as before, and the second "gas" or reduction period of twenty minutes begins. These alternate periods of reduction and oxidation are continued for from eight to ten hours, and the charge is drawn at the end of the last "gas," or, what seems to assure better results is, instead of withdrawing the charge now, to complete the treatment by admitting steam for