142 AGRICULTURAL CHEMISTRY 



The carbon dioxid produced first is reduced to carbon 

 monoxid which passes over the heated ore in the upper 

 part of the furnace, and is the main reducing agent of the 

 blast-furnace. The carbon monoxid given off at the top 

 of the furnace is collected and used for heating the blast. 

 The furnace is constructed so as to utilize the heat to the 

 best advantage and so that the blast can act efficiently. 

 The slag which carries a large portion of the impurities 

 of the ore, being lighter than the molten iron, collects on 

 the surface and is removed from time to time. The 

 molten iron is run off from the bottom of the furnace 

 into molds ; iron that is produced in this way is known 

 as pig iron. It contains a number of impurities as phos- 

 phorus, carbon, silicon and sulfur. 



180. Wrought Iron. Wrought iron is produced from 

 cast iron by two processes : ( i ) the puddling process 

 which consists of oxidizing the impurities by means of a 

 blast of hot air which is passed over or blown throuhg 

 the iron, this is known as the Bessemer process ; 

 and (2) the cementation process by which the cast 

 iron is mixed with iron ores reasonably pure and heated 

 to a high temperature so that the oxygen of the ores may 

 oxidize the carbon, phosphorus and sulfur of the cast 

 iron. Wrought iron is the purest commercial form of 

 iron. It usually contains about 0.5 per cent, of carbon, 

 and melts at about 2000 C. The nature of the 

 impurities determines the character of both wrought iron 

 and steel, as any increase in the amount of carbon de- 

 creases its malleability and other desirable properties. 



181. Steel. This form of iron contains less carbon 



