824 PRINCIPLES OF CHEMISTRY 



designed to serve for the continuous production of cast iron by charging 

 the ore, fuel, and flux into the mouth of the furnace, forcing a blast of 

 air into the lower part, and running out the molten iron and slag from 

 below. The whole operation is conducted in furnaces known as blast 

 furnaces. The annexed illustration, fig. 93 (which is taken by kind 

 permission from Thorpe's Dictionary of Applied Chemistry), represents 

 the vertical section of such a furnace. These furnaces are generally 

 of large dimensions varying from 50 to 90 feet in height. They are 

 sometimes built against rising ground in order to afford easy access to 

 the top where the ore, flux, and charcoal or coke are charged. 8 



8 The section of a blast furnace is represented by two truncated cones joined at their 

 bases, the upper cone being longer than the lower one ; the lower cone is terminated by 

 the hearth, or almost cylindrical cavity in whichj the cast iron and slag collect, one 

 side being provided with apertures for drawing off the iron and slag. The air is blown 

 into the blast furnace through special pipes, situated, over the hearth, as shown in the 

 section. The air previously passes through a series ;of cast-iron pipes, heated by the 

 combustion of the carbonic oxide obtained from Jthe upper parts of the furnace, where 

 it is formed as in a ' gas-producer.' The blast furnace acts continuously until it is worn 

 out ; the iron is tapped off twicer day, and the furnace is allowed to cool a little from 

 time to time so as not to be spoilt by the increasing heat, and to enable it to withstand 

 long usage. 



Blast furnaces worked", with charcoal fuel are not so high, and in general give a 

 smaller yield than those using coke, because the latter are worked with heavier charges 

 than those in which charcoal is employed. Coke furnaces yield 20,000 tons and over of pig 

 iron a year. In the United States there are blast furnaces 30 metres high, and upwards 

 of 600 cubic metres capacity, yielding as much as 130,000 tons of pig iron, requiring a blast 

 of about 750 cubic metres of air per minute, heated to' 600, and consuming about 0*85 

 part of coke per 1 part of pig iron produced. At the present time the world produces as 

 much as 30 million tons of pig iron a year, about T % of which is converted into wrought 

 iron and steel. The chief producers are the United States (about 10 million tons a year) 

 and England (about 9 million tons a year) ; Russia yields about 1 million tons a year. 

 The world's production has doubled during the last 20 years,, and in this respect the 

 United States have outrun all other countries. The reason of this increase of production 

 must be looked for in the increased demand for iron and steel for railway purposes, for 

 structures (especially ship-building), and in the fact that : (a)' the cost of pig iron has 

 fallen, thanks to the erection of large furnaces and a fuller study of the processes taking 

 place in them, and (6) that every kind of iron ore (even sulphurous and phosphoritic) can 

 now be converted into a homogeneous steel. 



In order to more thoroughly grasp the chemical process which takes place in blast 

 furnaces, it is necessary to follow the course of the material charged in at the top and of 

 'the air passing through the furnace. From 50 to 200 parts of carbon are expended on 100 

 parts of iron. The ore, flux, and coke are charged into the top of the furnace, in 

 layers, as the cast iron is formed in the lower parts and flowing down to the bottom 

 causes the whole contents of the furnace to subside, thus forming an empty space at 

 the top, which is again filled up with the afore-mentioned mixture. During its down* 

 ward course this mixture is subjected to increasing heat. This rise of temperature 

 first drives off the moisture of the ore mixture, and then leads to the formation of 

 the products of the dry distillation of coal or charcoal. Little by little the subsiding 

 mass attains a temperature at which the heated carbon reacts with the carbonic anhydride 

 passing upwards through the furnace and transforms it into carbonic oxide. This is 

 the reason why carbonic anhydride is not evolved from the furnace, but only carbonic 

 oxide. As regards the ore itself, on being heated to about 600 to 800 it is reduced at 

 the expense of the carbonic oxide ascending the furnace, and formed by the contact of 



