Metals. 251 



hammers, wrought by machinery. This pro- 

 cess is necessary to render it malleable, and it is 

 thus wrought into bars. 



Steel is iron combined with a less portion of 

 carbon than cast iron, .ibout one-sixtieth part of 

 its weight. It may of course be prepared from 

 cast iron, by expelling part of the carbon by heat. 

 It is then called natural steel, but is less pure 

 than what is called steel of cementation. This 

 process consists in laying bars of pure iron be- 

 tween strata of powdered charcoal ; and heating 

 them in a close furnace for eight or ten days. 

 This is also called blistered, or common steel; 

 what is called cast steel contains a still larger 

 proportion of carbon obtained by heating blis- 

 tered steel with chalk. 



Thus iron is capable of combining with dif- 

 ferent portions of carbon. When the carbon pre- 

 dominates, the compound is carburet of iron, 

 plumbago, or black-lead. When the iron exceeds, 

 the compound is cast iron or steel, in its various 

 states, which may be called subcarburet of iron. 



Iron combines with the acids. Sulphat of 

 iron (iron with sulphuric acid) is well known by 

 the dyers, as striking a black dye with infusion 

 of galls, Sec. ; it is commonly called green vitriol, 

 or copperas. Common ink is made by means 

 of this compound of infusion of galls and cop- 

 peras, with a small portion of gum to keep the 

 colouring matter suspended. 



With the prussic acid iron forms that beauti- 



