396 THE POPULAR SCIENCE MONTHLY. 



either alone or mixed with hydrocarbons, formed by the decomposi- 

 tion 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-pro- 

 ducers, 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 re- 

 move 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. Dur- 

 ing 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 oxidiz- 

 ing 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 withdraw- 

 ing the charge now, to complete the treatment by admitting steam for 



