CHEMICAL SCIENCE. 207 



mar be illustrated by the following series, comprising the various degrees of 

 wrought iron, steel, and cast iron, arranged according to the amount of car- 

 bon in each, beginning with the softest wrought iron, that is, with iron con- 

 taining no carbon, or the least amount of carbon : 



Soft wrought iron, containing 0-0 per cent, of carbon. 



Hard wrought iron, " 0.4 



Soft steel, 05 



Hard steel, 2.4 



Cast iron, 2 5 



Hard cast iron, 5.0 



In this series, beginning with the softest wrought iron, containing little or 

 no carbon, the proportion of carbon increases until there is one-half per 

 cent., which then forms soft steel; a further increase of carbon, up to two 

 and one-half per cent., forms cast iron ; and the proportion of carbon in- 

 creasing to five per cent., gives the hardest cast iron. Hence, it appears 

 that the operation of steel-making may be effected in two methods, cither 

 by adding a certain amount of carbon to pure wrought iron ; or conversely, 

 by taking away a certain amount of carbon from cast iron, removing at the 

 same time the impurities of the cast iron. 



The English, or converting process, is earned on according to the first of 

 these methods, by adding a certain amount of carbon to wrought iron. The 

 cast iron is first made into wrought iron, which is then converted into steel, 

 forming blister steel ; this is broken into small pieces and melted in cruci- 

 bles, which renders it homogeneous, and is then poured, while fluid, into 

 ingot moulds, after which it is known as cast steel. The chemical changes 

 which the cast iron has undergone in this process are firstly, when it was 

 manufactured into wrought iron, all or nearly all the carbon was abstracted 

 from it ; and secondly, by the converting process a certain amount of car- 

 bon was restored to it; and finally, the steel thus produced was made homo- 

 geneous by melting and casting. It is evident that this is a very circuitous 

 way of manufacturing cast steel, and it has the following disadvantages : 

 the great loss of weight in manufacturing the cast iron into wrought, the 

 difficulty in converting the wrought iron so as to carbonize it equally in all 

 parts, the great length of time that this process requires for the production 

 of cast steel, and the great cost of manufacture. 



The German, or puddling process, is effected by the converse method, by 

 taking away a certain amount of carbon from cast iron. The pig iron is 

 puddled in the same way as in making wrought iron, except that the process 

 is stopped when a certain amount of carbon has been taken away, a point 

 which it is difficult to judge of. This partially puddled iron, so-called pud- 

 dled steel, is then made homogeneous by melting it in crucibles in the ordi- 

 nary way. The chemical change which the cast iron has undergone by this 

 process is, the abstraction of a portion of the carbon in the puddling fur- 

 nace, and the puddled steel has then been rendered homogeneous by melting 

 and casting. The disadvantages of this method are the waste of iron by 

 the puddling process; the uncertainty of getting equally discarbonized iron, 

 owing to the difficulty of measuring the quantity of oxygen acting on the 

 puddled metal; and also the cost of manufacture. 



The Uchatius process is based upon the same principle as that last de- 

 scribed, consisting in taking away as much carbon only as is required to 

 produce steel, and removing at the same time the impurities of the cast iron. 



